Seth Sheffler‐Collins, MPH

Mycoplasma pneumoniae is a common cause of community‐acquired pneumonia (CAP), among school‐age children and adolescents.14 Though pneumonia caused by M. pneumoniae is typically self‐limited, severe illness may occur.5 M. pneumoniae has also been implicated in airway inflammation, which may lead to the onset and development of chronic pulmonary disease.610 Few studies have directly addressed appropriate treatment strategies for M. pneumoniae pneumonia,11 and, despite its high prevalence and potential for causing severe complications, treatment recommendations remain inconsistent.

The efficacy of macrolide therapy in particular for M. pneumoniae remains unclear. In vitro susceptibility studies have shown bacteriostatic activity of erythromycin, clarithromycin, and azithromycin against M. pneumoniae.1218 Additionally, several small retrospective studies have shown that among children with atypical CAP (including M. pneumoniae pneumonia), those treated with macrolides were less likely to have persistence or progression of signs and symptoms after 3 days of therapy.19, 20 Lu et al21 found a shorter duration of fever among macrolide recipients compared with non‐recipients. In adults, Shames et al22 found a shorter duration of fever and hospitalization among erythromycin recipients compared with controls. Other randomized controlled trials have also addressed the use of macrolides in treatment of M. pneumoniae, but the ability to draw meaningful conclusions is limited by small samples sizes and by lack of details about the number of patients with M. pneumoniae.11

In addition to their antimicrobial effect, macrolides also have anti‐inflammatory properties.2327 The importance of these anti‐inflammatory properties is supported by studies showing clinical cure in patients treated with macrolides despite persistence of M. pneumoniae organisms,2831 clinical improvement despite the administration of doses that provide tissue levels below the minimum inhibitory concentration of the organism,3234 and clinical cure in patients with macrolide‐resistant M. pneumoniae.18, 35

The objectives of the current study were to examine the impact of macrolide therapy on the length of stay (LOS) and short‐ and longer‐term readmissions, including longer‐term asthma‐related readmissions, in children hospitalized with M. pneumoniae pneumonia.

METHODS

RESULTS

DISCUSSION

This multicenter study examined the role of macrolide therapy in children hospitalized with M. pneumoniae pneumonia. Empiric macrolide therapy was associated with an approximately 30% shorter hospital LOS and, in stratified analysis, remained associated with a significantly shorter hospital LOS in both systemic corticosteroid recipients and non‐recipients. Empiric macrolide therapy was not associated with short‐ or longer‐term hospital readmission.

Previous small randomized trials have been inconclusive regarding the potential benefit of macrolide therapy in M. pneumoniae pneumonia.11 Our study, which demonstrated a shorter LOS among macrolides recipients compared with non‐recipients, has several advantages over prior studies including a substantively larger sample size and multicenter design. Animal models support our observations regarding the potential beneficial antimicrobial role of macrolides. M. pneumoniae concentrations in bronchoalveolar lavage specimens were significantly lower among experimentally infected mice treated with clarithromycin, a macolide‐class antibiotic, compared with either placebo or dexamethasone.45 Combination therapy with clarithromycin and dexamethasone reduced histopathologic inflammation to a greater degree than dexamethasone alone.45

While the relative importance of the antimicrobial and anti‐inflammatory properties of macrolides is not known, observational studies of children infected with macrolide‐resistant M. pneumoniae suggest that the antimicrobial properties of macrolides may provide disproportionate clinical benefit. The duration of fever in macrolide recipients with macrolide‐resistant M. pneumoniae (median duration, 9 days) reported by Suzuki et al46 was significantly longer than those with macrolide‐susceptible infections (median duration, 5 days), and similar to the duration of fever in patients with M. pneumoniae infection treated with placebo (median duration, 8 days) reported by Kingston et al.47 Additionally, macrolide therapy was associated with significant improvements in lung function in patients with asthma and concomitant M. pneumoniae infection, but not in patients with asthma without documented M. pneumoniae infection.9 As corticosteroids also have anti‐inflammatory properties, we expect that any anti‐inflammatory benefit of macrolide therapy would be mitigated by the concomitant administration of corticosteroids. The shorter LOS associated with empiric macrolide therapy in our study was comparable among corticosteroid recipients and non‐recipients.

Atypical bacterial pathogens, including M. pneumoniae, are associated with diffuse lower airway inflammation6, 48 and airway hyperresponsiveness,6 and have been implicated as a cause of acute asthma exacerbations.7, 4954 Among patients with previously diagnosed asthma, acute M. pneumoniae infection was identified in up to 20% of those having acute exacerbations.7, 54 Macrolide therapy has a beneficial effect on lung function and airway hyperresponsiveness in adults with asthma.9, 55 Among mice infected with M. pneumoniae, 3 days of macrolide therapy resulted in a significant reduction in airway hyperresponsiveness compared with placebo or dexamethasone; however, after 6 days of therapy, there was no significant difference in airway hyperresponsiveness between those receiving macrolides, dexamethasone, or placebo, suggesting that the benefit of macrolides on airway hyperresponsiveness may be brief. Our findings of a shorter LOS but no difference in readmissions at 28 days or longer, for macrolide recipients compared with non‐recipients, support the limited benefit of macrolide therapy beyond the initial reduction in bacterial load seen in the first few days of therapy.

M. pneumoniae infection has also been implicated as a cause of chronic pulmonary disease, including asthma.610 In the mouse model, peribronchial and perivascular mononuclear infiltrates, increased airway methacholine reactivity, and increased airway obstruction were observed 530 days after M. pneumoniae inoculation.6 M. pneumoniae has been identified in 26 (50%) of 51 children experiencing their first asthma attack,7 and 23 (42%) of 55 adults with chronic, stable asthma.9 Nevertheless, results of other studies addressing the issue are inconsistent, and the role of M. pneumoniae in the development of asthma remains unclear.56 In order to investigate the impact of macrolide therapy on the development of chronic pulmonary disease requiring hospitalization, we examined the readmission rates in the 15 months following index discharge. The proportion of children hospitalized with asthma following the hospitalization for M. pneumoniae pneumonia was higher for both macrolide recipients and non‐recipients compared with the 24‐months prior to infection. These results support a possible role for M. pneumoniae in chronic pulmonary disease. However, macrolide therapy was not associated with long‐term overall hospital readmission or long‐term asthma readmission, either in the entire cohort or in the subset of patients without prior asthma hospitalizations or medications.

This study had several limitations. First, because the identification of children with M. pneumoniae pneumonia relied on ICD‐9 discharge diagnosis codes, it is possible that there was misclassification of disease. We minimized the inclusion of children without M. pneumoniae by including only children who received antibiotic therapy on the first day of hospitalization and by excluding patients younger than 6 years of age, a group at relatively low‐risk for M. pneumoniae infection. Further, our algorithm for identification of M. pneumoniae pneumonia was validated through review of the medical records at 1 institution and was found to have a high positive predictive value. However, the positive predictive value of these ICD‐9 codes may vary across institutions. Additionally, the sensitivity of ICD‐9 codes for identifying children with M. pneumoniae pneumonia is not known. Also, not all children with pneumonia undergo testing for M. pneumoniae, and different tests have varying sensitivity and specificity.57, 58 Thus, some children with M. pneumoniae pneumonia were not diagnosed and so were not included in our study. It is not known how inclusion of these children would affect our results.

Second, the antibiotic information used in this study was limited to empiric antibiotic therapy. It is possible that some patients received macrolide therapy before admission. It is also likely that identification of M. pneumoniae during the hospitalization prompted the addition or substitution of macrolide therapy for some patients. If this therapy was initiated beyond the first day of hospitalization, these children would be classified as macrolide non‐recipients. Since macrolide administration was associated with a shorter hospital LOS, such misclassification would bias our results towards finding no difference in LOS between macrolide recipients and non‐recipients. It is therefore possible that the benefit of macrolide therapy is even greater than found in our study.

Third, there may be unmeasured confounding or residual confounding by indication for adjunct corticosteroid therapy related to clinical presentation. We expect that corticosteroid recipients would be sicker than non‐recipients. We included variables associated with a greater severity of illness (such as intensive care unit admission) in the multivariable analysis. Additionally, the shorter LOS among macrolide recipients remained when the analysis was stratified by receipt or non‐receipt of systemic corticosteroid therapy.

Fourth, we were only able to record readmissions occurring at the same hospital as the index admission; any readmission presenting to a different hospital following their index admission did not appear in our records, and was therefore not counted. It is thus possible that the true number of readmissions is higher than that represented here. Finally, despite the large number of patients included in this study, the number of short‐term readmissions was relatively small. Thus, we may have been underpowered to detect small but significant differences in short‐term readmission rates.

In conclusion, macrolide therapy was associated with shorter hospital LOS, but not with short‐term or longer‐term readmission in children presenting with M. pneumoniae pneumonia.

Mycoplasma pneumoniae is a common cause of community‐acquired pneumonia (CAP), among school‐age children and adolescents.14 Though pneumonia caused by M. pneumoniae is typically self‐limited, severe illness may occur.5 M. pneumoniae has also been implicated in airway inflammation, which may lead to the onset and development of chronic pulmonary disease.610 Few studies have directly addressed appropriate treatment strategies for M. pneumoniae pneumonia,11 and, despite its high prevalence and potential for causing severe complications, treatment recommendations remain inconsistent.

The efficacy of macrolide therapy in particular for M. pneumoniae remains unclear. In vitro susceptibility studies have shown bacteriostatic activity of erythromycin, clarithromycin, and azithromycin against M. pneumoniae.1218 Additionally, several small retrospective studies have shown that among children with atypical CAP (including M. pneumoniae pneumonia), those treated with macrolides were less likely to have persistence or progression of signs and symptoms after 3 days of therapy.19, 20 Lu et al21 found a shorter duration of fever among macrolide recipients compared with non‐recipients. In adults, Shames et al22 found a shorter duration of fever and hospitalization among erythromycin recipients compared with controls. Other randomized controlled trials have also addressed the use of macrolides in treatment of M. pneumoniae, but the ability to draw meaningful conclusions is limited by small samples sizes and by lack of details about the number of patients with M. pneumoniae.11

In addition to their antimicrobial effect, macrolides also have anti‐inflammatory properties.2327 The importance of these anti‐inflammatory properties is supported by studies showing clinical cure in patients treated with macrolides despite persistence of M. pneumoniae organisms,2831 clinical improvement despite the administration of doses that provide tissue levels below the minimum inhibitory concentration of the organism,3234 and clinical cure in patients with macrolide‐resistant M. pneumoniae.18, 35

The objectives of the current study were to examine the impact of macrolide therapy on the length of stay (LOS) and short‐ and longer‐term readmissions, including longer‐term asthma‐related readmissions, in children hospitalized with M. pneumoniae pneumonia.

METHODS

RESULTS

DISCUSSION

This multicenter study examined the role of macrolide therapy in children hospitalized with M. pneumoniae pneumonia. Empiric macrolide therapy was associated with an approximately 30% shorter hospital LOS and, in stratified analysis, remained associated with a significantly shorter hospital LOS in both systemic corticosteroid recipients and non‐recipients. Empiric macrolide therapy was not associated with short‐ or longer‐term hospital readmission.

Previous small randomized trials have been inconclusive regarding the potential benefit of macrolide therapy in M. pneumoniae pneumonia.11 Our study, which demonstrated a shorter LOS among macrolides recipients compared with non‐recipients, has several advantages over prior studies including a substantively larger sample size and multicenter design. Animal models support our observations regarding the potential beneficial antimicrobial role of macrolides. M. pneumoniae concentrations in bronchoalveolar lavage specimens were significantly lower among experimentally infected mice treated with clarithromycin, a macolide‐class antibiotic, compared with either placebo or dexamethasone.45 Combination therapy with clarithromycin and dexamethasone reduced histopathologic inflammation to a greater degree than dexamethasone alone.45

While the relative importance of the antimicrobial and anti‐inflammatory properties of macrolides is not known, observational studies of children infected with macrolide‐resistant M. pneumoniae suggest that the antimicrobial properties of macrolides may provide disproportionate clinical benefit. The duration of fever in macrolide recipients with macrolide‐resistant M. pneumoniae (median duration, 9 days) reported by Suzuki et al46 was significantly longer than those with macrolide‐susceptible infections (median duration, 5 days), and similar to the duration of fever in patients with M. pneumoniae infection treated with placebo (median duration, 8 days) reported by Kingston et al.47 Additionally, macrolide therapy was associated with significant improvements in lung function in patients with asthma and concomitant M. pneumoniae infection, but not in patients with asthma without documented M. pneumoniae infection.9 As corticosteroids also have anti‐inflammatory properties, we expect that any anti‐inflammatory benefit of macrolide therapy would be mitigated by the concomitant administration of corticosteroids. The shorter LOS associated with empiric macrolide therapy in our study was comparable among corticosteroid recipients and non‐recipients.

Atypical bacterial pathogens, including M. pneumoniae, are associated with diffuse lower airway inflammation6, 48 and airway hyperresponsiveness,6 and have been implicated as a cause of acute asthma exacerbations.7, 4954 Among patients with previously diagnosed asthma, acute M. pneumoniae infection was identified in up to 20% of those having acute exacerbations.7, 54 Macrolide therapy has a beneficial effect on lung function and airway hyperresponsiveness in adults with asthma.9, 55 Among mice infected with M. pneumoniae, 3 days of macrolide therapy resulted in a significant reduction in airway hyperresponsiveness compared with placebo or dexamethasone; however, after 6 days of therapy, there was no significant difference in airway hyperresponsiveness between those receiving macrolides, dexamethasone, or placebo, suggesting that the benefit of macrolides on airway hyperresponsiveness may be brief. Our findings of a shorter LOS but no difference in readmissions at 28 days or longer, for macrolide recipients compared with non‐recipients, support the limited benefit of macrolide therapy beyond the initial reduction in bacterial load seen in the first few days of therapy.

M. pneumoniae infection has also been implicated as a cause of chronic pulmonary disease, including asthma.610 In the mouse model, peribronchial and perivascular mononuclear infiltrates, increased airway methacholine reactivity, and increased airway obstruction were observed 530 days after M. pneumoniae inoculation.6 M. pneumoniae has been identified in 26 (50%) of 51 children experiencing their first asthma attack,7 and 23 (42%) of 55 adults with chronic, stable asthma.9 Nevertheless, results of other studies addressing the issue are inconsistent, and the role of M. pneumoniae in the development of asthma remains unclear.56 In order to investigate the impact of macrolide therapy on the development of chronic pulmonary disease requiring hospitalization, we examined the readmission rates in the 15 months following index discharge. The proportion of children hospitalized with asthma following the hospitalization for M. pneumoniae pneumonia was higher for both macrolide recipients and non‐recipients compared with the 24‐months prior to infection. These results support a possible role for M. pneumoniae in chronic pulmonary disease. However, macrolide therapy was not associated with long‐term overall hospital readmission or long‐term asthma readmission, either in the entire cohort or in the subset of patients without prior asthma hospitalizations or medications.

This study had several limitations. First, because the identification of children with M. pneumoniae pneumonia relied on ICD‐9 discharge diagnosis codes, it is possible that there was misclassification of disease. We minimized the inclusion of children without M. pneumoniae by including only children who received antibiotic therapy on the first day of hospitalization and by excluding patients younger than 6 years of age, a group at relatively low‐risk for M. pneumoniae infection. Further, our algorithm for identification of M. pneumoniae pneumonia was validated through review of the medical records at 1 institution and was found to have a high positive predictive value. However, the positive predictive value of these ICD‐9 codes may vary across institutions. Additionally, the sensitivity of ICD‐9 codes for identifying children with M. pneumoniae pneumonia is not known. Also, not all children with pneumonia undergo testing for M. pneumoniae, and different tests have varying sensitivity and specificity.57, 58 Thus, some children with M. pneumoniae pneumonia were not diagnosed and so were not included in our study. It is not known how inclusion of these children would affect our results.

Second, the antibiotic information used in this study was limited to empiric antibiotic therapy. It is possible that some patients received macrolide therapy before admission. It is also likely that identification of M. pneumoniae during the hospitalization prompted the addition or substitution of macrolide therapy for some patients. If this therapy was initiated beyond the first day of hospitalization, these children would be classified as macrolide non‐recipients. Since macrolide administration was associated with a shorter hospital LOS, such misclassification would bias our results towards finding no difference in LOS between macrolide recipients and non‐recipients. It is therefore possible that the benefit of macrolide therapy is even greater than found in our study.

Third, there may be unmeasured confounding or residual confounding by indication for adjunct corticosteroid therapy related to clinical presentation. We expect that corticosteroid recipients would be sicker than non‐recipients. We included variables associated with a greater severity of illness (such as intensive care unit admission) in the multivariable analysis. Additionally, the shorter LOS among macrolide recipients remained when the analysis was stratified by receipt or non‐receipt of systemic corticosteroid therapy.

Fourth, we were only able to record readmissions occurring at the same hospital as the index admission; any readmission presenting to a different hospital following their index admission did not appear in our records, and was therefore not counted. It is thus possible that the true number of readmissions is higher than that represented here. Finally, despite the large number of patients included in this study, the number of short‐term readmissions was relatively small. Thus, we may have been underpowered to detect small but significant differences in short‐term readmission rates.

In conclusion, macrolide therapy was associated with shorter hospital LOS, but not with short‐term or longer‐term readmission in children presenting with M. pneumoniae pneumonia.

Mycoplasma pneumoniae is a common cause of community‐acquired pneumonia (CAP), among school‐age children and adolescents.14 Though pneumonia caused by M. pneumoniae is typically self‐limited, severe illness may occur.5 M. pneumoniae has also been implicated in airway inflammation, which may lead to the onset and development of chronic pulmonary disease.610 Few studies have directly addressed appropriate treatment strategies for M. pneumoniae pneumonia,11 and, despite its high prevalence and potential for causing severe complications, treatment recommendations remain inconsistent.

The efficacy of macrolide therapy in particular for M. pneumoniae remains unclear. In vitro susceptibility studies have shown bacteriostatic activity of erythromycin, clarithromycin, and azithromycin against M. pneumoniae.1218 Additionally, several small retrospective studies have shown that among children with atypical CAP (including M. pneumoniae pneumonia), those treated with macrolides were less likely to have persistence or progression of signs and symptoms after 3 days of therapy.19, 20 Lu et al21 found a shorter duration of fever among macrolide recipients compared with non‐recipients. In adults, Shames et al22 found a shorter duration of fever and hospitalization among erythromycin recipients compared with controls. Other randomized controlled trials have also addressed the use of macrolides in treatment of M. pneumoniae, but the ability to draw meaningful conclusions is limited by small samples sizes and by lack of details about the number of patients with M. pneumoniae.11

In addition to their antimicrobial effect, macrolides also have anti‐inflammatory properties.2327 The importance of these anti‐inflammatory properties is supported by studies showing clinical cure in patients treated with macrolides despite persistence of M. pneumoniae organisms,2831 clinical improvement despite the administration of doses that provide tissue levels below the minimum inhibitory concentration of the organism,3234 and clinical cure in patients with macrolide‐resistant M. pneumoniae.18, 35

The objectives of the current study were to examine the impact of macrolide therapy on the length of stay (LOS) and short‐ and longer‐term readmissions, including longer‐term asthma‐related readmissions, in children hospitalized with M. pneumoniae pneumonia.

METHODS

RESULTS

DISCUSSION

This multicenter study examined the role of macrolide therapy in children hospitalized with M. pneumoniae pneumonia. Empiric macrolide therapy was associated with an approximately 30% shorter hospital LOS and, in stratified analysis, remained associated with a significantly shorter hospital LOS in both systemic corticosteroid recipients and non‐recipients. Empiric macrolide therapy was not associated with short‐ or longer‐term hospital readmission.

Previous small randomized trials have been inconclusive regarding the potential benefit of macrolide therapy in M. pneumoniae pneumonia.11 Our study, which demonstrated a shorter LOS among macrolides recipients compared with non‐recipients, has several advantages over prior studies including a substantively larger sample size and multicenter design. Animal models support our observations regarding the potential beneficial antimicrobial role of macrolides. M. pneumoniae concentrations in bronchoalveolar lavage specimens were significantly lower among experimentally infected mice treated with clarithromycin, a macolide‐class antibiotic, compared with either placebo or dexamethasone.45 Combination therapy with clarithromycin and dexamethasone reduced histopathologic inflammation to a greater degree than dexamethasone alone.45

While the relative importance of the antimicrobial and anti‐inflammatory properties of macrolides is not known, observational studies of children infected with macrolide‐resistant M. pneumoniae suggest that the antimicrobial properties of macrolides may provide disproportionate clinical benefit. The duration of fever in macrolide recipients with macrolide‐resistant M. pneumoniae (median duration, 9 days) reported by Suzuki et al46 was significantly longer than those with macrolide‐susceptible infections (median duration, 5 days), and similar to the duration of fever in patients with M. pneumoniae infection treated with placebo (median duration, 8 days) reported by Kingston et al.47 Additionally, macrolide therapy was associated with significant improvements in lung function in patients with asthma and concomitant M. pneumoniae infection, but not in patients with asthma without documented M. pneumoniae infection.9 As corticosteroids also have anti‐inflammatory properties, we expect that any anti‐inflammatory benefit of macrolide therapy would be mitigated by the concomitant administration of corticosteroids. The shorter LOS associated with empiric macrolide therapy in our study was comparable among corticosteroid recipients and non‐recipients.

Atypical bacterial pathogens, including M. pneumoniae, are associated with diffuse lower airway inflammation6, 48 and airway hyperresponsiveness,6 and have been implicated as a cause of acute asthma exacerbations.7, 4954 Among patients with previously diagnosed asthma, acute M. pneumoniae infection was identified in up to 20% of those having acute exacerbations.7, 54 Macrolide therapy has a beneficial effect on lung function and airway hyperresponsiveness in adults with asthma.9, 55 Among mice infected with M. pneumoniae, 3 days of macrolide therapy resulted in a significant reduction in airway hyperresponsiveness compared with placebo or dexamethasone; however, after 6 days of therapy, there was no significant difference in airway hyperresponsiveness between those receiving macrolides, dexamethasone, or placebo, suggesting that the benefit of macrolides on airway hyperresponsiveness may be brief. Our findings of a shorter LOS but no difference in readmissions at 28 days or longer, for macrolide recipients compared with non‐recipients, support the limited benefit of macrolide therapy beyond the initial reduction in bacterial load seen in the first few days of therapy.

M. pneumoniae infection has also been implicated as a cause of chronic pulmonary disease, including asthma.610 In the mouse model, peribronchial and perivascular mononuclear infiltrates, increased airway methacholine reactivity, and increased airway obstruction were observed 530 days after M. pneumoniae inoculation.6 M. pneumoniae has been identified in 26 (50%) of 51 children experiencing their first asthma attack,7 and 23 (42%) of 55 adults with chronic, stable asthma.9 Nevertheless, results of other studies addressing the issue are inconsistent, and the role of M. pneumoniae in the development of asthma remains unclear.56 In order to investigate the impact of macrolide therapy on the development of chronic pulmonary disease requiring hospitalization, we examined the readmission rates in the 15 months following index discharge. The proportion of children hospitalized with asthma following the hospitalization for M. pneumoniae pneumonia was higher for both macrolide recipients and non‐recipients compared with the 24‐months prior to infection. These results support a possible role for M. pneumoniae in chronic pulmonary disease. However, macrolide therapy was not associated with long‐term overall hospital readmission or long‐term asthma readmission, either in the entire cohort or in the subset of patients without prior asthma hospitalizations or medications.

This study had several limitations. First, because the identification of children with M. pneumoniae pneumonia relied on ICD‐9 discharge diagnosis codes, it is possible that there was misclassification of disease. We minimized the inclusion of children without M. pneumoniae by including only children who received antibiotic therapy on the first day of hospitalization and by excluding patients younger than 6 years of age, a group at relatively low‐risk for M. pneumoniae infection. Further, our algorithm for identification of M. pneumoniae pneumonia was validated through review of the medical records at 1 institution and was found to have a high positive predictive value. However, the positive predictive value of these ICD‐9 codes may vary across institutions. Additionally, the sensitivity of ICD‐9 codes for identifying children with M. pneumoniae pneumonia is not known. Also, not all children with pneumonia undergo testing for M. pneumoniae, and different tests have varying sensitivity and specificity.57, 58 Thus, some children with M. pneumoniae pneumonia were not diagnosed and so were not included in our study. It is not known how inclusion of these children would affect our results.

Second, the antibiotic information used in this study was limited to empiric antibiotic therapy. It is possible that some patients received macrolide therapy before admission. It is also likely that identification of M. pneumoniae during the hospitalization prompted the addition or substitution of macrolide therapy for some patients. If this therapy was initiated beyond the first day of hospitalization, these children would be classified as macrolide non‐recipients. Since macrolide administration was associated with a shorter hospital LOS, such misclassification would bias our results towards finding no difference in LOS between macrolide recipients and non‐recipients. It is therefore possible that the benefit of macrolide therapy is even greater than found in our study.

Third, there may be unmeasured confounding or residual confounding by indication for adjunct corticosteroid therapy related to clinical presentation. We expect that corticosteroid recipients would be sicker than non‐recipients. We included variables associated with a greater severity of illness (such as intensive care unit admission) in the multivariable analysis. Additionally, the shorter LOS among macrolide recipients remained when the analysis was stratified by receipt or non‐receipt of systemic corticosteroid therapy.

Fourth, we were only able to record readmissions occurring at the same hospital as the index admission; any readmission presenting to a different hospital following their index admission did not appear in our records, and was therefore not counted. It is thus possible that the true number of readmissions is higher than that represented here. Finally, despite the large number of patients included in this study, the number of short‐term readmissions was relatively small. Thus, we may have been underpowered to detect small but significant differences in short‐term readmission rates.

In conclusion, macrolide therapy was associated with shorter hospital LOS, but not with short‐term or longer‐term readmission in children presenting with M. pneumoniae pneumonia.

Community‐acquired pneumonia (CAP), the most common serious bacterial infection in childhood, may be complicated by parapneumonic effusion (ie, complicated pneumonia).1, 2 The clinical outcome of children with complicated pneumonia is directly influenced by the causative organism, and precise identification of the infectious agent has the potential to improve clinical management.35 The incidence of complicated pneumonia has recently increased, highlighting the need to better understand the reasons for this changing epidemiology.68 However, using conventional bacterial culture, bacteria are isolated from clinical samples obtained from children with complicated pneumonia in only 17%42% of cases.1, 9, 10 The low rate of positive culture results may be related to stringent bacterial growth requirements or to administration of broad‐spectrum antibiotics before obtaining blood or pleural fluid samples for culture.

Unlike bacterial culture, polymerase chain reaction (PCR) relies on the detection of bacterial DNA rather than on the recovery of viable bacteria and is therefore less affected by the prior administration of antibiotics. Broad‐range or universal primer 16S rRNA PCR detects a conserved region of the 16S ribosomal RNA (rRNA) gene and can detect a wide range of bacterial species with a single assay.11 However, few studies have evaluated the role of 16S rRNA PCR in detecting bacteria in the pleural fluid of children with complicated pneumonia.12, 13 The purpose of this study was to determine the frequency of positive blood and pleural fluid cultures in children with complicated pneumonia, and to determine whether broad‐range 16S rRNA PCR can increase the proportion of children with an identifiable microbiologic cause of complicated pneumonia.

Methods

Results

During the study period, 124 patients with complicated pneumonia were identified; the median age was 4.9 years (IQR, 2.78.8 years) and the ratio of female to male patients was 1:1. The racial distribution was as follows: non‐Hispanic white, 62 (50%); non‐Hispanic black, 43 (34%); and Hispanic, 7 (6%). The median length of stay was 11 days (range, 240 days; IQR, 811 days). Forty‐one (33.1%) patients were admitted to the intensive care unit, and nine (7.3%) patients required mechanical ventilation. Overall, 5 of the 71 blood cultures performed (7.0%; 95% CI: 2.3%15.7%) were positive.

Pleural fluid drainage was performed in 64 (51.6%) patients. The median duration of antibiotic treatment before pleural fluid drainage was two days (IQR, 04 days). Differences in duration of antibiotic pretreatment between those with and without pleural fluid drainage were not significant. Patients received beta‐lactam agents (76.6%), clindamycin (51.6%), and vancomycin (23.4%) before pleural drainage. Blood cultures were performed in 27 (45.0%) of 60 patients not undergoing pleural fluid drainage; 2 of these 27 (7.4%; 95% CI: 0.9%24.3%) blood cultures were positive, and Streptococcus pneumoniae was isolated in both cases.

Using a combination of pleural fluid culture, blood culture, and broad‐range PCR, a microbiologic cause of infection was identified in 11 of 64 (17.2%; 95% CI: 8.9%28.7%) patients undergoing pleural fluid drainage (Figure 1). Patients with an identified bacterial cause were younger than those without an identified bacterial cause (Table 1). However, there were no statistically significant differences between the groups with and without identified bacteria with respect to sex, race, clinical examination findings and laboratory results at admission, duration of antibiotic therapy before pleural fluid drainage, or length of stay (Table 1). The median pleural fluid white blood cell count was 6880 per mm³ (IQR, 154227,918 per mm³).

Figure 1

Blood was obtained for culture from 44 (68.8%) of 64 patients that underwent pleural fluid drainage. Blood cultures were positive in three (6.8%; 95% CI: 1.4%18.7%) of these patients; causative bacteria were S. pneumoniae (n = 1), Haemophilus influenzae (n = 1), and Staphylococcus aureus (n = 1). Pleural fluid cultures were positive from 6 of 64 patients (9.3%; 95% CI: 3.5%19.3%) that underwent pleural fluid drainage; causative bacteria were Staphylococcus aureus (n = 5) and Streptococcus pneumoniae (n = 1). Three of the 19 pleural fluid samples (15.8%, CI 3.4%39.6%) tested by 16S rRNA PCR yielded positive results; S. pneumoniae was identified by DNA sequencing in all three of these samples (Figure 1). Of these three specimens, two had both negative Gram stains and negative pleural fluid cultures, while one specimen had Gram‐positive cocci in pairs identified on Gram stain along with a pleural fluid culture‐positive for S. pneumoniae. Of the 16 patients with negative PCR results, one was found to have a pleural fluid culture‐positive for S. aureus; no bacteria were detected on the pleural fluid Gram stain (Figure 1). Differences in the demographic characteristics between patients in whom broad‐range PCR was performed and not performed were not statistically significant (Table 2). Differences in the median length of hospital stay between patients who had PCR performed (9 days; IQR, 712 days) and those who did not (11 days; IQR, 914 days) were not statistically significant (P = 0.19). Antibiotic therapy was simplified from treatment with multiple antibiotics to a single antibiotic in each instance of a positive culture, though the number of positive cultures was too small to lead to meaningful reductions in antibiotic use or spectrum.

Discussion

Identification of the causative organism can improve the treatment of children with complicated pneumonia by enabling clinicians to target the infection with effective, narrow‐spectrum antibiotics. However, broad‐spectrum antibiotics are typically given before blood or pleural fluid samples are obtained, lowering the yield of conventional bacterial cultures. In our study, pleural fluid and blood cultures were infrequently positive. However, the use of 16S rRNA broad‐range PCR and DNA sequencing as ancillary tests only modestly improved our diagnostic yield.

Two prior studies have shown that broad‐range PCR analysis of pleural fluid can detect pathogenic organisms from pleural fluid even after the administration of antibiotics. Saglani et al.12 used bacterial culture and broad‐range PCR to analyze pleural fluid from 32 children with complicated pneumonia. Although the cohort had received a median of eight days of antibiotic therapy prior to fluid aspiration, a combination of broad‐range PCR and DNA sequencing identified organisms, predominantly S. pneumoniae, in 17 of 26 (65.4%) pleural fluid samples with negative culture. Five of the six culture‐positive samples also had positive PCR results, suggesting that a low proportion of the PCR results were false‐negatives. Le Monnier et al.13 cultured the pleural fluid from 78 children with complicated pneumonia; 15 samples were excluded from PCR testing because they grew bacteria other than S. pneumoniae. Broad‐range 16S rRNA PCR detected bacteria in 22 of 40 (55.0%) samples that were culture‐negative; subsequent DNA sequencing identified S. pneumoniae (n = 17), S. pyogenes (n = 3), S. aureus (n = 1), and H. influenzae (n = 1). S. pneumoniae was identified by 16S rRNA PCR followed by DNA sequencing in 20 of the 23 (87.0%) pleural fluid samples that grew S. pneumoniae on culture.

PCR with organism‐specific primers has also been shown to detect pathogenic bacteria in 35%70% of pleural fluid samples from patients with complicated pneumonia.15, 16 These rates of detection are comparable to the results of prior studies that used broad‐range PCR, and suggest that 16S rRNA and organism‐specific PCR are similarly sensitive tests.

Our study found that the proportion of positive results with broad‐range PCR was greater than the proportion observed with conventional pleural fluid culture. We were also able to identify S. pneumoniae by broad‐range PCR in two culture‐negative pleural fluid samples. The detection of S. pneumoniae by PCR in the setting of negative pleural fluid culture is not surprising, as most patients received empiric antibiotic therapy against S. pneumoniae before undergoing pleural fluid drainage. This prior antibiotic therapy would be expected to decrease the yield of pleural fluid culture but have a less significant impact on PCR. The reason for the failure to detect S. aureus by PCR from our clinical samples is not known. We explored whether this issue could be attributable to test characteristics during validation of our assay (as described in the technical Appendix), and S. aureus was consistently identified in pleural fluid samples spiked with S. aureus. While our diagnostic yield was low compared with prior studies that used broad‐range PCR, the distribution of causative bacteria was similar to prior studies of complicated pneumonia.9, 10 There were too few positive cultures among the specimens available for broad‐range PCR testing for us to reliably assess 16S rRNA PCR sensitivity and specificity. Thus, it was not possible to reliably assess the value of 16S rRNA PCR as an ancillary test in culture‐negative complicated pneumonia.

Several factors may have contributed to the low yield of broad‐range PCR in our study. First, all patients in our study received broad‐spectrum antibiotics prior to pleural fluid drainage; most patients received treatment with a beta‐lactam agent in combination with either clindamycin or vancomycin. Although PCR is less affected than culture by the prior administration of antibiotics, it is still possible that exposure to antibiotics accelerated degradation of the bacterial genome, thus decreasing the sensitivity of broad‐range PCR. The median duration of antibiotic therapy prior to drainage was shorter for patients in whom a bacterial pathogen was identified, compared with those in whom a pathogen was not identified. Though this difference was not statistically significant, this difference emphasizes that early pleural fluid collection may improve bacterial detection. The median duration of prior antibiotic therapy was eight days, in the study by Saglani et al.,12 however details regarding anti‐staphylococcal therapy were not reported. Second, several studies using 16S rRNA PCR in blood or cerebrospinal fluid (CSF) specimens for children with sepsis or meningitis, respectively, have noted decreased sensitivity for detection of Gram‐positive bacteria.1720 The cell wall composition makes Gram‐positive bacteria particularly difficult to lyse for DNA extraction. Prior studies used a different approach to DNA extraction compared with our study. Saglani et al.12 used the QIAmp minikit for DNA extraction (Qiagen Ltd, West Sussex, UK) and Le Monnier et al.13 used the MagnaPure System (Roche Diagnostics, Indianapolis, IN) for DNA extraction; additionally Saglani et al.12 included an additional 15 minutes of incubation at 95C following Proteinase K digestion to ensure complete lysis of the bacterial cells. We used the MagMAX Total Nucleic Acid Isolation Kit with a bead beating step to degrade the samples prior to lysis. It is unlikely that any of these differences contributed to differences in our study results. Third, human DNA may cause a nonspecific background signal, which could decrease PCR sensitivity. This issue may be particularly important in complicated pneumonia where the pleural fluid white blood cell counts are substantially elevated. Human DNA from white blood cells might be present at much higher concentrations than bacterial DNA, which would create a competitive advantage for binding of human, rather than bacterial, DNA on to the bead matrix.21 Saglani et al.12 did not report pleural fluid white blood cell counts for comparison. However, Le Monnier et al.13 reported pleural fluid white blood cell counts slightly higher than those observed in our patients. Thus, differences in pleural fluid white blood cell counts do not necessarily explain the differences in yield across studies. Fourth, while the universal primers used in our study have been validated, including for detection of S. aureus, in previous studies,14 Saglani et al.12 and Le Monnier et al.13 each used a different set of primers. It is unclear whether or not the choice of different primers affected the microbiologic yield.

An important limitation of this study is the relatively small number of patients with pleural fluid available for PCR testing combined with the low PCR yield. This limitation may have caused us to underestimate the true benefit of 16S rRNA PCR as an ancillary diagnostic test, as suggested by the wide confidence intervals around the estimates of PCR yield. Additionally, not all patients underwent pleural drainage, and not all patients undergoing pleural drainage had pleural fluid available for PCR testing. The latter issue would likely have only minimal impact on our study results, as there were no differences in demographics or clinical or laboratory features among those with and without pleural fluid available for PCR testing. However, differences among physicians, and across institutions, may play an important role in the decision to perform pleural drainage. We do not know whether patients undergoing pleural drainage at our institution were more or less likely to have bacteria detected by PCR than patients not undergoing drainage. If they were more likely to have bacteria detected, then our study would underestimate the benefit of PCR as an adjunct diagnostic test. However, there was no difference in the duration of antibiotic pretreatment between these two groups, and the yield from blood culture was similar.

In conclusion, blood and pleural fluid cultures infrequently identify the causative bacteria in children with complicated pneumonia. The use of broad‐range PCR increased the microbiologic yield only modestly. Further refinements to improve the diagnostic accuracy of broad‐range PCR testing are needed before this technique can be recommended for widespread use in clinical practice.

Community‐acquired pneumonia (CAP), the most common serious bacterial infection in childhood, may be complicated by parapneumonic effusion (ie, complicated pneumonia).1, 2 The clinical outcome of children with complicated pneumonia is directly influenced by the causative organism, and precise identification of the infectious agent has the potential to improve clinical management.35 The incidence of complicated pneumonia has recently increased, highlighting the need to better understand the reasons for this changing epidemiology.68 However, using conventional bacterial culture, bacteria are isolated from clinical samples obtained from children with complicated pneumonia in only 17%42% of cases.1, 9, 10 The low rate of positive culture results may be related to stringent bacterial growth requirements or to administration of broad‐spectrum antibiotics before obtaining blood or pleural fluid samples for culture.

Unlike bacterial culture, polymerase chain reaction (PCR) relies on the detection of bacterial DNA rather than on the recovery of viable bacteria and is therefore less affected by the prior administration of antibiotics. Broad‐range or universal primer 16S rRNA PCR detects a conserved region of the 16S ribosomal RNA (rRNA) gene and can detect a wide range of bacterial species with a single assay.11 However, few studies have evaluated the role of 16S rRNA PCR in detecting bacteria in the pleural fluid of children with complicated pneumonia.12, 13 The purpose of this study was to determine the frequency of positive blood and pleural fluid cultures in children with complicated pneumonia, and to determine whether broad‐range 16S rRNA PCR can increase the proportion of children with an identifiable microbiologic cause of complicated pneumonia.

Methods

Results

During the study period, 124 patients with complicated pneumonia were identified; the median age was 4.9 years (IQR, 2.78.8 years) and the ratio of female to male patients was 1:1. The racial distribution was as follows: non‐Hispanic white, 62 (50%); non‐Hispanic black, 43 (34%); and Hispanic, 7 (6%). The median length of stay was 11 days (range, 240 days; IQR, 811 days). Forty‐one (33.1%) patients were admitted to the intensive care unit, and nine (7.3%) patients required mechanical ventilation. Overall, 5 of the 71 blood cultures performed (7.0%; 95% CI: 2.3%15.7%) were positive.

Pleural fluid drainage was performed in 64 (51.6%) patients. The median duration of antibiotic treatment before pleural fluid drainage was two days (IQR, 04 days). Differences in duration of antibiotic pretreatment between those with and without pleural fluid drainage were not significant. Patients received beta‐lactam agents (76.6%), clindamycin (51.6%), and vancomycin (23.4%) before pleural drainage. Blood cultures were performed in 27 (45.0%) of 60 patients not undergoing pleural fluid drainage; 2 of these 27 (7.4%; 95% CI: 0.9%24.3%) blood cultures were positive, and Streptococcus pneumoniae was isolated in both cases.

Using a combination of pleural fluid culture, blood culture, and broad‐range PCR, a microbiologic cause of infection was identified in 11 of 64 (17.2%; 95% CI: 8.9%28.7%) patients undergoing pleural fluid drainage (Figure 1). Patients with an identified bacterial cause were younger than those without an identified bacterial cause (Table 1). However, there were no statistically significant differences between the groups with and without identified bacteria with respect to sex, race, clinical examination findings and laboratory results at admission, duration of antibiotic therapy before pleural fluid drainage, or length of stay (Table 1). The median pleural fluid white blood cell count was 6880 per mm³ (IQR, 154227,918 per mm³).

Figure 1

Blood was obtained for culture from 44 (68.8%) of 64 patients that underwent pleural fluid drainage. Blood cultures were positive in three (6.8%; 95% CI: 1.4%18.7%) of these patients; causative bacteria were S. pneumoniae (n = 1), Haemophilus influenzae (n = 1), and Staphylococcus aureus (n = 1). Pleural fluid cultures were positive from 6 of 64 patients (9.3%; 95% CI: 3.5%19.3%) that underwent pleural fluid drainage; causative bacteria were Staphylococcus aureus (n = 5) and Streptococcus pneumoniae (n = 1). Three of the 19 pleural fluid samples (15.8%, CI 3.4%39.6%) tested by 16S rRNA PCR yielded positive results; S. pneumoniae was identified by DNA sequencing in all three of these samples (Figure 1). Of these three specimens, two had both negative Gram stains and negative pleural fluid cultures, while one specimen had Gram‐positive cocci in pairs identified on Gram stain along with a pleural fluid culture‐positive for S. pneumoniae. Of the 16 patients with negative PCR results, one was found to have a pleural fluid culture‐positive for S. aureus; no bacteria were detected on the pleural fluid Gram stain (Figure 1). Differences in the demographic characteristics between patients in whom broad‐range PCR was performed and not performed were not statistically significant (Table 2). Differences in the median length of hospital stay between patients who had PCR performed (9 days; IQR, 712 days) and those who did not (11 days; IQR, 914 days) were not statistically significant (P = 0.19). Antibiotic therapy was simplified from treatment with multiple antibiotics to a single antibiotic in each instance of a positive culture, though the number of positive cultures was too small to lead to meaningful reductions in antibiotic use or spectrum.

Discussion

Identification of the causative organism can improve the treatment of children with complicated pneumonia by enabling clinicians to target the infection with effective, narrow‐spectrum antibiotics. However, broad‐spectrum antibiotics are typically given before blood or pleural fluid samples are obtained, lowering the yield of conventional bacterial cultures. In our study, pleural fluid and blood cultures were infrequently positive. However, the use of 16S rRNA broad‐range PCR and DNA sequencing as ancillary tests only modestly improved our diagnostic yield.

Two prior studies have shown that broad‐range PCR analysis of pleural fluid can detect pathogenic organisms from pleural fluid even after the administration of antibiotics. Saglani et al.12 used bacterial culture and broad‐range PCR to analyze pleural fluid from 32 children with complicated pneumonia. Although the cohort had received a median of eight days of antibiotic therapy prior to fluid aspiration, a combination of broad‐range PCR and DNA sequencing identified organisms, predominantly S. pneumoniae, in 17 of 26 (65.4%) pleural fluid samples with negative culture. Five of the six culture‐positive samples also had positive PCR results, suggesting that a low proportion of the PCR results were false‐negatives. Le Monnier et al.13 cultured the pleural fluid from 78 children with complicated pneumonia; 15 samples were excluded from PCR testing because they grew bacteria other than S. pneumoniae. Broad‐range 16S rRNA PCR detected bacteria in 22 of 40 (55.0%) samples that were culture‐negative; subsequent DNA sequencing identified S. pneumoniae (n = 17), S. pyogenes (n = 3), S. aureus (n = 1), and H. influenzae (n = 1). S. pneumoniae was identified by 16S rRNA PCR followed by DNA sequencing in 20 of the 23 (87.0%) pleural fluid samples that grew S. pneumoniae on culture.

PCR with organism‐specific primers has also been shown to detect pathogenic bacteria in 35%70% of pleural fluid samples from patients with complicated pneumonia.15, 16 These rates of detection are comparable to the results of prior studies that used broad‐range PCR, and suggest that 16S rRNA and organism‐specific PCR are similarly sensitive tests.

Our study found that the proportion of positive results with broad‐range PCR was greater than the proportion observed with conventional pleural fluid culture. We were also able to identify S. pneumoniae by broad‐range PCR in two culture‐negative pleural fluid samples. The detection of S. pneumoniae by PCR in the setting of negative pleural fluid culture is not surprising, as most patients received empiric antibiotic therapy against S. pneumoniae before undergoing pleural fluid drainage. This prior antibiotic therapy would be expected to decrease the yield of pleural fluid culture but have a less significant impact on PCR. The reason for the failure to detect S. aureus by PCR from our clinical samples is not known. We explored whether this issue could be attributable to test characteristics during validation of our assay (as described in the technical Appendix), and S. aureus was consistently identified in pleural fluid samples spiked with S. aureus. While our diagnostic yield was low compared with prior studies that used broad‐range PCR, the distribution of causative bacteria was similar to prior studies of complicated pneumonia.9, 10 There were too few positive cultures among the specimens available for broad‐range PCR testing for us to reliably assess 16S rRNA PCR sensitivity and specificity. Thus, it was not possible to reliably assess the value of 16S rRNA PCR as an ancillary test in culture‐negative complicated pneumonia.

Several factors may have contributed to the low yield of broad‐range PCR in our study. First, all patients in our study received broad‐spectrum antibiotics prior to pleural fluid drainage; most patients received treatment with a beta‐lactam agent in combination with either clindamycin or vancomycin. Although PCR is less affected than culture by the prior administration of antibiotics, it is still possible that exposure to antibiotics accelerated degradation of the bacterial genome, thus decreasing the sensitivity of broad‐range PCR. The median duration of antibiotic therapy prior to drainage was shorter for patients in whom a bacterial pathogen was identified, compared with those in whom a pathogen was not identified. Though this difference was not statistically significant, this difference emphasizes that early pleural fluid collection may improve bacterial detection. The median duration of prior antibiotic therapy was eight days, in the study by Saglani et al.,12 however details regarding anti‐staphylococcal therapy were not reported. Second, several studies using 16S rRNA PCR in blood or cerebrospinal fluid (CSF) specimens for children with sepsis or meningitis, respectively, have noted decreased sensitivity for detection of Gram‐positive bacteria.1720 The cell wall composition makes Gram‐positive bacteria particularly difficult to lyse for DNA extraction. Prior studies used a different approach to DNA extraction compared with our study. Saglani et al.12 used the QIAmp minikit for DNA extraction (Qiagen Ltd, West Sussex, UK) and Le Monnier et al.13 used the MagnaPure System (Roche Diagnostics, Indianapolis, IN) for DNA extraction; additionally Saglani et al.12 included an additional 15 minutes of incubation at 95C following Proteinase K digestion to ensure complete lysis of the bacterial cells. We used the MagMAX Total Nucleic Acid Isolation Kit with a bead beating step to degrade the samples prior to lysis. It is unlikely that any of these differences contributed to differences in our study results. Third, human DNA may cause a nonspecific background signal, which could decrease PCR sensitivity. This issue may be particularly important in complicated pneumonia where the pleural fluid white blood cell counts are substantially elevated. Human DNA from white blood cells might be present at much higher concentrations than bacterial DNA, which would create a competitive advantage for binding of human, rather than bacterial, DNA on to the bead matrix.21 Saglani et al.12 did not report pleural fluid white blood cell counts for comparison. However, Le Monnier et al.13 reported pleural fluid white blood cell counts slightly higher than those observed in our patients. Thus, differences in pleural fluid white blood cell counts do not necessarily explain the differences in yield across studies. Fourth, while the universal primers used in our study have been validated, including for detection of S. aureus, in previous studies,14 Saglani et al.12 and Le Monnier et al.13 each used a different set of primers. It is unclear whether or not the choice of different primers affected the microbiologic yield.

An important limitation of this study is the relatively small number of patients with pleural fluid available for PCR testing combined with the low PCR yield. This limitation may have caused us to underestimate the true benefit of 16S rRNA PCR as an ancillary diagnostic test, as suggested by the wide confidence intervals around the estimates of PCR yield. Additionally, not all patients underwent pleural drainage, and not all patients undergoing pleural drainage had pleural fluid available for PCR testing. The latter issue would likely have only minimal impact on our study results, as there were no differences in demographics or clinical or laboratory features among those with and without pleural fluid available for PCR testing. However, differences among physicians, and across institutions, may play an important role in the decision to perform pleural drainage. We do not know whether patients undergoing pleural drainage at our institution were more or less likely to have bacteria detected by PCR than patients not undergoing drainage. If they were more likely to have bacteria detected, then our study would underestimate the benefit of PCR as an adjunct diagnostic test. However, there was no difference in the duration of antibiotic pretreatment between these two groups, and the yield from blood culture was similar.

In conclusion, blood and pleural fluid cultures infrequently identify the causative bacteria in children with complicated pneumonia. The use of broad‐range PCR increased the microbiologic yield only modestly. Further refinements to improve the diagnostic accuracy of broad‐range PCR testing are needed before this technique can be recommended for widespread use in clinical practice.

Community‐acquired pneumonia (CAP), the most common serious bacterial infection in childhood, may be complicated by parapneumonic effusion (ie, complicated pneumonia).1, 2 The clinical outcome of children with complicated pneumonia is directly influenced by the causative organism, and precise identification of the infectious agent has the potential to improve clinical management.35 The incidence of complicated pneumonia has recently increased, highlighting the need to better understand the reasons for this changing epidemiology.68 However, using conventional bacterial culture, bacteria are isolated from clinical samples obtained from children with complicated pneumonia in only 17%42% of cases.1, 9, 10 The low rate of positive culture results may be related to stringent bacterial growth requirements or to administration of broad‐spectrum antibiotics before obtaining blood or pleural fluid samples for culture.

Unlike bacterial culture, polymerase chain reaction (PCR) relies on the detection of bacterial DNA rather than on the recovery of viable bacteria and is therefore less affected by the prior administration of antibiotics. Broad‐range or universal primer 16S rRNA PCR detects a conserved region of the 16S ribosomal RNA (rRNA) gene and can detect a wide range of bacterial species with a single assay.11 However, few studies have evaluated the role of 16S rRNA PCR in detecting bacteria in the pleural fluid of children with complicated pneumonia.12, 13 The purpose of this study was to determine the frequency of positive blood and pleural fluid cultures in children with complicated pneumonia, and to determine whether broad‐range 16S rRNA PCR can increase the proportion of children with an identifiable microbiologic cause of complicated pneumonia.

Methods

Results

During the study period, 124 patients with complicated pneumonia were identified; the median age was 4.9 years (IQR, 2.78.8 years) and the ratio of female to male patients was 1:1. The racial distribution was as follows: non‐Hispanic white, 62 (50%); non‐Hispanic black, 43 (34%); and Hispanic, 7 (6%). The median length of stay was 11 days (range, 240 days; IQR, 811 days). Forty‐one (33.1%) patients were admitted to the intensive care unit, and nine (7.3%) patients required mechanical ventilation. Overall, 5 of the 71 blood cultures performed (7.0%; 95% CI: 2.3%15.7%) were positive.

Pleural fluid drainage was performed in 64 (51.6%) patients. The median duration of antibiotic treatment before pleural fluid drainage was two days (IQR, 04 days). Differences in duration of antibiotic pretreatment between those with and without pleural fluid drainage were not significant. Patients received beta‐lactam agents (76.6%), clindamycin (51.6%), and vancomycin (23.4%) before pleural drainage. Blood cultures were performed in 27 (45.0%) of 60 patients not undergoing pleural fluid drainage; 2 of these 27 (7.4%; 95% CI: 0.9%24.3%) blood cultures were positive, and Streptococcus pneumoniae was isolated in both cases.

Using a combination of pleural fluid culture, blood culture, and broad‐range PCR, a microbiologic cause of infection was identified in 11 of 64 (17.2%; 95% CI: 8.9%28.7%) patients undergoing pleural fluid drainage (Figure 1). Patients with an identified bacterial cause were younger than those without an identified bacterial cause (Table 1). However, there were no statistically significant differences between the groups with and without identified bacteria with respect to sex, race, clinical examination findings and laboratory results at admission, duration of antibiotic therapy before pleural fluid drainage, or length of stay (Table 1). The median pleural fluid white blood cell count was 6880 per mm³ (IQR, 154227,918 per mm³).

Figure 1

Blood was obtained for culture from 44 (68.8%) of 64 patients that underwent pleural fluid drainage. Blood cultures were positive in three (6.8%; 95% CI: 1.4%18.7%) of these patients; causative bacteria were S. pneumoniae (n = 1), Haemophilus influenzae (n = 1), and Staphylococcus aureus (n = 1). Pleural fluid cultures were positive from 6 of 64 patients (9.3%; 95% CI: 3.5%19.3%) that underwent pleural fluid drainage; causative bacteria were Staphylococcus aureus (n = 5) and Streptococcus pneumoniae (n = 1). Three of the 19 pleural fluid samples (15.8%, CI 3.4%39.6%) tested by 16S rRNA PCR yielded positive results; S. pneumoniae was identified by DNA sequencing in all three of these samples (Figure 1). Of these three specimens, two had both negative Gram stains and negative pleural fluid cultures, while one specimen had Gram‐positive cocci in pairs identified on Gram stain along with a pleural fluid culture‐positive for S. pneumoniae. Of the 16 patients with negative PCR results, one was found to have a pleural fluid culture‐positive for S. aureus; no bacteria were detected on the pleural fluid Gram stain (Figure 1). Differences in the demographic characteristics between patients in whom broad‐range PCR was performed and not performed were not statistically significant (Table 2). Differences in the median length of hospital stay between patients who had PCR performed (9 days; IQR, 712 days) and those who did not (11 days; IQR, 914 days) were not statistically significant (P = 0.19). Antibiotic therapy was simplified from treatment with multiple antibiotics to a single antibiotic in each instance of a positive culture, though the number of positive cultures was too small to lead to meaningful reductions in antibiotic use or spectrum.

Discussion

Identification of the causative organism can improve the treatment of children with complicated pneumonia by enabling clinicians to target the infection with effective, narrow‐spectrum antibiotics. However, broad‐spectrum antibiotics are typically given before blood or pleural fluid samples are obtained, lowering the yield of conventional bacterial cultures. In our study, pleural fluid and blood cultures were infrequently positive. However, the use of 16S rRNA broad‐range PCR and DNA sequencing as ancillary tests only modestly improved our diagnostic yield.

Two prior studies have shown that broad‐range PCR analysis of pleural fluid can detect pathogenic organisms from pleural fluid even after the administration of antibiotics. Saglani et al.12 used bacterial culture and broad‐range PCR to analyze pleural fluid from 32 children with complicated pneumonia. Although the cohort had received a median of eight days of antibiotic therapy prior to fluid aspiration, a combination of broad‐range PCR and DNA sequencing identified organisms, predominantly S. pneumoniae, in 17 of 26 (65.4%) pleural fluid samples with negative culture. Five of the six culture‐positive samples also had positive PCR results, suggesting that a low proportion of the PCR results were false‐negatives. Le Monnier et al.13 cultured the pleural fluid from 78 children with complicated pneumonia; 15 samples were excluded from PCR testing because they grew bacteria other than S. pneumoniae. Broad‐range 16S rRNA PCR detected bacteria in 22 of 40 (55.0%) samples that were culture‐negative; subsequent DNA sequencing identified S. pneumoniae (n = 17), S. pyogenes (n = 3), S. aureus (n = 1), and H. influenzae (n = 1). S. pneumoniae was identified by 16S rRNA PCR followed by DNA sequencing in 20 of the 23 (87.0%) pleural fluid samples that grew S. pneumoniae on culture.

PCR with organism‐specific primers has also been shown to detect pathogenic bacteria in 35%70% of pleural fluid samples from patients with complicated pneumonia.15, 16 These rates of detection are comparable to the results of prior studies that used broad‐range PCR, and suggest that 16S rRNA and organism‐specific PCR are similarly sensitive tests.

Our study found that the proportion of positive results with broad‐range PCR was greater than the proportion observed with conventional pleural fluid culture. We were also able to identify S. pneumoniae by broad‐range PCR in two culture‐negative pleural fluid samples. The detection of S. pneumoniae by PCR in the setting of negative pleural fluid culture is not surprising, as most patients received empiric antibiotic therapy against S. pneumoniae before undergoing pleural fluid drainage. This prior antibiotic therapy would be expected to decrease the yield of pleural fluid culture but have a less significant impact on PCR. The reason for the failure to detect S. aureus by PCR from our clinical samples is not known. We explored whether this issue could be attributable to test characteristics during validation of our assay (as described in the technical Appendix), and S. aureus was consistently identified in pleural fluid samples spiked with S. aureus. While our diagnostic yield was low compared with prior studies that used broad‐range PCR, the distribution of causative bacteria was similar to prior studies of complicated pneumonia.9, 10 There were too few positive cultures among the specimens available for broad‐range PCR testing for us to reliably assess 16S rRNA PCR sensitivity and specificity. Thus, it was not possible to reliably assess the value of 16S rRNA PCR as an ancillary test in culture‐negative complicated pneumonia.

Several factors may have contributed to the low yield of broad‐range PCR in our study. First, all patients in our study received broad‐spectrum antibiotics prior to pleural fluid drainage; most patients received treatment with a beta‐lactam agent in combination with either clindamycin or vancomycin. Although PCR is less affected than culture by the prior administration of antibiotics, it is still possible that exposure to antibiotics accelerated degradation of the bacterial genome, thus decreasing the sensitivity of broad‐range PCR. The median duration of antibiotic therapy prior to drainage was shorter for patients in whom a bacterial pathogen was identified, compared with those in whom a pathogen was not identified. Though this difference was not statistically significant, this difference emphasizes that early pleural fluid collection may improve bacterial detection. The median duration of prior antibiotic therapy was eight days, in the study by Saglani et al.,12 however details regarding anti‐staphylococcal therapy were not reported. Second, several studies using 16S rRNA PCR in blood or cerebrospinal fluid (CSF) specimens for children with sepsis or meningitis, respectively, have noted decreased sensitivity for detection of Gram‐positive bacteria.1720 The cell wall composition makes Gram‐positive bacteria particularly difficult to lyse for DNA extraction. Prior studies used a different approach to DNA extraction compared with our study. Saglani et al.12 used the QIAmp minikit for DNA extraction (Qiagen Ltd, West Sussex, UK) and Le Monnier et al.13 used the MagnaPure System (Roche Diagnostics, Indianapolis, IN) for DNA extraction; additionally Saglani et al.12 included an additional 15 minutes of incubation at 95C following Proteinase K digestion to ensure complete lysis of the bacterial cells. We used the MagMAX Total Nucleic Acid Isolation Kit with a bead beating step to degrade the samples prior to lysis. It is unlikely that any of these differences contributed to differences in our study results. Third, human DNA may cause a nonspecific background signal, which could decrease PCR sensitivity. This issue may be particularly important in complicated pneumonia where the pleural fluid white blood cell counts are substantially elevated. Human DNA from white blood cells might be present at much higher concentrations than bacterial DNA, which would create a competitive advantage for binding of human, rather than bacterial, DNA on to the bead matrix.21 Saglani et al.12 did not report pleural fluid white blood cell counts for comparison. However, Le Monnier et al.13 reported pleural fluid white blood cell counts slightly higher than those observed in our patients. Thus, differences in pleural fluid white blood cell counts do not necessarily explain the differences in yield across studies. Fourth, while the universal primers used in our study have been validated, including for detection of S. aureus, in previous studies,14 Saglani et al.12 and Le Monnier et al.13 each used a different set of primers. It is unclear whether or not the choice of different primers affected the microbiologic yield.

An important limitation of this study is the relatively small number of patients with pleural fluid available for PCR testing combined with the low PCR yield. This limitation may have caused us to underestimate the true benefit of 16S rRNA PCR as an ancillary diagnostic test, as suggested by the wide confidence intervals around the estimates of PCR yield. Additionally, not all patients underwent pleural drainage, and not all patients undergoing pleural drainage had pleural fluid available for PCR testing. The latter issue would likely have only minimal impact on our study results, as there were no differences in demographics or clinical or laboratory features among those with and without pleural fluid available for PCR testing. However, differences among physicians, and across institutions, may play an important role in the decision to perform pleural drainage. We do not know whether patients undergoing pleural drainage at our institution were more or less likely to have bacteria detected by PCR than patients not undergoing drainage. If they were more likely to have bacteria detected, then our study would underestimate the benefit of PCR as an adjunct diagnostic test. However, there was no difference in the duration of antibiotic pretreatment between these two groups, and the yield from blood culture was similar.

In conclusion, blood and pleural fluid cultures infrequently identify the causative bacteria in children with complicated pneumonia. The use of broad‐range PCR increased the microbiologic yield only modestly. Further refinements to improve the diagnostic accuracy of broad‐range PCR testing are needed before this technique can be recommended for widespread use in clinical practice.

Disparities in patterns of care and outcomes for ambulatory‐care sensitive conditions remain a persistent problem for children.19 Many studies have focused on disparities in hospitalization rates and length of stay (LOS) related to asthma, however, few studies have focused on community‐acquired pneumonia (CAP) despite the fact that pneumonia is the most common, preventable, and potentially serious infection in childhood.10 Providers, payers, and families have a common interest in minimizing hospital LOS for different reasons (eg, minimizing costs, lost wages, exposure to antibiotic‐resistant bacteria), however, this interest is balanced against the potentially greater risk of readmission and adverse outcomes if LOS is inappropriately short. To date, the relationship between insurance status and LOS for CAP remains unexplored.

As in other conditions, substantial variation exists with respect to patterns of care and outcomes for children hospitalized with CAP.11 For example, children hospitalized in rural settings have a shorter LOS for pneumonia than those hospitalized in large urban settings.12 Children from racial/ethnic minorities tend to have higher rates of CAP‐associated complications, including death.11 Decades of prior studies have documented that uninsured children are less likely than insured children to make preventive care visits and obtain prescription medications, but differences in LOS or hospitalization rates between insured and uninsured children with CAP have not been studied.6, 8, 13, 14 Though imperfect, insurance status is 1 proxy for healthcare access, and current healthcare reform efforts aim to improve healthcare access and decrease socioeconomic gradients in health by increasing the number of insured American children. Nonetheless, quantifying the relationship between insurance status on LOS for children hospitalized with CAP is a first step towards understanding the influence of ambulatory care access on hospitalization for ambulatory‐care sensitive conditions.

The purpose of this study was to investigate the influence of insurance status and type on LOS for children hospitalized with CAP. In addition, we sought to determine if there were consistent trends over time in the association between insurance status and type with LOS for children hospitalized with CAP.

METHODS

RESULTS

The more than 10.5 million children sampled (unweighted) in KID during these 4 time periods (1997, 2000, 2003, and 2006) are representative of the more than 28.9 million children hospitalized in the United States. In each of these sample years, there were approximately 150,000 children hospitalized with pneumonia across the United States (Table 1). Of those hospitalized, 23% to 28% had a concomitant diagnosis of asthma; 6% to 8% had a pneumonia‐associated complication; and mortality was <0.01% in each sample year for patients hospitalized with pneumonia. In all years, among those with racial/ethnic data, the sample population was predominantly white boys less than 6 years old. The greatest proportion of children were hospitalized in urban non‐teaching settings, and also those children living in the southern regions of the United States.

There was little variation in the insurance status of children hospitalized with CAP between 1997 and 2006. In each of the sampled years, at least 40% of sampled children were privately insured, at least 40% were publicly insured, and approximately 5% were uninsured (Table 1). In all years, there were significant racial/ethnic disparities in insurance coverage such that whites were 4 to 6 times more likely to have private insurance than blacks, however, the large amount of missing race/ethnicity data warrant caution in interpreting this finding (Table 2; also see Supporting Information Appendix B in the online version of this article). We also found that children less than 1 year old were the most likely to be publicly insured in all years (see Supporting Appendix C in the online version of this article). There were also regional differences related to insurance coverage such that a greater proportion of children hospitalized in facilities located in the southern part of the United States were publicly insured. Notably, there were no significant differences in CAP‐associated mortality or asthma related to insurance coverage (Table 2). In 2006, CAP‐associated complications occurred in 8.5% of children with private insurance, 6.5% of children with public insurance, and 7.7% of uninsured children; the relative distribution of complications by insurance type were similar in previous years of the KID survey.

After examining the general and demographic characteristics, we then examined mean LOS for all children with CAP in each sample year (Table 3). The mean LOS for children with CAP was 3.44 days in 1997, with marginal decreases in subsequent years to a mean LOS of 3.18 days in 2006. The distribution of LOS for children with CAP revealed that nearly 70% of children were hospitalized for fewer than 3 days, another 22% to 28% were hospitalized for less than 1 week, and only 3% were hospitalized for more than 1 week. This distribution did not change substantially between 1997 and 2006. Next, we compared mean LOS by insurance type and race/ethnicity in unadjusted analyses. In each sample year, publicly insured children hospitalized with CAP had significantly longer LOS than privately insured children (P < 0.001). Similarly, in all years excepting 1997, uninsured children hospitalized with CAP had significantly shorter LOS than privately insured children. There were also significant racial differences in LOS for children with CAP, such that black children had longer LOS than white children with CAP. However, the large amount of missing data for race/ethnicity limited the robustness of this finding, and subsequent sensitivity analyses demonstrated that there were no consistent racial/ethnic disparities in LOS (see Supporting Appendix B in the online version of this article). These sensitivity analyses for missing race data did not alter our primary finding of shorter LOS for uninsured versus publicly or privately insured children.

After controlling for child age, race/ethnicity, gender, hospital type, transfer status, and presence of asthma or pneumonia‐associated complications, our multivariable analyses examining the relationship between insurance coverage and hospital LOS yielded the following results (Table 4). First, publicly insured children had significantly longer hospital stays than privately insured children, and uninsured children had significantly shorter hospital stays than privately insured children in all years except 1997. Second, children admitted with CAP at urban teaching children's hospitals had significantly longer LOS than those admitted to urban non‐teaching hospitals, and, in 2003, children admitted with CAP to rural hospitals had significantly shorter LOS than those admitted to urban non‐teaching hospitals. Third, children older than 1 year consistently had shorter hospital stays than infants less than 1 year old. Finally, though concomitant diagnosis of asthma did not consistently influence LOS, children who developed any complications had significantly longer LOS than those who did not. The cumulative impact of seemingly small differences in LOS is great. For example, in 2006, our model suggests that, for every 1000 children hospitalized with CAP in a given year, after adjusting for differences in sex, age, race, hospital‐type, region, transfer status, and diagnosis of asthma or complications, publicly insured children spend 90 to 130 more days in the hospital than privately insured children, whereas uninsured children spend between 40 to 90 fewer days in the hospital than privately insured children.