Abstract
BackgroundWe aimed to study if certain clinical and/or microbiological factors are associated with a high nasopharyngeal (NP) density of Streptococcus pneumoniae in pneumococcal pneumonia. In addition, we aimed to study if a high NP pneumococcal density could be useful to detect severe pneumococcal pneumonia.MethodsAdult patients hospitalized for radiologically confirmed community-acquired pneumonia were included in a prospective study. NP aspirates were collected at admission and were subjected to quantitative PCR for pneumococcal DNA (Spn9802 DNA). Patients were considered to have pneumococcal etiology if S. pneumoniae was detected in blood culture and/or culture of respiratory secretions and/or urinary antigen test.ResultsOf 166 included patients, 68 patients had pneumococcal DNA detected in NP aspirate. Pneumococcal etiology was noted in 57 patients (84%) with positive and 8 patients (8.2%) with negative test for pneumococcal DNA (p<0.0001). The median NP pneumococcal density of DNA positive patients with pneumococcal etiology was 6.83 log10 DNA copies/mL (range 1.79–9.50). In a multivariate analysis of patients with pneumococcal etiology, a high pneumococcal density was independently associated with severe pneumonia (Pneumonia Severity Index risk class IV-V), symptom duration ≥2 days prior to admission, and a medium/high serum immunoglobulin titer against the patient’s own pneumococcal serotype. NP pneumococcal density was not associated with sex, age, smoking, co-morbidity, viral co-infection, pneumococcal serotype, or bacteremia. Severe pneumococcal pneumonia was noted in 28 study patients. When we studied the performance of PCR with different DNA cut-off levels for detection of severe pneumococcal pneumonia, we found sensitivities of 54–82% and positive predictive values of 37–56%, indicating suboptimal performance.ConclusionsPneumonia severity, symptom duration ≥2 days, and a medium/high serum immunoglobulin titer against the patient’s own serotype were independently associated with a high NP pneumococcal density. NP pneumococcal density has limited value for detection of severe pneumococcal pneumonia.
Highlights
Streptococcus pneumoniae is the most common microbiological cause of community-acquired pneumonia (CAP) [1]
In a multivariate analysis of patients with pneumococcal etiology, a high pneumococcal density was independently associated with severe pneumonia (Pneumonia Severity Index risk class IV-V), symptom duration 2 days prior to admission, and a PLOS ONE | DOI:10.1371/journal.pone
Severe pneumococcal pneumonia was noted in 28 study patients
Summary
Streptococcus pneumoniae is the most common microbiological cause of community-acquired pneumonia (CAP) [1]. With a quantitative PCR for the pneumococcal gene lytA, Albrich et al [8] found that a pneumococcal density of 8000 DNA copies /mL in NP secretions could distinguish pneumococcal pneumonia from asymptomatic colonization, with a sensitivity of 82.2% and a specificity of 92.0%. With a quantitative PCR for the pneumococcal gene fragment Spn9802 on NP aspirate, at cutoff 104 DNA copies/mL, our group found positivity rates of 84% in CAP patients with NP culture positive for S. pneumoniae, 6.0% in CAP patients with NP culture negative for S. pneumoniae, and 3.6% in asymptomatic controls [9]. We aimed to study if certain clinical and/or microbiological factors are associated with a high nasopharyngeal (NP) density of Streptococcus pneumoniae in pneumococcal pneumonia. We aimed to study if a high NP pneumococcal density could be useful to detect severe pneumococcal pneumonia
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