Background: 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. In addition, we aimed to study if a high NP pneumococcal density could be useful to detect severe pneumococcal pneumonia. Methods: Adult patients hospitalized for radiologically confirmed community-acquired pneumoniawere included in a prospective study. NP aspirates were collected at admission and were subjected to quantitative PCR for pneumococcal DNA (Spn9802 DNA). Patients were consideredto have pneumococcal etiology if S. pneumoniae was detected in blood culture and/ or culture of respiratory secretions and/or urinary antigen test. Results: Of 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 densityof 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 highpneumococcal 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 pneumoniawas 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 sensitivitiesof 54-82% and positive predictive values of 37-56%, indicating suboptimal performance. Conclusions: Pneumonia severity, symptom duration ≥2 days, and a medium/high serum immunoglobulin titer against the patient's own serotype were independently associated with a high NPpneumococcal density. NP pneumococcal density has limited value for detection of severe pneumococcal pneumonia.
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© 2015 Alpkvist et al.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.