5 years ago

LytA quantitative PCR on sputum and nasopharyngeal swab samples in the detection of pneumococcal pneumonia among the elderly.

Jukka Jokinen, Vincent Verlant, Thierry Pascal, Arto A Palmu, Annika Saukkoriipi, William P Hausdorff
Quantitative real-time PCR (qPCR) on sputum or nasopharyngeal specimens has shown promising results in the detection of pneumococcal community-acquired pneumonia (PncCAP). We applied qPCR for the autolysin gene (lytA) and compared sputum and nasopharyngeal swab (NPS) pneumococcal loads in elderly patients with community-acquired pneumonia (CAP), and specifically in patients with PncCAP, to those in patient groups with other respiratory disease. We studied patients aged ≥65 years with radiologically confirmed CAP, clinical CAP not retrospectively radiologically confirmed, other acute respiratory infection, or stable chronic lung disease. Pneumococcal etiology of CAP was ascertained using a combination of multiple diagnostic methods. We analyzed sputum and NPS specimens by lytA qPCR with 10(4) pneumococcal genome equivalents (GE)/ml as a cutoff for positivity. Among PncCAP patients, lytA qPCR detected pneumococcus in 94% of the sputum samples and in high quantity (mean 6.82±1.02 log10GE/ml), but less frequently in NPS (44%) and in lower quantity (5.55±0.92 log10GE/ml). In all other patient groups, ≤10% of sputum and <5% of NPS samples were lytA qPCR-positive; but when positive, the sputum pneumococcal loads were similar to those in the PncCAP patients, suggesting pneumococcal etiology in these patients. This was supported by other pneumococcal assay results. Overall, sputum lytA qPCR positivity was more common in PncCAP patients than in the other patient groups, but the quantitative results were mainly similar. NPS lytA qPCR was less sensitive than sputum lytA qPCR in detecting PncCAP.

Publisher URL: http://doi.org/10.1128/JCM.01231-17

DOI: 10.1128/JCM.01231-17

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