Detection and serotyping of pneumococci in community acquired pneumonia patients without culture using blood and urine samples.

Background: Treatment of community acquired pneumonia (CAP) patients with antibiotics before laboratory-confirmed diagnosis leads to loss of knowledge on the causative bacterial pathogen. Therefore, an increasing number of pneumococcal infections is identified using non-culture based techniques. However, methods for serotyping directly on the clinical specimen remain scarce. Here we present three approaches for detection and serotyping of pneumococci using samples from patients with CAP.

Methods: The first approach is quantitative PCR (qPCR) analysis on blood samples (n = 211) followed by capsular sequence typing (CST) to identify the serotype. The second approach, a urinary antigen assay (n = 223), designated as inhibition multiplex immunoassay (IMIA), is based on Luminex technology targeting 14 serotypes. The third approach is a multiplex immunoassay (MIA) (n = 171) also based on Luminex technology which detects serologic antibody responses against 14 serotypes. The three alternative assays were performed on samples obtained from 309 adult hospitalized CAP patients in 2007-2010 and the results were compared with those obtained from conventional laboratory methods to detect pneumococcal CAP, i.e. blood cultures, sputum cultures and BinaxNOW urinary antigen tests.

Results: Using qPCR, MIA and IMIA, we were able to detect the pneumococcus in samples of 56% more patients compared to conventional methods. Furthermore, we were able to assign a serotype to the infecting pneumococcus from samples of 25% of all CAP patients, using any of the three serotyping methods (CST, IMIA and MIA).

Conclusion: This study indicates the usefulness of additional molecular methods to conventional laboratory methods for the detection of pneumococcal pneumonia. Direct detection and subsequent serotyping on clinical samples will improve the accuracy of pneumococcal surveillance to monitor vaccine effectiveness.