Antigen Test Diagnoses Pediatric Invasive Pneumococcal Disease

An immunochromatographic pneumococcal antigen test has been used for the identification of Streptococcus pneumoniae in pleural and cerebrospinal fluids from children.

The immunochromatographic pneumococcal antigen test was compared with a polymerase chain reaction assay, which detected of pneumococcal DNA by targeting the autolysin gene (lytA) encoding for N-acetylmuramoyl-l-alanine amidase.

Scientists at the Hospital Clínico San Carlos (Madrid, Spain) carried out a three-year prospective study from May 2007 to May 2010 and obtained 12 cerebrospinal fluids (CSF) and 205 pleural fluids (PF) from children less than 15 years old with suspected invasive pneumococcal disease (IPD). Conventional microbiological cultures were performed, and all the samples were analyzed using the Binax NOW S. pneumoniae antigen detection test (Alere Healthcare; Barcelona., Spain) and PCR. The Binax NOW test and PCR were also performed on blood culture bottles collected in the laboratory to evaluate which microorganisms could cause a false-positive result by Binax.

Of the 199 samples analyzed, 131 were positive by both Binax NOW and lytA PCR, and 36 samples were negative by both techniques. Using the real-time PCR as a comparative method to the Binax for the detection of S. pneumoniae, the sensitivity of Binax NOW was 88% and the specificity was 72.5%. Of the 145 positive samples analyzed by Binax NOW, 119 showed intense coloring of the sample line and 26 showed weak intensities.

The authors concluded that Binax NOW is easy to perform and feasible in any laboratory and an intense positive result indicates a high probability of the presence of S. pneumoniae in the clinical sample. Despite culture is the most common method in clinical settings, the Binax NOW might be considered a first screening technique for the detection of pneumococci in CSF and PF. Binax NOW offers significant advantages for the diagnosis of invasive pneumococcal disease, although the result should be confirmed by culture or PCR. The study was published in the May 2013 issue of the Journal of Microbiological Methods.

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