Development of an Extended-Specificity Multiplex Immunoassay for Detection of Streptococcus pneumoniae Serotype-Specific Antigen in Urine by Use of Human Monoclonal Antibodies

Current pneumococcal vaccines cover the most common 10 to 23 serotypes of the 92 presently described. However, with the increased usage of pneumococcal serotype-based vaccines the risk of serotype-replacement and an increase in disease caused by non-vaccine serotypes remains. Serotype surveillance of pneumococcal infection relies heavily on culture techniques, which are known to be insensitive, particularly in non-invasive disease. Pneumococcal serotype-specific urine assays offer an alternative method of serotyping both invasive and non-invasive disease. However, the previously described assays cover mainly conjugate vaccine serotypes, give little information about circulating non-vaccine serotypes and are currently only available in one or two specialist laboratories. Our laboratory has developed an extended range antigen capture Luminex based assay to detect pneumococcal serotype specific antigen in urine samples. The assay targets 24 distinct serotypes/serogroups plus the cell wall polysaccharide (CWP) and some cross-reactive serotypes. We report that the assay is capable of detecting all the targeted serotypes and the CWP at 0.1ng/ml with some serotypes detected as low as 0.3 pg/ml. The analytical serotype specificity was determined as 98.4% using a panel of polysaccharide negative urine specimens spiked with non-pneumococcal bacterial antigens. We also report clinical sensitivities of 96.2% and specificities of 89.9% established using a panel of urine specimens from patients diagnosed with community acquired pneumonia or pneumococcal disease. This assay can be extended for testing other clinical samples and has the potential to greatly improve serotype-specific surveillance in the many cases of pneumococcal disease from which a culture is never obtained.