Development of a Sensitive, Multiplexed Immunoassay Using XMAP Beads for Detection of Serotype-specific Streptococcus Pneumoniae Antigen in Urine Samples

In support of the surveillance of pneumococcal infections in the era of conjugate vaccines, a sensitive and specific multiplex immunoassay using xMAP beads has been developed for direct detection of pneumococcal serotype-specific polysaccharides in clinical samples, particularly urine. The assay was tested on panels of spiked urine specimens, clinical urine specimens and bacterial isolates. Each of the 14 serotypes in the multiplex assay can be detected to 0.1 ng purified polysaccharide ml(-1), or less. Testing of a panel of urine specimens from patients with culture-confirmed pneumococcal or non-pneumococcal disease indicated that the multiplex assay is both sensitive and specific. The correct pneumococcal serotype was identified directly from urine in 46/58 (79.3 %) patients who had a contemporaneous blood culture isolate of a multiplex assay serotype. Furthermore, the specificity of the assay on this panel of samples was 99.3 % (145/146). This multiplex assay could be useful, in conjunction with the pneumococcal screening test Binax NOW, in urine for diagnosis of pneumococcal disease and the identification of the aetiological serotype, and potentially be of benefit in culture-negative patients.