Detection of group B streptococcal antigen in body fluids by a latex-coupled monoclonal antibody assay

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Abstract
A commercially available latex agglutination reagent, Directigen, in which a murine monoclonal antibody to group B streptococcal (GBS) antigen is the active component, was evaluated by using body fluid specimens from 94 sick infants. Antigen was detected in 1 or more admission specimens from 18 of 19 (94.7%) infants with symptomatic GBS infection. In 15 patients with GBS meningitis, CSF, serum and 10-fold-concentrated urine specimens were positive in 87, 50 and 100%, respectively. GBS antigen was detected in 50% of unconcentrated urines, but in no sera from infants with nonmeningitic GBS sepsis. Among specimens from 27 infants with invasive infection due to organisms other than GBS and from 48 culture-negative sick infants, false-positive latex agglutination reactions occurred in only 4 (9.5%) urine specimens and in no CSF or serum specimens. The 94.7% sensitivity and specificity of the Directigen GBS test indicate that it is a useful reagent for the rapid diagnosis of invasive GBS infection in young infants.