Assessment of a rapid latex agglutination test for group B streptococcal colonization of the genital tract.

OBJECTIVE: The purpose of this study was to determine the reliability of a rapid enzyme extraction-latex agglutination test in detecting intrapartum colonization of the maternal genital tract by group B streptococci.
METHODS: Swabs of vaginal secretions were obtained from 314 patients in labor with either ruptured or intact membranes. Four tests were performed on each specimen: 1) qualitative culture on blood agar, 2) semiquantitative culture on blood agar, 3) culture in selective Todd-Hewitt broth, and 4) latex agglutination preceded by enzyme extraction.
RESULTS: The prevalence of positive cultures was 29%. When compared with culture in Todd-Hewitt broth, the latex agglutination test had a sensitivity of 30%, specificity 93%, positive predictive value 64%, and negative predictive value 76%. In patients with heavy colonization the test had a sensitivity of 76%, compared with 17% in patients with light growth (P less than .001). The lower limit of sensitivity of the test was 4 x 10(5) cfu/mL. The performance of the test was not affected by rupture of the membranes.
CONCLUSION: Although the latex agglutination test is reasonably sensitive in detecting heavy colonization, low overall performance combined with technical difficulties in assessment of particle agglutination make the test unsuitable for general screening.