Rapid diagnosis of vaginal carriage of group B beta haemolytic streptococcus by an enrichment cum antigen detection test.

BACKGROUND & OBJECTIVES Group B beta haemolytic streptococcus (GBS) is a frequent colonizer of the maternal genital tract causing peripartum fever, puerperal sepsis, neonatal sepsis and neonatal meningitis. The conventional methods for detection of maternal colonization take 24-48 h. We made an attempt to standardize a rapid enrichment cum antigen detection test to screen pregnant women for GBS colonization in less than 8 h, so as to enable early institution of measures to prevent neonatal sepsis. METHODS Vaginal swabs of 100 women >36 wk of gestation were inoculated onto enrichment broth (Todd Hewitt broth with lysed horse blood and antibiotics). After incubation for 1,2,4,6, and 18 h, the broth was cultured on sheep blood agar. In culture positive cases, the enrichment broth was subjected to antigen detection by latex agglutination test (LAT). For further evaluation of the rapid test, another group of 100 pregnant women were screened for GBS carriage by 6 h enrichment broth culture followed by antigen detection test. RESULTS Five of the first group yielded GBS on culture and all were positive for GBS antigen after 6 h enrichment. Thirteen of the second group were positive for the antigen, but GBS could be isolated in ten only. This enrichment cum antigen detection test showed sensitivity, specificity, and positive and negative predictive values of 100, 98.4, 83.3 and 100 per cent respectively and could detect as few as 10(3) cfu/ml organisms. Maternal vaginal carriage of GBS was 7.5 per cent (15/200). INTERPRETATION & CONCLUSION Six hours of enrichment followed by antigen detection proved to be a rapid and reliable method for detection of GBS colonization. This test is easy to perform making it an ideal test for screening GBS vaginal colonization at labour and starting chemoprophylaxis, where indicated on the same day, before the woman is discharged.