Comparison of rapid tests for detection of group B streptococcal colonization

Accurate rapid detection of maternal lower genital tract colonization with group B streptococci (GBS) in high-risk patients is essential for selective institution of intrapartum antibiotic treatment to reduce neonatal GBS infection. In this study, pure GBS isolates were used to evaluate five commercially available rapid tests in terms of speed, ease of use, and sensitivity. The products tested were Directigen, Equate, Bactigen, PathoDx, and Phadebact. Although each test could be performed relatively quickly, the ease of performance and level of sensitivity (10(5) to 10(8) CFU/ml) varied markedly. Quantitative cultures obtained from 17 known GBS carriers showed concentrations ranging from less than 10(2) to greater than 10(8) CFU/gm of vaginal material. Since only 40% of the women had greater than or equal to 10(5) CFU/gm of vaginal material, it appears that many colonized women would not be identified by these rapid tests.