Evaluation of three rapid methods for intrapartum detection of group B streptococcus

OBJECTIVE: The goal of this study was to evaluate three methods for rapid group B streptococcus (GBS) intrapartum vaginal detection. MATERIALS AND METHODS: In 330 women, at risk of delivering an infant with GBS disease, vaginal exudates were collected and a culture performed. The following rapid tests were also performed: 1) Equate Strep B immunoassay in 133 samples. 2) Icon Strep B immunoassay in 192 samples. 3) Co-agglutination with Phadebact Strep B, with a previous incubation (> 4 hours) of the vaginal swabs in Lim Group B Strep broth, in 88 samples. In some patients, two of these methods were performed simultaneously. RESULTS: GBS was detected in 37 women (11.2%) by culture. The sensitivity of Equate Strep B was 47%, Icon Strep B was 35% and co-agglutination with Phadebact Strep B was 38%. The specificity was 91%, 99% and 100% for each one of these methods. PPV 44%, 90% and 100%, respectively and NPV 92%, 91% and 90%, respectively. CONCLUSION: In conclusion, none of these methods was shown sensitive enough to be used for the routine detection of GBS. Therefore, in order to know the GBS carrier status and prevent its vertical transmission, the practice of vaginal culture during late pregnancy is mandatory.