Evaluation of a rapid optical immunoassay-based test for group B streptococcus colonization in intrapartum patients

OBJECTIVE: To compare an optical immunoassay (OIA) rapid diagnostic kit to standard culture for the diagnosis of vaginal colonization with group B streptococcus (GBS) and to assess the accuracy and reproducibility of the OIA results. METHOD: A total of 301 patients in labor were prospectively evaluated for GBS colonization with a test approved by the Food and Drug Administration (STREP B OIA kit, Biostar, Boulder, CO, USA) and by culture. The vagina was simultaneously sampled with two swabs. Rectal culture was obtained separately. RESULTS: By the criterion of a positive culture, the vagina was colonized by GBS in 33 of 301 (11%) patients; and the rectum in 42 of 301 (13.9%). The vagina or rectum or both were colonized by CBS in 54 of 301 (17.9%) of patients. The OIA had sensitivity, specificity, positive predictive value and negative predictive value of 63.6%, 86.3%, 37.5% and 94.8%, respectively. The OIA had a kappa statistic score of 0.59. CONCLUSION: The OIA is not an adequately sensitive rapid kit for reliable detection of GBS colonization of the vagina. The results of the OIA were only moderately accurate and reproducible.