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

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.

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.

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.

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.