Effect of specimen storage, antibiotics, and feminine hygiene products on the detection of group B Streptococcus by culture and the STREP B OIA test.

Agar culture from vaginal swabs is the routine method for diagnosis of maternal Group B Streptococcus (GBS) colonization. Swab specimens are often transported to a clinical laboratory for processing. In these studies, specimen transport was simulated by inoculating swabs with GBS and storing them at selected temperatures and with or without transport medium. The recovery of viable GBS was assessed by agar culture. GBS antigen was detected immunologically with an Optical ImmunoAssay (OIA) method. Swabs that were stored with transport medium harbored viable but rapidly declining numbers of GBS. In contrast, a strong OIA signal was maintained. Recovery of viable GBS organisms declined more quickly when swabs were stored in the absence of transport medium, whereas detection of GBS antigen remained consistent. Both methods were tested for interference from either antibiotics or feminine hygiene products. These compounds inhibited the detection of GBS by culture but had no detrimental effect on the OIA result.