RAPID DETECTION OF GROUP-B STREPTOCOCCAL COLONIZATION OF THE GENITAL-TRACT BY A COMMERCIAL OPTICAL IMMUNOASSAY

The performance of a commercial optical immunoassay (OIA) was compared at two institutions with that of routine agar and broth culture metho ds for the detection of group B streptococcal (GBS) colonization of th e genital tract. The Strep B OIA (Bio Star, USA) was used to test 962 vaginal swabs from pregnant women for the presence of GBS antigen. The prevalence of GBS vaginal colonization in this population was 22.4%. The OIA results were compared with those of culture on trypticase soy agar with 5% sheep blood (TSA) and broth enhanced culture (Lim broth), Sensitivity and specificity values of the OIA method compared to TSA culture alone were 82.5% and 91.8%, respectively. The sensitivity of t he OIA method was equivalent to that of TSA culture (62.4% vs. 64.4%; p>0.5, chi(2)=0.01) when the data were compared with broth culture, Th e extent of colonization affected the sensitivity of the OIA method: 1 00% of 4+, 94% of 3+, 96% of 2+, and 63% of 1+ TSA plates were detecte d by the OIA test. The commercial OIA method demonstrated sensitivity equivalent to that of TSA culture for the detection of GBS colonizatio n. The OIA test offers two additional advantages over culture: reduced time required to obtain results (30 min vs, days) and the ability to detect GBS antigen in samples with compromised viability. The results of this study suggest that the Strep B OIA test can be a useful diagno stic tool in the management of early-onset GBS disease.