Rapid Detection of Group B Streptococci in Pregnant Women at Delivery

Abstract

Group B streptococcus (GBS) remains a leading cause of meningitis, sepsis, and death in newborn infants. Traditionally GBS colonization is detected by culturing combined vaginal and anal secretions in selective broth, but this requires 36 hours or longer and false-negative results may be obtained. In addition, many women unnecessarily receive antibiotic prophylaxis. This study compared culture with an alternative approach to screening for GBS: two DNA-based tests, one a conventional polymerase chain reaction (PCR) assay and the other a rapid fluorogenic PCR assay based on a new DNA-amplification apparatus. Anal, vaginal, and combined specimens were obtained from 112 pregnant women, from 57 of them before and after membrane rupture.

Culture of combined specimens identified 29.5% of the women tested as being GBS carriers. This approach was better than culturing only vaginal or anal specimens. All but 1 of 33 carriers were identified by both PCR assays. In the one exception case, only the postmembrane rupture culture was positive. In the specimens obtained after membrane rupture, the PCR assays had specificity and positive predictive values of 100%, were 97% sensitive, and had a negative predictive value of 98.8%. In general, GBS was detected slightly more often by PCR assay than by culture. Results were available in about 100 minutes with the conventional PCR assay and in 30 to 45 minutes with the rapid assay. Culture required at least 36 hours.

Analyzing combined vaginal and anal secretions obtained at the time of delivery by a PCR assay is a rapid and reliable screening measure for GBS colonization. Ultimately this test may lower morbidity and mortality caused by GBS infection in both mothers and infants.