Rapid Test Has Its Place in GBS Infection Prevention


CHARLESTON, S.C. — Rapid real-time polymerase chain reaction testing for group B streptococcus detection proved at least as sensitive and specific as standard culture screening at 35–37 weeks' gestation in a recent study.

Two vaginal-rectal swabs were collected from each of 190 women enrolled in the study after presenting in labor. One sample was tested using the Food and Drug Administration-approved IDI-Strep B assay and analyzed using the FDA-approved Smart Cycler I instrument; the other sample was used for enriched culture for GBS, Deborah M. Money, M.D., reported at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology.

In the more than 150 women in the study who also underwent the currently recommended 35- to 37-week culture screening and had results available for analysis, the rapid test had a sensitivity of 89%, compared with 85% for the 35- to 37-week culture, and a positive predictive value of 97%, compared with 94% for the 35- to 37-week culture. The values were based on comparison with culture at delivery, said Dr. Money of the University of British Columbia, Vancouver.

The median time from specimen acquisition to availability of results with the rapid test was 90 minutes, with a range of 30 minutes to 4 hours. About 87% of results were available within 2 hours; cultures can require a few days for results. Colonization rates were about 30% with both the rapid test and the culture, she said.

Theoretically, the rapid test could be used during labor to circumvent some of the potential problems inherent in the 35− to 37-week culture method of screening, such as its reliance on the provider to do the screening properly, the uncertainty of the availability of results by delivery (which can jeopardize the chance of a colonized patient receiving the recommended 4 hours of antibiotic therapy during labor for preventing vertical transmission), and the fact that some women do not have prenatal care and would therefore not present for the 35− to 37-week culture. But with the similar sensitivity and specificity to 35− to 37-week culture demonstrated by the rapid test in this study, its usefulness for routine care is unclear.

“We were a little surprised by the lack of superiority of PCR to the culture methodology,” said Dr. Money, adding that larger studies will be required to determine if there is a statistically significant sensitivity and cost advantage with the rapid test over the 35− to 37-week culture.

One setting in which the rapid test can be of particular use now, however, is in patients who present in labor without information regarding their group B strep status. For those patients, the test is feasible, it has a reasonable turnaround time and a comparable result to culture screening, and it can be performed in a busy labor and delivery room, she said.

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