WASHINGTON — Use of real-time polymerase chain reaction to screen for group B Streptococcus in the delivery room could reduce the use of intrapartum antibiotics by more than half, compared with antenatal screening alone, the findings of a single-center study of 232 pregnant women suggest.
Current CDC guidelines call for vaginal and rectal swabs at 35–37 weeks' gestation and for all women with cultures positive for group B Streptococcus (GBS) to receive intravenous antibiotic prophylaxis during labor and delivery (MMWR 2002;51[RR11]:1–22). This practice has greatly reduced the rates of neonatal sepsis in the United States, but it is imperfect. Women whose status is unknown at the time of labor also must receive prophylaxis, resulting in overtreatment, while cultures can fail to detect GBS in women who are lightly colonized, resulting in failure to treat.
Rapid testing at the time of delivery using real-time polymerase chain reaction (RT-PCR) has the potential to solve these problems, Dr. Stefan Gerber and his associates said in a poster presentation at the jointly held annual Interscience Conference on Antimicrobial Agents and Chemotherapy and the annual meeting of the Infectious Diseases Society of America.
Of 232 women presenting for vaginal birth at University Center Hospital, Lausanne (Switzerland) in an 8-month span, 19% (44) had positive GBS cultures at 35–37 weeks, 65% (152) had negative cultures, and 16% (36) had unknown GBS status at the time of delivery. Per the guidelines, 34% of the women (80) received prophylactic antibiotics during labor, but treatment was completed (at least two doses or at least 4 hours of intravenous antibiotics) in just 21% (17).
Lower vaginal and rectal swabs were obtained in all the women in the delivery room, and GBS detection was performed by both culture and RT-PCR, using Cepheid's Xpert GBS test, which runs on the GeneXpert System, a fully automated molecular testing system. Results were available in 75 minutes (compared with 2 days for cultures). By RT-PCR, just 15% (35) of the women were GBS positive, suggesting that 19% (45) of the women had received unnecessary prophylaxis, Dr. Gerber and his associates at the hospital reported.
Of the 35 PCR-positive women, 7 had negative cultures—presumably because they were only lightly colonized—and therefore would not have received antibiotics under the antenatal screening guidelines.
All 35 PCR-positive women received prophylaxis but just 7 (22%) completed it.
Since further work-up of the newborn is required when the mother doesn't receive complete antimicrobial prophylaxis, RT-PCR could potentially represent a significant cost saving. An ongoing study is investigating the cost-effectiveness of the approach, Dr. Gerber said in an interview.
Moreover, unlike cultures, which must be performed by technicians, the RT-PCR was performed by the midwives themselves. The technology could also be used by labor and delivery nurses or obstetricians, Dr. Gerber said in an interview.
Dr. Gerber stated that he had no financial ties to Cepheid. The company provided the equipment for the study, but no additional funding.
Most insurance plans cover the Xpert GBS test, which was approved by the Food and Drug Administration in 2006. It is categorized as “moderate complexity” by the FDA, meaning that non-laboratory health care professionals such as physicians and nurses can run the test, a Cepheid spokesman said in an interview.
The spokesman declined to say how many Xpert GBS tests are currently in use, but he did say that as of the last quarter of 2008, there were 848 GeneExpert Systems installed worldwide, capable of running the GBS test.