Late third-trimester treatment of rectovaginal group B streptococci with benzathine penicillin G

We sought to determine the efficacy of late third-trimester benzathine penicillin G administration in eradicating maternal group B streptococcal colonization at delivery.

We performed a prospective trial of late third-trimester treatment with benzathine penicillin G versus observation in 78 obstetric patients colonized with group B streptococci. Patients were screened by use of rectovaginal swabs cultured in selective media between 34 and 37 completed weeks' gestation. Patients with positive cultures were offered antepartum treatment with 4.8 million units of intramuscular benzathine penicillin G or observation. Participants in both groups were recultured at their delivery admission before receiving standard intrapartum therapy. The primary outcome was the frequency of persistent maternal group B streptococcal colonization at the delivery admission. Other outcome variables included semiquantitative growth characteristics of all group B streptococcal cultures, the frequency of neonatal sepsis, and adverse maternal effects. Data were analyzed by the Student t test for continuous variables and the chi(2) or Fisher exact test for categoric variables, with significance established at P <.05.

Both groups were similar with respect to selected demographics, gestational age at delivery, and frequency of heavy group B streptococcal growth in initial screening cultures. The mean interval from treatment until delivery was 19.4 +/- 7.5 days (mean +/- SD). There were no cases of neonatal sepsis in either group or any adverse maternal effects attributed to the treatment. Group B streptococcal culture characteristics at delivery admission were as follows. Positive results for group B streptococci were found in 7 (25%) treated patients and 41 (82%) patients under observation (relative risk, 0.30; 95% confidence interval, 0.16-0.59; P <.0001). Positive results for heavy growth of group B streptococci were found in 0 (0%) treated patients and 31 (62%) patients under observation (relative risk, 0.01; 95% confidence interval, 0.00-0.12; P <.0001).

Treating group B streptococci carriers with benzathine penicillin G in the late third trimester eradicates or significantly reduces maternal group B streptococcal colonization at delivery. This may provide an adjuvant therapy to those mothers at risk for receiving inadequate intrapartum antibiotic prophylaxis against group B streptococci.