Neonatal group B streptococcus (GBS) infection can be largely prevented with the use of intrapartum antibiotic prophylaxis. Uncertainty about the optimal therapy prompted the Centers for Disease Control and Prevention to recommend two possible strategies: one based on maternal risk factors and the other using a combination of risk factors and anogenital cultures performed at 35 to 37 weeks of gestation. The latter strategy was proposed to reduce GBS infection in otherwise low-risk situations that would not be targeted by the first strategy. Wendel and associates studied the incidence of GBS disease at a large urban hospital.
They noted that intrapartum treatment based on risk factors and antepartum cultures was difficult without clear documentation of efficacy, but selective treatment based on risk factors alone would miss a substantial number of infections. A new protocol, combining intrapartum risk-factor assessment as well as universal neonatal penicillin prophylaxis in low-risk pregnancies, would eliminate the need to identify women who carried GBS infection. Beginning in 1995, women who had clinical risk factors during labor were given ampicillin in a dosage of 2 g intravenously every six hours until delivery, while patients who were allergic to penicillin were given clindamycin in a dosage of 900 mg intravenously every eight hours until delivery. Women with chorioamnionitis, which was defined as a fever of 38°C (100°F) or higher, were also given gentamicin until delivery. All newborn s received either penicillin G intramuscularly or ampicillin plus gentamicin if they had signs of sepsis or were born to mothers with chorioamnionitis.
The incidence of early-onset neonatal GBS infection decreased from 2.2 per 1,000 infants before the universal prophylaxis protocol to 0.4 per 1,000 after implementation in 1995. This decrease in GBS incidence was noted among term and preterm infants. The mortality rate from other causes of sepsis did not change significantly.
The authors conclude that universal pro phylaxis, using ampicillin in high-risk pregnancies and penicillin in all other pregnancies, is a cost-effective way to decrease the incidence of neonatal GBS infection without increasing undesirable infection rates from other organ isms. The recommended dosage of penicillin is 60,000 U intramuscularly for infants who weigh more than 2,000 g (4 lb, 6 oz) and 30,000 U for those who weigh less than 2,000 g.