July 1996
ATLANTA — The Centers for Disease Control and Prevention (CDC) recently published guidelines to reduce the incidence of group B streptococcal (GBS) infections among newborns. As a result of the guidelines, many more pregnant women may receive antibiotics after they are admitted to a hospital to give birth.
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The guidelines offer health care providers two approaches. In one approach, pregnant women would be cultured for group B streptococci at 35 weeks to 37 weeks' gestation and penicillin would be offered to women colonized with group B strep. Penicillin would be administered intravenously during the intrapartum period, the interval after onset of labor or the rupture of amniotic membranes, until delivery. Regardless of culture findings, women would be treated with intrapartum penicillin if they have risk factors for delivering a newborn in whom GBS disease could develop.
Of the 4 million women who give birth annually in the United States, about 1 million carry group B streptococci without clinical signs or symptoms, according to Carol J. Baker, MD, professor of pediatrics at Baylor College of Medicine, Houston.
The CDC recommendations differ from those issued by the American Academy of Pediatrics in 1992, which recommended that women be cultured for group B strep at 26 weeks' to 28 weeks' gestation and that intrapartum prophylaxis be offered to women who had one or more risk factors in addition to a positive GBS culture.
In the other approach, risk factors alone would guide the use of intrapartum penicillin. This approach had been recommended by the American College of Obstetricians and Gynecologists (ACOG).
Risk factors include having previously given birth to an infant who contracted invasive GBS disease; GBS bacteriuria during pregnancy; giving birth at less than 37 weeks' gestation; having an intrapartum temperature of 100.4° F (38° C) or higher; and having ruptured membranes for 18 hours or more.
The CDC published its guidelines in Morbidity and Mortality Weekly Report.
The CDC estimates that prenatal culture screening at 35 to 37 weeks' duration would prevent 86% of cases of early onset GBS disease, whereas a risk-based approach would prevent about 69% of cases. Using risk factors alone as a basis for intrapartum penicillin prophylaxis would miss about 25% of cases of neonatal invasive GBS disease, said Baker, who served as a consultant for drafting the guidelines.
The two approaches have not been compared in a clinical trial, however, Baker told Infectious Diseases in Children. "Both [approaches] are perceived to be based on good scientific evidence, and both should be quite cost effective."
It is possible that the two strategies have comparable efficacy, said Michael Mennuti, MD, professor of obstetrics and gynecology at the University of Pennsylvania in Philadelphia and former chair of ACOG's Committee on Obstetrical Practice. Consequently, it is appropriate to recommend both approaches to clinicians, said Mennuti, who also assisted in the development of the CDC's guidelines.
Invasive group B strep disease emerged in the 1970s as the most common cause of sepsis in newborns. Of the 18,000 cases of invasive GBS disease that occur in the United States each year, 7,500 occur in newborns, according to the CDC. Neonatal infection occurs in about two in every 1,000 live births. Six percent of infants with invasive GBS disease die. Onset usually occurs from birth to 7 days of age. Invasive GBS disease may result in hearing loss and mental retardation.
The direct medical costs for treating neonates with GBS is $300 million a year, according to the CDC. The costs are compounded by long-term care for disabled children and the emotional costs of parents associated with a newborn's illness, disability or death.
The benefits of intrapartum penicillin do not come without risk. Serious drug reactions, such as anaphylactic shock, can occur, albeit rarely, and widespread use of penicillin could contribute to the development of drug-resistant bacteria.
Research data suggest that a deficiency in certain maternal antibodies increases susceptibility to neonatal invasive GBS disease. Consequently, if researchers develop a safe and effective vaccine against group B strep, then health providers may be able to immunize pregnant women against GBS infection. In theory, antibodies would protect the mother and pass through the placenta to the fetus.
The recommended strategy of administering antibiotics during the intrapartum period is supported in part by a study of pregnant women colonized with group B strep who had preterm labor or whose membranes ruptured more than 12 hours before delivery. Investigators randomly assigned the women to receive intravenous ampicillin or no treatment. Of 85 infants born to women in the treatment group, none had early onset of invasive disease, and 9% were colonized with group B strep. By comparison, of 79 infants born to untreated women, 6% had early onset of invasive disease, and 51% were colonized with group B strep. The differences between the two groups were statistically significant.
Studies suggest that giving antibiotics to pregnant women before onset of labor or membrane rupture is unlikely to prevent GBS disease in newborns, according to the CDC. In one study, investigators gave a week of oral antibiotic prophylaxis to asymptomatic pregnant women colonized with group B strep who were in their third trimester. More than 30% of treated women remained colonized at delivery. Investigators observed no substantial difference between treated and untreated women in carriage of group B strep at delivery.
In another study, investigators showed that about 70% of colonized women who were treated for 12 days to 14 days during the third trimester were colonized three weeks later and again at delivery even when their sex partners also had been treated.
Furthermore, a controlled, prospective and randomized study of low birth-weight infants showed that giving intramuscular penicillin to the infants just after birth made no difference in the incidence of early- or late-onset GBS disease or in mortality. "Because the majority of neonatal GBS infections are acquired in utero, antimicrobial agents administered to neonates, although useful for treatment, are unlikely to prevent the majority of GBS disease," the CDC stated in its report.
For more information, see:
- CDC. Prevention of perinatal group B streptococcal disease: A public health perspective. MMWR 1996;45:1-24.
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