By Carol Baker, MD
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On May 31, 1996, the Center for Disease Control & Prevention (CDC) published
guidelines for the prevention of early-onset group B streptococcal (GBS) disease
in newborn infants and post-delivery associated infection in their mothers. CDC,
the American College of Obstetricians & Gynecologists (ACOG), the American Academy
of Pediatrics (AAP) and other groups, including the Group B Strep Association developed
these more comprehensive guidelines, and ACOG and AAP support their implementation
by physicians caring for pregnant women and newborns.The guidelines provide a choice of prevention strategies to the obstetrician. One is based on screening cultures during pregnancy and the other on identifiable risk factors without culture screening. Those choosing to do cultures would do so at 35th to 37th week of pregnancy (not at 26-28 weeks). Lower vaginal and rectal swabs would be collected, and processed in antibiotic-containing liquid growth media (selective broth media). All women identified as GBS carriers by culture (even those with no risk factors) would be offered antibiotic treatment (chemoprophylaxis) by vein during labor until delivery. Also, all women who have previously delivered a baby with GBS disease, who have GBS cultured from their urine (bacteriuria), or who have labor before the 37th week of pregnancy should be given chemoprophylaxis and screening cultures are not needed.
In the second strategy, cultures would not be done. Chemoprophylaxis would be given to women with risk factors at hospital admission. These include the three above and all women with fever during labor or membranes ruptured more than 18 hours before delivery.
Like previous recommendations, treatment with oral antibiotics during pregnancy is condemned unless GBS is found in the urine. The preferred antibiotic for chemoprophylaxis during labor has been changed from ampicillin to penicillin, as the latter is effective and less likely to promote development of resistance to antibiotics. Women allergic to penicillin would be treated with clindamycin.
The AAP recommends that healthy-appearing infants born at 35 or more weeks gestation to women receiving two or more doses of penicillin before delivery not be tested or treated. However, these babies would remain in the hospital for 48 hours of observation (they can room-in with the mother). All other infants would have some laboratory tests performed (blood culture and blood count), but would not receive treatment unless signs of infection (for example, breathing or feeding difficulties, poor activity or color) develop.
Either strategy should prevent most (but not all) early-onset GBS disease in infants, and both will be more effective if the antibiotic is given to the mother as soon as possible after admission to the hospital. The CDC has estimated that the culture-based strategy will prevent 86% and the risk factor-based method 68% of cases of early-onset disease. Chemoprophylaxis is an interim prevention method. Development of vaccines continues to be a desirable future goal, since vaccine-induced protection would last longer, cost less and not risk the development of antibiotic-resistant GBS.
Dr. Baker is a Pediatric Infectious Disease Specialist at Baylor College of Medicine. She has dedicated her career to GBS Research.
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