August 2000
LOS ANGELES - Four years after their introduction, prevention guidelines for group B streptococcal (GBS) infections appear to be making a positive impact.
In 1996, the Centers for Disease Control and Prevention (CDC), along with the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics, recommended that obstetric care givers adopt a GBS prevention strategy. Two approaches, screening and risk assessment, may be used. Screening uses prenatal cultures collected late in gestation. Intrapartum prophylaxis is given when culture results are positive or when women deliver preterm before results are available.
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During labor, the physician assesses for prematurity, membrane rupture of longer than 18 hours or intrapartum fever. Women with these conditions are offered antibiotics. Regardless of strategy, women who have previously given birth to an infant with early-onset GBS or who have developed GBS bacteriurea during pregnancy should be treated with intrapartum antibiotics.
Before the guidelines, less than 20% of U.S. hospitals had a GBS prevention policy, said Anne Schuchat, MD, chief of the Respiratory Disease Branch at the CDC. This has since increased to more than two-thirds of hospitals. Additionally, early-onset GBS has decreased dramatically since 1993, when 6,100 cases of early-onset disease occurred. In 1998, 2,200 cases occurred, meaning that more than 4,000 cases and 200 deaths were prevented. Also, the gap in disease rates between blacks and whites has narrowed by 75% since 1993. "This is exciting news and suggests that prevention is reaching the population with the highest prevalence of disease in the United States," Schuchat said.
The CDC examined case rates at 66 hospitals that had no policy in 1996 and 45 hospitals that either implemented a new policy or revised an old one at that time. The number of births in both groups was close, and the number of GBS cases was also similar. In 1997 however, they differed greatly.
"Hospitals that did not have GBS prevention policies had a modest decline in cases, but this was not statistically significant," said Schuchat, who spoke here at the American Society for Microbiology 100th General Meeting. "In contrast, hospitals that put in place a new policy or updated an old policy had a decline of more than 50% in their cases. This made us concerned that many hospitals did not have policies."
While not all hospitals have a prevention policy in place, most clinicians do. A recent survey in Connecticut and Minnesota found that more than 95% of Connecticut obstetricians are implementing a policy, and 90% of Minnesota obstetricians are as well.
With implementation of the guidelines, antibiotic use increased. At a practice in Seattle, 12% of women received intrapartum antibiotics prior to guidelines going into effect. This has since doubled, resulting in a shortage of penicillin, the first-line agent for GBS prevention, in the last year, said Schuchat.
"Demand greatly outstripped supply, and it required at least a temporary switch to broader-spectrum agents by many caregivers," she said.
Preliminary results of a survey of obstetricians is showing that two-thirds of them could not obtain penicillin in 1999. The CDC is evaluating the effects of this shortage, she added.
"GBS remains sensitive to penicillin as well as to ampicillin, but there is increasing concern about GBS resistance to other agents," Schuchat said.
"In the consensus recommendations, we had suggested penicillin as a first-line agent and ampicillin as an alternative. But for women with penicillin allergies, the use of either erythromycin or clindamycin ... were suggested as alternatives. Unfortunately, there's quite a bit of macrolide resistance ... as well as a variable amount of clindamycin resistance."
To circumvent potential resistance issues, use of a cephalosporin might be a reasonable alternative in some cases of penicillin allergy, Schuchat said.
Besides resistance, there are concerns about changes in other organisms during the peripartum period as a result of GBS prevention.
A small study of GBS prevention using ampicillin began in California in 1991. Researchers found a decrease in GBS sepsis in the first few days of life and an increase in the number of other infections. By 1996, this number was much higher than expected.
However, results of another study disagreed with these results. In Australia, where ampicillin is also primarily used, a significant decrease in GBS sepsis as well as other causes of sepsis has been observed.
"How long that will last we don't know," Schuchat said. "We really don't know what's going to happen, but this is an important area to track. It's too soon to tell if increased or widespread resistance in other pathogens will occur. And if it occurs, is it going to be attributable to GBS prevention? It's too soon to tell if intrapartum antibiotics will have a net benefit or risk related to other sepsis."
Whether GBS cases can be reduced even further is difficult to ascertain. A total of 273 cases have been reviewed from 1998 and 1999. Of these, 21% occurred despite intrapartum antibiotics. Only 29% occurred despite maternal screening, and only 40% had a risk factor present during labor. Forty-one percent of cases had no risk factors or screening.
"The continuing burden of GBS early-onset disease in the United States represents a mixture of missed opportunities for prevention, protocol failure and cases that just won't be preventable with this approach," Schuchat said. "Not all perinatal GBS cases are going to be prevented using this approach. There will be some false-negative culture results; antibiotic efficacy is less than 100%."
Additionally, current GBS prevention strategies do not address late-onset infections and stillbirths. The sustainability of increased antibiotic use is also unclear, Schuchat said. "Will the risks eventually outweigh the benefits?"
For more information:
- Schuchat A. Prevention of GBS disease: intrapartum prophylaxis. Session 247C. Presented at the American Society for Microbiology 100th General Meeting. May 21-25, 2000. Los Angeles.
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