Infant GBS risk halved with universal screenings: resultant rise in antibiotic use a drawback

OB/GYN News, Nov 15, 2001 by Kathryn DeMott

QUEBEC CITY -- Universal culture screening of all pregnant women for group B streptococcus reduces by half the risk of a newborn developing early-onset group B streptococcal disease, compared with screening based on a risk-based approach, according to data presented at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology.

But experts are still wrangling over whether the benefits of a universal screening strategy outweigh the downsides of this approach, including an increase in antibiotic usage.

In a retrospective cohort study, researchers at the Centers for Disease Control and Prevention examined 4,517 randomly selected labor and delivery records from live births. In all cases where there was no mention of screening on the birth or labor and delivery records, it was assumed that a risk-based strategy was followed, whereby women were given chemoprophylaxis if they had any risks factors for group B streptococcal (GBS) disease.

A preliminary analysis indicates that there were 272 cases of early-onset CBS neonatal diseases. In 54% of the cases, there was no indication for CBS prophylaxis under the risk-based approach. Meanwhile, compared with those women managed by a risk-based approach, those mothers who were screened by culture had an odds ratio of 0.47 for having newborns that developed early-onset GBS diseases, said Sharon Hillier, Ph.D., of Magee-Womens Hospital, Pittsburgh, who presented the study on behalf of her colleagues at the CDC.

Under guidelines currently endorsed by the CDC, the American College of Obstetricians and Gynecologists, and the American Academy of Pediatrics, physicians have two choices: Either universally conduct culture screening at the 35th through the 37th gestational week and treat only those who are positive, or take a risk-based approach in which no cultures are done and chemoprophylaxis is given to every pregnant patient with risk factors at hospital admission. But it's not clear how much better universal screening has to be than a risk-based approach to warrant a shift in practice.

Dr. Ronald Gibbs of the University of Colorado, Denver, noted that his institution follows a risk-based approach in part to stem the overuse of antibiotics. "We are looking at an organism that's [associated with] neonatal sepsis in somewhere around a half a case per 1,000. We have to look at this in terms of worldwide issues such as use of antibiotics and selection pressure for resistant organisms."

With a risk-based approach, it's estimated that 15%-18% of mothers would receive intrapartum prophylaxis. With a culture-based approach, however, that figure would be around 25%, depending on the population.

A culture-based approach reduces the risk of early-onset disease cases by 89%, compared with a 69% reduction if a risk-based approach is taken, Dr. Gibbs said. But the decrease in deaths from GBS sepsis would not be quite so dramatic, because the cases that would develop in the risk-based approach almost by definition would be term neonates for whom the mortality rate of CBS sepsis is very low.

Dr. Richard L. Sweet of Magee-Womens Hospital maintained that the risk-based approach may no longer be appropriate. "I'm not sure we can continue to support an alternative, which, theoretically and now demonstratively is less effective," he said.

Others don't think the CDC data justify a shift in practice. A key weakness of the study is that it was assumed that obstetricians whose patients had no notation about GBS screening in their records were following a risk-based approach, when in fact they might have been doing nothing at all, noted Dr. Laura Riley of Harvard Medical School, Boston.