ATLANTA - The incidence of early-onset neonatal group B streptococcal (GBS) disease declined 65% over a six-year period, according to recent study data. The decrease, the researchers concluded, occurred in part because of a decrease in the incidence of early-onset disease in black neonates.
The decline reportedly coincided with risk-reduction guidelines issued by the American Academy of Pediatrics, the American College of Obstetricians and Gynecologists and the Centers for Disease Control and Prevention (CDC).
Data from 1993 to 1998 identified 7,867 cases of GBS; 2,196 occurred in infants younger than 3 months, with 72% of the cases presenting as early-onset. Early-onset neonatal disease, occurring in infants younger than 7 days, presented as bacteremia (80%), pneumonia (7%) or meningitis (6%), with a case fatality rate of 4%. Preterm infants had a higher fatality rate than term infants; however, 75% of infants who contract GBS are full-term. The study was published in a recent issue of The New England Journal of Medicine.
Late-onset disease, occurring in infants 7 to 89 days old, was more likely to present as meningitis (24%) than in the early-onset group, but was less likely to present as bacteremia (63%) or pneumonia (2%). The fatality rate for late-onset disease was 2.8%.
In 1998, the rate of early-onset disease in black neonates (0.8 per 1,000 live births) and white neonates (0.5 per 1,000 live births) approached Healthy People 2010 objectives of a reduced incidence of early-onset disease. The rate dropped to 0.6 per 1,000 live births for all races. Between 1993 and 1998, there was a 75% reduction in the gap between rates of early-onset disease in black neonates vs. white neonates.
"We don't fully understand the reasons for the difference (in the rate of early-onset disease in black neonates vs. white neonates)," said Stephanie Schrag, PhD, CDC epidemic intelligence service. "The good news from the data we analyzed is the prevention strategy has made a big difference in reducing the differential in that group."
"With the CDC surveillance, I think there are enough data now on the greater efficacy of screening-based vs. risk-based for us to reconsider refinement of the guidelines," said Carol J. Baker, MD, professor of pediatrics, Baylor College of Medicine, Houston. "I think we should move to a single, screening-based guideline. We should routinely screen every pregnant woman with cultures for GBS and give intrapartum chemoprophylaxis to all carriers. The good news is that the disease is decreasing by two-thirds, but the fact that you still have one-third of potentially preventable cases means we have a lot more work to do."
Race is not a strong risk factor compared with those in risk-based prevention strategies, but data still show a higher incidence of disease in black neonates. There's also a higher incidence of disease in mothers younger than 20 years of age.
"The risk-based approach is simpler," said Baker. "The disadvantage is that it was never submitted for clinical trial until it was recommended. The other major disadvantage is that you have to have a risk factor before a physician knows to give prophylaxis.
"Some risks are easy to identify and there's lots of time for planning. If you go into premature labor, that's easy too. But one of the causes of premature labor might be GBS, so by the time labor starts, infection is already beginning. It's a timing issue. We know efficacy relates to the number of doses of antibiotics or the amount of time prophylaxis is given before delivery."
The screening-based approach doesn't exclude any woman, and it includes women who don't have a risk factor but who carry the organism, said Baker, who noted if a woman doesn't show signs of risk, the only way to detect GBS is a positive culture.
The study revealed the number of hospitals with a policy for early-onset disease prevention increased from 39% to 58% between 1994 and 1997. According to the Group B Strep Association, for best protection GBS-positive mothers should receive intravenous (IV) antibiotics at least four hours before delivery. The association also recommends administration of IV antibiotics at hospital admission if a mother had a previous GBS baby or if her membranes rupture before 37 weeks of pregnancy.
One-quarter, or 900,000 pregnant women, carry the bacteria. Current guidelines call for screen testing between 35 and 37 weeks of gestation. Carriers identified by the screen-based approach should be offered intrapartum chemoprophylaxis. According to the CDC, oral antibiotics should not be administered before labor because antibiotic treatment does not prevent GBS in newborns prior to labor. However, GBS urinary tract infection in the urine (bacteriuria) should be treated when diagnosed.
According to the risk-based approach, women who present risk factors at the time of labor should be offered intrapartum chemoprophylaxis.
At least one in four pregnant women is, or should be, given IV prophylaxis for GBS, said Baker. This amount of antibiotic use stirs concerns about evolving resistance.
Schrag noted there is an ongoing surveillance system monitoring antibiotic resistance. Penicillin is the most commonly used intrapartum antibiotic prophylaxis, followed by erythromycin and clindamycin. "Our concerns are twofold," said Schrag. "One is about the GBS bacteria itself and whether it will develop resistance to penicillin. To date no penicillin-resistant isolates have been identified, but there are low levels of resistance for some second-line antibiotics. The other concern, in some ways a bigger concern, is whether antibiotic use aimed at preventing GBS will increase resistance in other pathogens that cause neonatal infections."
Phase 2 trials are currently underway for a conjugate GBS vaccine that Schrag said "seems to hold more promise for introducing immunity." The vaccine could also be effective in pregnant women, infants with late-onset disease and high-risk groups in the adult population.
"In my own medical center where we've seen a great decrease in early-onset disease, we now see four cases of late-onset disease for every early-onset case," said Baker. Late-onset meningitis survivors may be left with neurologic devastation (Figures 1 and 2). "It's still an important group of patients, and the vaccine approach is the only one aimed at late-onset disease."
GBS is the most common cause of sepsis and meningitis in newborns, and is a frequent cause of newborn pneumonia. One in 20 infants infected with GBS dies from the infection, and babies that survive, especially those with meningitis, can have cerebral palsy, retardation, hearing loss or learning disabilities. In pregnant women, GBS can cause bladder infections, womb infections and stillbirth.
Adults who are not pregnant and become infected with the disease can get blood infections, skin or soft tissue infections and pneumonia; 20% of cases in adults 65 years and older are fatal.
Figure 1: Computed tomography (CT) of the head after 18 days of treatment of a previously healthy 25-day-old infant for late-onset meningitis reveals meningeal enhancement, multiple focal cerebral infarcts and small bilateral intraparenchymal hemorrhages. Figure 2: CT of the head 14 months later demonstrates the evolution of the severe previous findings and reveals almost no remaining cerebral parenchyma.
For more information:
- Schrag S, Zywicki S, Farley M, et. al. Group B streptococcal disease in the era of intrapartum antibiotic prophylaxis. N Engl J Med. 2000;342(1):15-20.2.
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