Group B Strep in the U.S.

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Summary and Comment

Group B Strep in the U.S.

Between 1999 and 2005, incidence of invasive group B streptococcal disease decreased in neonates but increased in adults.

Group B streptococcus is a major neonatal and adult pathogen. Current guidelines call for targeted culture-based intrapartum chemoprophylaxis to prevent infections in newborns, and vaccines are under development. To guide and evaluate preventive strategies, the Active Bacterial Core surveillance/Emerging Infections Program Network monitors the incidence of invasive group B streptococcal infections through active, population-based, laboratory surveillance in 10 states. Researchers recently analyzed the data for 1999 through 2005. During this period, 14,573 cases of invasive group B streptococcal infections, including 1438 that were fatal, occurred in the study population.

In 2005, the observed incidence was 7.5 per 100,000 population, with a case fatality rate of 7.9%. Rates were highest among newborns and individuals aged $≥$ 65. The overall incidence among blacks was double that among whites, with the disparity greatest for newborns and pregnant women.

After the CDC released revised recommendations on intrapartum chemoprophylaxis in 2002, the incidence of early-onset neonatal disease decreased significantly (from 0.47 cases/1000 live births in 1999–2001 to 0.34 cases/1000 live births in 2003–2005). Rates of late-onset neonatal disease, pregnancy-associated infections in women, and childhood disease remained relatively stable from 1999 through 2005, but disease incidence in nonpregnant adults increased steadily throughout the study period. A seasonal variation was noted, with infections peaking during the late summer. Serotyping, performed on 6156 isolates, showed that five serotypes (Ia, Ib, II, III, and V) accounted for >90% of infections. The most common clinical syndromes varied by age: bacteremia, pneumonia, and meningitis among infants and children; infection of the upper genital tract, placenta, or amniotic sac, and bacteremia, among pregnant women; and bacteremia, bacteremic cellulitis, pneumonia, osteomyelitis, and arthritis among nonpregnant adults.

Comment: These data show the importance of group B streptococcal infections, particularly among blacks. They confirm a significant gain against early-onset neonatal disease after the revised CDC guidelines were released in 2002. A pentavalent group B streptococcal vaccine targeting the five major serotypes could provide substantial additional benefit.

— Richard T. Ellison III, MD

Published in Journal Watch Infectious Diseases May 7, 2008