Group B streptococcal infections.

1. Samuel P. Gotoff, MD*

1. *Professor and Chairman, Department of Pediatrics, Rush Children’s Hospital, Chicago, IL

After completing this article, readers should be able to:

1. Delineate the epidemiologic factors in the transmission of group B Streptococcus (GBS) neonatal infections.

2. List the major factors that increase the risk of neonatal GBS infections.

3. Describe four clinical presentations of neonatal GBS infections.

4. List the laboratory methods for isolating and identifying GBS in mixed flora, normally sterile biologic fluids, and a patient treated with a penicillin.

The group B Streptococcus (GBS) initially was isolated by Nocard in 1887 and described as Streptococcus agalactiae , a cause of bovine mastitis. The organism is an encapsulated gram-positive diplococcus that usually produces a narrow zone of beta-hemolysis on blood agar. Most strains are resistant to bacitracin. The streptococci were classified serologically in the 1930s by Lancefield, based on cell wall polysaccharides. The GBS organisms are differentiated further by type-specific capsular polysaccharides and protein antigens. Current serotypes include: Ia, Ib, Ia/c, II, III, IV, V, VI, VII, and VIII.

Since the mid-1960s, GBS has become the major cause of bacterial infections in the perinatal period, including bacteremia, amnionitis, endometritis, and urinary tract infection in pregnant women as well as focal and systemic infections in newborns. It is a relatively rare cause of infection in older children and nonpregnant adults. GBS early-onset disease (EOD) occurs within the first week after birth, usually before 72 hours. GBS late-onset disease (LOD) accounts for about 20% of cases, usually occurring between 1 to 4 weeks after birth, but rarely seen up to 6 months of age. Late, late-onset infections, which occur from 1 to 6 months of age, and infections in nonpregnant adults often are associated with immunodeficiency. All of the serotypes have been associated with GBS EOD, with Ia, II, III, and V being most common in the United States. GBS LOD is caused by serotype III …