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Section 3. Summaries of Infectious Diseases
Group B Streptococcal Infections
Clinical Manifestations
Etiology
Epidemiology
Diagnostic Tests
Treatment
Isolation of the Hospitalized Patient
Control Measures
CLINICAL MANIFESTATIONS: Group B streptococci are a major cause of perinatal bacterial infections, including bacteremia, endometritis, chorioamnionitis, and urinary tract infections in parturient women and systemic and focal infections in infants from birth until 3 months of age or older. Invasive disease in young infants is categorized into 2 entities on the basis of chronologic age at onset. Early-onset disease usually occurs within the first 24 hours of life (range, 06 days) and is characterized by signs of systemic infection, respiratory distress, apnea, shock, pneumonia, and less often, meningitis (5%10% of cases). Late-onset disease, which typically occurs at 3 to 4 weeks of age (range, 7 days3 months), commonly manifests as occult bacteremia or meningitis; other focal infections, such as osteomyelitis, septic arthritis, adenitis, and cellulitis, can occur. Group B streptococci also cause systemic infections in nonpregnant adults with underlying medical conditions, such as diabetes mellitus, chronic liver or renal disease, malignancy, or other immunocompromising conditions, and adults 65 years of age and older.
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ETIOLOGY: Group B streptococci (Streptococcus agalactiae) are gram-positive, aerobic diplococci that typically produce beta hemolysis and are divided into 9 serotypes on the basis of capsular polysaccharides (Ia, Ib, II, and III through VIII). Serotypes Ia, Ib, II, III, and V account for approximately 95% of cases in the United States. Serotype III is the predominant cause of early-onset meningitis and most late-onset infections.
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EPIDEMIOLOGY: Group B streptococci are common inhabitants of the gastrointestinal and genitourinary tracts. Less commonly, they colonize the pharynx. The colonization rate in pregnant women and newborn infants ranges from 15% to 40%. Colonization during pregnancy can be constant or intermittent.
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