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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, urinary tract infections in parturient women,
and systemic and focal infections in infants from birth until
3 months of age or rarely older. Invasive disease in young infants
is categorized on the basis of chronologic age at onset. Early-onset
disease usually occurs within the first 24 hours of life (range,
0–6 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 days–3
months), commonly manifests as occult bacteremia or meningitis;
other focal infections, such as osteomyelitis, septic arthritis,
adenitis, and cellulitis, can occur. Very late-onset disease
has onset beyond 3 months of age in very preterm infants requiring
prolonged hospitalization. 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.
ETIOLOGY: Group B streptococci
(Streptococcus agalactiae) are
gram-positive, aerobic diplococci that typically produce a narrow
zone of beta hemolysis on 5% sheep blood agar. These organisms
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 in infants.
EPIDEMIOLOGY: Group B streptococci are common inhabitants of
the gastrointestinal and genitourinary tracts. Less commonly,
they colonize the pharynx. The colonization rate
. . . [Go to Full Text]
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