Group B Streptococcus has been a common cause of invasive infection in neonates and young infants for several decades. Group B Streptococcus also is an important cause of maternal obstetrical morbidity and fetal loss. The incidence of early-onset group B streptococcal neonatal infections has declined 85% in the United States in association with universal culture-based screening of pregnant women and administration of intrapartum antibiotic prophylaxis to women colonized with group B Streptococcus.
PATHOGENESIS AND EPIDEMIOLOGY
Group B streptococci are gram-positive cocci that grow readily as white to gray-white colony-forming units with a narrow zone of β-hemolysis when inoculated on blood agar. Group B streptococci have been classified, based on capsular polysaccharide antigens, into 10 types. Contemporary data indicate that types Ia, III, and V predominate in early-onset disease, accounting for more than three-fourths of isolates from infants with invasive infection. Together with types Ib and II, these 5 types account for approximately 98% of isolates from infant invasive early-onset disease. Among late-onset cases of group B streptococcal infection, type III strains predominate, accounting for more than one-half of infections. Serotype IV, formerly uncommon, appears to be emerging as a cause of invasive disease in neonates.
Rates of maternal rectal and vaginal colonization with group B streptococci during pregnancy range from 20% to 30%. Without interruption of transmission, approximately 50% of infants delivered of a colonized mother acquire mucous membrane colonization. The risk for invasive disease among colonized infants is approximately 1%. This risk is increased when there is premature onset of labor, maternal chorioamnionitis, a prolonged interval between rupture of membranes and delivery, twin pregnancy, or maternal postpartum bacteremia, among other factors. Heavy maternal colonization also increases the risk for neonatal infection. Fetal aspiration of infected amniotic fluid can result in the development of congenital pneumonia with symptoms at or shortly after birth.
The clinical features of early-onset and later-onset group B streptococcal infections are shown in Table 281-1. Risk for early-onset infection is increased in the setting of maternal obstetric complications, but term infants usually present with no risk factors other than maternal colonization. The 3 common presentations for early-onset disease are septicemia without a focus, pneumonia, and meningitis. Most infants (~75%) present with respiratory signs, including tachypnea, grunting, or cyanosis. Radiographic findings can be suggestive of surfactant deficiency, transient tachypnea, or congenital pneumonia. Other signs of early-onset infection include temperature or vascular instability, poor feeding, and lethargy. Clinical signs suggesting meningeal involvement can be unapparent at the initial presentation, but seizures develop within 24 hours of presentation in 50% of infants with meningitis.
TABLE 281-1DIFFERENTIAL CHARACTERISTICS OF EARLY- VERSUS LATE-ONSET GROUP B STREPTOCOCCAL INFECTIONS IN EARLY INFANCY ||Download (.pdf) TABLE 281-1DIFFERENTIAL CHARACTERISTICS OF EARLY- VERSUS LATE-ONSET GROUP B STREPTOCOCCAL INFECTIONS IN EARLY INFANCY