Group B streptococcus is a type of bacteria that is generally harmless in adults—and a good thing, too, because around one in four people is a carrier. It lives in the intestines or reproductive tract, doing nothing much in most people, but causing symptoms in people who are chronically ill or have weakened immune systems. One of the biggest dangers it poses, however, is for pregnant women, or, more specifically, the babies they give birth to. One in 2,000 infants is born with group B strep disease.
These children usually develop symptoms within a few months—sometimes a few hours—after birth. The infant will become lethargic, have difficulty feeding, and develop a fever. In many cases, the disease leads to seizures. Children who develop the disease relatively late—at more than a week old—are more prone to certain symptoms, such as irritability and breathing troubles.
Because group B streptococcus colonization so rarely produces symptoms in adults, pregnant women are routinely tested for the bacterium, generally at around 35 weeks. Because colonization is not permanent, the swab must be done with every pregnancy. It also means that testing before the 35th week usually doesn’t provide useful information—by the time labor comes, the colonization may have cleared up and therefore won’t be passed on to the child. However, having had a child with group B strep disease previously is considered a risk factor.
Other risk factors include labor lasting more than 18 hours from when the water breaks to delivery, multiple births, a fever over 100 during labor, a urinary tract infection, and a placental infection called chorioamnionitis. Babies born before 37 weeks gestation are considered high-risk simply because group B streptococcus results are not typically available, and the test might not have been performed. Women with sign of adult group B strep disease—pneumonia, skin infections, or infections of the bones or joints—are considered to be high fist for passing it on, though colonized children are unharmed by it more often than not. If the mother’s group B status is unknown but there are risk factors present, antibiotics are often given as a precautionary measure.