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Transmission and Risk Factors

Transmission

For early-onset disease, the group B strep bacteria are passed from the mother to the baby, most often during labor and birth. Antibiotics given during labor can be very effective at preventing this transmission.

Late-onset disease is sometimes due to passing of the bacteria from mother to newborn, but sometimes the bacteria come from another source. For a baby whose mother does not test positive for group B strep, the source of infection for late-onset disease can be hard to figure out and is often unknown. CDC collects information on babies with late-onset disease in 10 states to better understand transmission.

Women who are group B strep positive can breastfeed safely. There are many benefits for both the mother and child.

Risk Factors

Some pregnant women are at higher risk of having a baby with early-onset disease. The factors that increase risk include:

  • Testing positive for group B strep late in the current pregnancy (35-37 weeks gestation)
  • Detecting group B strep in urine during the current pregnancy
  • Delivering early (before 37 weeks gestation)
  • Developing fever during labor
  • Having a long period between water breaking and delivering
  • Having a previous infant with early-onset disease

These risk factors guided the early-onset disease prevention strategy used today.

Late-onset disease is more common among babies who are born prematurely (< 37 weeks). This is the strongest risk. Babies whose mothers tested group B strep positive also have a higher risk of late onset disease. The risk factors for late onset disease are not as well understood as for early-onset disease.


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