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How it Spreads and Risk Factors

EspaƱol: TransmisiĆ³n y factores de riesgo

How it Spreads

In cases of early-onset disease (occurs in babies younger than 1 week old), group B strep bacteria are most often passed from mother to baby during labor and birth. Antibiotics given to the mother during labor can be very effective at preventing the spread of group B strep bacteria to the baby.

Late-onset disease (occurs in babies 1 week through 3 months old) is sometimes due to passing of the bacteria from mother to newborn, but the bacteria may come from another source. For a baby whose mother does not test positive for group B strep bacteria, 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 how group B strep bacteria are spread.

Risk Factors

Some pregnant women are at an increased risk of having a baby who develops early-onset group B strep disease. Some risk factors include:

  • Testing positive for group B strep bacteria late in the current pregnancy (35-37 weeks pregnant)
  • Detecting group B strep bacteria in urine (pee) during the current pregnancy
  • Delivering early (before 37 weeks of pregnancy) 
  • Developing a fever during labor
  • Having a long time between water breaking and delivering (18 hours or more)
  • Having a previous baby who developed early-onset disease

The risk factors for late-onset group B strep disease are not as well understood as those for early-onset disease. Late-onset disease is more common among babies who are born prematurely (before 37 weeks of pregnancy). Babies whose mothers tested positive for group B strep bacteria also are at increased risk of late-onset disease.