Women's health | Group B strep

Approximately 25 percent of pregnant women become infected with Group B strep, which may be passed along to newborn babies and can cause life-threatening health conditions.

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Group B streptococcus (GBS), or group B strep, is a type of bacterial infection caused by Streptococcus agalactiae, a Gram-positive bacterium which can be naturally found in the gastrointestinal and genital tracts. Most adults and children with colonization of GBS present little or no symptoms. Colonization of GBS within the gastrointestinal or genital tracts is generally not harmful to the individual, however, more invasive infection of the pathogen, particularly among newborns, the elderly, and the immunocompromised, can cause much more serious medical complications. Individuals at increased risk includes those over the age of 65 years and those  with weakened immune systems due to medical conditions, such as:


  • Diabetes
  • Heart conditions
  • Liver disease
  • HIV
  • Cancer 


Group B strep is especially dangerous to newborns. A newborn who contracts GBS may develop life-threatening infections, that may include:


  • Meningitis
  • Pneumonia
  • Septicemia


Babies who have symptoms within the first week of birth likely have early-onset GBS disease. Infection that occurs after the first week of life is referred to as late-onset GBS disease. Signs and symptoms of GBS disease in babies may include:


  • Fever
  • Difficulty feeding
  • Low body temperature
  • Difficulty waking up
  • Irritability
  • Difficulty breathing

It is not always clear how individuals spread group B strep. But the best understood pathology of disease transmission is from the mother to the baby during birth. Pregnant women can pass GBS along to their newborns during labor and vaginal delivery when fluid colonized with the bacteria is ingested by the newborns.

To prevent group B strep transmission to babies, pregnant women are frequently screened for GBS. If the individual tests positive, IV antibiotics (commonly penicillin or clindamycin) are administered at the start of labor to prevent transmission.

Vaccines to prevent group B strep are in development; however, as of 2023, there currently exists no vaccination against GBS. A World Health Organization and London School of Hygiene & Tropical Medicine report in 2021 estimated that if GBS vaccination was administered to over 70 percent of pregnant women, more than approximately 50,000 GBS-related deaths and 170,000 preterm births could be prevented worldwide each year.1

A diagnostic test for GBS is performed for women in the third trimester prior to the 37th week of pregnancy. Either a swab test or urine test will be ordered by the obstetrician.

Babies with a GBS-positive mother may also be tested for group B strep disease using specimens from blood samples or spinal fluid. If a baby shows symptoms of GBS disease, other tests may be ordered, including:

  • Urine culture

  • Lumbar puncture

  • Chest X-ray

Current treatment for GBS disease in babies includes IV antibiotics and possible admittance into the neonatal intensive care unit. If a pregnant woman develops GBS infection, oral antibiotics that are safe during pregnancy will commonly be administered. For other adults with GBS complications, antibiotics are typically prescribed to treat the area affected.