Group B strep (streptococcus) is a common bacterium often carried in the intestines or lower genital tract. The bacterium is usually harmless in healthy adults. In newborns, however, it can cause a serious illness known as group B strep disease.

Group B strep can also cause dangerous infections in adults with certain chronic medical conditions, such as diabetes or liver disease. Older adults are at increased risk of illness due to group B strep, too.

If you're a healthy adult, there's nothing you need to do about group B strep. If you're pregnant, get a group B strep screening test during your third trimester. If you have group B strep, antibiotic treatment during labor can protect your baby.



Most babies born to women carrying group B strep are healthy. But the few who are infected by group B strep during labor can become critically ill.

In infants, illness caused by group B strep can be within six hours of birth (early onset) — or weeks or months after birth (late onset).

Signs and symptoms might include:

  • Fever
  • Difficulty feeding
  • Sluggishness and a lack of energy (lethargy)
  • Difficulty breathing
  • Irritability
  • Jaundice


Many adults carry group B strep in their bodies, usually in the bowel, vagina, rectum, bladder or throat, and have no signs or symptoms.

In some cases, however, group B strep can cause a urinary tract infection or more-serious infections such as blood infections (bacteremia) or pneumonia.

When to see a doctor

If you have signs or symptoms of group B strep infection — particularly if you're pregnant, you have a chronic medical condition or you're older than 65 — contact your doctor right away.

If you notice your infant has signs or symptoms of group B strep disease, contact your baby's doctor immediately.


Many healthy people carry group B strep bacteria in their bodies. You might carry the bacteria in your body for a short time — it can come and go — or you might always have it. Group B strep bacteria aren't sexually transmitted, and they're not spread through food or water. How the bacteria are spread to anyone other than newborns isn't known.

Group B strep can spread to a baby during a vaginal delivery if the baby is exposed to — or swallows — fluids containing group B strep.

Risk factors


An infant is at increased risk of developing group B strep disease if:

  • The mother carries group B strep in her body
  • The baby is born prematurely (earlier than 37 weeks)
  • The mother's water breaks 18 hours or more before delivery
  • The mother has an infection of the placental tissues and amniotic fluid (chorioamnionitis)
  • The mother has a urinary tract infection during the pregnancy
  • The mother's temperature is greater than 100.4 F (38 C) during labor
  • The mother previously delivered an infant with group B strep disease


You're at increased risk of a group B strep infection if:

  • You have a medical condition that impairs your immune system, such as diabetes, HIV infection, cancer or liver disease
  • You're older than 65


Group B strep infection can lead to life-threatening complications in infants, including:

  • Pneumonia
  • Inflammation of the membranes and fluid surrounding the brain and spinal cord (meningitis)
  • Infection in the bloodstream (bacteremia)

If you're pregnant, group B strep can cause infection in the following areas:

  • Urinary tract
  • Placenta and amniotic fluid
  • Membrane lining the uterus
  • Bloodstream

If you're an older adult or you have a chronic health condition, group B strep bacteria can cause complications such as:

  • Skin infection
  • Infection of the bloodstream
  • Urinary tract infection
  • Pneumonia
  • Bone and joint infections
  • Infection of the heart valves (endocarditis)
  • Inflammation of the membranes and fluid surrounding the brain and spinal cord (meningitis)


To prevent group B bacteria from spreading to your baby during labor, your doctor can give you an IV antibiotic — usually penicillin or a related drug — when labor begins. If you're allergic to penicillin and related drugs, you might receive cefazolin or clindamycin as an alternative.

Taking oral antibiotics ahead of time won't help because the bacteria can return before labor begins.

Antibiotic treatment during labor is also recommended if you:

  • Have a urinary tract infection
  • Delivered a previous baby with group B strep disease
  • Develop a fever during labor
  • Haven't delivered your baby within 18 hours of your water breaking
  • Go into labor before 37 weeks and haven't been tested for group B strep

If you tested positive for group B strep, remind your health care team during labor.

Vaccine in development

Although it's not available yet, researchers are working on a group B strep vaccine that could help prevent group B strep infections in the future.

April 07, 2020
  1. AskMayoExpert. Group B streptococcus (GBS) infection. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2019.
  2. Puopolo KM, et al. Group B streptococcal infection in neonates and young infants. https://www.uptodate.com/contents/search. Accessed July 16, 2019.
  3. Group B strep (GBS). Centers for Disease Control and Prevention. https://www.cdc.gov/groupbstrep/index.html. Accessed July 16, 2019.
  4. Puopolo KM, et al. Management of infants at risk for Group B streptococcal disease. Pediatrics. 2019;144:e1881.
  5. Puopolo KM, et al. Group B streptococcal infection in pregnant women. https://www.uptodate.com/contents/search. Accessed July 16, 2019.


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