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:
- Low body temperature
- Difficulty feeding
- Sluggishness, limpness or weak muscle tone
- Difficulty breathing
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 other more-serious infections. Signs and symptoms of infections that may be caused by group B strep include the following.
Urinary tract infection
- A strong, persistent urge to urinate
- A burning sensation or pain when urinating
- Passing frequent, small amounts of urine
- Urine that appears red, bright pink or cola colored — a sign of blood in the urine
- Pelvic pain
Blood infection (bacteremia)
- Confusion or lack of alertness
- Shortness of breath
- Chest pain when you breathe or cough
Skin or soft-tissue infection
- Swelling, warmth or redness in the area of the infection
- Pain in the area of the infection
- Lesions with pus or drainage
Bone or joint infection
- Swelling, warmth or redness over the area of the infection
- Pain in the area of the infection
- Stiffness or inability to use a limb or joint
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.
From Mayo Clinic to your inbox
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.
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
Adults age 65 and older are at increased risk of group B strep. You're also at increased risk of if you have a condition that impairs your immune system or other serious diseases, including the following:
- HIV infection
- Liver disease
- Heart disease
- Cancer or history of cancer
Group B strep infection can lead to life-threatening disease in infants, including:
- 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 the following:
- Urinary tract infection
- Infection of the placenta and amniotic fluid (chorioamnionitis)
- Infection of the membrane lining the uterus (endometritis)
If you're an older adult or you have a chronic health condition, group B strep bacteria can lead to any of the following conditions:
- Skin infection
- Urinary tract infection
- Bone and joint infections
- Infection of the heart valves (endocarditis)
If you're pregnant, the American College of Obstetricians and Gynecologists recommends a group B strep screening during weeks 36 to 37 of pregnancy. Your doctor will take swab samples from your vagina and rectum and send them to a lab for testing.
A positive test indicates that you carry group B strep. It doesn't mean that you're ill or that your baby will be affected, but that you're at increased risk of passing the bacteria to your baby.
To prevent group B bacteria from spreading to your baby during labor or delivery, your doctor can give you an IV antibiotic — usually penicillin or a related drug — when labor begins.
If you're allergic to penicillin or related drugs, you might receive clindamycin or vancomycin as an alternative. Because the effectiveness of these alternatives is not well understood, your baby will be monitored for up to 48 hours.
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
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.
Sep 21, 2021
- AskMayoExpert. Group B streptococcus (GBS) infection. Mayo Clinic; 2021.
- Puopolo KM, et al. Group B streptococcal infection in neonates and young infants. https://www.uptodate.com/contents/search. Accessed July 16, 2019.
- Group B strep (GBS). Centers for Disease Control and Prevention. https://www.cdc.gov/groupbstrep/index. Accessed July 16, 2019.
- Puopolo KM, et al. Management of infants at risk for Group B streptococcal disease. Pediatrics. 2019;144:e1881.
- Puopolo KM, et al. Group B streptococcal infection in pregnant women. https://www.uptodate.com/contents/search. Accessed July 12, 2021.
- Partin AW, et al., eds. Infections of the urinary tract. In: Campbell-Walsh-Wein Urology. 12th ed. Elsevier; 2021. https://www.clinicalkey.com. Accessed July 12, 2021.
- American College of Obstetricians and Gynecologists Committee on Obstetric Practice. Committee opinion No. 797: Prevention of group B streptococcal early-onset disease in newborns. Obstetrics and Gynecology. 2020; doi: 10.1097/AOG.0000000000003668.