What is group B strep?

Group B streptococcus (often called group B strep or GBS) is a type of bacteria found in the vagina (birth canal) and/or lower intestine of about 10–30 percent of women. It's not a sexually transmitted disease, and is considered harmless in women with no signs or symptoms. While a pregnant woman with GBS seldom feels sick, she can pass the bacteria to her baby during birth, causing a life-threatening infection in her newborn. GBS affects about 1 in every 2,000 babies born in the U.S., but not every baby who is born to a GBS-positive mother becomes infected.

Also, GBS typically doesn't affect the length of time you and your baby spend in the hospital, and it doesn't affect your ability to breastfeed safely. The levels of bacteria in a woman's body can change over time, and symptom-free GBS is not generally a cause for concern for the mother after pregnancy.

Prevention at birth 

Prevention of GBS infection in the newborn relies on screening of the mother during pregnancy and administration of antibiotics during labor. 

Screening: The Centers for Disease Control and Prevention (CDC) recommends that all pregnant women without a medical history of GBS be screened late in pregnancy, when they are approximately 35 to 37 weeks along. Screening doesn’t occur sooner because a woman’s GBS status can change. Plus, there is a greater risk for “missed” cases when the screening is done too long before labor begins. The screening process is simple—a cotton swab is used to collect a sample from the vagina and rectum and then sent to a lab for testing. If you test positive, remind your health care team during labor.

Antibiotics: Pregnant women, who meet any of the following criteria, should receive intravenous (IV) antibiotics during labor (ideally for at least four hours) to protect their newborns from infection. Criteria for receiving antibiotics during labor include:

  • Test positive for GBS during routine screening. 
  • Have group B detected in their urine during the current pregnancy. 
  • Have given birth to a baby with group B strep infection in the past. 
  • Go into labor before 37 weeks and haven't been tested for GBS
  • Have a fever (100.4 F or higher) during labor
  • Haven't delivered your baby within 18 hours of your water breaking 

IV antibiotics—safe for both mother and baby—dramatically cut the baby’s risk of infection. An infant born to a GBS-positive woman who has not received antibiotics has a 1 in 200 chance of group B strep disease. The risk is just 1 in 4,000—that’s more than 20 times lower—for babies of GBS-positive mothers treated with antibiotics. Women who are allergic to penicillin (the recommended treatment) can be given an alternative antibiotic instead. 

Because the bacteria can grow back quickly, the antibiotics must be given during labor; antibiotics won’t help if taken prior to labor. According to the CDC, IV antibiotics are the “only proven strategy” to prevent group B strep infection in newborns. 

Even though passing through the birth canal (vagina) puts a baby into contact with GBS, the risk associated with vaginal birth and antibiotic treatment is still less than that of cesarean birth.

Symptoms in babies 

It can be difficult to diagnose group B strep disease in babies because the symptoms are similar to those seen with other health problems. Also, while most symptoms usually occur within the first six hours after birth, they can appear anytime during the first week (early-onset) or even later, throughout the first three months (late-onset).

Early-onset symptoms include: 

  • Fever 
  • Difficulty feeding 
  • Lethargy

Late-onset symptoms include: 

  • Difficulty breathing 
  • Fever
  • Difficulty feeding
  • Lethargy
  • Irritiability

When GBS infection is suspected, samples of blood and spinal fluid are collected from the baby and sent to a lab for testing. IV antibiotics are the first step in treatment. If left untreated, GBS infection can cause serious and potentially fatal illness for the baby, including lung infections (pneumonia), blood infections (septicemia), or brain infections (meningitis). According to the American Congress of Obstetricians and Gynecologists (ACOG), GBS infections cause death in about 5 percent of infected babies. 

For more information, including the latest GBS Prevention Guidelines (endorsed by the CDC and written by the American Society for Microbiology in 2020), visit the CDC website.

Last updated March 30, 2021

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