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Group B Streptococcus

What is group B streptococcus?

Group B streptococcus (GBS) is a bacterium that can be found in the digestive tract, urinary tract, and genital area of adults. Although GBS infection usually does not cause problems in healthy women before pregnancy, it can cause serious illness for a newborn baby.

Why is group B streptococcus a concern?

About 25% of pregnant women carry GBS in their rectum or vagina. In some pregnant women, GBS infection may cause chorioamnionitis (infection of the amniotic fluid, membranes, decidua, and placental tissues) and postpartum (after birth) infection, called endometritis. Urinary tract infections caused by GBS can lead to preterm labor and birth.

Newborns can contract GBS during pregnancy, or from the mother's genital tract during labor and delivery. GBS is the most common cause of life-threatening infections in newborns, including pneumonia and meningitis. If a pregnant woman who is a group B strep carrier does not get antibiotics at the time of delivery, her baby has a 1 in 200 chance of developing GBS disease. Nearly 75% of the cases of GBS disease among newborns occur in the first week of life, called early-onset disease. Premature babies are more susceptible to GBS infection than full-term babies.

Although it is very rare, GBS infection may also develop in babies one week to several months after birth, called late-onset disease. Meningitis is more common with late-onset GBS disease. Only about half of late-onset GBS disease among newborns comes from a mother who is a GBS carrier. The source of infection for others with late-onset GBS disease is unknown.

How is group B streptococcus diagnosed?

GBS can be cultured from the mother's vagina and rectum with a swab during a pelvic exam. GBS can also be cultured from a mother's urine. Cultures are usually done between 35 and 37 weeks of pregnancy and may take a few days to complete. Cultures collected earlier in pregnancy do not accurately predict whether a mother will have GBS at delivery.

In infants, GBS may be cultured from samples of sterile body fluids, such as blood or spinal fluid. Most newborns with GBS infection have symptoms in the first few hours after birth. Symptoms are related to the body systems that are affected by the infection and may include breathing problems, changes in blood pressure, or neurologic problems such as seizures.

Treatment for group B streptococcus

Treatment of GBS depends on when GBS infection is diagnosed -- during pregnancy or after delivery.

If the mother has a positive GBS culture during pregnancy, treatment with intravenous (IV) antibiotics during labor is recommended to reduce the risk of transmission of the infection to the baby. Penicillin is the most common antibiotic that is given. A woman should tell her health care provider about any medication allergies. Treatment may also be needed for women with certain risk factors, including the following:

  • Fever during labor

  • Rupture of membranes (bag of waters) for 18 hours or longer if the GBS status is unknown in a full-term pregnancy 

  • Labor or rupture of membranes if the GBS status is unknown before 37 weeks gestation (preterm)

  • History of GBS infection in a previous baby

Newborns who become ill with GBS infection may require care in the newborn intensive care unit (NICU). They are usually treated with IV antibiotics. Other treatments and specialized care may be needed depending on the severity of the infection and whether the infection causes serious problems such as meningitis or pneumonia.

Prevention of group B streptococcus

It is important to understand that, in spite of testing and treatment, some babies still develop GBS disease. Research is ongoing to develop vaccines to prevent GBS disease. In the future, women who are vaccinated against GBS may make antibodies that cross the placenta and protect the baby during birth and early infancy.

Online Medical Reviewer: MMI board-certified, academically affiliated clinician
Online Medical Reviewer: Trevino, Healther, M., BSN, RNC
Date Last Reviewed: 9/28/2014
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