Group B streptococcus (GBS or Group B strep) is a type of bacteria that can cause life-threatening infections in newborns. Each year, about 1,700 babies (1 in 3,000) in the United States develop an early (occurring in the first week of life) GBS infection (1). Infected babies usually contract GBS from their mother during vaginal birth.
About 25 percent of pregnant women carry GBS in the vagina or rectal area (1). The Centers for Disease Control and Prevention (CDC) recommend that all pregnant women be screened for GBS and, when necessary, receive treatment during labor and delivery (2). These steps usually can prevent early GBS infection in newborns.
Group B streptococcus should not be confused with Group A streptococcus, which commonly causes strep throat and, rarely, a potentially deadly destruction of flesh.
How does a pregnant woman get GBS?
Anyone can carry GBS, but few become sick from it. GBS lives in the lower genital tract or gastrointestinal system, along with many other bacteria that are harmless to most people. The bacterium causes illness primarily in pregnant women and their babies. It also sometimes affects the elderly and adults with other illnesses, such as cancer and diabetes.
How does a baby become infected with GBS?
There are two forms of GBS infection in infants:
- Early-onset: Babies with early-onset infection develop symptoms within 7 days of birth, most commonly within the first day of life. About half of all GBS infections in newborns are early-onset (1, 3). Early-onset infections almost always are transmitted from mother to baby around the time of birth.
- Late-onset: Babies with late-onset infection develop symptoms between 7 days and 3 months of age. Babies can get late-onset infections at birth or after birth from contact with the mother. They also can get infected after birth from contact with other people who are GBS carriers.
If an untreated pregnant woman carries GBS in her vagina or rectum at the time of labor and birth, there is a 1-in-200 chance that her baby will become sick from GBS infection (1). The risk is higher if an untreated pregnant woman carries GBS and has certain risk factors. These include (4):
- Preterm birth (before 37 completed weeks of pregnancy)
- Ruptured membranes (bag of waters) for longer than 18 hours before having the baby
- Fever (100.4 F or higher) during labor
- Previous pregnancy resulting in a GBS-infected baby
- A urinary tract infection in this pregnancy caused by GBS
Babies who become sick with GBS infection may take the bacterium into their bodies by ingesting GBS-containing amniotic or vaginal fluids during labor and birth.
What are the symptoms of GBS infection in the newborn?
Babies with an early-onset infection suffer from one or more of the following conditions:
- Pneumonia
- Sepsis (blood infection)
- Meningitis (infection of the membranes around the brain)
Meningitis is less common than the other complications. Babies with a late-onset infection usually have sepsis or meningitis.
In spite of treatment with antibiotics, 3 to 5 percent of babies with GBS die (4). Premature babies (born at less than 37 completed weeks of pregnancy) are more likely to die from the illness than full-term babies (born at 39 to 41 weeks of pregnancy). Most babies who survive GBS go on to develop normally. However, among those who develop meningitis, 20 to 30 percent suffer lasting neurologic damage that can include cerebral palsy, sight and hearing loss, mental retardation, learning disabilities and seizures (3).
How can newborn GBS infection be prevented?
All pregnant women should be tested for GBS at 35 to 37 weeks of pregnancy (2). Women who had a previous baby with GBS infection or a urinary tract infection caused by GBS in the current pregnancy do not need testing. Instead, they require treatment.
To test for GBS, a health care provider takes a swab of the vagina and rectum and sends the sample to a laboratory. Test results are usually available in 24 to 48 hours.
Rapid tests that can be used during labor also are available. Most rapid tests are not considered accurate enough to be reliable in identifying women who should receive antibiotic treatment in labor. However, a new rapid test appears to detect more than 90 percent of women who carry GBS (6). Accurate rapid tests may be beneficial for:
- Women in preterm labor for whom culture testing is not useful because of the time it takes to receive test results
- Women who have not had prenatal care (and so did not receive a GBS test)
Women who test positive for GBS, and certain other women known to be at high risk of having an infected baby, are treated with intravenous (through a vein) antibiotics during labor and birth. Antibiotic treatment is highly effective in preventing early-onset infections in newborns, but does not appear to help prevent late-onset infections.
Who should have antibiotic treatment in labor?
Antibiotic treatment is recommended for women who (2):
- Had a previous baby with GBS infection
- Had a urinary tract infection caused by GBS in the current pregnancy
- Had a positive GBS test in the current pregnancy
- Go into labor before the results of the GBS test are available, or before they have been tested, and have any of the following risk factors:
- Preterm labor
- Ruptured membranes for longer than 18 hours before having the baby
- Fever of at least 100.4 F or higher during labor
Taking oral antibiotics before labor to eliminate GBS is not recommended because the bacteria can return quickly.
When a woman who has had a positive GBS test goes to the hospital to have her baby, she should remind the providers of her test result so she can be treated promptly. Treatment appears most effective when it begins at least 4 hours before birth (2).
Does a woman with a positive GBS test need antibiotics if she has a cesarean birth?
If a woman who carries GBS is having a cesarean birth before the onset of labor and before rupture of membranes, she probably does not need antibiotics (1, 2).
What antibiotics are used during labor and birth to prevent GBS infection in the baby?
Penicillin is the preferred drug (2). A related antibiotic called ampicillin is an alternative. Other antibiotics should be substituted in women who are allergic to penicillin. While these drugs are generally safe for mother and baby, studies suggest that up to 10 percent of women treated with penicillin have a mild allergic reaction (usually a rash) (1). One in 10,000 women has a serious allergic reaction (anaphylactic shock) to penicillin, which requires prompt treatment and, in rare instances, can be fatal (1).
Women who are allergic to penicillin usually are treated with a cephalosporin drug called cefazolin (2). However, a small number of individuals who are allergic to penicillin also are allergic to cephalosporins. If the health care provider believes the woman is at high risk for a serious allergic reaction, she can be treated with erythromycin or clindamycin, as long as lab tests show that the GBS bacterium is not resistant to these drugs. If her infection cannot be treated with these drugs (about one-third of cases are resistant), she should be treated with vancomycin (2, 5).
Can GBS cause complications in the mother, unrelated to newborn infection?
GBS can cause uterine infection before or after birth. Infection before birth is called chorioamnionitis. This infection can cause fever and uterine tenderness, as well as increased heart rate in the baby. Chorioamnionitis is treated with antibiotics. However, before birth, a uterine infection may be symptomless and, therefore, not detected. The infection may increase the risk of (3):
- Premature rupture of the membranes (before 37 weeks gestation)
- Preterm labor
- Stillbirth
After birth, the symptoms of a uterine infection include fever, abdominal pain and rapid pulse. With antibiotic treatment, a postpartum (after birth) uterine infection usually goes away in a few days. Women who are screened and treated for GBS during labor and birth are less likely to develop postpartum uterine infections (5).
GBS also can cause a urinary tract infection during pregnancy. Symptoms of a urinary tract infection include fever and pain and burning during urination. Some women have a symptomless urinary tract infection, which may be diagnosed during a routine urine test during a prenatal visit.
Women with a urinary tract infection caused by GBS should be treated with oral (by mouth) antibiotics during pregnancy. They also should be treated with intravenous antibiotics during labor and birth, as they are likely to have high levels of the bacterium in the vagina.
Do babies of women treated for GBS in labor require additional treatment?
Most babies of treated women do not require special treatment after birth unless they have symptoms of developing sepsis. However, if the mother is diagnosed with a uterine infection (chorioamnionitis) during labor and birth, her baby should be tested for GBS. The baby often is treated with antibiotics while waiting for the results of the test.
How are babies with GBS infection treated?
Babies who are diagnosed with a GBS infection are treated with antibiotics through a vein or by injection.
Is there a vaccine for GBS?
No. However, researchers are developing and testing vaccines, to be given before or during pregnancy, to prevent GBS infection in mothers and their babies.
Does the March of Dimes support research on GBS?
The March of Dimes supports a number of grants aimed at improving understanding of how certain bacteria and other organisms cause severe infections in the fetus and newborn, with the ultimate goal of preventing these infections. A current grantee is investigating the interactions between a group B strep bacterium gene and cells that line the lungs. This could show how the bacterium may bypass protective barriers in the lungs to cause infection, with possible relevance to vaccine development.
For more information
The CDC has a special Web site devoted to Group B strep.
References
- Centers for Disease Control and Prevention (CDC). (2008). Group B Strep Prevention. Retrieved October 29, 2009.
- Centers for Disease Control and Prevention (CDC). (2002). Prevention of Perinatal Group B Streptococcal Disease: Revised Guidelines from CDC. Morbidity and Mortality Weekly Report, 51 (RR-11). Retrieved October 29, 2009.
- Pannaraj, P.S. & Baker, C.J. (2009). Group B Streptococcal Infections. In Feigin, R.D., et al (Eds.), Feigin & Cherry’s Textbook of Pediatric Infectious Diseases (6th ed., pp.1239-1257). Philadelphia, Penn.: Saunders Elsevier.
- American Academy of Pediatrics (AAP). (2009). Group B Streptococcal Infections. In Pickering, L.K. (Ed.), Red Book: 2009 Report of the Committee on Infectious Diseases (28th ed., pp.628-635). Elk Grove Village, Ill.: American Academy of Pediatrics.
- Phares, C.R., Lynfield, R., Farley, M.M., Mohle-Boetani, J., Harrison, L.H., et al. (2008). Epidemiology of Invasive Group B Streptococcal Disease in the United States, 1999-2005. Journal of the American Medical Association, 299 (17), 2056-2065.
- Edwards, M.S., Novak-Weekly, S., Koty, P.P., Davis, T., Leeds, L.J., et al. (2008). Rapid Group B Streptococci Screening Using a Real-Time Polymerase Chain Reaction Assay. Obstetrics and Gynecology, 111 (6), 1135-1141.
March 2010
