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GROUP B STREP INFECTIONS
Group B streptococcus (GBS) infection is a bacterial infection that causes 2 of every 1,000 babies born in the United States to become sick or die. It should not be confused with Group A streptococcus, which commonly causes strep throat and, rarely, a potentially deadly destruction of flesh. Between 10 and 30% of pregnant women carry the GBS bacterium in the vagina or rectal area, but few babies of these women actually develop an infection.
Doctors are making progress in preventing GBS infection in newborns. In 1996, both the federal Centers for Disease Control and Prevention (CDCP) and the American College of Obstetricians and Gynecologists (ACOG) issued guidelines to help health care providers identify and treat pregnant women who are at risk of transmitting GBS to their babies. The steps they recommend usually can prevent the infection in newborns of treated women.
Q. How does a pregnant woman get GBS?
A. Anyone can carry GBS, but few become sick from it. The bacterium lives in the gastrointestinal system, along with many other bacteria that are harmless to most people. The bacterium causes illness primarily in pregnant women and their babies and, occasionally, in the elderly and in adults with other illnesses such as cancer and diabetes.
Q. How does a baby acquire GBS infection?
A. There are two forms of GBS infection in infants, early- and late-onset. Babies with an early-onset infection develop symptoms within 7 days of birth, most commonly within the first 6 hours of life. Babies with a late-onset infection develop symptoms at between 7 days and 3 months of age.
About 80% of all GBS infections in newborns are early onset. Early-onset infections almost always are transmitted from mother to baby around the time of delivery. Late-onset infections can be contracted at delivery or acquired after birth from other sources (such as from inadequate handwashing by hospital personnel or from family members).
If a pregnant woman carries the GBS bacterium in her vagina or rectum at the time of labor and delivery, there is a 1-in-200 chance that her baby will become sick from GBS infection. The risk rises to 4% if a pregnant woman carries the bacterium and develops certain risk factors. These include: preterm (before 37 weeks gestation) labor, premature rupture of the membranes, prolonged rupture of the membranes (longer than 18 hours without delivering the baby), or fever (100.4? F or higher) during labor. Doctors believe that babies who become sick with GBS infection have taken the bacterium into their bodies -- for example, by ingesting GBS-containing vaginal fluids during labor and delivery. Thirty to 70% of the babies of women who carry GBS in the vagina or rectum are born with the bacterium on their skin but most of these babies have no illness.
Q. What types of symptoms does GBS infection produce in the newborn?
A. Babies with an early-onset infection suffer from one or more of the following conditions: pneumonia, sepsis (blood infection), and meningitis (infection of the membranes surrounding the brain). Babies with a late-onset infection are more likely than babies with an early-onset infection to have meningitis as their major illness.
In spite of treatment with antibiotics, about 6% of babies with GBS die. Of the babies who live, about 90% do not develop meningitis and go on to develop normally. Fifteen to 30% of GBS-infected babies who develop meningitis suffer lasting neurologic damage in the form of cerebral palsy, sight and hearing loss, and/or mental retardation.
Q. How can GBS infection of the newborn be prevented?
A. According to the CDC and ACOG guidelines, two approaches can prevent most (up to 80%) early-onset GBS infections in the newborn. These approaches generally do not help prevent late-onset infections. Both approaches involve treating certain women with intravenous antibiotics during labor and delivery.
Penicillin, or a related drug called ampicillin, usually is used, though clindamycin or erythromycin can be substituted in women who are allergic to penicillin. All of these antibiotics are considered safe for mother and baby, though there is some concern about allergic reactions. Studies to date suggest that 1 to 10% of women treated with penicillin will have a mild allergic reaction (usually a rash), and 1 in 10,000 will have a serious allergic reaction (anaphylactic shock), which requires prompt treatment and, in rare instances, can be fatal.
The first approach involves taking a swab of the vagina and rectum at 35 to 37 weeks of pregnancy. This sample is sent to a laboratory for a culture to test for the presence of GBS. Test results are available in 24 to 48 hours. If a pregnant woman is found to carry GBS, she will be treated with intravenous antibiotics during labor and delivery. Taking oral antibiotics prior to labor is not recommended, as they are not effective in preventing GBS infection in the newborn. Some studies found that 20 to 70% of women treated with oral antibiotics during the third trimester still carried the bacterium at labor and delivery.
If a pregnant woman develops preterm labor before her culture test results are available, or before her provider has taken a culture, antibiotic treatment during labor and delivery is recommended. If a pregnant woman develops premature rupture of the membranes at less than 37 weeks gestation, her doctor will test her for GBS. If labor begins before test results are available (24 to 48 hours), intravenous antibiotics are recommended. However, if the pregnant woman does not go into labor right away, her doctor may either begin intravenous antibiotic treatment, then stop it if results come back negative, or may delay antibiotic treatment until either the results come back positive or she goes into labor (both approaches are considered effective).
Until recently, health care providers often tested women for GBS at 26 to 28 weeks of pregnancy. While this approach has helped to prevent many newborn GBS infections, the CDC and ACOG believe that doing the culture test at 35 to 37 weeks gestation is more accurate in detecting women who carry GBS at delivery. Because the GBS bacterium can come and go, testing at 26 to 28 weeks fails to identify the 7% of women who test negative at this time, but carry the bacterium at birth. Nearly all women who carry GBS at 35 to 37 weeks gestation will still carry the bacterium at delivery.
The second approach does not involve a culture test, but treats only those women who develop risk factors that increase the likelihood of passing GBS (if they carry it) on to their babies. Providers who recommend this approach treat pregnant women with intravenous antibiotics in labor and delivery only if the following high-risk situations occur:
- Pre-term (before 37 weeks gestation) labor
- Premature rupture of the membranes (prior to 37 weeks gestation)
- Prolonged rupture of the membranes (longer than 18 hours without delivering the baby, at any gestational age)
- Fever (100.4? F. or higher) during labor
Both approaches recommend that all women who have previously delivered a baby with GBS infection be treated with intravenous antibiotics in labor and delivery. Antibiotic treatment during labor and delivery also is recommended for all women who have had a urinary-tract infection caused by GBS during pregnancy.
All pregnant women should discuss with their health care provider his or her approach to preventing GBS infection in the newborn. Both of the approaches discussed above will help prevent newborn GBS. More studies are needed to determine whether one of these approaches is more effective.
Q. Can GBS cause complications in the mother, unrelated to newborn infection?
A. GBS can cause uterine infection prior to or following delivery. Before delivery, such an infection often is symptomless and therefore usually untreated. It may increase the risk of pre-term (before 37 weeks gestation) premature rupture of the membranes and pre-term labor. Following delivery, the symptoms of a uterine infection include fever, abdominal pain, and rapid pulse. With antibiotic treatment, such an infection usually subsides within a few days.
A urinary-tract infection also may result from GBS and should be treated during pregnancy with oral antibiotics. Symptoms of a urinary-tract infection include fever, and pain and burning during urination. Women with a urinary-tract infection caused by GBS also should be treated with intravenous antibiotics during labor and delivery, since they are likely to have high levels of the bacterium in their bodies.
Thomas G. Stovall, M.D.
Dr. Stovall is a Clinical Professor of Obstetrics and Gynecology at the University of Tennessee Health Science Center in Memphis, Tennessee and Partner of Women's Health Specialists, Inc.
Date Published: 2004-03-10
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