What is group B streptococcal infection?

Definition

Group B streptococcal (GBS) disease is a bacterial
infection. These bacteria live in the gastrointestinal and
genitourinary tracts and are found in the vaginal or rectal areas of 10 to 35
percent of all healthy adult women.

GBS can cause illness in newborns, pregnant women, the elderly, and adults with
other chronic medical conditions, such as diabetes or liver disease. In newborns, GBS is the most common cause of bacteremia or
septicemia (blood infection) and meningitis
(infection of the fluid and lining surrounding the brain). GBS in pregnant women
and their fetuses and newborns are discussed here.

Causes

GBS is caused by the bacterium
Streptococcus agalactiae. Not all fetuses and babies who are exposed to the bacterium will become infected, but those who have become infected with GBS got the infection in one of three ways: before birth, during delivery, and after birth. Before birth, bacteria in the vagina spread up the birth canal into the uterus and infect the amniotic fluid surrounding the fetus. The fetus becomes infected by ingesting the infected fluid. During delivery, the fetus can become infected by contact with bacteria in the birth canal; after birth, the newborn can be infected through physical contact with the mother.

Risk Factors

Factors that increase the risk of a baby contracting GBS are the mother having
already had a baby with GBS disease, the presence of GBS bacteria in the current
pregnancy, the mother having a urinary tract infection caused by GBS,
going through labor or experiencing a rupture of the membranes before thirty-seven
weeks gestation, experiencing a rupture of the membranes for eighteen hours or
more before delivery, and the mother having a fever during labor.

Symptoms

In pregnant women, GBS infections can cause endometritis, amnionitis, and septic abortion. In newborns, two forms of infection occur: early-onset and late-onset. Early-onset GBS disease usually causes illness within the first twenty-four hours of life. However, illness can occur up to six days after birth. Late-onset disease usually occurs at three to four weeks of age; it can occur any time from seven days to three months of age. Symptoms of both kinds of GBS include breathing problems, not eating well, irritability, extreme drowsiness, unstable temperature (low or high), and weakness or listlessness (in late-onset disease).

Screening and Diagnosis

GBS can be diagnosed in a pregnant woman at a doctor’s office. Testing for GBS should be done about one month before the baby is due. The doctor swabs the pregnant woman’s vagina and rectum and sends these samples to a laboratory to test for GBS. Test results are available in twenty-four to forty-eight hours. The doctor may also order blood tests.

Treatment and Therapy

Women who test positive for GBS or who are at high risk may receive intravenous
antibiotics during labor and delivery. Penicillin or
ampicillin is usually used. Women who are allergic to penicillin or ampicillin may
be given clindamycin or erythromycin instead. It is generally not recommended that
women take antibiotics before labor to prevent GBS (unless GBS is identified in
the urine). Studies have shown that antibiotics are not effective at earlier
stages.

If the doctor suspects strep B infection in the newborn, the newborn might be kept in the hospital for observation by staff. If the baby is diagnosed with GBS, he or she will be treated with intravenous antibiotics for ten days. Even with the existence of screening tests and antibiotic treatment, some babies can still get GBS disease.

Prevention and Outcomes

Methods to prevent GBS include screening pregnant women at thirty-five to thirty-seven weeks into the pregnancy and giving antibiotics during labor and delivery to women who are carriers of GBS bacteria, who have previously had an infant with invasive GBS disease, who have GBS bacterium in the present pregnancy, who go into labor or have a rupture of the membranes before the fetus has reached an estimated gestational age of thirty-seven weeks, who have a rupture of membranes for eighteen hours or more before delivery, who have a fever during labor, or who have a urinary tract infection with GBS. Another option is to give antibiotics (usually penicillin) to newborns who were exposed to the bacterium. No vaccine exists for the disease.

Bibliography

Centers for Disease Control and Prevention. “Provisional Recommendations for the Prevention of Perinatal Group B Streptococcal Disease.” Available at http://www.cdc.gov/groupbstrep/guidelines/provisional-recs.htm.

Cunningham, F. Gary, et al., eds. Williams Obstetrics. 23d ed. New York: McGraw-Hill, 2010.

Martin, Richard J., Avroy A. Fanaroff, and Michele C. Walsh, eds. Fanaroff and Martin’s Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 2 vols. 8th ed. Philadelphia: Mosby/Elsevier, 2006.

Phares, C. R., et al. “Epidemiology of Invasive Group B Streptococcal Disease in the United States, 1999-2005.” Journal of the American Medical Association 299, no. 17 (2008): 2056-2065.

Remington, Jack S., et al., eds. Infectious Diseases of the Fetus and Newborn Infant. 6th ed. Philadelphia: Saunders/Elsevier, 2006.

Wilson, Michael, Brian Henderson, and Rod McNab. Bacterial Disease Mechanisms: An Introduction to Cellular Microbiology. New York: Cambridge University Press, 2002.