Group B streptococcal infection

• ANATOMY OR SYSTEM AFFECTED: Gastrointestinal system, genitalia, genitourinary tract
• ALSO KNOWN AS: Group B strep, Streptococcus agalactiae infection, GBS

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 about 18 percent of pregnant women worldwide, while between 20 and 40 percent of all individuals carry GBS according to the US Centers for Disease Control.

GBS can cause illness in newborns, pregnant women, older adults, and adults with other chronic medical conditions, such as diabetes or liver disease. In infants under ninety days old, 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, amoxicillin, cephalosporin, or vancomycin are usually used. Women who are allergic to these medications 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, they will be treated with intravenous antibiotics for ten days, usually gentamicin with amoxicillin. 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

“About Group B Strep Disease.” Centers for Disease Control and Prevention, 3 Jan. 2024, www.cdc.gov/group-b-strep/about/index.html. Accessed 1 Nov. 2024.

Cunningham, F. Gary, et al. Williams Obstetrics. 26th ed., McGraw-Hill, 2022.

Francois Watkins, Louise K., et al. “Epidemiology of Invasive Group B Streptococcal Infections among Nonpregnant Adults in the United States, 2008-2016.” JAMA Internal Medicine, vol. 179, no. 4, 2019, pp. 479–88, doi.org/10.1001/jamainternmed.2018.7269. Accessed 1 Nov. 2024.

Martin, Richard J., et al. Fanaroff and Martin's Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 12th ed., Mosby/Elsevier, 2024.

Remington, Jack S., et al., editors. Infectious Diseases of the Fetus and Newborn Infant. 8th ed., Saunders/Elsevier, 2016.

Wilson, Michael, et al. Bacterial Disease Mechanisms: An Introduction to Cellular Microbiology. Cambridge UP, 2002.