Group B Strep Infection

What Is Group B Strep Infection?

Antibiotics can treat group B strep infections.
Antibiotics can treat group B strep infections.
  • Group B strep (GBS) causes serious infections in newborn infants and pregnant women.
  • Increasingly, group B strep also causes bloodstream infections and pneumonias in nonpregnant adults. Group B strep infections are treated with antibiotics.
  • To reduce the risk of infection in pregnant women and newborns, cultures are taken from pregnant women during late pregnancy, and intravenous antibiotics are given to those with positive cultures.
  • This practice has significantly reduced the number of serious infections in newborns and pregnant women.

What Causes Group B Strep Infection?

Group B strep infections are caused by bacteria from the species and genus Streptococcus agalactiae. Streptococci were divided into groups in 1933 by mixing the strains with antibodies that were produced in rabbits. Group B streptococci (GBS) have an outer cell wall that serves as a protective capsule which helps the organism resist the body's attempts to fight off the bacteria.

Group B strep may live harmlessly in the human body, which is called "colonization" or "carriage." During colonization, the organism lives on surfaces and membranes but does not invade tissues or organs. The most common site of colonization for group B strep is in the bowels. A significant percentage of women are colonized with group B strep in the vagina or cervix. Colonization is more common in people with diabetes and those who are sexually active.

An infection occurs when the bacteria invade the bloodstream, tissues, or organs. Newborns can become infected with group B strep as they pass through the birth canal if the mother carries the organism in her vagina. These infections are early-onset since they appear within the first week of life, often in the first hours after birth. In mothers colonized with group B strep, a small percentage of newborns will have early-onset infection. Since group B strep is carried in the bowels, the organism may also be spread if a person does not wash their hands properly after using the bathroom. Babies can also be infected this way, usually in the home, causing late-onset infections, which occur when the baby is 1 week to 3 months old.

Group B strep is not a cause of birth defects or autism and is not a sexually transmitted disease. Although babies may contract infections by contact with contaminated hands, washing with simple soap and water eliminates the organism. Group B strep is not contagious through coughing or sneezing.

Group B strep is a cause of infection in pregnant women. The organism may infect the bloodstream or the uterus. Older children and nonpregnant adults, especially older adults in nursing homes, may also get infections with group B strep.

What Are the Symptoms and Signs of Group B Strep Infection?

Group B strep may cause severe or fatal infections in newborn infants. Early-onset disease is the most serious. The bacteria may cause pneumonia or bloodstream infection (sepsis) or may infect the lining tissues of the brain, causing meningitis. Infected newborns are listless, don't feed well, and may have a condition called jaundice. Jaundice causes the skin and membranes to look yellowish. Infected babies have trouble breathing and may have low blood pressure. Even with the best of care, a significant percentage of babies with early-onset infections die. Babies who have low birth weights are at highest risk for death. Meningitis is a particularly severe manifestation of the infection, with some survivors having permanent brain damage.

Infants who become infected later in life (after 1 week of age) have late-onset disease. Although the infections can occur as late as 3 months after birth, most late-onset infections occur at about 3 weeks of age. Although usually less severe than early-onset infection, late-onset infection can sometimes cause sepsis, pneumonia, infected bones, seizures, and meningitis. Infected babies become listless, stop feeding well, and have fever. If treated promptly, late-onset disease is fatal in a small percentage of babies.

Pregnant women who are infected have fever, abdominal pain, and/or low blood pressure. The infection may cause a miscarriage, stillbirth, or pre-term labor. Infection may occur before labor or as late as 48 hours after delivery.

In non-pregnant adults, group B strep causes bloodstream infection, pneumonia, abscesses, or infections of the bone (osteomyelitis). People with bloodstream infections usually have fever and aches, and they may have low blood pressure. Bloodstream infections may lead to infection of the heart valves (endocarditis). Pneumonia causes shortness of breath and fever with cough. Abscesses are local collections of pus and may occur deep in the abdomen.

When Should I Call the Doctor About Group B Strep?

Pregnant women should call their physician promptly if they have fever or abdominal pain. Newborns and infants should be seen by a medical provider if they have fever, trouble breathing, or appear listless. Nonpregnant adults should seek medical attention for fever, shortness of breath, or other general signs of infection.


Bacterial Infections 101: Types, Symptoms, and Treatments See Slideshow

What Are the Exams and Tests Used to Diagnose Group B Strep?

The physician will perform a physical examination to help identify where the infection is located. If pneumonia is suspected, a chest X-ray will be done and a sample of the sputum will be sent for culture. If bloodstream infection is being considered, blood will be drawn and sent to the laboratory to be cultured. If an abscess is suspected, a CT scan or MRI may be done. A needle may be placed in the abscess to get a sample for culture.

Infected bone (osteomyelitis) may be diagnosed by taking a small piece (biopsy) of the bone in the operating room. Osteomyelitis may also be diagnosed by X-rays or other imaging studies showing that part of the normal bone has been destroyed.

If meningitis is suspected, the physician will do a spinal tap. To do this, a needle is put in the lower back under sterile conditions and a sample of the cerebrospinal fluid is drawn off. Local anesthetic is used to make the patient comfortable during the spinal tap. The fluid is examined under the microscope to see if it has pus or visible bacteria. A sample of the fluid is cultured.

It is important to identify pregnant women who are colonized with group B strep so they can be treated before the baby enters the birth canal. To do this, the doctor swabs the inside of the vagina and/or rectum and sends the swab to the laboratory for culture. It is also possible for the woman to swab her own vagina and rectum and submit the specimen to her clinic or laboratory for testing.

What Is the Treatment for Group B Strep Infection?

Serious infections with group B strep require intravenous antibiotics. Fortunately, group B strep remains sensitive to many types of antibiotics, including penicillin. Treatment is usually continued for 10-14 days but may be continued longer (six to eight weeks) if there is an abscess, infected heart valve, or osteomyelitis.

If the infection is an abscess, it is almost always necessary to drain the abscess. Draining may be done at the bedside using a needle if the abscess is small and near the surface. For larger or deeper abscesses, draining is often done in the operating room.

Are There Home Remedies for Group B Strep?

Diagnosis and management of group B strep infections cannot be done at home. Serious group B strep infections require intravenous antibiotics. If prolonged treatment is needed and the patient is stable, intravenous antibiotics may be administered at home if this can be arranged safely. Milder infections like urinary tract infections (bladder infections) may be treated with oral antibiotics.

What Are the Medications for Group B Strep?

The usual choice for antibiotics is intravenous penicillin. If a person is allergic to penicillin, other intravenous antibiotics such as the cephalosporins or vancomycin may be used.

What Is the Follow-up for Group B Strep?

Antibiotics cure infections due to group B strep. However, approximately 4% of infected nonpregnant adults will have a second infection within the next year. It is possible that these people have a weakened immune system that puts them at risk for recurrent infection.

How Do You Prevent Group B Strep Infections?

Great strides have been made in reducing group B strep infections in mothers and infants. This has happened because doctors now test all pregnant women for group B strep by doing vaginal and rectal cultures. It is recommended that all pregnant women be tested for group B strep between 35-37 weeks of pregnancy. Women who carry group B strep are treated with intravenous antibiotics during labor. Women who plan to have cesarean sections do not necessarily need to be treated since the baby will not pass through the vagina, but most doctors will administer pre-operative antibiotics anyway. If a woman has not been tested before she is in labor, she may be treated with antibiotics to reduce the risk of group B strep infection in the baby, especially if the baby is premature, the mother has fever, or the water breaks more than 18 hours before delivery. If group B strep is grown from the urine at any time during the pregnancy, she will be given antibiotics during labor regardless of what her rectal/vaginal cultures show.

As a result of using antibiotics during labor in colonized women, there has been a large reduction in invasive disease of newborns.

What Is the Prognosis for Group B Strep?

Scientists are trying hard to make a vaccine against group B strep. There are some promising results, and it is possible that a vaccine will be developed in the next several years.

Although culture is the recommended test of choice for pregnant women, results take up to three days to come back. Several more rapid tests have been developed and are being tested to determine if they could replace culture.

Support Groups and Counseling

The March of Dimes provides a list of resources for women who have had premature babies, stillbirth, miscarriages, or death of an infant.

For More Information on Group B Strep

Additional information is available from your doctor or clinic. The U.S. Centers for Disease Control and Prevention (CDC) and the American College of Obstetrics and Gynecology also provide informational booklets and resources for patients and health-care professionals.

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Medically reviewed by Wayne Blocker, MD; Board Certified Obstetrics and Gynecology


Larsen, J.W., Sever, J.L. "Group B Streptococcus and Pregnancy: A Review." Am J Obstet Gynecol 198 (2008): 440-8.

Phares, C.R., Lynfield, R., Farley, M.M., Mohle-Boetani, J., Harrison, L.H., Petit, S., Craig, A.S., Schaffner, W., Zansky, S.M., Gershman, K., Stefonek, K.R., Albanese, B.A., Zell, E.R., Schuchat, A., Schrag, S.J.; Active Bacterial Core Surveillance/Emerging Infections Program Network. "Epidemiology of Invasive Group B Streptococcal Disease in the United States, 1999-2005." JAMA 299 (2008): 2056-65.

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