Group B Streptococcus


Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is a bacterium commonly found in the gut and genitourinary tract of healthy adults. However, it is also an important cause of serious, life-threatening infections in newborns. Adults with certain chronic medical conditions, such as diabetes or liver disease, are also at risk for infection by GBS. Group B strep should not be confused with Group A strep (the bacterium that causes strep throat).


In adults, GBS typically does not cause disease. However, urinary tract infections and blood infections are two of the most common infections that can be found in adults.

In newborns, GBS can take two forms: 1) Early-onset GBS disease and 2) Late-onset GBS disease. Early-onset GBS disease occurs within the first 12 hours after delivery and is characterized by:

  • Fever
  • Difficulty breathing
  • Sluggishness

Late-onset GBS disease usually appears within a week to a few months after birth and is characterized by:

  • Upper respiratory tract infection
  • Fever
  • Difficulty breathing
  • Sluggishness
  • Seizures


Streptococcus agalactiae often live inside the gut and genitourinary tracts of healthy people. However, when the bacteria infect newborns or people with poor immune systems, it can cause disease.

Infection of newborns occurs during vaginal delivery when the mother is colonized by GBS and has not received proper antibiotic treatment. However, it is now common practice to check all pregnant women in their third trimester for GBS colonization. If GBS are found, antibiotics can be administered to stop the bacteria from infecting the newborn during delivery.

Risk Factors

Adults are at increased risk for disease caused by GBS if they:

  • Have a compromised immune system such as people with HIV/AIDS, diabetes, cancer, or liver disease
  • Are older than 65 years old

Infants are at increased risk for GBS infection if:

  • They are born prematurely
  • Mother is colonized by GBS
  • Rupture of membranes occurred >18 hours prior to birth
  • Infection of the placenta or amniotic fluid occurred during pregnancy
  • Mother’s temperature was greater than 100°F during delivery
  • They have a sustained increased heart rate during labor
  • Mother has had a prior infant infected with GBS


The Centers for Disease Control and Prevention (CDC) has created guidelines for the prevention of perinatal group B streptococcal disease which include:

  • Universal prenatal culture-based screening for vaginal and rectal GBS colonization between 35 to 37 weeks gestation

Give mother antibiotics before delivery if:

  • GBS culture is unknown
  • Mother’s water broke 18 or more hours ago and delivery has not occurred
  • GBS blood infection occurred at any time during infection
  • Mother has previously delivered an infant who was infected with GBS
  • Mother goes into labor before 37 weeks and hasn’t been tested for GBS


Antibiotics are an effective treatment for GBS infection in adults.

For infant infections, intravenous (IV) antibiotics are the treatment of choice. IV fluids, other medications, and supplemental oxygen may also be given depending on the needs of the infant.

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