Causes and How It Spreads

Group B strep (GBS) bacteria commonly live in people’s bodies and usually are not harmful. Babies can be exposed to GBS bacteria during delivery. How other people are exposed to these bacteria is not completely known.


Bacteria called group B Streptococcus (group B strep, GBS) cause GBS disease. GBS bacteria commonly live in people’s gastrointestinal and genital tracts. The gastrointestinal tract is the part of the body that digests food and includes the stomach and intestines. The genital tract is the part of the body involved in reproduction and includes the vagina in women.

Most of the time the bacteria are not harmful and do not make people feel sick or have any symptoms. Sometimes the bacteria invade the body and cause certain infections, which are known as GBS disease.

Learn about signs and symptoms of GBS disease.

How it spreads

How people spread GBS bacteria to others is generally unknown. However, experts know that pregnant women can pass the bacteria to their babies during delivery. Most babies who get GBS disease in the first week of life are exposed to the bacteria this way. It can be hard to figure out how babies who develop GBS disease later got the bacteria. The bacteria may have come from the mother during birth or from another source.

Other people who live with someone who has GBS bacteria, including other children, are not at increased risk of getting sick.

In the United States, there’s no evidence that GBS bacteria spread through food, water, or anything that people might have come into contact with.