What causes gbs positive

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Last updated: April 4, 2026

Quick Answer: Group B Streptococcus (GBS) is a common bacterium that many people carry in their bodies without experiencing any symptoms. It is not a sexually transmitted infection and is typically found in the lower genital tract of women and the rectum of both men and women. The presence of GBS is usually detected through screening tests during pregnancy.

Key Facts

What is Group B Streptococcus (GBS)?

Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is a type of bacterium that commonly lives in the lower genital tract of women and the rectum of both men and women. It's important to understand that GBS is a very common bacteria, and its presence does not necessarily indicate an infection or a health problem for the carrier. Many people carry GBS without any symptoms or ill effects. In fact, it's estimated that between 10% and 30% of pregnant women carry GBS in their vagina or rectum.

How is GBS Transmitted?

GBS is not a sexually transmitted infection (STI). Transmission typically occurs when a baby passes through the birth canal during labor and delivery. If a pregnant woman carries GBS, there is a chance she can pass it to her baby. This transmission can happen during labor, either vaginally or rectally. While GBS can be present in the vagina and rectum, it doesn't cause symptoms in most adults. However, if it colonizes the urinary tract, it can lead to a urinary tract infection (UTI), which is more common in pregnant women.

Risks Associated with GBS

For most healthy adults, carrying GBS poses no significant risk. However, there are risks associated with GBS transmission to newborns. When a baby is exposed to GBS during birth, it can lead to serious infections such as:

It is crucial to note that while these infections can be severe, most babies exposed to GBS do not become ill. The risk of a baby developing early-onset GBS disease (symptoms appearing within the first week of life) is relatively low, but the consequences can be significant. Late-onset GBS disease, which appears after the first week of life, is less common but can also occur.

GBS Screening During Pregnancy

To mitigate the risks of GBS transmission to newborns, screening is a standard part of prenatal care in many countries. Pregnant women are typically screened for GBS between 35 and 37 weeks of gestation. This screening involves taking a swab from the lower vagina and the rectum. The collected sample is then sent to a laboratory to check for the presence of GBS bacteria.

Prevention and Treatment

If a pregnant woman tests positive for GBS, she will be offered intravenous (IV) antibiotics during labor. The antibiotics are administered every four hours while she is in labor and until the baby is born. This treatment significantly reduces the risk of the baby contracting a GBS infection. It's important to note that antibiotics are not given before labor begins, as they would likely be cleared from the system by the time labor starts. The decision to administer antibiotics is based on the GBS screening result, not on whether the mother has symptoms.

Women who have previously had a baby with a GBS infection or who develop a GBS urinary tract infection during pregnancy are also typically given IV antibiotics during labor, regardless of their screening result.

Who is at Risk?

While GBS is common, certain factors can increase the risk of a baby developing a GBS infection:

Understanding GBS and the importance of screening can help expectant parents and healthcare providers work together to ensure the safest possible delivery and a healthy start for the baby.

Sources

  1. Group B Streptococcus - WikipediaCC-BY-SA-4.0
  2. Group B Strep Infection | CDCfair-use
  3. Group B Strep infection - NHSfair-use

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