What Causes Vaginal Strep B Infection?

Step B is infection with bacteria called group B streptococcus. Many healthy adults carry these bacteria in their bodies, generally in the vagina, bowel, rectum, bladder or throat. For most adults, carrying the bacteria does not result in any health problems -- they do not have any signs or symptoms.

The causes and risk factors for infection with strep B in adults are poorly understood. About 25% of pregnant women carry group B strep in the vagina or rectum. You may carry group B strep in your body for just a short period of time, it may come and go, or you may always have it.

While one or two studies have suggested that the bacteria could be transmitted during sex or through other intimate contact, strep B is generally not considered to be a sexually transmitted infection.

While strep B does not usually cause adults any problems, screening is very important for pregnant women. The bacteria can be spread to a baby during vaginal delivery. In infants, strep B can cause sepsis (infection of the blood), pneumonia (infection in the lungs), and meningitis (infection of the fluid and lining around the brain). But if the mother takes antibiotics during labor, these outcomes can be avoided.

Sometimes strep B can cause mild disease in adults, such as urinary tract infections (UTIs, also called bladder infections). Older people and individuals with a pre-existing health condition (such as diabetes mellitus, heart disease, cancer or obesity) may have more serious disease.

Strep B infections are usually treated with penicillin or other common antibiotics.

More on Strep at TheBody.com

To find out more about strep B infections, we recommend the following article:

In addition, our Q&A experts sometimes address questions about strep B in our "Ask the Experts" forums. Here are some of those questions and our experts' responses:

  • Vaginal strep B infection
    A few months ago I thought I was suffering from a vaginal yeast infection, although it hurt and it wasn't itchy. Well I treated it over and over again with anti fungals the doc gave me but he didn't culture it. Finally he did a culture and said I had a vaginal strep b infection.
  • UTI caused by unprotected sex?
    Was the urinary tract infection caused by me having unprotected sex? Should I have it checked out to see if I have an STD as well?

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