According to Mayo Clinic, strep B, also referred to as group B streptococcus, is a bacterium that is commonly found the intestines and lower genital tracts. Strep B is typically not harmful to adults but can cause illness in infants and individuals with diabetes, liver disease or other chronic conditions.
WebMD explains that approximately one in four individuals carries the strep B bacteria. Pregnant women must be tested for strep B due to the fact that the bacteria can be passed from mother to child. During the test, a physician removes cells from the vagina and rectum with a cotton swab. If the cells test positive for the bacteria, pregnant women are provided with antibiotics during labor.