From the Guidelines
Group B streptococcus (GBS) primarily colonizes the gastrointestinal and genitourinary tracts of humans, with the main sources including the rectum, vagina, and perianal region. The main sources of GBS include:
- The rectum
- Vagina
- Perianal region where it can exist as part of the normal flora in approximately 10-30% of healthy adults, particularly women 1. GBS can also be found in the throat and urinary tract. This bacterium can be transmitted from mother to baby during childbirth when the infant passes through the birth canal of a colonized mother, which is why pregnant women are routinely screened for GBS between 35-37 weeks of pregnancy 1. GBS can also spread through person-to-person contact, including sexual contact. In rare cases, GBS has been found in food sources, particularly dairy products and fish. The bacterium can cause serious infections in newborns, pregnant women, elderly individuals, and those with compromised immune systems or chronic medical conditions. Understanding these sources is important for preventing transmission, especially in healthcare settings and during pregnancy to reduce the risk of neonatal GBS disease. The gastrointestinal tract serves as the natural reservoir for GBS and is the likely source of vaginal colonization 1. Approximately 10% to 30% of pregnant women are colonized with GBS in the vagina or rectum 1. Maternal intrapartum GBS colonization is a major risk factor for early-onset disease in infants, and vertical transmission of GBS from mother to fetus primarily occurs after the onset of labor or membrane rupture 1. Culture screening of both the vagina and rectum for GBS late in gestation during prenatal care can detect women who are likely to be colonized with GBS at the time of delivery and are thus at higher risk of perinatal transmission of the organism 1.
From the Research
Sources of Group B Streptococcus (GBS)
- Group B Streptococcus (GBS) is a β-hemolytic, Gram-positive bacterium that commonly colonizes the lower gastrointestinal and genital tracts 2
- GBS is a common inhabitant of the maternal genital and gastrointestinal tracts, and colonizes approximately 20% of pregnant women 3
- GBS can be found in the gastrointestinal and urogenital tracts 4
- The bacterium can be transmitted to neonates during pregnancy, particularly during labor and delivery, putting them at risk of infection 2, 5
- About 50% of infants born to colonized women will become colonized with GBS at birth 3