Many people carry GBS in their bodies but do not become ill. Adults can be colonized in the bowel, genital tract, urinary tract, throat, or respiratory tract. Sepsis, pneumonia, and meningitis are the most common problems. Meningitis is more common with late-onset GBS disease. GBS disease is diagnosed when the bacterium is grown from usual sterile body fluids, such as blood or spinal fluid.
Cultures take a few days to complete.
GBS colonization can be detected during pregnancy or just before delivery by a vaginal and rectal swab for special culture or rapid screening. Rapid screening tests are not as good at detecting the bacteria but can be completed in 30 minutes to a few hours. Physicians who culture for GBS colonization during prenatal visits should do so late in pregnancy because cultures collected before 25 weeks' gestation do not predict whether a mother will be colonized with GBS at delivery. Authorities suggest that cultures be done at 35-37 weeks' gestation, by swabbing both the vagina and rectum. Colonized women should not be given oral antibiotics before labor because antibiotic treatment at this time does not prevent GBS disease in newborns.