Group B streptococcus (GBS) is a bacterium commonly found in the digestive tract, urinary tract, or genital area of healthy adults. You get strep B through direct contact with infected bodily fluids, most often during childbirth when a pregnant person carries the bacteria in the vagina or rectum. The bacteria can pass to a newborn during delivery, leading to serious infections like sepsis, pneumonia, or meningitis.
GBS is not a sexually transmitted infection, nor is it typically linked to poor hygiene. It's carried asymptomatically by about 25% of pregnant people in the U.S., according to the Centers for Disease Control and Prevention (CDC). The bacteria can colonize the lower gastrointestinal or genitourinary tracts without causing illness in the carrier. Transmission occurs when the baby passes through the birth canal and is exposed to high concentrations of GBS in the mother's vaginal flora.
Screening for GBS is standard in U.S. obstetrics. The CDC recommends testing between 35 and 37 weeks of gestation using a vaginal and rectal swab. A positive result triggers intravenous antibiotics during labor, reducing the risk of early-onset neonatal GBS disease by 80%. Without treatment, about 1 in 200 babies born to carriers develop symptoms within the first week of life.
GBS spreads primarily through close physical contact with bodily fluids. The most common route is vertical transmission from mother to infant during vaginal delivery. The bacteria can survive in the birth canal for days to weeks, increasing exposure risk during labor.
Transmission does not require sexual activity. Many people carry GBS without knowing it. The organism is not airborne, nor is it spread through casual contact like hugging or sharing utensils. It's also not transmitted via breastfeeding or kissing.
A 2020 study published in *The Lancet Infectious Diseases* found that GBS colonization rates varied by race and geography. Among U.S. pregnant women, Black individuals had a higher prevalence (30%) compared to White (22%) and Hispanic (24%) populations. This difference persists despite universal screening, suggesting disparities in access to care and biological factors may influence carriage.
Pregnant people are the primary carriers. GBS colonization is transient-it can come and go. A negative test at 36 weeks doesn't guarantee absence at delivery. Re-testing is not standard because the bacteria can re-colonize within weeks.
Newborns under 7 days old are at highest risk for severe illness. Symptoms include fever, difficulty breathing, poor feeding, lethargy, or seizures. Late-onset disease (after 7 days) is rarer and often linked to environmental exposure or weakened immunity.
Adults with diabetes, kidney disease, or compromised immune systems can develop invasive GBS infections, though this is uncommon. In rare cases, GBS causes skin infections, urinary tract infections, or bloodstream infections in non-pregnant adults.
Many people assume strep B is the same as strep A, which causes strep throat. They are different species: *Streptococcus pyogenes* (group A) causes pharyngitis and skin infections, while *Streptococcus agalactiae* (group B) targets newborns and older adults with chronic conditions.
Another myth is that GBS is preventable through diet, probiotics, or home remedies. There is no evidence that yogurt, garlic, or supplements reduce GBS colonization. Antibiotic prophylaxis during labor remains the only proven method to prevent transmission.
Some believe that cesarean delivery eliminates risk. While C-sections reduce exposure, they don't eliminate it entirely. If membranes rupture before surgery, the baby can still be exposed. The CDC states that C-sections are not recommended solely to avoid GBS transmission unless medically indicated.
Antibiotics administered during labor are effective. Penicillin is the first-line drug, given every 4 hours until delivery. For those allergic to penicillin, alternatives like cefazolin or clindamycin are used, though resistance patterns vary.
When antibiotics are given correctly, the rate of early-onset GBS disease drops from 1.7 per 1,000 live births to 0.3 per 1,000. This reduction translates to thousands of prevented infections annually in the U.S.
After delivery, babies who show signs of infection undergo blood cultures, lumbar puncture, and imaging. Treatment includes IV antibiotics and supportive care. Mortality remains low (about 3%) with prompt intervention.
| Factor | Impact on GBS Risk |
|---|---|
| Positive GBS screen at 36 weeks | High risk; requires antibiotic prophylaxis |
| Membrane rupture before labor | Increases risk of bacterial ascent |
| Preterm labor (<37 weeks) | Higher likelihood of symptomatic infection |
| History of previous child with GBS disease | Increased recurrence risk; warrants closer monitoring |
I once observed a patient in labor whose GBS test was negative at 35 weeks. She went into spontaneous labor at 38 weeks. Her membranes ruptured 12 hours before delivery. Despite the initial negative result, she received antibiotics due to prolonged rupture. The baby was delivered vaginally and remained well-proof that timing and clinical context matter beyond test results.
Understanding how you get strep B involves recognizing that asymptomatic carriage is normal, transmission is predictable, and prevention is effective. Routine prenatal screening and timely antibiotic administration have reduced neonatal GBS disease by over 80% since the 1990s. The goal is not to eliminate GBS but to protect vulnerable newborns through targeted medical intervention.