Group B strep (GBS) can cause serious infections in newborns, including bloodstream infections, pneumonia, and meningitis. The good news: routine screening and antibiotics given during labor have reduced early infections by more than 80% since the early 1990s, bringing the current rate down to about 0.2 cases per 1,000 live births. Still, GBS remains one of the leading causes of severe infection in newborns, so understanding how it works and what to watch for matters.
How GBS Passes From Mother to Baby
About 20% to 30% of women in the United States carry GBS bacteria in their gastrointestinal or vaginal tract. Carrying the bacteria is completely normal and doesn’t cause symptoms in healthy adults. The problem arises during labor and delivery, when GBS can travel upward into the uterine cavity and reach the baby. The baby can pick up the bacteria through direct contact during a vaginal birth or by swallowing or breathing in infected amniotic fluid.
Without preventive antibiotics, roughly half of colonized mothers transmit GBS to their baby during delivery. That doesn’t mean half of those babies get sick, but it does mean exposure is common enough that screening became standard practice.
Early-Onset Infection: The First Week
Early-onset GBS disease strikes within the first seven days of life, and most affected newborns show symptoms on the day they’re born. The three main forms it takes are bloodstream infection (sepsis), pneumonia, and meningitis.
Signs to watch for include fever, difficulty breathing, a bluish tint to the skin, difficulty feeding, and unusual limpness or difficulty waking the baby. These symptoms can escalate quickly. A baby with a bloodstream infection may develop a dangerously exaggerated immune response (sepsis), while pneumonia causes rapid or labored breathing. Meningitis, an infection of the membranes surrounding the brain and spinal cord, is the most concerning form because of its potential for lasting damage.
Late-Onset Infection: Week One Through Three Months
Late-onset GBS disease appears between 7 and 90 days after birth. The symptoms overlap with early-onset disease: fever, irritability, poor feeding, lethargy, and breathing problems. The key difference is that late-onset infection is more likely to show up as meningitis.
Late-onset GBS isn’t always passed during delivery. Babies can pick up the bacteria from their mother or other caregivers after birth. Because of this, the antibiotics given during labor don’t prevent late-onset disease the way they prevent early-onset disease.
How GBS Damages a Newborn’s Body
GBS bacteria produce proteins that help them cross barriers most germs can’t. One protein, found on especially aggressive strains, allows the bacteria to break through both the intestinal lining and the protective barrier between the bloodstream and the brain. Once past those defenses, the bacteria can spread to the lungs, blood, and central nervous system.
In the lungs, GBS can trigger inflammation and tissue injury that makes it hard for a newborn to get enough oxygen. In the bloodstream, the bacteria multiply and provoke a body-wide inflammatory response. If they reach the brain, the resulting meningitis can damage developing neural tissue during a critical window of growth.
Long-Term Effects for Survivors
Most babies who are treated promptly for GBS bloodstream infections or pneumonia recover fully. Meningitis, however, carries a much higher risk of lasting consequences. Among infants who survived meningitis in one large study, about 24% developed cerebral palsy, 8% had hearing loss in both ears, and 4% experienced significant vision impairment. Seizure disorders, smaller-than-expected head growth, and cognitive delays are also documented outcomes.
Not every baby with GBS meningitis will have these complications, but the risk is real enough that children who had it are typically monitored closely through early childhood for developmental milestones, hearing, and vision.
What Increases a Baby’s Risk
Three factors raise the chances of a newborn developing GBS disease:
- Positive GBS test late in pregnancy. This confirms the bacteria are present in the birth canal.
- Fever during labor. Maternal fever suggests the body may already be fighting an infection, which can mean the bacteria are more active.
- Prolonged rupture of membranes. When 18 hours or more pass between your water breaking and delivery, bacteria have more time to reach the baby.
How Screening and Prevention Work
Pregnant women are screened for GBS between 35 and 37 weeks of pregnancy with a simple vaginal and rectal swab. This timing is chosen because colonization status in the late third trimester closely predicts whether the bacteria will be present during labor.
If you test positive, you’ll receive intravenous antibiotics during labor. This approach is about 86% effective at preventing early-onset GBS disease overall, and effectiveness climbs to around 91% for full-term babies when antibiotics are given at least four hours before delivery. Even with less than two hours of antibiotics, there’s still a meaningful protective effect, though somewhat lower. The treatment doesn’t require any extra steps from you beyond the IV that’s already standard during hospital births.
What Treatment Looks Like for an Infected Baby
A baby diagnosed with GBS infection receives intravenous antibiotics for the full course of treatment. For a bloodstream infection without other complications, that typically means about 10 days. Meningitis requires at least 14 days, and more complicated infections involving bones, joints, or deeper brain structures can require three to four weeks or longer.
During treatment, the baby stays in the hospital, usually in a neonatal intensive care unit where breathing, heart rate, and temperature can be closely monitored. Recovery depends on which type of infection the baby has and how quickly treatment started. Babies with bloodstream infections generally recover well with prompt treatment. Meningitis requires a longer hospital stay and closer follow-up after discharge.