Group B Streptococcus (GBS) can cause serious, potentially life-threatening infections in newborns, including sepsis (a bloodstream infection), pneumonia, and meningitis. About 25% of pregnant women carry GBS bacteria naturally in their vaginal or rectal area, and without preventive treatment, roughly half of those mothers will pass the bacteria to their baby during delivery. The good news: routine screening and antibiotics during labor have dramatically reduced how often these infections occur.
How GBS Reaches the Baby
GBS bacteria live harmlessly in many adults, but a newborn’s immune system isn’t mature enough to fight them off. During a vaginal delivery, the baby can inhale or swallow fluid containing the bacteria. Once GBS enters the lungs, it can cross into the tiny blood vessels of the lung tissue and spread into the bloodstream. From there, it can travel to virtually any organ, including the brain.
Infection can also begin before delivery. If GBS bacteria travel upward into the amniotic fluid, the baby may aspirate contaminated fluid while still in the womb. After birth, swallowing breast milk or contact with colonized caregivers are additional, less common routes.
Early-Onset Disease: The First Week
Early-onset GBS disease appears within the first six days of life, often within hours of birth. It is the more common and typically more sudden form. The bacteria that the baby picked up during delivery take hold quickly, most often causing:
- Sepsis: a widespread bloodstream infection that can cause organ damage rapidly.
- Pneumonia: infection in the lungs, which is frequently the first site the bacteria colonize.
- Meningitis: infection of the membranes surrounding the brain and spinal cord, which occurs in a smaller subset of cases but carries the highest risk of lasting harm.
Warning signs include fever, poor feeding, lethargy or unusual irritability, difficulty breathing, and bluish or pale skin. Babies with meningitis may also have seizures or a noticeably bulging soft spot on the head. These symptoms can escalate within hours, which is why newborns showing any combination of them are treated as a medical emergency.
Late-Onset Disease: Week One Through Three Months
Late-onset GBS disease develops between 7 and 90 days after birth. In rare cases, infections can appear as late as six months of age (sometimes called ultra-late onset). Unlike early-onset disease, late-onset infections don’t always trace back to the delivery itself. The bacteria may come from the mother after birth, from other caregivers, or from the environment.
Meningitis is more prominent in late-onset disease than in early-onset. The symptoms are similar (fever, fussiness, poor feeding, breathing trouble), but because the baby is older, parents may initially mistake early signs for a common virus. A key difference: a baby who was healthy for weeks and then rapidly develops a high fever with lethargy or unusual stiffness warrants immediate evaluation.
Long-Term Effects of GBS Infection
Most babies who are treated promptly recover fully. But GBS infections, particularly meningitis, can leave lasting damage. The inflammation and pressure that meningitis creates inside the skull can injure developing brain tissue, potentially leading to cerebral palsy, hearing loss, vision problems, or learning difficulties. The risk of these outcomes rises with how severe the infection was and how quickly treatment began.
Sepsis without meningitis carries a lower risk of long-term complications, though very severe cases can damage organs if blood pressure drops dangerously low. Premature babies face higher odds of complications at every stage because their immune systems and organs are even less developed.
GBS infections are also fatal in a small percentage of cases. Premature infants and those with meningitis face the highest mortality risk. Early detection and aggressive treatment in a neonatal intensive care unit significantly improve survival odds.
How Screening and Prevention Work
The standard prevention strategy is straightforward. The CDC and the American College of Obstetricians and Gynecologists recommend that every pregnant person be screened for GBS bacteria during the 36th or 37th week of pregnancy. The test is a simple swab of the vagina and rectum. Screening is recommended even when a cesarean delivery is planned, because labor can begin unexpectedly.
If the test comes back positive, you’ll receive IV antibiotics during labor (called intrapartum antibiotic prophylaxis). When antibiotics run for at least four hours before delivery, the risk of the baby developing an early-onset GBS infection drops by about 75% compared to just two hours of treatment. This approach has been the single biggest reason early-onset GBS rates have fallen sharply since the 1990s.
There is one important limitation: antibiotics given during labor are effective against early-onset disease but do not prevent late-onset disease. Because late-onset infections can come from sources other than the birth canal, no current screening or treatment protocol eliminates that risk entirely.
What to Watch For After Going Home
Even if your labor and delivery went smoothly, it helps to know the signs of GBS infection during the first three months. The symptoms to watch for are the same regardless of whether the infection is early or late onset:
- Fever or unusually low temperature
- Difficulty breathing, including grunting, flaring nostrils, or fast breathing
- Poor feeding or refusal to eat
- Unusual sleepiness or difficulty waking
- Irritability that doesn’t improve with comfort
- Bluish, grayish, or pale skin
Newborns can deteriorate quickly, so any combination of these symptoms in the first few months of life warrants urgent medical attention. GBS infections are treatable with antibiotics, and outcomes are best when treatment starts early.