Group B strep (GBS) is primarily treated with intravenous antibiotics, though the specifics depend on who is being treated and why. For most people searching this question, the answer involves antibiotics given through an IV during labor to prevent the infection from passing to the baby. But GBS can also cause infections in newborns and in adults outside of pregnancy, and each situation calls for a different approach.
Screening During Pregnancy
Before treatment even comes into play, screening determines who needs it. The American College of Obstetricians and Gynecologists recommends that all pregnant women receive a vaginal-rectal swab between 36 and 37 weeks of gestation. About 1 in 4 pregnant women carry GBS in their vaginal or rectal tract without any symptoms. Carrying the bacteria isn’t harmful to you, but it can be dangerous for a baby exposed to it during birth.
If your culture comes back positive, you’ll be flagged for antibiotic treatment during labor. Women who had GBS bacteria in their urine at any point during the pregnancy, or who previously had a baby affected by a GBS infection, automatically qualify for treatment without needing the late-pregnancy swab.
Antibiotics During Labor
The standard treatment for GBS-positive pregnant women is intravenous penicillin G given during labor. You receive an initial dose of 5 million units, followed by 2.5 to 3 million units every 4 hours until the baby is delivered. This is called intrapartum antibiotic prophylaxis, and the goal is to reduce the concentration of GBS bacteria in the birth canal so the baby passes through with minimal exposure.
Timing matters. At least 4 hours of antibiotic coverage before delivery is recommended for the best protection. Research shows that penicillin levels in the baby’s blood don’t accumulate over time. Instead, they peak after each dose and drop back to baseline before the next one. That means sticking to the every-4-hour schedule is more important than simply starting the antibiotics early.
If penicillin isn’t an option, ampicillin is the main alternative, given as a 2-gram initial IV dose followed by 1 gram every 4 hours. Both antibiotics work well against GBS, and ampicillin is equally effective for preventing transmission during delivery.
Options if You’re Allergic to Penicillin
Penicillin allergies complicate GBS treatment because the most effective antibiotics belong to the same drug family. How your allergy is classified determines what you’ll receive instead.
If your allergy was mild, such as a rash without breathing problems or swelling, a related antibiotic called cefazolin is typically used. It’s in the same broad class as penicillin but carries a very low risk of cross-reaction in people with minor allergies.
If you’ve had a severe reaction to penicillin, like anaphylaxis, difficulty breathing, or significant swelling, the options narrow. Clindamycin was once the go-to alternative, but resistance has become a serious problem. More than 40% of invasive GBS infections now involve strains resistant to clindamycin, and over half are resistant to erythromycin. Because of this, clindamycin can only be used if lab testing confirms the specific GBS strain you carry is susceptible to it. When resistance testing isn’t available or shows the bacteria are resistant, vancomycin is used instead.
Treatment for Newborns With GBS Infection
Despite preventive antibiotics during labor, some newborns still develop GBS infections. Early-onset disease appears within the first week of life, usually within 24 to 48 hours, and can cause sepsis, pneumonia, or meningitis. Late-onset disease shows up between one week and three months of age.
When a newborn is suspected of having a bacterial infection, doctors start empiric treatment with ampicillin combined with an aminoglycoside antibiotic before culture results come back. This combination covers GBS along with other common newborn pathogens. If GBS is confirmed, the treatment course depends on how severe the infection is. Bloodstream infections without meningitis are typically treated for 10 to 14 days. GBS meningitis requires 14 to 21 days of treatment, assuming the bacteria clear from the spinal fluid promptly.
GBS Infections in Non-Pregnant Adults
GBS isn’t only a concern during pregnancy. It can cause bloodstream infections, urinary tract infections, pneumonia, skin infections, and bone or joint infections in adults, particularly older adults and people with chronic conditions like diabetes. Penicillin G remains the first-line treatment for invasive GBS disease in adults, just as it is during labor.
Treatment length varies by the type of infection. Bloodstream infections, pneumonia, kidney infections, and skin infections generally require about 10 days of antibiotic therapy. Meningitis calls for a minimum of 14 days. More serious or slow-healing infections like endocarditis (a heart valve infection) or osteomyelitis (a bone infection) need at least 4 weeks of treatment. Heart valve infections also call for a second antibiotic, gentamicin, during the first 2 weeks to improve bacterial clearance.
For adults with severe penicillin allergies, clindamycin, erythromycin, fluoroquinolones, and vancomycin are potential alternatives. However, rising resistance rates across all three non-vancomycin options mean they should only be used after lab testing confirms the bacteria are susceptible. Vancomycin remains reliable when other choices are ruled out.
Why Resistance Testing Matters
One of the biggest shifts in GBS management over the past decade is the growing importance of susceptibility testing. When GBS is isolated from a culture, labs can test whether the specific strain responds to various antibiotics. This step is especially critical for anyone who can’t take penicillin. The CDC reported that 43% of invasive GBS infections in 2016 were caused by clindamycin-resistant strains, and 58% were resistant to erythromycin. These numbers mean that prescribing either drug without lab confirmation is essentially a coin flip.
If you’re pregnant and know you have a penicillin allergy, let your provider know early. Requesting sensitivity testing on your GBS culture at 36 to 37 weeks gives the lab time to determine which antibiotics will actually work, so there’s a clear plan in place before labor begins.