Group B Streptococcus (GBS): Symptoms, Treatment, and Pregnancy in Singapore
Group B Streptococcus (GBS, Streptococcus agalactiae) is a beta-haemolytic bacterium that lives harmlessly in the vagina, rectum, or urinary tract of about 10 to 30% of healthy adults. Most carriers have no symptoms. GBS becomes clinically important during pregnancy (where it can cause neonatal sepsis), in urinary tract infections, and as invasive disease in elderly or immunocompromised adults.
Medically reviewed by Dr. Qiao Yufei, MD
This guide covers what GBS is, why it matters in pregnancy, antenatal screening at 35–37 weeks, intrapartum antibiotic prophylaxis, and how testing works at Mediway Medical Centre. GBS sits in our broader STDs in Singapore overview because of its genitourinary location, although it is not strictly a sexually transmitted infection.
What is Group B Streptococcus?
Group B Streptococcus (GBS), also called Streptococcus agalactiae, is a Gram-positive, beta-haemolytic bacterium classified into the Lancefield Group B by its cell-wall carbohydrate. The "beta-haemolytic" label refers to the lab pattern of complete red-cell destruction on a blood agar plate, which helps distinguish GBS from other streptococcal species.
GBS is part of the normal genital and gut flora in 10 to 30% of healthy adults. Most colonised people have no symptoms and never need treatment. Per the US Centers for Disease Control and Prevention (CDC), GBS becomes a clinical concern in three specific settings:
"Streptococcus" is a large genus with many species. Common ones include Group A Streptococcus (S. pyogenes: strep throat, scarlet fever), Streptococcus pneumoniae (pneumonia, meningitis), and Group B Streptococcus (S. agalactiae: the genitourinary species this page covers). They are all beta-haemolytic in lab terms but cause different infections at different anatomical sites.
Three settings where GBS matters
Most people with GBS colonisation never need treatment. The bacterium becomes clinically important in three specific contexts:
Pregnancy
The most important setting. Maternal GBS colonisation can pass to the baby during childbirth, causing neonatal sepsis, pneumonia, or meningitis. Antenatal screening at 35–37 weeks plus intrapartum antibiotics reduce this risk by around 80%.
Urinary tract infection
GBS in urine (GBS bacteriuria) causes UTI symptoms (burning urination, frequency, urgency). In pregnancy, GBS bacteriuria signals heavy colonisation and warrants antibiotic treatment plus intrapartum prophylaxis.
Invasive disease in adults
Older adults, people with diabetes, and immunocompromised patients can develop serious GBS infections: skin and soft tissue infections, pneumonia, bone and joint infections, sepsis, or meningitis. Treatment is typically penicillin or amoxicillin.
How GBS colonisation occurs and spreads
GBS is part of the normal flora in many healthy people. It is not classified as a sexually transmitted infection in the strict sense, but its presence in the genital tract means partner-to-partner sharing can occur. Key transmission and risk routes:
- Mother-to-baby transmission during childbirth (the most clinically significant route). Without intervention, around 1 to 2% of babies born to GBS-positive mothers develop early-onset GBS disease.
- Sexual contact: GBS can be transmitted between partners through unprotected sex, although this is not how most people initially acquire it
- Healthcare or environmental exposure: rare in healthy adults, but a concern for hospitalised or immunocompromised patients
Who is at higher risk?
- Pregnant women: routine antenatal screening and intrapartum prophylaxis are now standard of care
- Newborns, particularly preterm babies, babies of GBS-positive mothers, and babies born after prolonged rupture of membranes
- Older adults (over 65) and people with chronic illness
- People with diabetes, kidney disease, or weakened immunity (HIV, cancer, organ transplant)
- People with structural genitourinary abnormalities or indwelling catheters
Signs and symptoms of GBS infection
The symptoms depend on the type of infection. Most people with GBS colonisation have no symptoms at all.
In adults: GBS UTI
- Burning or pain on urination
- Frequent urgency to urinate
- Lower abdominal or pelvic discomfort
- Cloudy or foul-smelling urine
- In pregnancy: often asymptomatic but detected on routine urine culture
In newborns: GBS disease
- Early onset (first week): respiratory distress, poor feeding, lethargy, fever, sepsis
- Late onset (1 week to 3 months): meningitis, fever, irritability, seizures
- Both forms are medical emergencies and require urgent hospital care
GBS can cause skin and soft tissue infections (cellulitis), bone and joint infections, pneumonia, endocarditis, and bloodstream infection (sepsis), particularly in older or immunocompromised adults. These present with the symptoms typical of those infections, plus systemic signs (fever, malaise).
How GBS is diagnosed
GBS testing is selected based on the clinical setting:
- Antenatal GBS screening (gold standard in pregnancy): a vaginal-rectal swab taken at 35 to 37 weeks of pregnancy and cultured in the lab. Can also use NAAT for faster results in some settings.
- Urine culture: detects GBS bacteriuria. In pregnancy, GBS in urine at any time is a sign of heavy colonisation and warrants both treatment and intrapartum prophylaxis.
- Wound or tissue culture: for skin or soft tissue infections.
- Blood culture: for suspected sepsis or invasive disease.
- Cerebrospinal fluid (CSF) culture: for suspected meningitis (typically in newborns).
At Mediway Medical Centre, antenatal GBS screening swabs and urine cultures are routinely available. Hospital-based testing is required for blood and CSF cultures.
GBS treatment
GBS remains susceptible to penicillin, which is the first-line antibiotic in almost all settings. Treatment depends on the type of infection and the clinical context:
Asymptomatic colonisation
Generally not treated in non-pregnant adults. Asymptomatic GBS in the vagina or rectum is part of the normal flora and antibiotics are not usually indicated.
GBS bacteriuria (UTI)
- Oral antibiotics: penicillin V, amoxicillin, or cephalexin for 5 to 7 days
- In pregnancy: treat the UTI plus give intrapartum prophylaxis during labour
Intrapartum antibiotic prophylaxis (IAP) for GBS-positive pregnant women
- IV penicillin G (5 million units initially, then 2.5–3 million units every 4 hours during labour) as first-line
- Cefazolin if mild penicillin allergy
- Clindamycin or vancomycin if severe penicillin allergy (selection guided by GBS susceptibility testing)
- IAP starts at least 4 hours before delivery if possible, to maximise effectiveness
Invasive disease in adults
Treated with IV penicillin or ampicillin, often combined with an aminoglycoside (gentamicin) for severe infections. Course length varies by site (10 to 14 days for sepsis, 4 to 6 weeks for endocarditis or bone/joint infection). These cases are managed in hospital.
Prevention of neonatal GBS disease
GBS colonisation in adults cannot really be prevented (it is normal flora), but neonatal GBS disease is highly preventable through routine antenatal care.
Universal antenatal GBS screening
All pregnant women are offered a vaginal-rectal swab at 35–37 weeks of pregnancy. GBS-positive women receive intrapartum antibiotic prophylaxis during labour.
GBS detected in urine during pregnancy
GBS in urine at any time during pregnancy indicates heavy colonisation and is treated as a positive screen: the woman receives treatment for the UTI plus intrapartum antibiotic prophylaxis without further screening.
Other preventive considerations
- Pregnancy after a previous baby with invasive GBS disease: automatic IAP for subsequent pregnancies
- Preterm labour or premature rupture of membranes: empirical IAP if GBS status is unknown
- Women with prolonged rupture of membranes (over 18 hours) or fever during labour: IAP recommended
Is there a GBS vaccine?
No GBS vaccine is currently licensed, but several maternal-vaccination candidates are in late-stage clinical trials and may become available within the next few years. A vaccine would simplify prevention by giving immunity rather than relying on intrapartum antibiotics.
What happens if GBS is left untreated in key settings?
Most asymptomatic GBS colonisation is harmless and does not need treatment. Untreated GBS in clinically important settings can cause serious harm:
- Neonatal early-onset disease (within first week of life): sepsis, pneumonia, meningitis. Mortality is around 4 to 6% with treatment, much higher without intrapartum prophylaxis.
- Neonatal late-onset disease (1 week to 3 months): meningitis is the most common presentation; survivors may have long-term neurological complications.
- Postpartum endometritis (uterine infection after birth) in mothers
- Untreated GBS bacteriuria in pregnancy: increased risk of preterm labour, premature rupture of membranes, and chorioamnionitis
- Invasive disease in elderly or immunocompromised adults: cellulitis, pneumonia, sepsis, endocarditis; can be life-threatening if not promptly treated
The combination of routine antenatal screening and intrapartum prophylaxis has dramatically reduced neonatal GBS disease in countries where it is universal. Singapore follows similar protocols in obstetric care.
Frequently asked questions
01 What is Group B Streptococcus (GBS)?
Group B Streptococcus (GBS, Streptococcus agalactiae) is a bacterium that lives harmlessly in the vagina, rectum, or urinary tract of about 10 to 30% of healthy adults. Most carriers have no symptoms. GBS becomes clinically important in three settings: pregnancy (where it can cause serious infection in newborns), urinary tract infections, and invasive disease in elderly or immunocompromised adults. It is different from Group A Streptococcus, which causes strep throat.
02 Is Group B Strep a sexually transmitted infection?
No. GBS is not classified as a sexually transmitted infection. It is part of the normal genital and gut flora in many healthy people and can pass intermittently between partners through close contact, but it is not considered an STI. It is grouped with our STI information because it shares the genitourinary anatomical site and because of its critical importance in pregnancy and newborn infection.
03 What are the symptoms of GBS infection?
Most healthy adults who carry GBS have no symptoms. When GBS does cause infection, symptoms depend on the site: a urinary tract infection may cause burning when urinating, frequent urination, or pelvic pain; skin or wound infection may cause redness, warmth, and pus; and invasive infection (more common in older adults or those with weakened immunity) may cause fever, chills, and a feeling of being unwell. In newborns, signs of GBS sepsis include poor feeding, lethargy, fever, breathing difficulty, or jaundice.
04 How is GBS diagnosed during pregnancy?
Antenatal GBS screening is performed around 36 to 37 weeks of pregnancy, or according to your obstetrician's protocol, by taking a vaginal-rectal swab and culturing it for GBS. A positive swab identifies women who should receive intrapartum antibiotic prophylaxis (IAP) during labour to reduce the risk of GBS infection in the newborn. GBS detected in the urine at any time during pregnancy also indicates the need for antibiotic prophylaxis in labour, without needing further screening.
05 Can GBS be passed to my baby, and what are the risks?
Yes. A GBS-positive mother can pass the bacteria to her baby during labour or delivery. Most exposed babies are not affected, but a small number develop early-onset GBS disease in the first week of life (sepsis, pneumonia, or meningitis). Late-onset disease can occur from 1 week to 3 months of age. Antibiotics during labour reduce early-onset GBS risk but do not prevent all late-onset GBS infections, and most affected babies recover with prompt antibiotic treatment.
06 What is intrapartum antibiotic prophylaxis (IAP)?
IAP means giving intravenous antibiotics during labour to reduce the risk of early-onset GBS infection in the newborn. Penicillin is commonly used, while alternatives may be chosen by the obstetric team if there is a penicillin allergy. Your obstetrician will decide the appropriate antibiotic. IAP greatly reduces the risk of early-onset GBS disease, but does not prevent all late-onset GBS infections.
07 Can GBS in urine be treated?
Yes. GBS in urine (GBS bacteriuria) may be treated with antibiotics chosen by the doctor based on pregnancy status, symptoms, urine culture results, and allergy history. Treatment is particularly important in pregnancy because GBS bacteriuria signals heavy colonisation and may increase the risk of preterm labour and newborn infection. Pregnant women with GBS bacteriuria also receive intrapartum antibiotic prophylaxis during labour. See our urine culture test page for more on bacterial urine testing.
08 Can GBS cause infection in non-pregnant adults?
Yes, though much less commonly. GBS can cause urinary tract infections, skin and soft tissue infections, bone and joint infections, and invasive disease (pneumonia, sepsis, or meningitis), particularly in older adults, people with diabetes, and those with weakened immunity. Treatment depends on the infection site, severity, culture results, and the patient's health background, and your doctor will choose the appropriate antibiotic and duration.
09 If I had GBS in a previous pregnancy, will I have it again?
Possibly, but not always. GBS colonisation can come and go, so a previous positive result does not guarantee a future one. However, women who have previously had a baby with GBS disease, or who had GBS bacteriuria in the current pregnancy, are usually offered intrapartum antibiotic prophylaxis automatically without further screening. For other pregnancies, routine screening at around 36 to 37 weeks is repeated to assess current carrier status.
10 Where can I get GBS testing or treatment in Singapore?
Mediway Medical Centre can assess urinary symptoms, arrange urine testing including urine culture where appropriate, and treat selected GBS-related urinary or skin infections in non-pregnant adults at our Clarke Quay clinic. Antenatal GBS screening and labour antibiotics are usually managed by your obstetrician. Book a consultation through our online booking, WhatsApp, or call 6909 0190.
Related conditions and next steps
References: CDC: Group B Strep · CDC: GBS clinical overview · WHO · HealthHub Singapore
This page is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Consult a qualified healthcare professional for diagnosis and treatment of suspected Group B Streptococcus infection, particularly during pregnancy.