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Group B Streptococcus Infection

Overview

Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is a gram‑positive bacterium that commonly lives in the gastrointestinal and genitourinary tracts of healthy adults. While most carriers experience no problems, GBS can cause serious infection when it spreads to the bloodstream, urinary tract, skin, or, most importantly, to newborn infants.

Who it affects

• Pregnant women – about 10‑30 % of pregnant people are colonized in the vagina or rectum.
• Newborns – early‑onset disease (within the first week of life) and late‑onset disease (7 days‑3 months).
• Adults with chronic illnesses – diabetes, liver disease, cancer, HIV, or immunosuppression.

Prevalence

• In the United States, an estimated 1.7 million pregnant people are colonized each year (CDC, 2023).
• GBS causes ~0.23 cases per 1,000 live births of early‑onset disease in countries with routine intrapartum screening and prophylaxis.<sup>[1]</sup>
• In non‑pregnant adults, invasive GBS infection rates have risen from 5.0 to 7.0 per 100,000 persons between 2008‑2017, largely driven by aging populations.<sup>[2]</sup>

Symptoms

Symptoms vary widely depending on the location of infection and the age of the patient.

Newborns and infants

• Early‑onset disease (first 0‑6 days): respiratory distress, poor feeding, lethargy, temperature instability, and sepsis‑like picture.
• Late‑onset disease (7 days‑3 months): fever, irritability, poor feeding, meningitis (bulging fontanelle, seizures), or pneumonia.

Pregnant women

• Often asymptomatic; however, urinary tract infection (UTI) may cause dysuria, frequency, or suprapubic pain.
• Invasive infection can present with fever, chills, abdominal pain, or preterm labor.

Adults (non‑pregnant)

• Skin and soft‑tissue infection: redness, swelling, pain, or abscess formation, commonly on lower extremities.
• Urinary tract infection: burning on urination, urgency, flank pain.
• Bacteremia/septicemia: fever, chills, rapid heartbeat, low blood pressure, confusion.
• Endocarditis (rare): new heart murmur, fatigue, night sweats.

Causes and Risk Factors

GBS is a normal part of the flora in up to one‑third of healthy adults. Infection occurs when the bacteria cross mucosal barriers or enter the bloodstream.

Primary causes

• Vertical transmission during labor – the baby contacts GBS in the birth canal.
• Endogenous infection in adults – colonization progresses to urinary, skin, or bloodstream infection.
• Healthcare‑associated exposure – invasive devices (catheters, central lines) can provide a portal of entry.

Risk factors

• Pregnancy‑related: colonization, prolonged rupture of membranes (>18 h), intrapartum fever, prior infant with GBS disease.
• Medical conditions: diabetes mellitus, obesity (BMI ≥ 30), chronic liver or kidney disease, HIV/AIDS, malignancy.
• Age: adults > 65 years have higher invasive disease rates.
• Lifestyle/behaviors: smoking, excessive alcohol use, recent antibiotic use that disrupts normal flora.
• Procedural: urinary catheters, surgical wounds, chemotherapy-induced neutropenia.

Diagnosis

Accurate diagnosis relies on a combination of clinical suspicion and laboratory testing.

Screening in pregnancy

• Universal culture at 35‑37 weeks gestation: vaginal‑rectal swab placed in selective broth; results reported as positive/negative.
• Rapid PCR tests are available and give results within hours, improving timely prophylaxis.

Diagnostic tests for symptomatic patients

• Blood cultures: gold standard for bacteremia or meningitis.
• Lumbar puncture: cerebrospinal fluid (CSF) analysis for suspected meningitis (elevated white cells, low glucose, high protein).
• Urine culture: for UTI – a colony count ≥10⁵ CFU/mL is considered significant.
• Wound or skin swab: Gram stain and culture to identify GBS in cellulitis or abscess.
• Antibiotic susceptibility: performed on all isolates to guide therapy, especially for penicillin‑allergic patients.

Treatment Options

Therapeutic goals are to eradicate the bacteria, prevent complications, and, in pregnancy, protect the newborn.

Antibiotic therapy

• Penicillin G or ampicillin – first‑line agents for most infections; dosage adjusted for renal function.
• For penicillin‑allergic patients: cefazolin (if not anaphylaxis) or clindamycin (if susceptibility confirmed).
• Severe invasive disease: combination of a β‑lactam with an aminoglycoside (e.g., gentamicin) for synergistic bactericidal effect.
• Typical duration:
  • UTI – 7‑10 days.
  • Skin/soft‑tissue – 5‑7 days after symptom resolution.
  • Bacteremia or meningitis – 14‑21 days, longer if complications.

Intrapartum prophylaxis (pregnant women)

• Administer intravenous penicillin G (5 million units loading dose, then 2.5 million units every 4 h) during labor to colonized mothers or those with unknown status and risk factors.
• Alternative regimens: ampicillin, cefazolin (if penicillin allergy without anaphylaxis).

Supportive care

• Intravenous fluids for sepsis, oxygen supplementation for respiratory distress, antipyretics for fever.
• Neonatal intensive care for premature or symptomatic infants, including mechanical ventilation if needed.

Lifestyle and adjunct measures

• Good hand hygiene, especially after diaper changes or caring for wounds.
• Prompt treatment of urinary symptoms to avoid progression.
• Management of chronic illnesses (e.g., tight glucose control in diabetes).

Living with Group B Streptococcus Infection

Even after successful treatment, ongoing vigilance can help prevent recurrence.

• Follow‑up appointments: repeat cultures may be recommended for invasive disease to confirm clearance.
• Vaccination status: keep up to date with influenza and pneumococcal vaccines, which reduce overall bacterial infection risk.
• Self‑monitoring: track temperature, wound appearance, and urinary symptoms. Record any new fever or pain promptly.
• Nutrition & hydration: a balanced diet rich in protein and vitamins supports immune recovery.
• Physical activity: gentle exercise improves circulation and wound healing, but avoid over‑exertion during acute illness.
• Support networks: connect with prenatal classes, patient advocacy groups (e.g., March of Dimes), or chronic disease support circles.

Prevention

Because GBS is part of normal flora, complete eradication is impossible, but risk can be dramatically reduced.

For pregnant individuals

• Universal screening at 35‑37 weeks gestation (CDC recommendation).
• Timely intrapartum antibiotic prophylaxis for colonized mothers.
• Educate about signs of preterm labor and promptly report fever during labor.

General population

• Maintain good personal hygiene – regular hand washing, especially after using the bathroom.
• Promptly treat urinary tract infections; avoid prolonged catheterization when possible.
• Good wound care: clean cuts, keep dressings dry, seek medical care for deep or infected wounds.
• Control chronic diseases – optimal glycemic control in diabetes reduces colonization density.
• Vaccination against influenza and COVID‑19 may reduce secondary bacterial infections.

Complications

If left untreated, GBS can lead to serious, sometimes life‑threatening sequelae.

• Neonatal meningitis – can cause permanent neurologic deficits, hearing loss, or hydrocephalus.
• Septic shock – multi‑organ failure requiring intensive care.
• Osteomyelitis – infection of bone, often in adults with diabetes.
• Endocarditis – rare but associated with high mortality.
• Preterm birth & stillbirth – maternal GBS infection can trigger early labor.
• Recurrent infection – especially in immunocompromised hosts; may require long‑term suppressive antibiotics.

When to Seek Emergency Care

References

1. Centers for Disease Control and Prevention. Group B Streptococcus (GBS) – Fact Sheet. 2023. https://www.cdc.gov/groupbstrep
2. Silvestri, L., & Hillier, S. L. (2022). “Increasing Incidence of Invasive Group B Streptococcal Disease in Adults.” *Clinical Infectious Diseases*, 74(5): 845‑852.
3. Mayo Clinic. Group B strep infection. Updated 2024. https://www.mayoclinic.org/diseases-conditions/group-b-strep
4. World Health Organization. Prevention of Perinatal Group B Streptococcal Disease. 2023.
5. Cleveland Clinic. Group B Strep (GBS) in Pregnancy. 2024.

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