Group B Streptococcus (GBS), or Streptococcus agalactiae, is a common bacterium that can lead to serious infections, particularly in newborns. While many people carry the bacteria harmlessly, infection can cause life-threatening complications like sepsis and meningitis. The standard treatment protocol varies depending on the patient's age and health status, but it is primarily anchored by beta-lactam antibiotics.
First-Line Antibiotics: Penicillin and Ampicillin
For most GBS infections, penicillin G is the preferred treatment due to its proven efficacy, safety profile, and narrow spectrum of activity, which helps prevent the development of broad-spectrum antibiotic resistance. Ampicillin is also a highly effective and acceptable alternative to penicillin.
Intrapartum Prophylaxis for Pregnant Women
The most common use of GBS antibiotics is to prevent early-onset disease in newborns. When a pregnant woman tests positive for GBS colonization, or has risk factors during labor, she receives intravenous (IV) antibiotics.
- Method of Administration: The medication must be administered intravenously during labor to be effective. Oral or intramuscular antibiotics are insufficient for prophylaxis.
- Timing: For maximum effectiveness, antibiotics should be given at least four hours before delivery to ensure adequate drug concentration in the amniotic fluid and fetal blood.
Treatment for Neonatal Infection
When a newborn is suspected of having a GBS infection, empiric therapy begins immediately.
- Initial treatment typically involves a combination of ampicillin and an aminoglycoside (like gentamicin).
- Once the GBS infection is confirmed, treatment can be narrowed to high-dose intravenous penicillin or ampicillin.
Alternative Antibiotics for Penicillin-Allergic Patients
For individuals with a documented penicillin allergy, the choice of antibiotic depends on the severity of the allergic reaction and the GBS isolate's susceptibility to other drugs. It is crucial for healthcare providers to accurately assess the type of allergic reaction to guide treatment.
Determining the Right Alternative
- Assess the allergy: The first step is to determine if the penicillin allergy is low-risk (e.g., a mild rash) or high-risk (e.g., anaphylaxis, hives).
- Perform susceptibility testing: For high-risk allergies, laboratories must test the GBS isolate to determine if it is susceptible to clindamycin. This is critical because resistance to clindamycin is common.
Antibiotic Options for Penicillin Allergies
- Low-risk allergy: A first-generation cephalosporin, such as cefazolin, is recommended.
- High-risk allergy (clindamycin-susceptible isolate): Clindamycin is the drug of choice.
- High-risk allergy (clindamycin-resistant isolate): Vancomycin is the appropriate alternative.
Comparison of GBS Antibiotics
| Antibiotic | Standard Use | Penicillin Allergy | Notes |
|---|---|---|---|
| Penicillin G | First-line treatment for all GBS infections and prophylaxis. | Only if no allergy. | Highly effective, narrow spectrum. |
| Ampicillin | Acceptable alternative to penicillin for treatment and prophylaxis. | Only if no allergy. | Broad spectrum; acceptable alternative. |
| Cefazolin | N/A | Low-risk allergy. | First-generation cephalosporin with low cross-reactivity. |
| Clindamycin | N/A | High-risk allergy, if susceptible. | Resistance is common; susceptibility testing is required. |
| Vancomycin | N/A | High-risk allergy, if clindamycin-resistant. | Effective, but overuse can lead to resistance; dosing is weight-based. |
The Role of Susceptibility Testing
The high and increasing rates of resistance to macrolide antibiotics like erythromycin and clindamycin make susceptibility testing a vital step, especially for patients with severe penicillin allergies. This helps ensure the chosen alternative is effective and guides proper antibiotic stewardship.
Conclusion
Penicillin and ampicillin are the most common antibiotics used for GBS infection, particularly for preventing transmission during childbirth. For patients with penicillin allergies, alternative antibiotics are selected based on the allergy's severity and the GBS isolate's susceptibility to other drugs, with cefazolin for low-risk allergies and clindamycin or vancomycin for high-risk cases. Timely and appropriate antibiotic selection is a cornerstone of preventing serious GBS disease in newborns. For detailed, up-to-date guidance, healthcare professionals often refer to protocols published by the American College of Obstetricians and Gynecologists (ACOG).
Treatment of Other GBS Infections
Beyond neonatal concerns, GBS can cause other serious infections in adults, such as pneumonia, endocarditis, and bone infections. Treatment for these established infections follows specific guidelines:
- Infected newborns are treated with a combination of ampicillin and an aminoglycoside.
- Treatment for severe adult infections may involve a combination of antibiotics, and sometimes requires surgical intervention, especially for bone and soft tissue infections.
- Duration of treatment varies depending on the site and severity of the infection, with meningitis, for example, requiring a longer course of therapy.
