What is the recommended antibiotic treatment for a patient with a urinary tract infection (UTI) caused by Group B strep (Streptococcus agalactiae), considering potential penicillin allergy and possible pregnancy?

Antibiotic Treatment for Group B Streptococcus UTI

Primary Recommendation

For Group B Streptococcus (GBS) urinary tract infections, penicillin or ampicillin is the first-line treatment in non-allergic patients, as all GBS isolates worldwide remain 100% susceptible to penicillin. 1, 2

Treatment Algorithm Based on Penicillin Allergy Status

Non-Penicillin Allergic Patients

• Penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours is the preferred regimen 3
• Ampicillin 2g IV initially, then 1g IV every 4 hours is an acceptable alternative 3
• Penicillin is preferred over ampicillin due to its narrower spectrum of activity 3
• All GBS strains demonstrate complete susceptibility to penicillin, ampicillin, and vancomycin 2

Patients with Non-Severe Penicillin Allergy

Cefazolin 2g IV initially, then 1g IV every 8 hours is recommended for patients without history of anaphylaxis, angioedema, respiratory distress, or urticaria 3, 1

• Cross-reactivity between penicillins and cephalosporins occurs in approximately 10% of patients 1
• Most patients reporting penicillin allergy are not truly allergic and can safely receive cephalosporins with careful history-taking 1

Patients with Severe Penicillin Allergy (High Risk for Anaphylaxis)

Severe allergy is defined as history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration. 3, 1

When Susceptibility Testing is Available:

• Clindamycin 900 mg IV every 8 hours if the isolate is susceptible to both clindamycin and erythromycin 3, 1
• Clindamycin may be used if susceptible to clindamycin but resistant to erythromycin, provided D-zone testing for inducible clindamycin resistance is negative 3, 1
• Vancomycin 1g IV every 12 hours if the isolate is resistant to clindamycin or erythromycin, demonstrates inducible clindamycin resistance, or if susceptibility is unknown 3, 1

When Susceptibility Testing is Not Available:

• Vancomycin 1g IV every 12 hours is the recommended first-line treatment when susceptibility results are pending or unavailable 1

Critical Laboratory Considerations

Mandatory Susceptibility Testing

• Always obtain clindamycin and erythromycin susceptibility testing for penicillin-allergic patients at high risk for anaphylaxis 3, 1
• Clinicians must explicitly inform laboratories of the need for susceptibility testing in these cases 3

D-Zone Testing Requirements

• Perform D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance 3, 1
• This is critical because resistance to erythromycin is frequently but not always associated with clindamycin resistance 1

Resistance Patterns and Clinical Pitfalls

Current Resistance Data

• Clindamycin resistance ranges from 3-15% among invasive GBS isolates, with recent data showing resistance as high as 77% in some populations 1, 2
• Tetracycline resistance is extremely high at 88% and should not be used 2
• Erythromycin is no longer recommended due to increasing resistance rates (12% in recent studies) 1, 4
• No confirmed resistance to penicillin or ampicillin has been observed worldwide 1, 2

Common Pitfalls to Avoid

• Do not use cefazolin in patients with severe penicillin allergy due to cross-reactivity risk 1
• Do not use erythromycin for GBS infections as it is no longer recommended 1
• Avoid empiric clindamycin without susceptibility testing in severely allergic patients, given resistance rates of 3-15% 1

Special Considerations for Pregnancy

In pregnant women with GBS bacteriuria (≥10⁴ CFU/ml), treatment is mandatory regardless of symptoms, as this indicates heavy colonization and requires intrapartum prophylaxis 3

• The same antibiotic algorithm applies based on allergy status 3
• Laboratories should report GBS in urine when present at concentrations ≥10⁴ CFU/ml 3
• Antimicrobial treatment before the intrapartum period for colonization alone (without UTI) is not effective and should be avoided 3

When to Consult Infectious Disease

Consider infectious disease consultation for:

• Complicated cases with limited treatment options due to severe allergies and resistant organisms 1
• Patients with recurrent GBS UTI requiring identification of extraurinary reservoirs (vagina, gastrointestinal tract) 5
• Cases requiring prolonged therapy where resistance development is a concern 6