Treatment of Uncomplicated Cystitis Positive for Group B Streptococcus
For uncomplicated cystitis caused by Group B Streptococcus (GBS), treat with standard first-line antibiotics for uncomplicated UTI—specifically nitrofurantoin 100 mg twice daily for 5-7 days, fosfomycin 3g single dose, or a beta-lactam agent such as amoxicillin or cephalexin for 3-5 days.
Rationale for Treatment Approach
GBS is an uncommon cause of uncomplicated cystitis, as the typical pathogens are E. coli (75-95%), with occasional other Enterobacteriaceae and Staphylococcus saprophyticus 1. However, when GBS is isolated from urine culture in the setting of symptomatic cystitis, it should be treated as a true pathogen.
Key Treatment Principles
GBS is universally susceptible to penicillins and cephalosporins, making beta-lactam antibiotics highly effective choices despite their generally lower efficacy for typical E. coli cystitis 1, 2.
Nitrofurantoin remains an excellent option as it maintains good in vitro activity against most uropathogens including GBS, with minimal resistance patterns 1, 2.
Fosfomycin 3g single dose is appropriate as it demonstrates broad-spectrum activity and minimal resistance 1, 2.
Specific Antibiotic Recommendations
First-Line Options:
- Nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5-7 days 2
- Fosfomycin trometamol 3g as a single dose 1, 2
- Amoxicillin 500 mg three times daily for 3-5 days (particularly effective for GBS given universal susceptibility to penicillins)
- Cephalexin 500 mg twice daily for 3-5 days (first-generation cephalosporin with excellent GBS coverage)
Alternative Options:
- Trimethoprim-sulfamethoxazole can be used if local E. coli resistance is <20%, though GBS susceptibility should be confirmed 1, 3
- Fluoroquinolones for 3 days are effective but should be reserved for cases where first-line agents are contraindicated given concerns about collateral damage 1
Important Clinical Caveats
Do NOT treat asymptomatic GBS bacteriuria in non-pregnant women—antimicrobial treatment before the intrapartum period is not effective in eliminating carriage and may cause adverse consequences 1.
Pregnancy changes everything: If the patient is pregnant, GBS bacteriuria (even asymptomatic) requires treatment as it indicates heavy colonization and increases risk of neonatal GBS disease 1, 4. Appropriate options include nitrofurantoin (avoid near term), fosfomycin, or beta-lactams 5, 6.
Obtain urine culture to confirm GBS as the causative organism and guide therapy, particularly if symptoms persist or recur within 2-4 weeks 2.
Beta-lactams are more effective for GBS than for typical E. coli cystitis, so they represent a particularly good choice when GBS is confirmed on culture 1.
Treatment Duration
Standard 3-5 day courses are appropriate for uncomplicated cystitis caused by GBS, similar to other uropathogens 3, 7.
Nitrofurantoin requires 5-7 days rather than the shorter 3-day courses used for other agents 2, 7.
Fosfomycin single-dose therapy is convenient and effective 1, 2.
Common Pitfalls to Avoid
Do not confuse GBS cystitis with GBS colonization—only treat symptomatic infections in non-pregnant women 1.
Do not use fluoroquinolones as first-line when GBS is confirmed, as beta-lactams are equally or more effective with narrower spectrum 1.
Avoid trimethoprim-sulfamethoxazole in the first trimester of pregnancy if the patient is pregnant, due to teratogenic concerns 5, 6.
Resistance patterns matter less for GBS than for E. coli—GBS remains universally susceptible to penicillins, making empiric beta-lactam therapy highly reliable once GBS is identified 8.