Treatment of Suspected Shigella Infection
For suspected Shigella infection (shigellosis), initiate empiric antibiotic therapy based on local resistance patterns, with azithromycin, ciprofloxacin, or ceftriaxone as first-line agents, while avoiding fluoroquinolones if local ciprofloxacin MIC is ≥0.12 μg/mL. 1
Initial Approach
When a patient presents with bloody diarrhea (dysentery) or clinical suspicion of shigellosis, begin antibiotic treatment empirically without waiting for culture confirmation, as appropriate antimicrobial therapy decreases severity, duration of illness, and pathogen excretion 2.
Critical Caveat About Diagnosis
Do not rely on bloody stools to identify Shigella infection. The majority of Shigella cases present with watery diarrhea without blood 3, 4. Dysentery identifies only 1.9-85.9% of confirmed Shigella infections, with sensitivity decreasing over time 3. Importantly, Shigella infection is associated with mortality (OR 2.8), whereas dysentery presentation is not 3.
First-Line Antibiotic Choices
The most recent IDSA guidelines 1 recommend:
Primary Options:
- Azithromycin (preferred in many settings)
- Ciprofloxacin (if local resistance patterns permit)
- Ceftriaxone
Alternative if susceptible:
- TMP-SMX
- Ampicillin
However, substantial resistance exists to older agents. US surveillance shows approximately 37% of Shigella isolates are resistant to both ampicillin and TMP-SMX 5. Globally, resistance to ciprofloxacin (37.2%), azithromycin (22.1%), and ceftriaxone (16.2%) varies significantly by region 6.
Specific Dosing Regimens
While the 1992 guidelines [@1-10@] provided these historical regimens, these should be adjusted based on current local resistance patterns:
Children:
- Azithromycin: Standard pediatric dosing
- Ceftriaxone: Standard pediatric dosing
- Ampicillin: 100 mg/kg/day in 4 divided doses × 5 days (if susceptible)
- TMP-SMX: 10 mg/kg/day TMP + 50 mg/kg/day SMX in 2 divided doses × 5 days (if susceptible)
Adults:
- Azithromycin: Standard adult dosing
- Ciprofloxacin: Standard adult dosing (avoid if MIC ≥0.12 μg/mL)
- Ampicillin: 500 mg four times daily × 5 days (if susceptible)
- TMP-SMX: 160 mg