Treatment of Shigella Infections
Ciprofloxacin 500mg twice daily for 3-7 days is the preferred first-line treatment for Shigella infections in adults, based on CDC recommendations. 1
First-Line Treatment Approach
For Adults
- Ciprofloxacin is the drug of choice at 500mg twice daily for 3-7 days 1
- TMP-SMX (160mg TMP/800mg SMX twice daily for 5 days) remains an alternative option only if local susceptibility is confirmed 1, 2
- Azithromycin (500mg day 1, then 250mg daily for 4 days) should be reserved for resistant strains 1
For Children
- TMP-SMX at 10mg/kg/day TMP and 50mg/kg/day SMX in two divided doses for 5 days if the strain is susceptible 1, 2
- Alternative agents include cefixime, ceftriaxone, or azithromycin when resistance is documented 3
- Fluoroquinolones are not FDA-approved for children, though they are highly effective 4
Treatment Algorithm
Initial Antibiotic Selection
- Base your choice on local susceptibility patterns whenever possible 1
- For travel-acquired cases, assume high TMP-SMX resistance and start with fluoroquinolones 1
- When resistance patterns are unknown, fluoroquinolones are preferred as empiric therapy 1
Monitoring Response
- Assess clinical response within 48 hours of starting treatment 1
- If no improvement occurs within 2 days, switch to an alternative antibiotic 4, 1
- If no improvement after an additional 2 days on the second antibiotic, obtain stool microscopy to rule out amebiasis 4
Treatment Duration
- Standard treatment is 5 days for most regimens 4, 2
- Ciprofloxacin can be given for 3-7 days 1
- For Shigella bacteremia, extend treatment to 14 days using the same agents 1
Critical Resistance Considerations
The global resistance landscape has dramatically shifted, making older guidelines obsolete:
- Multiresistant Shigella strains are now widespread globally 1
- Approximately 37% of U.S. isolates show resistance to both ampicillin and TMP-SMX 3
- Fluoroquinolone resistance is alarmingly high at 61.9% in some regions like Bangladesh 5
- Azithromycin resistance has emerged, particularly among men who have sex with men in the U.S. 6
- Periodic antibiotic susceptibility testing is essential in endemic and epidemic settings 1
Special Populations
HIV-Infected Patients
- All HIV-associated Shigella infections require treatment due to higher complication risk 1
- HIV-infected persons have higher rates of adverse effects with TMP-SMX 1
- Consider fluoroquinolones or azithromycin as preferred agents in this population 1
Pregnant and Lactating Women
- Fluoroquinolones have not been approved for use in pregnancy or lactation 4
- Consider azithromycin or ceftriaxone as safer alternatives 3
Common Pitfalls and How to Avoid Them
Misdiagnosis of Amebic Dysentery
- Amebic dysentery is frequently misdiagnosed as shigellosis 4, 1
- If two different antibiotics for shigellosis fail, consider amebiasis and obtain stool microscopy for trophozoites 4, 7
- Treatment for amebiasis should not be initiated unless trophozoites are definitively identified 7
Inappropriate Prophylaxis
- WHO explicitly does not recommend mass prophylaxis or family member prophylaxis for shigellosis control 4, 1
- Single-dose doxycycline for family members may be considered only in refugee settings with transmission rates >15% and adequate resources 4
Follow-Up Requirements
- Follow-up cultures are generally not required if complete clinical response occurs 1
- Exception: Food service workers and healthcare workers require negative cultures before returning to work 1
- Monitor for improvement in systemic symptoms and resolution of diarrhea 1
Outdated First-Line Agents
- Ampicillin and TMP-SMX should no longer be considered first-line empiric therapy given widespread resistance 3, 5
- The 1992 guideline recommendations for ampicillin as first-line treatment are obsolete 4
- Nalidixic acid and tetracycline, listed as alternatives in older guidelines, have been superseded by fluoroquinolones 4