Treatment of Shigellosis
Ciprofloxacin 500 mg twice daily for 3-7 days is the preferred first-line treatment for shigellosis in adults, based on current CDC recommendations and FDA approval for this indication. 1, 2
Initial Antibiotic Selection
The choice of first-line antibiotic must be guided by local antimicrobial susceptibility patterns, as multiresistant Shigella strains are now widespread globally. 3, 1 When local resistance patterns are unknown or for travel-acquired cases, fluoroquinolones should be prioritized as first-line therapy. 1
First-Line Options for Adults:
- Ciprofloxacin: 500 mg twice daily for 3-7 days (preferred agent) 1, 2
- TMP-SMX: 160 mg TMP/800 mg SMX twice daily for 5 days (only if strain is susceptible) 3, 1
- Azithromycin: 500 mg on day 1, then 250 mg daily for 4 days (for resistant strains) 1, 4
First-Line Options for Children:
- TMP-SMX: 10 mg/kg/day TMP and 50 mg/kg/day SMX in two divided doses for 5 days (if susceptible) 3, 1
- Azithromycin: Same dosing as adults, adjusted by weight 1
Important caveat: Fluoroquinolones are not FDA-approved for children, pregnant women, or lactating women, despite their high efficacy. 3, 1 For these populations, azithromycin or ceftriaxone should be considered as alternatives. 1
Treatment Algorithm and Monitoring
Assess clinical response within 48 hours of initiating therapy. 3, 1 If no clinical improvement occurs (persistent dysentery, fever >37.8°C, or >6 stools/day), change to an alternative antibiotic immediately. 3, 1
If no improvement occurs after an additional 2 days on the second antibiotic, refer the patient for stool microscopy to rule out amebiasis, as amebic dysentery is frequently misdiagnosed as shigellosis. 3, 1, 5 At this stage, resistant shigellosis remains more likely than amebiasis, but microscopic examination for Entamoeba histolytica trophozoites is essential. 3, 5
Alternative Agents for Resistant Strains
When first-line agents fail or resistance is documented:
- Nalidixic acid: 55 mg/kg/day in four divided doses for 5 days 3
- Tetracycline: 50 mg/kg/day in four divided doses for 5 days 3
- Ceftriaxone: Effective for multidrug-resistant strains 6, 7
Special Clinical Situations
Shigella Bacteremia:
Extend treatment duration to 14 days using the same antimicrobial agents. 1
HIV-Infected Patients:
All HIV-associated Shigella infections require treatment due to higher complication risk. 1 Be aware that HIV-infected persons have higher rates of adverse effects from TMP-SMX. 1
Food Service/Healthcare Workers:
Follow-up stool cultures are required before return to work, even with complete clinical response. 1 For other patients, follow-up cultures are not necessary if complete clinical improvement is demonstrated. 1
Critical Pitfalls to Avoid
Do not use mass prophylaxis or prophylaxis of family members—WHO explicitly does not recommend this as a control measure for shigellosis. 3, 1 The single exception is in refugee settings with transmission rates >15% and adequate resources, where single-dose doxycycline for immediate family members may be considered. 1
Do not use antimotility agents—these are contraindicated in shigellosis. 6
Do not delay switching antibiotics—the 48-hour rule for assessing response is critical, as Shigella can rapidly acquire resistance during treatment. 3, 1
Supportive Care
Oral rehydration therapy should be administered concurrently to prevent or correct dehydration. 6 Early refeeding during and after shigellosis is emphasized. 6 Dehydration is typically not severe and responds well to oral rehydration. 8
Resistance Surveillance
Periodic antibiotic susceptibility testing should be performed by reference laboratories, particularly in endemic and epidemic settings, as Shigella strains can rapidly acquire resistance. 3, 1, 7 Fluoroquinolone resistance is emerging globally, and azithromycin plus third-generation cephalosporins remain effective but require ongoing monitoring. 7