What is the recommended treatment for Shigella infections?

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 prioritizing fluoroquinolones due to widespread resistance to older agents. 1

Initial Antibiotic Selection

The choice of first-line therapy must be guided by local antimicrobial susceptibility patterns, as multiresistant Shigella strains have become widespread globally. 2, 1

For adults:

• Ciprofloxacin 500mg twice daily for 3-7 days is the preferred agent 1
• Alternative: Azithromycin 500mg on day 1, then 250mg daily for 4 days (particularly useful for resistant strains or when fluoroquinolones are contraindicated) 1
• TMP-SMX 160mg/800mg twice daily for 5 days may be used if the strain is susceptible, but resistance rates are high, especially in internationally-acquired cases 2, 1, 3

For children:

• TMP-SMX 10mg/kg/day TMP and 50mg/kg/day SMX in two divided doses for 5 days (if susceptible) 2, 1, 3
• Fluoroquinolones are highly effective but not FDA-approved for pediatric use 1
• Azithromycin is an alternative for resistant strains 2

For pregnant/lactating women:

• Fluoroquinolones have not been approved for use in this population 1
• Consider azithromycin or ceftriaxone as alternatives 1

Treatment Algorithm and Monitoring

Assess clinical response within 48 hours of initiating therapy. 2, 1 This is critical given the high prevalence of resistance.

• If no clinical improvement occurs within 2 days, switch to an alternative antibiotic recommended for that strain 2, 1
• If no improvement occurs after an additional 2 days on the second antibiotic, refer for stool microscopy to rule out amebiasis 2
• At this stage, resistant shigellosis remains more likely than amebiasis 2

Monitor for:

• Improvement in systemic signs and symptoms 2
• Resolution of diarrhea 2
• Follow-up stool cultures are generally not required if complete clinical response is demonstrated 1

Special Clinical Scenarios

Shigella bacteremia:

• Extend treatment duration to 14 days using the same first-line agents 2, 1
• Consider adding a second active agent (e.g., aminoglycoside) for severe cases 2

HIV-infected patients:

• All HIV-associated Shigella infections should be treated due to higher risk of bacteremia and complications 2, 1
• For patients with CD4+ counts >200 cells/µL: 7-14 days of treatment 2
• For advanced HIV disease (CD4+ <200 cells/µL): 2-6 weeks of treatment 2
• HIV-infected persons have higher rates of adverse effects with TMP-SMX, making fluoroquinolones preferred 2, 1

Alternative Agents for Resistant Strains

When first-line agents fail or resistance is documented:

• Nalidixic acid 55mg/kg/day in four divided doses for 5 days 2
• Tetracycline 50mg/kg/day in four divided doses for 5 days 2
• Ceftriaxone or cefotaxime (expanded spectrum cephalosporins) 2

Critical Pitfalls and Caveats

Do NOT provide mass prophylaxis or prophylaxis to family members - this is explicitly not recommended by WHO as a control measure for shigellosis. 2, 1

Distinguish from amebic dysentery:

• Amebic dysentery is frequently misdiagnosed as shigellosis 2, 1
• If two different antibiotics for shigellosis fail to produce clinical improvement, obtain stool microscopy for Entamoeba histolytica trophozoites 2, 1
• Only treat for amebiasis if trophozoites are definitively identified on microscopy 2

Resistance considerations:

• TMP-SMX resistance is particularly high in internationally-acquired cases 2, 1
• Fluoroquinolone resistance is increasingly reported, especially from Asia 4, 5
• Periodic antibiotic susceptibility testing is advisable in endemic and epidemic settings 2, 1
• Shigella strains can rapidly acquire resistance 2

Treatment is indicated for all cases to shorten illness duration and prevent transmission to others, unlike some other bacterial gastroenteritides. 2