What is the recommended treatment for gastroenteritis caused by Plesiomonas shigelloides?

Treatment of Plesiomonas shigelloides Gastroenteritis

For most cases of Plesiomonas shigelloides gastroenteritis, antimicrobial therapy is recommended, with fluoroquinolones (ciprofloxacin or levofloxacin) or azithromycin as first-line agents, though treatment decisions should be guided by severity and patient risk factors.

Treatment Algorithm

Mild, Self-Limited Disease

• Consider observation without antibiotics in immunocompetent patients with mild symptoms
• The organism can cause self-limiting diarrhea that may not require treatment 1, 2
• However, this approach carries risk as some patients develop prolonged symptoms

Moderate to Severe Disease or High-Risk Patients

Antimicrobial therapy is indicated and significantly reduces illness duration 3. The evidence shows antibiotics can shorten symptom duration in P. shigelloides infections, particularly in patients with:

• Colitis symptoms (present in 78% of cases) 3
• Prolonged diarrhea
• Recent tropical travel (71% of cases) 3
• Immunocompromised status or asplenia (risk of fatal sepsis) 4

Recommended Antibiotic Regimens

First-Line Options:

• Fluoroquinolones:

  • Ciprofloxacin 500-750 mg PO (single dose or 3-day course) 5
  • Levofloxacin 500 mg PO (single dose or 3-day course) 5
  • Norfloxacin (demonstrated efficacy in Thai children) 6

• Azithromycin: 500-1000 mg PO (single dose or 3-day course) 5

Alternative Options Based on Susceptibility:

• Trimethoprim-sulfamethoxazole 1, 7
• Third-generation cephalosporins (ceftriaxone, ceftazidime, cefuroxime) 6, 1
• Tetracycline (for small bowel overgrowth) 8
• Gentamicin or amikacin 6, 9

Critical Susceptibility Considerations

Avoid ampicillin - only 9% susceptibility in published studies 6, 1. The organism shows consistent resistance to:

• Ampicillin/penicillins
• Carbenicillin
• First-generation cephalosporins (variable)

Emerging resistance patterns 9:

• Increasing resistance to cefoxitin (37.91%), cefuroxime (35.17%), and cefepime (31.87%)
• Lower resistance to carbapenems (imipenem 0.55%, meropenem 1.10%)
• Ciprofloxacin resistance reaching 18.13% in some regions

Important Caveats

Conflicting Evidence on Treatment Benefit

One Thai pediatric study found no significant difference in symptom duration between treated and untreated children 6, contradicting earlier findings 3. However, the 1989 study 3 showed clear benefit with antimicrobial therapy reducing illness duration. Given the potential for severe complications including fatal sepsis 4, err on the side of treatment for moderate-severe disease.

Geographic Considerations

• Southeast Asia and India: Consider azithromycin first-line due to fluoroquinolone-resistant patterns 5
• Tropical travel history: 71% of cases have this association 3
• Local acquisition: Associated with seafood or untreated water consumption 3

High-Risk Populations Requiring Aggressive Treatment

• Asplenic patients (risk of overwhelming sepsis and death) 4
• Immunocompromised hosts
• Patients with hemochromatosis or iron overload 4
• Those with small bowel diverticula or achlorhydria (risk of bacterial overgrowth) 8

Practical Approach

1. Assess severity: Look for colitis features (abdominal pain, bloody diarrhea, fever)
2. Identify risk factors: Immunosuppression, asplenia, recent travel
3. Initiate empiric therapy for moderate-severe cases while awaiting culture
4. Adjust based on susceptibilities when available
5. Monitor for treatment failure - if symptoms worsen, consider resistance and obtain susceptibilities

Single-dose regimens are acceptable for moderate disease based on travelers' diarrhea guidelines 5, though 3-day courses provide additional coverage for more severe presentations.