Treatment of Uncomplicated Infectious Diarrhea in Adults
For most adults with acute watery diarrhea without recent international travel, empiric antimicrobial therapy is not recommended; instead, focus on oral rehydration solution as first-line therapy. 1, 2
Rehydration: The Cornerstone of Treatment
Reduced osmolarity oral rehydration solution (ORS) is the first-line therapy for mild to moderate dehydration in adults with infectious diarrhea. 1, 2, 3 This approach is superior to intravenous fluids when oral intake is tolerated—it is safer, less painful, less costly, and equally effective. 3
Rehydration Protocol by Severity:
Mild to Moderate Dehydration:
- Administer ORS until clinical dehydration is corrected (assess by thirst, orthostasis, decreased urination, dry mucous membranes). 1, 3
- Continue ORS to replace ongoing stool losses until diarrhea resolves. 1, 2
Severe Dehydration (shock, altered mental status, or ORS failure):
- Start isotonic intravenous fluids (lactated Ringer's or normal saline) immediately. 1, 2, 3
- Continue IV rehydration until pulse, perfusion, and mental status normalize. 1, 2
- Transition to ORS to replace remaining deficit once stabilized. 1, 2
Nutritional Management
Resume your normal age-appropriate diet immediately during or after rehydration—do not withhold food. 1, 2, 3 Early realimentation prevents malnutrition and may reduce stool output. 3 Withholding food is a common pitfall that should be avoided. 4
Antimicrobial Therapy: When to Treat
The IDSA guidelines are clear: empiric antimicrobials are NOT indicated for routine acute watery diarrhea in adults without recent international travel. 1, 2, 3
Specific Exceptions Where Antimicrobials Should Be Considered:
- Immunocompromised patients with severe illness 1, 2, 3
- Bloody diarrhea with presumptive shigellosis 2, 3
- Recent international travelers with fever ≥38.5°C or signs of sepsis 2, 3
- Clinical features of sepsis with suspected enteric fever 2, 3
Critical contraindication: Avoid antimicrobials in STEC O157 and other Shiga toxin 2-producing E. coli infections, as they increase the risk of hemolytic uremic syndrome. 1, 2, 3
When a specific pathogen is identified, antimicrobial treatment should be modified or discontinued accordingly. 1, 2
Adjunctive Therapies
Antimotility Agents (Loperamide):
Loperamide may be given to immunocompetent adults with acute watery diarrhea ONLY after adequate hydration. 1, 2, 3 The FDA-approved dosing is 4 mg initially, followed by 2 mg after each unformed stool, with a maximum of 16 mg daily. 5
Absolute contraindications for loperamide:
- Any patient with bloody diarrhea, fever, or suspected inflammatory diarrhea (risk of toxic megacolon) 1, 2, 3, 5
- Patients under 18 years of age 1, 2, 3
Antiemetics:
Ondansetron may be given to adults to facilitate oral rehydration when vomiting is present. 1, 2
Probiotics:
Probiotic preparations may be offered to reduce symptom severity and duration in immunocompetent adults, though the evidence is moderate. 1, 2, 3
Treatment Algorithm
Assess hydration status (thirst, orthostasis, decreased urination, dry mucous membranes, altered mental status). 3
Initiate appropriate rehydration:
Continue normal diet throughout illness. 3
Avoid empiric antimicrobials unless specific high-risk features present (immunocompromised, bloody diarrhea, fever ≥38.5°C with travel history, sepsis). 2, 3
Replace ongoing losses with ORS until symptoms resolve. 2
Consider adjunctive therapies only after adequate hydration (loperamide for watery diarrhea in immunocompetent adults, antiemetics if vomiting persists). 1, 2
Common Pitfalls to Avoid
- Using antimicrobials for routine acute watery diarrhea without high-risk features 2, 3
- Administering antimotility agents in bloody/inflammatory diarrhea or febrile illness (risk of toxic megacolon) 1, 2, 3
- Neglecting rehydration while focusing on antimicrobial therapy 2
- Withholding food during diarrheal episodes 2, 4
- Using antimicrobials in STEC infections, which increases hemolytic uremic syndrome risk 2, 3