Approach to Acute Watery Diarrhea in Adults
Begin immediate oral rehydration with reduced-osmolarity ORS (65-70 mEq/L sodium) as the cornerstone of therapy; empiric antibiotics are not indicated for uncomplicated watery diarrhea in immunocompetent adults without recent international travel. 1, 2
Immediate Assessment for Red-Flag Features
Evaluate every patient for the following high-risk features that change management:
Features Requiring Stool Testing and Possible Antibiotics
- Fever (≥38.5°C) with bloody or mucoid stools – suggests invasive bacterial pathogens (Shigella, Campylobacter, invasive E. coli) requiring empiric antibiotics 1, 3
- Recent international travel with severe symptoms – travelers' diarrhea warrants empiric antibiotics to reduce duration from 50-93 hours to 16-30 hours 3, 4
- Signs of sepsis (altered mental status, hypotension, tachycardia) – requires blood cultures and empiric broad-spectrum antibiotics 1
- Immunocompromised status with severe illness – lower threshold for antibiotics and diagnostic workup 1, 3
- Infants <3 months of age – require blood cultures and empiric third-generation cephalosporin 1
Features Requiring Immediate Stool Testing (BEFORE Antibiotics)
- Bloody diarrhea without fever – must rule out STEC O157:H7 and other Shiga toxin-producing E. coli before any antibiotics, as antibiotics markedly increase risk of hemolytic uremic syndrome 1, 3
- Severe abdominal cramping or tenderness – obtain Shiga toxin testing 1
Features Indicating Severe Dehydration (Requires IV Fluids)
- Altered mental status 1, 2
- Inability to tolerate oral intake 1, 2
- Prolonged skin tenting (>2 seconds) 2
- Cool extremities with decreased capillary refill 2
- Hypotension or shock 1, 2
Rehydration Strategy (All Patients)
Mild to Moderate Dehydration (First-Line)
- Prescribe reduced-osmolarity ORS containing 65-70 mEq/L sodium and 75-90 mmol/L glucose 1, 2
- Total daily fluid intake: 2,200-4,000 mL/day, exceeding ongoing losses (urine + 30-50 mL/hour insensible losses + stool volume) 2
- Replace each watery stool with 10 mL/kg of ORS 5
- Continue ORS until clinical dehydration resolves and diarrhea stops 1, 2
Severe Dehydration (Switch to IV)
- Administer isotonic IV fluids (lactated Ringer's or normal saline) immediately for severe dehydration, shock, altered mental status, or failure of oral rehydration 1, 2
- Continue IV rehydration until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit 1, 2
Antimicrobial Indications (Specific Scenarios Only)
DO NOT Give Antibiotics If:
- Uncomplicated watery diarrhea without fever, blood, or travel history – strong recommendation against empiric antibiotics 1, 3, 2
- Suspected or confirmed STEC O157:H7 or Shiga toxin 2-producing E. coli – antibiotics increase hemolytic uremic syndrome risk 1, 3
- Asymptomatic contacts of patients with diarrhea 1, 3
DO Give Empiric Antibiotics If:
- Fever with bloody diarrhea (bacillary dysentery) – presumptive Shigella 1, 3
- Recent international travel with fever ≥38.5°C or signs of sepsis 3
- Suspected enteric fever with sepsis features – after obtaining blood, stool, and urine cultures 1, 3
- Immunocompromised with severe illness and bloody diarrhea 1, 3
Antibiotic Selection When Indicated
Second-line: Fluoroquinolones (only if azithromycin unavailable or local susceptibility favorable) 3
Pediatric (<3 months with suspected bacterial etiology): Third-generation cephalosporin (ceftriaxone 50 mg/kg/day) 1, 3
Symptomatic Therapy (After Adequate Rehydration)
Antimotility Agents
Dietary Management
- Resume normal, age-appropriate diet immediately after rehydration 1, 2
- Small, light meals initially, avoiding fatty, heavy, spicy foods and caffeine 2, 5
Adjunctive Therapies
- Antiemetics (ondansetron) may be considered after adequate rehydration, but do not replace fluid therapy 2
- Probiotics may reduce symptom severity and duration (weak recommendation) 2
Diagnostic Testing (Selective, Not Routine)
Obtain Stool Studies If:
- Fever with bloody or mucoid stools 1
- Severe dehydration or illness 1
- Persistent fever 1
- Immunosuppression 1
- Symptoms persist >14 days 5, 6
- Suspected outbreak 1
- Recent hospitalization or antibiotic use (consider C. difficile) 1
Stool Panel Should Include:
- Bacterial culture (Salmonella, Shigella, Campylobacter, Yersinia) 1
- Shiga toxin testing (or genes encoding them) to distinguish E. coli O157:H7 from other STEC 1
- C. difficile toxin if recent healthcare exposure or antibiotics 1
- Multiplex PCR panel for comprehensive pathogen detection 5
Obtain Blood Cultures If:
- Infants <3 months 1
- Signs of septicemia 1
- Suspected enteric fever 1
- Immunocompromised with systemic manifestations 1
Critical Pitfalls to Avoid
- Never prioritize antimotility agents or antibiotics over rehydration – dehydration causes morbidity and mortality, not the diarrhea itself 2, 5
- Never give antibiotics for bloody diarrhea until STEC is ruled out – obtain Shiga toxin testing first 1, 3
- Never use loperamide when fever or bloody stools are present – risk of toxic megacolon 1, 2
- Never prescribe empiric antibiotics for uncomplicated watery diarrhea – promotes resistance without benefit 1, 3, 2
- Never use fluoroquinolones as first-line empiric therapy – >90% Campylobacter resistance in many regions 3
- Never delay IV rehydration in severe dehydration while attempting oral rehydration 1, 2