Management of Acute Infectious Diarrhea
Begin immediate oral rehydration with reduced-osmolarity ORS (65–70 mEq/L sodium, 75–90 mmol/L glucose) for all patients with acute watery diarrhea; empiric antibiotics are not indicated in immunocompetent adults without fever, bloody stools, or recent international travel. 1
Assess Dehydration Severity
Classify dehydration to guide fluid strategy: 1
- Mild (3–5% deficit): Slight thirst, mildly dry mucous membranes 1
- Moderate (6–9% deficit): Loss of skin turgor, skin tenting on pinch, dry mucous membranes, decreased urine output 1, 2
- Severe (≥10% deficit): Altered mental status, prolonged skin tenting (>2 seconds), cool extremities, decreased capillary refill, rapid deep breathing (acidosis), shock 1, 2
Rapid deep breathing, prolonged skin retraction, and poor perfusion are more reliable predictors of significant dehydration than sunken fontanelle or absence of tears. 1
Rehydration Strategy
Mild-to-Moderate Dehydration
- Administer reduced-osmolarity ORS (≈65–70 mEq/L sodium, 75–90 mmol/L glucose) immediately 1, 2
- Dose: 50 mL/kg for mild dehydration or 100 mL/kg for moderate dehydration over 2–4 hours 1, 2
- Total daily fluid prescription: 2,200–4,000 mL/day, matching ongoing losses (urine + 30–50 mL/h insensible + stool losses) 1
- Continue ORS until clinical dehydration resolves and diarrhea stops 1, 2
- Replace each watery stool with 10 mL/kg ORS and each vomiting episode with 2 mL/kg ORS 2
- For patients unable to drink, nasogastric delivery of ORS is acceptable 2, 3
Severe Dehydration or ORS Failure
- Switch immediately to isotonic IV fluids (lactated Ringer's or normal saline) for: 1, 2
- Severe dehydration (≥10% deficit)
- Altered mental status
- Inability to tolerate oral intake
- Shock (hypotension, tachycardia, poor perfusion)
- Prolonged skin tenting >2 seconds with cool extremities
- Maintain IV rehydration until pulse, perfusion, and mental status normalize, then transition to ORS to replace remaining deficit 1, 2
Identify Red Flags Requiring Antibiotics
Do NOT prescribe empiric antibiotics for uncomplicated watery diarrhea in stable, immunocompetent adults without recent international travel. 1, 2
Situations Requiring Antibiotics
- Fever ≥38.5°C with bloody or mucoid stools (suggests invasive pathogens: Shigella, Campylobacter, invasive E. coli) 1, 2
- Recent international travel with severe, incapacitating symptoms 1
- Immunocompromised patients with severe illness 1, 2
- Signs of sepsis (altered mental status, hypotension, tachycardia) 1
- Ill-appearing infants <3 months 1
Antibiotic Regimen (when indicated)
- First-line: Azithromycin 1
- 500 mg single dose for watery diarrhea
- 1,000 mg single dose for febrile dysentery
- Second-line: Fluoroquinolones (if azithromycin unavailable or local susceptibility favorable) 1
- Ciprofloxacin 750 mg single dose or 500 mg BID × 3 days
- Levofloxacin 500 mg single dose or daily × 3 days
Critical Antibiotic Contraindication
NEVER use antibiotics for suspected or confirmed Shiga-toxin-producing E. coli (STEC O157:H7 or toxin-2 producers)—antibiotics markedly increase the risk of hemolytic-uremic syndrome. 1, 2, 3
- Screen for STEC with Shiga-toxin testing before starting antibiotics in any patient with bloody diarrhea without fever or with severe abdominal cramping 1
Antimotility Therapy (Loperamide)
- Loperamide may be used ONLY after adequate rehydration in immunocompetent adults with watery diarrhea 1, 2
- Dosing: 4 mg initially, then 2 mg after each loose stool (maximum 16 mg/24 hours) 1
Absolute Contraindications to Loperamide
- Children <18 years 1, 2, 3
- Fever present 1, 2, 3
- Bloody stools 1, 2, 3
- Suspected inflammatory or invasive diarrhea (risk of toxic megacolon) 1, 2, 3
Dietary Management
- Resume normal, age-appropriate diet immediately during or after rehydration 1, 2
- Start with small, light meals; avoid fatty, heavy, spicy foods and caffeine initially 1
- Continue breastfeeding throughout the illness in infants 2, 3
- Do not withhold food—early refeeding prevents malnutrition and may reduce stool output 2
Adjunctive Therapies
- Ondansetron may be given to children >4 years and adults with vomiting to facilitate oral rehydration 2, 3
- Probiotics may be offered to reduce symptom severity and duration (weak recommendation, moderate evidence) 1, 2
Indications for Diagnostic Testing
Reserve stool studies for: 1, 4, 5
- Fever with bloody or mucoid stools
- Severe dehydration or illness
- Persistent fever
- Immunosuppression
- Suspected outbreak
- Recent hospitalization or antibiotic exposure (evaluate for C. difficile)
Stool panel should include: 1
- Bacterial culture (Salmonella, Shigella, Campylobacter, Yersinia)
- Shiga-toxin testing (or gene detection) to identify STEC
- C. difficile toxin assay when recent healthcare exposure or antibiotics noted
Blood cultures indicated for: 1
- Infants <3 months
- Signs of septicemia
- Suspected enteric fever
- Immunocompromised patients with systemic manifestations
Hospitalization Criteria
- Severe dehydration requiring IV fluids
- Altered mental status or toxic appearance
- Shock or hemodynamic instability
- Inability to tolerate oral intake despite ORS attempts
- Immunocompromised status with severe illness
Critical Pitfalls to Avoid
- Never prioritize antimotility agents or antibiotics over rehydration—dehydration, not diarrhea, drives morbidity and mortality 1, 3
- Never start antibiotics for bloody diarrhea before ruling out STEC with Shiga-toxin testing 1, 2
- Never use loperamide when fever or bloody stools are present 1, 2, 3
- Never prescribe empiric antibiotics for uncomplicated watery diarrhea—this promotes antimicrobial resistance without clinical benefit 1, 2
- Never delay IV rehydration in severe dehydration while attempting oral rehydration 1, 2
- Never use sports drinks, apple juice, or soft drinks for rehydration—incorrect osmolarity worsens electrolyte imbalances 3
- Never withhold ORS in favor of IV fluids for mild-to-moderate dehydration—ORS is equally effective and avoids IV complications 3