What is the recommended assessment and management for an adult with acute (<14 days) diarrhea, including rehydration, diet, anti‑motility therapy, antibiotic indications, intravenous fluid criteria, and stool testing?

Management of Acute Diarrhea in Adults

For adults with acute diarrhea (<14 days), oral rehydration solution is first-line therapy, empiric antibiotics are NOT recommended unless there is recent international travel with fever ≥38.5°C, bloody diarrhea suggesting shigellosis, or immunocompromise, and loperamide may be used in immunocompetent adults with watery diarrhea only after adequate hydration and in the absence of fever or blood. 1, 2

Initial Assessment

Evaluate the following key features to guide management:

• Duration of symptoms (acute <14 days vs persistent ≥14 days) 1
• Stool characteristics: watery vs bloody, frequency, volume 1
• Fever presence (≥38.5°C suggests invasive pathogen) 2
• Recent international travel (major risk factor for bacterial pathogens) 1, 2
• Immune status (immunocompromised patients require different approach) 1, 2
• Hydration status: assess for thirst, orthostasis, decreased urination, dry mucous membranes, altered mental status 2
• Vomiting presence and severity 1

Rehydration Protocol

Mild to Moderate Dehydration

Reduced osmolarity oral rehydration solution (ORS) is the first-line therapy for all patients with mild to moderate dehydration (strong recommendation). 1, 2

• Administer approximately 100 mL/kg ORS over 2-4 hours 2
• Replace ongoing losses with 10 mL/kg ORS for each additional watery stool 3
• Continue ORS until clinical dehydration is corrected 1, 2
• ORS is superior to IV fluids when oral intake is tolerated—safer, less costly, and equally effective 2

Nasogastric Administration

• Consider nasogastric ORS delivery in patients who cannot tolerate oral intake or are too weak to drink adequately 1, 3

Severe Dehydration—IV Fluid Criteria

Switch immediately to isotonic intravenous fluids (lactated Ringer's or normal saline) when: 1, 2

• Severe dehydration is present
• Shock or altered mental status develops
• ORS therapy fails despite proper administration
• Ileus is present 1
• Ketonemia may require initial IV bolus to enable subsequent oral tolerance 1, 2

Continue IV rehydration until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit replacement. 1, 2

Dietary Management

Resume age-appropriate usual diet during or immediately after rehydration is completed (strong recommendation)—do not withhold food. 1, 2

• Early refeeding prevents malnutrition and may reduce stool output 2
• Food restriction is not beneficial and delays recovery 1

Antimicrobial Therapy Decision Algorithm

DO NOT Give Empiric Antibiotics For:

Empiric antimicrobial therapy is NOT recommended for most adults with acute watery diarrhea without recent international travel (strong recommendation). 1, 3, 2

• Antibiotics promote resistance without benefit in viral and most bacterial diarrheas 3
• Empiric treatment should be avoided in persistent watery diarrhea lasting ≥14 days (strong recommendation) 1, 3

Consider Antibiotics ONLY When:

• Recent international travel with fever ≥38.5°C or signs of sepsis 2
• Bloody diarrhea with fever, abdominal pain, and tenesmus suggesting shigellosis 2
• Immunocompromised patients with severe illness 1, 2
• Clinical features of sepsis with suspected enteric fever 2

NEVER Use Antibiotics For:

Shiga toxin-producing E. coli (STEC) infections—antibiotics increase risk of hemolytic uremic syndrome (strong recommendation). 1, 3, 2

Antibiotic Modification:

• Modify or discontinue antimicrobials once a specific pathogen is identified 1, 2

Anti-Motility Therapy

Loperamide may be given to immunocompetent adults with acute watery diarrhea ONLY after adequate hydration (weak recommendation). 1, 2

Absolute Contraindications for Loperamide:

• Bloody diarrhea (risk of toxic megacolon) 1, 2
• Fever present (suggests inflammatory diarrhea) 1, 2
• Suspected inflammatory diarrhea from any cause 1, 2
• Loperamide is not a substitute for fluid and electrolyte therapy 1

Antiemetic Therapy

• Ondansetron may be given to facilitate tolerance of oral rehydration in adults with vomiting 1
• This is particularly useful when vomiting prevents adequate ORS intake 2

Adjunctive Therapies

• Probiotics may be offered to reduce symptom severity and duration in immunocompetent adults (weak recommendation) 1, 2
• Ancillary treatments are not substitutes for proper hydration 1

Stool Testing Indications

Reserve diagnostic investigation for patients with: 4

• Severe dehydration or illness
• Persistent fever
• Bloody stool
• Immunosuppression
• Suspected nosocomial infection or outbreak
• Most patients do not require laboratory workup or routine stool cultures 4

Hospitalization Criteria

Admit patients with: 2

• Toxic appearance
• Altered mental status
• Severe dehydration not responding to initial therapy
• Inability to tolerate oral intake despite antiemetics

Maintenance Phase

Once rehydrated: 1, 2

• Continue maintenance fluids with ORS
• Replace ongoing losses until diarrhea and vomiting resolve
• Reassess hydration status if symptoms persist or worsen

Critical Pitfalls to Avoid

• Do not prescribe empiric antibiotics for uncomplicated watery diarrhea—this promotes resistance without benefit 3, 2
• Never use antibiotics if STEC is suspected—this can precipitate hemolytic uremic syndrome 3
• Do not give loperamide with fever or bloody diarrhea—risk of toxic megacolon 1, 2
• Do not delay rehydration while awaiting diagnostic results 5
• Do not restrict diet during or after rehydration—early feeding improves outcomes 5, 2