Acute gastroenteritis (AGE): practical approach for adults and children

1. Immediate triage: who needs urgent assessment or admission?

• Shock, altered consciousness, poor perfusion, oliguria/anuria, inability to drink or persistent vomiting
• Severe dehydration: lethargy, very dry mucosa, sunken eyes, weak pulses, prolonged capillary refill, hypotension
• Bloody diarrhea, high fever, severe abdominal pain, guarding, distension, or peritonitis
• Sepsis or suspected enteric fever
• Infants, especially <3 months, older/frail adults, pregnancy, immunocompromise, significant renal/cardiac disease
• Recent antibiotics or healthcare exposure, raising concern for Clostridioides difficile
• Persistent diarrhea for ≥14 days, substantial weight loss, or failed outpatient oral rehydration
• Outbreak, food-handler, childcare, institutional, or travel-related illness

2. Focused clinical assessment

History

• Onset, stool frequency/volume, watery versus bloody or mucoid stool, vomiting, fever, pain
• Fluid intake, urine output, weight loss, ability to drink
• Food exposures: undercooked poultry/eggs, unpasteurized products, seafood, buffet food
• Travel, unsafe water, swimming/recreational-water exposure
• Sick contacts, daycare, healthcare/institutional exposure, outbreaks
• Recent antibiotics, proton-pump inhibitors, hospitalization
• Comorbidity, immunosuppression, pregnancy
• Medications and possible noninfectious causes

Examination

• Hydration: appearance, mucous membranes, tears, eyes, pulse, capillary refill, postural symptoms, skin perfusion, urine output
• Temperature and vital signs
• Abdominal examination for focal tenderness, guarding, distension, toxic megacolon
• Consider alternate diagnoses: appendicitis, intussusception in children, bowel obstruction, inflammatory bowel disease, diabetic ketoacidosis, urinary infection, pelvic pathology, ischemic colitis, adrenal crisis, poisoning.

3. Rehydration and feeding: treatment for nearly everyone

Mild to moderate dehydration

• Give frequent, small sips or spoonfuls, escalating as tolerated.
• In a vomiting child, give very small amounts frequently rather than stopping all fluids.
• Nasogastric ORS is an option if oral intake is inadequate but the gut is functioning.
• Avoid using cola, undiluted juice, energy drinks, and sports drinks as rehydration therapy. Their sodium-glucose composition is unsuitable and excess sugar can worsen diarrhea.

Severe dehydration, shock, or failed ORS

• Urgent IV isotonic crystalloid resuscitation and electrolyte/glucose assessment.
• Reassess frequently, then transition to ORS as soon as possible.
• Admit if ongoing losses, poor oral intake, concerning comorbidity, unreliable follow-up, or diagnostic uncertainty.

Nutrition

• Resume an age-appropriate usual diet early once rehydration begins.
• Continue breastfeeding without interruption.
• Do not routinely use bowel rest, clear-fluid-only diets, lactose-free formula, or restricted diets.
• Avoid high-sugar beverages and highly fatty foods initially.

4. When to investigate

Send stool testing, ideally multiplex PCR with culture/public-health follow-up when indicated, if:

• Fever, blood or mucus in stool, severe cramps or abdominal tenderness
• Sepsis or systemic toxicity
• Severe illness, significant dehydration, hospitalization
• Immunocompromise or major comorbidity
• Recent travel, suspected cholera, outbreak, foodborne exposure, or public-health implications
• Persistent diarrhea, generally ≥14 days
• Suspected C. difficile: recent antibiotics, hospitalization, or healthcare exposure

Additional tests

• CBC, electrolytes, renal function, glucose, blood gas if severe dehydration, significant illness, or sepsis is suspected.
• Blood cultures for sepsis, suspected enteric fever, systemic infection, high-risk immunocompromise, and selected very young infants.
• Ova/parasite testing or pathogen-specific testing for persistent disease, relevant travel, untreated water exposure, or immunocompromise.

5. Antimicrobials: targeted, not routine

Do not routinely prescribe antibiotics

• Do not treat uncomplicated watery diarrhea empirically.
• Do not routinely treat uncomplicated nontyphoidal Salmonella.
• Avoid antibiotics when STEC is suspected or confirmed, especially bloody diarrhea after undercooked beef or outbreak exposure, because they may increase the risk of hemolytic uremic syndrome. ROSEN's Emergency Medicine, p. 1300.

Consider empiric antibiotics only in selected severe/high-risk cases

• Presumed shigellosis with classic dysentery and marked systemic illness
• Recent international travel plus fever ≥38.5 C, sepsis, or severe disease
• Severe illness in immunocompromised patients
• Infant <3 months with suspected invasive bacterial enteritis
• Suspected cholera with severe high-output diarrhea after rehydration has started
• Suspected enteric fever or sepsis

6. Symptomatic medicines

7. Differences in approach

Adults

• Think particularly about traveler's diarrhea, medication-associated diarrhea, C. difficile, ischemic colitis in older adults, and inflammatory bowel disease.
• Antimotility medication is an option only for simple watery illness with no red flags.
• Older adults can deteriorate quickly because dehydration may precipitate acute kidney injury, delirium, or heart failure.

Children

• Prioritize rapid hydration assessment and ongoing urine output.
• ORS, breastfeeding, and early normal feeding are the core treatment.
• Lower threshold for escalation in infants, especially <6 months or <8 kg, premature children, or those with chronic disease.
• Avoid loperamide and routine antibiotics.
• Evaluate bloody diarrhea carefully for STEC and monitor for HUS: reduced urine, pallor, bruising, lethargy, edema, or hypertension.

8. Discharge advice and infection control

• Reduced urine output, inability to drink, repeated vomiting
• Lethargy, fainting, confusion, worsening weakness
• Blood in stool, persistent high fever, severe/localized abdominal pain
• Diarrhea lasting >7 days without improvement, or ≥14 days overall
• In children: no tears, sunken eyes, fewer wet diapers, unusual sleepiness/irritability.

• Handwashing with soap and water after toileting/diaper changes and before food preparation.
• Do not prepare food for others while symptomatic.
• Keep children out of childcare and workers out of food handling according to local regulations.
• Use chlorine-based cleaning for norovirus-contaminated surfaces when feasible.
• Maintain appropriate routine vaccines, including rotavirus vaccine in eligible infants.

Current-guideline note

Acute gastroenteritis: management with commonly used doses

1. Rehydration

A. Oral rehydration solution (ORS)

Adults

• Mild illness: small frequent sips, aiming to replace ongoing losses.
• Practical replacement: 200-250 mL ORS after each loose stool and additional fluid after vomiting, as tolerated.
• If vomiting: give 5-10 mL every 1-2 minutes, increasing gradually.

Children

B. IV fluids

Adults

• 0.9% saline or Ringer lactate: usually 1 L IV bolus, then reassess perfusion, blood pressure, lung status, urine output, and electrolytes.
• In severe hypovolemia/shock, repeat boluses as required under close monitoring.
• Use smaller boluses and more frequent reassessment in heart failure, advanced kidney disease, frail older adults, and pregnancy.

Children

• 0.9% saline or Ringer lactate 20 mL/kg IV over 5-20 minutes for shock/severe dehydration, then reassess.
• Repeat if shock persists, while urgently checking glucose and electrolytes.
• Once circulation improves, complete rehydration and switch to ORS as soon as feasible.

2. Antiemetic

Ondansetron

Children, usually age ≥6 months

• 8-15 kg: 2 mg PO/ODT once
• 15-30 kg: 4 mg PO/ODT once
• >30 kg: 8 mg PO/ODT once

• 0.15 mg/kg PO or IV once, maximum 8 mg

Adults

• 4-8 mg PO/ODT or IV once, then use only selectively, for example every 8-12 hours as needed for a very short period.

Avoid or use with particular caution

• Congenital long-QT syndrome
• Significant hypokalemia or hypomagnesemia
• Concomitant QT-prolonging drugs
• Known arrhythmia or severe cardiac disease
• Suspected bowel obstruction, bilious vomiting, or surgical abdomen

3. Antidiarrheal drugs

Loperamide: adults only

• 4 mg PO initially
• Then 2 mg PO after each unformed stool
• Maximum 16 mg/day
• Stop once stools are formed or if no improvement within 48 hours.

• Children
• Fever or bloody/mucoid stool
• Suspected invasive bacterial diarrhea, dysentery, STEC, or C. difficile
• Severe colitis, abdominal distension, ileus, toxic appearance
• Acute ulcerative colitis flare

Bismuth subsalicylate: selected adults

• 524 mg PO every 30-60 minutes as needed
• Maximum 8 doses in 24 hours
• Use for a maximum of about 2 days without reassessment.

• Children/adolescents with viral illness
• Aspirin/salicylate allergy
• Anticoagulant use or significant bleeding risk
• Significant renal impairment
• Pregnancy unless specifically advised

4. Antibiotics

Key principle

Consider empiric treatment only if there is:

• Sepsis, suspected enteric fever, or severe systemic disease
• Severe traveler-associated fever/dysentery
• Severe immunocompromise
• Selected young infants with suspected invasive bacterial AGE
• Clinically severe presumed shigellosis
• Suspected cholera with high-output diarrhea, after fluid resuscitation begins

A. Adults: common empiric regimens

Febrile diarrhea or dysentery, especially travel-associated

• 1 g PO once, or
• 500 mg PO once daily for 3 days

• 500 mg PO every 12 hours for 3 days

• 500 mg PO once daily for 3 days

Noninvasive traveler's diarrhea only

• 200 mg PO three times daily for 3 days

B. Children: antibiotics only after pediatric assessment

Selected suspected/confirmed bacterial invasive diarrhea

• 10 mg/kg PO once daily for 3 days, maximum 500 mg/dose

• 10-12 mg/kg on day 1, then
• 5-6 mg/kg once daily on days 2-3 or 2-5

• 50-75 mg/kg IV once daily
• Maximum commonly 2 g/day
• Duration depends entirely on pathogen and clinical syndrome.

• 8 mg/kg/day PO in 1-2 divided doses
• Maximum 400 mg/day
• Typical duration: 3-5 days, pathogen-dependent.

5. Pathogen-directed examples

6. Zinc and probiotics

Zinc, mainly in resource-limited settings or malnutrition

• Age <6 months: elemental zinc 10 mg PO daily for 10-14 days
• Age ≥6 months: elemental zinc 20 mg PO daily for 10-14 days

Probiotics

7. When to refer urgently or admit

• Shock, altered consciousness, or severe dehydration
• Oliguria/anuria, acute kidney injury, severe electrolyte disturbance
• Bilious vomiting, guarding, focal severe pain, abdominal distension
• Bloody stool with systemic illness
• Suspected HUS: pallor, reduced urine, bruising, edema, hypertension after bloody diarrhea
• Infant <3 months with fever or suspected invasive infection
• Older/frail adult, immunocompromised patient, pregnancy, major renal/cardiac disease
• Failure of ORS plus antiemetic or inability to ensure safe follow-up