Diarrhea in Children

Definition & Epidemiology

Diarrhea is defined as an increase in stool frequency, fluidity, or volume compared with normal for a given child. Acute gastroenteritis (AGE) accounts for over 500,000 deaths globally per year in children under 5, making it one of the leading causes of child mortality worldwide. In developed countries, the course is usually self-limited, but significant morbidity still results from dehydration and electrolyte disturbances.

Etiology

Infectious Causes (most common)

Category	Pathogens
Viruses (70–80%)	Norovirus (now #1 in US after vaccine era), Rotavirus, Astrovirus, Adenovirus
Bacteria (10–20%)	Salmonella, Shigella, Campylobacter jejuni, Yersinia enterocolitica, E. coli (ETEC, STEC O157:H7), C. difficile, Staph. aureus, Vibrio
Protozoa (<10%)	Cryptosporidium, Giardia intestinalis, Entamoeba histolytica

Key point: Rotavirus was historically the leading cause of severe childhood diarrhea. Since the introduction of the RotaTeq (RV5) and Rotarix (RV1) oral vaccines, US hospitalizations declined by 60–90% in children <5 years, with an estimated 177,000 hospitalizations and 242,000 ED visits averted. Norovirus is now the most common cause of diarrheal illness in children in the US. — ROSEN's Emergency Medicine, p. 3228–3232

Non-Infectious Causes

Category	Examples
Gastrointestinal	Malabsorption (milk intolerance, excessive juice), IBD, irritable bowel, short gut
Drug-related	Ingestion, overdose, antibiotic-associated
Endocrine	Thyrotoxicosis, adrenal insufficiency, diabetic enteropathy
Renal	UTI, pyelonephritis
Emergencies	Intussusception, appendicitis, HUS, pseudomembranous colitis, toxic megacolon
Other	Parental anxiety, chronic nonspecific diarrhea

Clinical Assessment

History Key Points

Onset, duration, frequency, character (watery, bloody, mucoid)
Vomiting, fever, abdominal pain
Urine output, oral intake
Similar illness in household contacts or school
Travel, water exposure, camping, household pets
Vaccine status, recent antibiotics, chronic medical conditions

Alarm Features (Indications for Medical Evaluation)

Per Box 167.3 — ROSEN's:

Age <6 months or weight <8 kg
History of prematurity or chronic illness
Fever ≥38°C in infants <3 months or ≥39°C in children 3–36 months
Bloody or mucoid stool
High-output or high-frequency diarrhea
Persistent vomiting
Signs of dehydration (sunken eyes, dry mucous membranes, decreased urine output, decreased tears)
Change in mental status (irritability, apathy, lethargy)
Failure or inability to administer ORT at home

Dehydration Assessment

Dehydration is the most important immediate complication. Clinical signs are used to classify severity:

Severity	% Body Weight Loss	Clinical Features
Mild	3–5%	Slightly dry mucous membranes, increased thirst, normal exam
Moderate	6–9%	Sunken eyes, decreased skin turgor, dry mouth, reduced urine output, tachycardia
Severe	≥10%	Markedly sunken eyes/fontanelle, poor skin turgor, lethargy, tachycardia, hypotension, mottling

Laboratory testing is recommended for moderate-to-severe dehydration: serum electrolytes, bicarbonate, BUN/creatinine, glucose. No single lab test is definitive. — ROSEN's, p. 3384

Diagnostic Workup

Stool cultures: NOT indicated in most uncomplicated AGE. Indicated for: systemic involvement, underlying chronic conditions, dysenteric features (bloody stool), or illness >2 weeks
- Always test separately for E. coli O157:H7 and non-O157 STEC (Shiga toxin)
- Test for ova & parasites if travel to endemic area
Fecal leukocytes: Positive (>5 per HPF) suggests invasive pathogen (Salmonella, Shigella, Campylobacter, invasive E. coli) → warrants stool culture
Culture-independent diagnostic tests (CIDTs): Increasingly used for antigen/genetic detection (e.g., EIA for rotavirus, PCR multiplex panels)
Immunosuppressed or critically ill: CBC, blood/urine cultures, CXR, consider LP

Management

1. Oral Rehydration Therapy (ORT) — First-Line

Recommended by AAP, ESPGHAN, and WHO for mild-to-moderate dehydration.

ORT formula:

Classify severity (mild 3–5%, moderate 6–9%)
Calculate ORS volume: 30–50 mL/kg for mild; 60–80 mL/kg for moderate depletion
Administer 25% of the total each hour for the first 4 hours
Replace ongoing losses: 10 mL/kg per stool, 2 mL/kg per emesis
Monitor and reassess hourly

Low-osmolarity ORS (<270 mOsm/L) is preferred
Polymer-based (rice/wheat) solutions show similar or slightly faster diarrhea resolution vs. low-osmolarity solutions (Cochrane 2016)
For minimal dehydration in children 6–60 months: dilute apple juice followed by preferred fluids was found non-inferior to ORS in the ED, with fewer treatment failures and less IV fluid need (Freedman et al.)

2. IV Rehydration — For Severe Dehydration or ORT Failure

Indications: severe dehydration, shock, lethargy, acute abdomen, suspected obstruction, significant electrolyte disturbance, or inability to take orals.

Start IV/IO access immediately; check finger-stick glucose and electrolytes
Isotonic crystalloid bolus; adjust based on electrolyte results

3. Antibiotic Therapy

Antibiotics are not needed for viral gastroenteritis or most uncomplicated bacterial AGE. Specific indications:

Indication	Treatment
C. difficile	Metronidazole or vancomycin (oral)
Giardia intestinalis	Metronidazole, tinidazole
E. histolytica	Metronidazole + luminal agent
Shigella	Consider antibiotics (azithromycin, ceftriaxone)
Campylobacter	Consider if early/severe (azithromycin)
Cryptosporidium	Nitazoxanide in immunocompetent; more aggressive in immunocompromised

⚠️ E. coli O157:H7 (STEC): Antibiotics are contraindicated due to increased risk of Hemolytic Uremic Syndrome (HUS).

High-risk groups needing lower threshold for antibiotics: neonates, infants <1 year, immunosuppressed, chronic disease, prosthetic valves/joints.

4. Diet & Nutrition

Do not restrict diet — early refeeding reduces illness duration and improves outcome
Continue breastfeeding throughout
Formula-fed infants: continue usual formula (lactose-free formula rarely necessary)
Age-appropriate diet should be resumed as soon as tolerated

5. Adjunct Therapies

Zinc supplementation: Recommended by WHO (10–20 mg/day × 10–14 days) in developing country settings; a 2024 systematic review and meta-analysis (PMID: 39641338) confirms benefit for acute and persistent watery diarrhea
Ondansetron: Reduces vomiting and improves ORT success; evidence-based in children
Probiotics: Some evidence for shortening illness duration (especially Lactobacillus rhamnosus GG); evidence is not uniform across formulations
Loperamide: Contraindicated in children <2 years and in bloody/febrile diarrhea

Complications

Complication	Notes
Dehydration	Most common; assess every visit
Electrolyte disturbance	Hypo/hypernatremia, hypokalemia, metabolic acidosis
Hemolytic Uremic Syndrome (HUS)	Associated with STEC O157:H7; triad: microangiopathic hemolytic anemia, thrombocytopenia, renal failure
Seizures	Occur in 2–3% of rotavirus infections
Malnutrition	Chronic/recurrent diarrhea in malnourished children creates vicious cycle of gut injury
Intussusception	Must exclude when diarrhea is blood-streaked with crampy abdominal pain

Prevention

Rotavirus vaccine: RotaTeq (3-dose) or Rotarix (2-dose); given orally at 2, 4 (and 6) months; reduced rotavirus hospitalizations by ~80%
Hand hygiene: Reduces diarrheal disease incidence by ~30% in high- and low-income countries alike
Safe water, sanitation: Critical in LMICs
Breastfeeding: Protective against enteric pathogens

Recent Evidence (2024–2026)

A 2024 systematic review (Lancet Glob Health, PMID 38648812) estimated global causes of diarrheal deaths in children <5 during 2000–2021, confirming rotavirus and Cryptosporidium as leading causes of mortality in LMICs even post-vaccine era.
A 2024 systematic review (PMID 39485019) on diarrhea aetiology in ages 0–9 in LMICs found Cryptosporidium, rotavirus, and ETEC dominate the pathogen burden in young children.
Zinc supplementation meta-analysis (PMID 39641338, J Glob Health 2024) confirms that zinc reduces diarrhea duration in both acute and persistent cases.

Sources:

ROSEN's Emergency Medicine: Concepts and Clinical Practice, Chapter 167
Tintinalli's Emergency Medicine: A Comprehensive Study, Chapter 131
Medical Microbiology 9e — Rotavirus section

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