Acute Gastroenteritis in Children

Overview & Definition

Acute gastroenteritis (AGE) is an inflammation of the stomach and intestinal mucosa of infectious origin, producing diarrhoea (passage of 3 or more loose or watery stools in 24 hours, or a stool frequency/looseness exceeding the child's normal baseline) and/or vomiting, lasting under 14 days.[1]

The clinical definition is operational. WHO defines diarrhoea as the passage of 3 or more loose or watery stools in 24 hours, with the caveat that a single large, watery stool or any stool containing visible blood is also diarrhoea. Passage of formed stools, even when frequent, is not diarrhoea. Breast-fed neonates may pass 6 to 10 semi-formed stools daily; this is physiological and not gastroenteritis.[1]

Three temporal categories are recognised:[1]

• Acute diarrhoea — under 14 days. By far the commonest (over 90% of cases). Mostly infective and self-limiting.
• Persistent diarrhoea — 14 to 29 days. Implicated organisms include Giardia, Cryptosporidium, enteroaggregative E coli, and (in endemic regions) HIV. Persistent diarrhoea signals underlying malnutrition, immune compromise, or a non-infectious cause.
• Chronic diarrhoea — 30 days or more. Includes coeliac disease, cow's milk protein allergy, inflammatory bowel disease, cystic fibrosis, congenital chloride-losing or sodium-losing diarrhoea, and toddler's diarrhoea.[5]

AGE is fundamentally a volume and electrolyte disorder: the entire threat to life comes from fluid and electrolyte loss. Most deaths occur not from the pathogen but from dehydration, hypovolaemic shock, electrolyte disturbance (hypo- or hypernatraemia, hypokalaemia), metabolic acidosis, and hypoglycaemia. The defining therapeutic insight of the past 60 years — recognised in the discovery of sodium-glucose co-transport by Hirschhorn and others — is that enterotoxin-stimulated intestine retains the capacity to absorb sodium and water in the presence of glucose, which is the molecular basis of oral rehydration solution (ORS).[6]

Classification

AGE can be classified along three clinically useful axes.[6]

By duration

• Acute — under 14 days (the focus of this chapter).
• Persistent — 14 to 29 days. Carry a different workup: stool for ova/cysts/parasites, HIV test, anti-tTG for coeliac, sweat chloride.
• Chronic — 30 days or more (non-infectious causes dominate).[1]

By stool character — the most useful clinical split

By pathogen class

The mnemonic "Viruses, Bacteria, Parasites" with their relative frequency and key features is captured below in the Classification figure and Epidemiology section.[11]

Epidemiology & Risk Factors

Global burden

Acute gastroenteritis remains a leading cause of death in children under 5 worldwide. Estimates of global diarrhoeal mortality have fallen substantially with scale-up of ORS, zinc, rotavirus vaccine, clean water, and improved nutrition, but diarrhoea still causes around 500,000 child deaths annually in developing countries.[3] In the GEMS cohort, the odds of dying during follow-up were 8.5-fold higher in children with moderate-to-severe diarrhoea than in matched controls, with most deaths (87.9%) in the first 2 years of life.[2]

The GEMS study

The Global Enteric Multicenter Study (GEMS), a prospective case-control study of over 9,400 children under 5 in seven sites across Africa and Asia (Kotloff et al., 2013), is the most authoritative modern dataset on diarrhoeal aetiology in developing countries. GEMS identified four pathogens accounting for the majority of moderate-to-severe diarrhoea:[2]

1. Rotavirus — the leading cause overall (about 20% of moderate-to-severe cases pre-vaccine).
2. Cryptosporidium — particularly in infants under 12 months and in HIV-positive children.
3. Shigella — the leading cause of dysentery and a major cause of mortality.
4. Heat-stable enterotoxigenic E. coli (ST-ETEC) — the major cause of travellers' diarrhoea and a leading cause of paediatric watery diarrhoea in developing settings.[2]

Risk factors

• Age: peak incidence 6 to 24 months — loss of transplacentally acquired immunity, introduction of weaning foods, mouthing behaviour, immature gut mucosa.
• Malnutrition: the single most important risk modifier. A wasted child has 2 to 3× the mortality risk for an identical pathogen load; oedematous severe malnutrition reduces the clinical signs of dehydration.
• Immunocompromise: HIV, primary immunodeficiency, chemotherapy. Persistent Cryptosporidium, Cystoisospora, CMV.
• Lack of exclusive breastfeeding: bottle-feeding in low-resource settings introduces contaminated formula.
• Unsafe water and poor sanitation: faecal-oral transmission.
• Day-care attendance, household crowding, season: viral AGE peaks in winter (rotavirus, norovirus); bacterial AGE peaks in hot/wet season.
• No rotavirus vaccination: in the first year of life RV1 prevents 84% of severe rotavirus diarrhoea in low-mortality countries (RV5 probably 92%); in high-mortality countries protection is lower (RV1 63%, RV5 57%) but more episodes are prevented because baseline risk is far higher.[10]
• Recent antibiotic exposure: risk of C. difficile.
• Travel: ETEC, cholera, amoebic dysentery.

Pathophysiology

The fundamental division of acute diarrhoea is between secretory and osmotic mechanisms. Understanding which mechanism is at work predicts the natural history, the response to fasting, and the choice of ORS.[11]

Secretory diarrhoea

The defining feature is active intestinal secretion of chloride and water that persists despite fasting. The stool is large-volume, watery, isotonic, and continues even when the patient takes nothing by mouth. The prototype is cholera, but rotavirus NSP4 also acts as an enterotoxin.[10]

Molecular cascade (cholera model):[6]

1. Vibrio cholerae elaborates cholera toxin (an A-B toxin). The B subunit binds GM1 ganglioside on the enterocyte; the A subunit enters the cell.
2. The A subunit ADP-ribosylates the stimulatory G-protein Gsα, locking it in the active (GTP-bound) state.
3. Constitutive activation of adenylate cyclase → sustained rise in intracellular cAMP.
4. cAMP opens the CFTR chloride channel on the apical membrane of the crypt enterocyte → massive Cl⁻ secretion into the lumen.
5. To maintain electroneutrality, Na⁺ follows, and water follows osmotically — producing "rice-water" stool.
6. Crucially, the absorptive villous cells remain intact. Sodium-glucose co-transport (SGLT1) on villous tips still functions. This is the molecular rationale for ORS: glucose-coupled sodium absorption bypasses the secretory defect and reclaims water.[6]

Rotavirus produces a similar picture through NSP4 (an enterotoxic viral protein), villous ischaemia, and transient malabsorption of disaccharidases (especially lactase — hence the temporary lactose intolerance that follows rotavirus infection).[10]

Osmotic diarrhoea

The defining feature is malabsorption of nutrients that remain in the lumen and draw water osmotically. The stool is smaller in volume, stops with fasting, has an osmotic gap (stool osmolality minus 2×(Na⁺ + K⁻) greater than 50 mOsm/kg), and may show reducing substances. Mechanisms:[6]

• Mucosal invasion and villous-tip destruction — Shigella, Campylobacter, Salmonella. Loss of mature absorptive enterocytes; transient brush-border enzyme deficiency; inflammatory exudate.
• Disaccharidase deficiency — lactase destroyed by rotavirus → undigested lactose ferments in the colon → osmotic load.
• Mucosal inflammation and protein loss — invasive bacteria produce mucosal ulceration and exudative, bloody stool.[10]

Fluid and electrolyte consequences

Diarrhoeal stool depletes water together with sodium, potassium and bicarbonate, and the electrolyte composition of rehydration fluids matters: in the CHOICE trial, hyponatraemia (serum sodium under 130 mmol/L) at 24 h occurred in 11% of children on reduced-osmolarity ORS versus 9% on standard WHO ORS — no significant difference.[13] The clinically important consequences are:[1]

• Dehydration — the dominant disturbance; severity is linked to aetiology (rotavirus is the most severe agent and is frequently associated with dehydration) and should be monitored with established score systems.[1] Hypernatraemic and hyponatraemic dehydration are both recognised and require slow correction of the sodium derangement.
• Hypokalaemia — stool potassium loss and intracellular shift as acidosis is corrected; presents with muscle weakness, ileus and cardiac arrhythmias.
• Metabolic acidosis — bicarbonate loss in stool, lactic acidosis from shock, and renal hypoperfusion; presents with tachypnoea and a low-serum bicarbonate on blood gas.
• Hypoglycaemia — risk in fasted, malnourished infants; may cause seizures and coma and is easily missed.

Clinical Presentation

The presenting complaint is almost always one of: acute-onset diarrhoea, vomiting, fever, abdominal cramps, reduced oral intake, lethargy, reduced urine output, or in young infants, fewer wet nappies. The history must establish:[6]

• Stool frequency, volume, character: watery vs bloody, presence of mucus or pus, smell (foul-smelling, greasy suggests Giardia), colour (rice-water in cholera; redcurrant-jelly in intussusception).
• Vomiting: frequency, bilious (surgical cause), coffee-ground (haematemesis).
• Fever: high swinging fever favours bacterial; absent fever with profuse watery stool favours cholera.
• Ability to drink: a key WHO discriminator.
• Urine output: number of wet nappies in past 12 to 24 h — last wet nappy is the bedside proxy.
• Preceding illness, contacts, travel, day-care, recent antibiotics, food history, water source.
• Immunisation status: rotavirus vaccine; measles in the differential of diarrhoea with rash.[10]

Stool patterns by pathogen — the clinical "fingerprint"

• Rotavirus: vomiting precedes watery diarrhoea by 12 to 24 h; fever low-grade; lasts 3 to 8 days.
• Norovirus: explosive vomiting prominent; diarrhoea brief (1 to 3 days); outbreak setting.
• Enterotoxigenic E. coli: watery diarrhoea without fever; travellers.
• Shigella (shigellosis): high fever, abdominal cramps, tenesmus, then bloody mucoid stool with faecal leucocytes; may cause seizures in young children (Shigella encephalopathy / "Shigellosis-associated encephalopathy").[9]
• Salmonella (non-typhoidal): watery or bloody diarrhoea, fever, bacteraemia in infants under 3 months; risk of osteomyelitis in sickle-cell disease.
• Campylobacter jejuni: bloody diarrhoea, abdominal pain mimicking appendicitis; Guillain-Barré syndrome 1 to 3 weeks later (anti-GQ1b antibody).
• EHEC (O157:H7): afebrile, bloody diarrhoea, abdominal pain, then 5 to 10 days later pallor, oliguria, petechiae — HUS.
• Entamoeba histolytica: abdominal pain, bloody mucoid stool, may form amoebic liver abscess (right upper quadrant pain, fever).
• Giardia lamblia: foul-smelling, greasy, floating stools, bloating, flatulence; persistent; no fever; no blood.
• Vibrio cholerae: profuse rice-water stool, vomiting, rapid severe dehydration, no fever.

Dehydration — the cardinal physical finding

Signs to elicit and document at every assessment are in the WHO dehydration table (see Clinical Assessment). The bedside set is: general appearance / alertness, eyes (sunken?), fontanelle (sunken in infants), mouth/tongue (dry?), tears when crying, skin pinch (elasticity), capillary refill, peripheral pulse, warmth of extremities, urine output, weight (most useful when a recent pre-illness weight exists).[6]

Extra-intestinal / atypical presentations

• Neonate / young infant: may present with poor feeding, lethargy, hypothermia, or apnoea — atypical and easily missed.
• Severe malnutrition: oedema masks dehydration; sunken eyes and reduced skin turgor are unreliable. Use WHO's modified assessment (see Special Populations).
• Immunocompromised: persistent watery diarrhoea (Cryptosporidium, Cystoisospora, CMV colitis).
• Shigella in infants: seizures may precede the diarrhoea and be mis-attributed to febrile convulsion.[6]

Differential Diagnosis

The list is broad — "diarrhoea and vomiting" is one of the commonest paediatric presentations and includes surgical, metabolic, and extra-intestinal emergencies. A structured differential is mandatory.[4]

Key distinguishing questions

1. Is the child toxic / systemically unwell beyond the dehydration grade? — think sepsis, meningitis, DKA, surgical abdomen.
2. Is there bile-stained vomit? — malrotation / volvulus until proven otherwise.
3. Is there blood in the stool? — invasive bacterial, amoebic, cow's-milk-protein colitis, intussusception (redcurrant-jelly).
4. Has the urine output been normal? — picture of dehydration without reduced urine output suggests an alternative diagnosis (DKA, diabetes insipidus).[6]

Clinical & Bedside Assessment

The WHO dehydration grading is the single most important bedside tool in paediatric AGE and must be reproduced verbatim — every NEET-PG/INICET candidate is expected to recall it fluently.[1]

[6]

Two signs suffice for SOME dehydration

WHO operational rule: two or more of the following → classify as SOME dehydration (and treat with Plan B): restlessness/irritability, sunken eyes, drinks eagerly/thirsty, skin pinch goes back slowly.[6]

Two signs suffice for SEVERE dehydration

Two or more of the following → classify as SEVERE dehydration (treat with Plan C): lethargy/unconsciousness, sunken eyes, not able to drink, skin pinch goes back very slowly.[6]

The skin pinch test (abdominal wall)

Pinch a fold of skin and subcutaneous tissue over the mid-abdominal wall between thumb and forefinger, lift it, and release. Time the return to flat.[1]

• Under 1 second — normal / no dehydration.
• 1 to 2 seconds — slow → some dehydration.
• More than 2 seconds — very slow → severe dehydration.[6]

Avoid pinching over the chest wall (less reliable in malnourished or obese children).[1]

Capillary refill time

Press the nail-bed of a finger or toe for 5 seconds, release. Refill over under 2 seconds is normal; 2 to 3 seconds indicates moderate compromise; over 3 seconds indicates shock. CRT is sensitive but non-specific — febrile, cold, or anxious children may have prolonged CRT.[12]

Other bedside assessments

• Weight — the most objective measure of dehydration when a recent pre-illness weight exists; severe dehydration corresponds to a deficit of about 10% of body weight. In the GASTRO trial of WHO plan C, day-7 re-weighing showed only 29% of children clinically classified as severely dehydrated truly had a deficit of 10% or more — clinical grading tends to overestimate the volume deficit.[18]
• Vital signs — tachycardia (early), weak thready pulse (shock), tachypnoea (acidosis or compensation), hypotension (late, pre-terminal), hypothermia in severe sepsis or malnutrition.
• Anterior fontanelle (infants under 18 months) — sunken fontanelle is a reliable sign of significant dehydration.
• Mucous membranes, tears, eyes — dry tongue and absent tears support dehydration.
• Urine output — falling urine output indicates significant dehydration; anuria raises the possibility of HUS or AKI and mandates review.[1]

[13] [18] [10] [14] [16]

Investigations

AGE is, in the vast majority of cases, a clinical diagnosis. Routine laboratory tests are unnecessary. The choice of investigation is dictated by severity, host risk factors, and outbreak setting.[12]

Stool tests — when to send

• Stool culture — send if bloody diarrhoea, severe/prolonged illness, immunocompromise, suspected sepsis, day-care or hospital outbreak, suspected HUS, recent foreign travel, suspected cholera. Specifically request culture for Salmonella, Shigella, Campylobacter, E. coli O157:H7 (sorbitol-MacConkey), Yersinia, Vibrio.
• Stool microscopy for ova, cysts, parasites — if persistent diarrhoea (over 14 days), or suspected Giardia / amoebiasis. Send three serial samples (parasite shedding is intermittent).
• Stool for C. difficile toxin — if recent antibiotic exposure, hospital-acquired diarrhoea, or severe colitis with leucocytosis.
• Stool multiplex PCR panel — increasingly available; rapid, sensitive, but detects DNA, not necessarily viable organisms — over-diagnosis of co-infection is a real pitfall. Use selectively.
• Fecal calprotectin / faecal leucocytes / lactoferrin — surrogate markers of intestinal inflammation (invasive vs non-invasive diarrhoea); supportive but rarely change management in AGE.
• Stool reducing substances / pH — supports osmotic (carbohydrate malabsorption) diarrhoea when lactose intolerance is suspected.[6]

Blood tests — when to send

• Urea and electrolytes (U&E) and creatinine — essential in severe dehydration, when IV fluids are needed, when sodium abnormality is suspected, or before potassium replacement. Look for hyponatraemia/hypernatraemia, hypokalaemia, metabolic acidosis (low bicarbonate), pre-renal AKI (raised urea, raised creatinine).
• Venous blood gas — bedside in any severely dehydrated or acidotic child. Confirms metabolic acidosis (low pH, low HCO₃⁻, normal PaCO₂ with compensatory fall) and identifies hyper- or hyponatraemia.
• Blood glucose — every severely dehydrated or malnourished child. Hypoglycaemia is easily missed and rapidly fatal.
• Full blood count — leucocytosis and left shift in bacterial invasive disease; marked leucocytosis with fragmented red cells and falling platelets is the HUS signature; thrombocytopenia also in sepsis and dengue.
• Blood culture — before antibiotics if bacteraemia suspected, especially infants under 3 months and immunocompromised.
• CRP / procalcitonin — non-specific; may support bacterial cause but not diagnostic alone.[6]

Urine tests

• Urinalysis and culture — mandatory in any infant under 3 months with vomiting or unexplained fever, and in any child where urine output is hard to assess. UTI commonly co-presents with or mimics AGE.[2]

Imaging

• Abdominal ultrasound — if intussusception, appendicitis, malrotation, or HUS (to look for colonic wall thickening) is suspected.
• Chest X-ray — if pneumonia is in the differential.
• Abdominal X-ray — only if toxic megacolon, perforation, or Hirschsprung enterocolitis is suspected (pneumatosis intestinalis, free air).[1]

What is NOT routinely required

• Routine stool culture in simple watery AGE.
• Routine electrolytes in no-dehydration / some-dehydration managed at home.
• Routine imaging.
• Sigmoidoscopy in acute AGE (reserved for suspected IBD or C. difficile with diagnostic uncertainty).[6]

Management — Resuscitation

Resuscitation is dictated by dehydration severity. The key principle is that most children can and should be rehydrated enterally — ESPGHAN states that enteral rehydration is superior to intravenous rehydration, and IV fluids are reserved for the severely dehydrated and those who cannot tolerate oral fluids.[1]

Plan C — severe dehydration (the resuscitation bundle)

Step 1 — IV access immediately (intraosseous if needed) and start intravenous rehydration.[18]

Step 2 — WHO plan C rapid rehydration: Ringer's lactate 100 mL/kg over 3 hours (over 6 hours if under 1 year), incorporating 0.9% saline boluses for children with shock — exactly as implemented in the GASTRO trial of plan C versus slow rehydration.[18]

Step 3 — reassess continuously between boluses: pulse, capillary refill, skin temperature, conscious level, urine output. Rapid large-volume regimens have not proved superior: a systematic review found large-volume (60 mL/kg/h) IV rehydration no better than standard (20 mL/kg/h), with possible longer time-to-discharge and higher readmission; standard-volume IV rehydration for 1 to 4 hours followed by oral hydration suffices for most children.[19] In GASTRO, slower rehydration (the same 100 mL/kg over 8 hours, without boluses) was as safe as plan C with no difference in correction of dehydration or time to discharge.[18]

Step 4 — once shock is reversed, switch to deficit correction with ORS where possible — enteral rehydration is superior to continued IV therapy, and ultrarapid IV schemes are not superior to standard schemes (and may carry higher readmission rates).[1] Add ongoing stool losses with ORS wherever tolerated.

Step 5 — check blood glucose and electrolytes early in every severely dehydrated child; treat hypoglycaemia promptly with IV dextrose and correct sodium derangements slowly (see Complications).[1]

Key resuscitation pitfalls

• Not reassessing between boluses — fluid overload risk, especially in cardiac or malnourished children.
• Treating with hypotonic or dextrose-containing fluids as the resuscitation fluid — ineffective for volume expansion.
• Stopping ORS / feeds prematurely — breastfeeding and feeding should not be interrupted.[1]
• Failing to give zinc — zinc supplementation during acute diarrhoea is recommended by WHO and UNICEF.[3]

Shock / collapse

If the child is in undifferentiated shock, secure IV access and give isotonic fluid per the plan C schedule above (with saline boluses for shock), check blood glucose, and treat suspected bacterial sepsis with antibiotics.[18] AGE may co-present with sepsis, or be the misdiagnosis for sepsis, DKA, or a surgical abdomen.

Management — Definitive & Stepwise

The four pillars of definitive management of acute watery AGE, in order of importance:[1]

1. Rehydrate — oral rehydration with hypo-osmolar ORS is the major treatment and should start as soon as possible.[1]
2. Give zinc — WHO recommends 20 mg of zinc per day for 10 to 14 days.[14]
3. Continue feeding (and breastfeeding — it should not be interrupted).[1]
4. Selective adjunctive therapy — a single oral dose of ondansetron for vomiting;[4] probiotics: current Cochrane evidence is that they probably make little or no difference to diarrhoea lasting 48 hours or longer.[5]

Plan A — no dehydration (home management)

Plan A is also the counselling plan given to every caregiver regardless of dehydration grade. The components are:[6]

1. Give extra fluids — ORS is the mainstay; continue breastfeeding. Avoid sugary or carbonated drinks and diluted/concentrated feeds.[1]
2. Give ORS after each loose stool, in small sips — continue for as long as the diarrhoea continues.
3. Give zinc — WHO recommends 20 mg of zinc per day for 10 to 14 days.[14] (Note: the Cochrane evidence base does not support benefit in infants under 6 months — see below.)
4. Continue feeding — never stop feeds; resume a normal age-appropriate diet as soon as rehydration is achieved; breastfeeding on demand.
5. Return immediately if danger signs develop (see below).[1]

Plan B — some dehydration (clinic management)

• Give ORS in the clinic under supervision — enteral rehydration with hypo-osmolar solution is the major treatment and the superior route.[1]
• Method: small, frequent sips by spoon or cup; if the child vomits, pause briefly, then resume slowly.
• If unable to tolerate orally, NG-tube ORS remains enteral rehydration and is preferable where IV therapy is not indicated.[1]
• Continue breastfeeding throughout — it should not be interrupted.[1]
• Reassess after the supervised rehydration period: re-classify dehydration, de-escalate to home care if improved, or escalate to IV therapy if now severe.

Zinc supplementation

Dose: WHO recommends 20 mg of zinc per day for 10 to 14 days for children with acute diarrhoea.[14] The Cochrane review (Lazzerini & Wanzira 2016 — 33 trials, 10,841 children) found that in children over 6 months zinc may shorten acute diarrhoea by around half a day (MD −11.46 hours, 95% CI −19.72 to −3.19) and probably reduces the proportion still with diarrhoea on day 7 (RR 0.73, 95% CI 0.61 to 0.88); in children with signs of malnutrition the effect is greater — around a day (MD −26.39 hours).[3] Zinc increased vomiting (RR 1.57 over 6 months of age), and the review does not support zinc in infants under 6 months (no benefit demonstrated), in well-nourished children, or where zinc deficiency is uncommon.[3] A 2020 randomized trial in 4,500 children aged 6 to 59 months found lower doses (5 mg or 10 mg daily for 14 days) non-inferior to 20 mg with significantly less vomiting.[14]

ORS formulation

[13] [6]

Antiemetics — ondansetron

A single oral dose of ondansetron reduces vomiting and facilitates oral rehydration. In the Freedman NEJM trial (215 children aged 6 months to 10 years), ondansetron reduced vomiting during oral rehydration (14% vs 35%; RR 0.40), increased oral intake, and reduced IV rehydration (14% vs 31%; RR 0.46), with no significant difference in hospitalisation (4% vs 5%).[4] Meta-analyses confirm a reduced risk of failed oral rehydration (RR 0.50), reduced hospitalisation (RR 0.53), and reduced need for IV rehydration (RR 0.45).[8] Cautions:

• Routine use requires safety clearance, given the warning about severe cardiac effects (QT prolongation) — check electrolytes and avoid other QT-prolonging drugs.[1]
• Diarrhoea was reported as a side-effect in four of the five ondansetron studies in the Cochrane review.[7]
• Do not substitute antiemetics for rehydration — they are an adjunct to oral rehydration therapy.[8]

Probiotics

Current Cochrane evidence (82 studies, 12,127 participants) is that probiotics probably make little or no difference to the number of children with diarrhoea lasting 48 hours or longer, and it remains uncertain whether they shorten the duration; ESPGHAN nonetheless lists specific probiotics (Lactobacillus GG, Saccharomyces boulardii) among interventions that may reduce the duration and severity of diarrhoea.[5][1]

Antibiotics — when (and when NOT)

[1]

Nutrition — continue feeding

WHO-aligned (ESPGHAN) guidance: continue breastfeeding throughout; regular feeding should continue with no dietary changes including milk; do not "rest the gut". In the hospital setting, in non-breast-fed infants and young children, lactose-free feeds can be considered; resume standard feeds once stools normalise.[1]

When to admit

• Severe dehydration requiring intravenous rehydration.
• Persistent vomiting unable to tolerate ORS despite ondansetron.
• Bloody diarrhoea with systemic toxicity, or suspected HUS.
• Infants under 6 months, malnourished, immunocompromised.
• High stool output needing measured replacement.
• Social concerns — caregiver unable to manage home care reliably. ESPGHAN: hospitalisation is generally reserved for children requiring enteral or parenteral rehydration; most cases are managed as outpatients.[1]

When to discharge

• Adequate rehydration, tolerating oral fluids.
• Caregiver competent in Plan A and zinc administration.
• No red flags (no bloody diarrhoea, no high output, no HUS).
• Clear "return immediately" advice given.[6]

Specific Subtypes & Scenarios

Rotavirus AGE

The single agent causing the most diarrhoea-related deaths in children under 5 in high-mortality countries, and a common cause of diarrhoea-related admissions in low-mortality countries; before routine vaccination about 80% of US children had rotavirus gastroenteritis by age 5, causing an estimated 55,000 to 70,000 hospitalisations annually.[10][17] It destroys mature villous enterocytes with transient lactase deficiency and reduced disaccharidase activity. Clinical: vomiting typically precedes watery diarrhoea, with low-grade fever. Vaccine (live-attenuated oral): ACIP schedules are RV5 (RotaTeq, pentavalent) at ages 2, 4 and 6 months or RV1 (Rotarix, monovalent) at ages 2 and 4 months; the recommendations also address maximum ages for doses.[17] Efficacy (Cochrane, 55 trials, 216,480 participants): RV1 prevents 84% and RV5 probably 92% of severe rotavirus diarrhoea in the first year of life in low-mortality countries; in high-mortality countries protection is lower (RV1 63%, RV5 57%, Rotavac 57% in India) but more episodes are prevented — and no increased risk of serious adverse events or intussusception was detected.[10]

E. coli — the pathotypes

• ETEC (enterotoxigenic): heat-labile (cholera-like, ADP-ribosylation) and heat-stable toxins; watery diarrhoea, no fever; the major cause of travellers' diarrhoea. Self-limiting; ORS.
• EPEC (enteropathogenic): attaching-and-effacing lesions; infantile diarrhoea in developing countries; persistent watery diarrhoea.
• EAEC (enteroaggregative): stacked-brick adherence; persistent diarrhoea in malnourished and HIV-positive children.
• EIEC (enteroinvasive): invasive, dysentery-like, similar to Shigella.
• EHEC / STEC (enterohaemorrhagic / Shiga-toxin-producing): O157:H7 and non-O157 serotypes. Shiga toxin (Stx1, Stx2) damages vascular endothelium → HUS. Source: undercooked beef, unpasteurised milk, contaminated water, petting zoos. Antibiotic benefit is unproven — a meta-analysis found no significantly increased HUS risk (pooled OR 1.15, 95% CI 0.79 to 1.68) — but routine use is not advised.[20]

Shigellosis

The prototype of bacillary dysentery. S. sonnei (mild), S. flexneri (developing countries), S. dysenteriae type 1 (most severe, produces Shiga toxin). Highly infectious — only 10 to 100 organisms. Clinical: high fever, abdominal cramps, tenesmus, bloody mucoid stool, faecal leucocytes. Complications: seizures (especially S. flexneri in infants — neurotoxic, may precede the diarrhoea), toxic megacolon, intestinal perforation, haemolytic-uraemic syndrome (with S. dysenteriae type 1), reactive arthritis, leukaemoid reaction. Treatment: azithromycin or ceftriaxone — multidrug resistance is now widespread.[9]

Non-typhoidal Salmonella

Food-borne (poultry, eggs, reptiles). Self-limiting watery diarrhoea, sometimes bloody, with fever and abdominal cramps; bacteraemia in infants under 3 months, immunocompromised, and sickle-cell disease (risk of osteomyelitis). Antibiotics reserved for high-risk groups; otherwise avoid (prolongs carriage).[10]

Campylobacter jejuni

Invasive; bloody diarrhoea with abdominal pain that may mimic appendicitis or surgical abdomen. Guillain-Barré syndrome in ~1 in 1,000 cases, 1 to 3 weeks after, mediated by anti-GQ1b antibodies. Treatment: azithromycin if severe; supportive otherwise.[3]

Vibrio cholerae

Profuse rice-water stool, vomiting, rapid and severe dehydration, no fever. Treatment is aggressive rehydration (WHO plan C: Ringer's lactate with saline boluses for shock[18]) plus an antimicrobial: single-dose azithromycin 20 mg/kg (max 1 g) is as effective as 3-day erythromycin in children and causes less vomiting.[15] Hand-washing, safe water, and cholera vaccination support outbreak control.

Giardia lamblia

Foul-smelling greasy stool that floats, bloating, flatulence, no blood, no fever, persistent (over 7 to 14 days). Microscopy shows trophozoites or cysts; antigen detection is more sensitive. Treatment: metronidazole or tinidazole — an exceptional, organism-specific indication for anti-infective therapy in AGE.[1]

Entamoeba histolytica

Bloody mucoid diarrhoea with abdominal pain; risk of amoebic liver abscess (right upper quadrant pain, swinging fever). Treatment: a nitroimidazole (metronidazole or tinidazole) followed by a luminal agent (e.g., paromomycin) to clear cysts — again an exceptional indication for anti-infectives.[1]

C. difficile colitis

Recent antibiotics or hospitalisation; watery or bloody diarrhoea, abdominal pain, marked leucocytosis, hypoalbuminaemia, pseudomembranous colitis. Treatment: stop inciting antibiotic; oral metronidazole (mild–moderate) or oral vancomycin (severe) for 10 to 14 days; fidaxomicin in recurrent disease.[3]

Cryptosporidium

Common in HIV / immunocompromised children; persistent watery diarrhoea; acid-fast oocysts on modified Ziehl-Neelsen stain. Treatment: nitazoxanide; supportive + immune reconstitution in HIV.[3]

Surgical mimics — intussusception

Age 6 to 36 months; intermittent colicky abdominal pain, drawing up of legs, vomiting, eventually redcurrant-jelly stool (late sign). Sausage-shaped mass in right upper quadrant; empty right lower quadrant (Dance sign). Ultrasound shows target / doughnut sign. Treat with air or contrast enema reduction (radiology) or surgery if unstable / unsuccessful. Distinguish from AGE: intussusception has episodic pain and mass, AGE has continuous diarrhoea.[3]

Complications & Pitfalls

[1]

Prognosis & Disposition

• Overall mortality is very low in well-nourished children with access to ORS; severe dehydration untreated can be fatal within hours (especially cholera in infants).
• Most viral AGE resolves in 5 to 7 days; bacterial invasive disease 1 to 2 weeks.
• HUS mortality 3 to 5%; long-term renal sequelae (hypertension, proteinuria, CKD) in 10 to 30% of survivors of typical HUS.
• Persistent diarrhoea suggests alternative diagnosis; needs investigation.
• Disposition: home (Plan A, reliable caregiver); short-stay / clinic observation (Plan B); inpatient (Plan C, infants under 6 months, malnourished, immunocompromised, suspected HUS, surgical differential); ICU (shock, severe sepsis, HUS with multi-organ failure).[6]

Special Populations

Infants under 6 months

• Higher risk of dehydration per kilogram of stool loss.
• Breastfeed on demand; feeding and breastfeeding should not be interrupted.[1]
• Zinc: the Cochrane evidence does not support zinc supplementation in infants under 6 months (no benefit on duration or day-7 persistence demonstrated).[3]
• Lower threshold to investigate — urinalysis and culture; consider sepsis workup.
• Use caution with antiemetics: ondansetron's routine use requires safety clearance because of the cardiac (QT) warning, and trial evidence starts at 6 months of age.[1][4]

Severe acute malnutrition (SAM)

• Oedema masks dehydration — weight change is unreliable in severe malnutrition; rely on lethargy, sunken eyes and skin pinch.
• Rehydrate slowly with a modified, lower-sodium ORS (ReSoMal) — slower than in well-nourished children; in the GASTRO trial even slower rehydration (100 mL/kg over 8 h) was as safe as rapid plan C in severe dehydration.[18]
• Avoid rapid IV boluses — risk of fluid overload and heart failure.
• Check and treat hypoglycaemia, hypothermia, and severe infection.
• Empirical broad-spectrum antibiotics for severe malnutrition with dehydration per WHO practice.[18]

Immunocompromised (HIV, chemotherapy, transplant)

• Persistent, atypical organisms: Cryptosporidium, Cystoisospora, Cyclospora, CMV colitis, Mycobacterium avium complex.
• Stool workup should include acid-fast staining, viral PCR (CMV), and special cultures.
• Avoid live rotavirus vaccine in SCID.
• Coordinate care with the immunology / infectious diseases team.[1]

Post-rotavirus vaccine era

In the post-rotavirus-vaccine era, norovirus has become the leading cause of medically attended acute gastroenteritis in US children — detected in 21% of children under 5 seeking care for AGE (vs 12% rotavirus), with nearly 1 million health-care visits annually — but management principles are unchanged.[16]

Travellers

• ETEC, Giardia, Entamoeba, cholera, hepatitis A, typhoid in the differential.
• Send stool microscopy and culture.
• Treat per organism.[2]

Children on long-term medications

• Steroids, immunosuppressants: invasive disease, CMV, atypical.
• Diuretics: electrolyte disturbance with AGE.
• Laxatives: confusion with cause of diarrhoea.
• Cardiac / renal: lower fluid-tolerance — manage in hospital.[3]

Evidence, Guidelines & Regional Differences

Landmark evidence

• GEMS (Kotloff 2013, Lancet) — most attributable cases of moderate-to-severe paediatric diarrhoea were due to four pathogens: rotavirus, Cryptosporidium, ST-ETEC and Shigella; odds of dying during follow-up were 8.5-fold higher in cases than controls.[2]
• Cochrane zinc (Lazzerini & Wanzira 2016) — in children over 6 months zinc may shorten acute diarrhoea by around half a day and probably reduces persistence to day 7; greater effect (about a day) with malnutrition; no support for use under 6 months.[3]
• Zinc dosing (Dhingra NEJM 2020) — WHO recommends 20 mg/day for 10 to 14 days; 5 mg and 10 mg doses were non-inferior with less vomiting.[14]
• Reduced-osmolarity ORS (Hahn et al. BMJ 2001; CHOICE Pediatrics 2001) — reduced-osmolarity ORS (245 mOsm/L, Na 75 mmol/L) means fewer unscheduled IV infusions, lower stool output and less vomiting than standard WHO ORS, without a significant difference in hyponatraemia.[6][13]
• Freedman NEJM 2006; Tomasik meta-analysis 2016; Fedorowicz Cochrane 2011 — a single oral dose of ondansetron reduces vomiting (14% vs 35%) and IV rehydration need (14% vs 31%); pooled: fewer hospitalisations (RR 0.53).[4][8][7]
• Probiotics for acute infectious diarrhoea (Collinson Cochrane 2020) — probiotics probably make little or no difference to diarrhoea lasting 48 hours or longer; duration effect uncertain.[5]
• Cochrane rotavirus vaccines (Soares-Weiser 2019) — RV1 prevents 84% and RV5 probably 92% of severe rotavirus diarrhoea at 1 year in low-mortality countries; lower in high-mortality countries (RV1 63%, RV5 57%); no increased risk of serious adverse events or intussusception.[10]
• WHO plan C evaluated (GASTRO, BMC Med 2019) — plan C rapid rehydration (Ringer's lactate 100 mL/kg over 3 h, 6 h if under 1 year, with 0.9% saline boluses for shock) versus slow rehydration over 8 h: no difference in safety, dehydration correction or discharge timing.[18]

Guidelines

• WHO — rehydration plans for no/some/severe dehydration; plan C for severe dehydration = Ringer's lactate 100 mL/kg over 3 h (6 h if under 1 year) with 0.9% saline boluses for shock (as formally evaluated in GASTRO); zinc 20 mg/day for 10 to 14 days; continued feeding.[18][14]
• ESPGHAN / ESPID 2014 — hypo-osmolar ORS is the major treatment; continue feeding/breastfeeding; enteral rehydration superior to IV; ultrarapid IV not superior; ondansetron effective but needs cardiac-safety clearance; anti-infectives exceptional.[1]
• ACIP (CDC, 2009) — routine rotavirus vaccination of infants: RV5 at 2, 4, 6 months or RV1 at 2 and 4 months, with maximum-age limits addressed in the recommendations.[17]
• India (ICMR/National programmes) — high-burden setting where rotavirus vaccine (including the India-developed Rotavac, WHO-prequalified) and ORS-plus-zinc co-packaging are central to national programme strategy.[10]

Regional / practice deltas

• India / South Asia: very high burden; cholera, Shigella, typhoid; rotavirus vaccine is part of the UIP (Rotavac / Rotasiil). Zinc-ORS co-packaging is government standard.
• Africa: high Cryptosporidium (HIV) and cholera outbreaks; ORS access a barrier; WHO programmes central.
• High-income / west: norovirus is now the leading cause of medically attended AGE in children (US data, post-rotavirus vaccine).[16]
• WHO programmes emphasise ORS, zinc and rotavirus vaccine as the priority interventions for reducing diarrhoea burden and mortality.[2][10]

Controversies

• Stool PCR panels detect DNA, not viable organisms — risk of treating colonisation rather than disease.
• Antiemetics and probiotics are recommended by Western guidelines but less universally adopted in WHO programmes.
• Eculizumab in typical HUS remains controversial; reserved for severe / atypical HUS.
• Lactose-free formula in routine AGE — not required; trial only in proven secondary lactose intolerance.[5]

Exam Pearls

• Rotavirus = the single agent causing most under-5 diarrhoeal deaths in high-mortality countries.[10]
• GEMS four: rotavirus, Cryptosporidium, ST-ETEC, Shigella.[2]
• WHO plan C (severe dehydration): Ringer's lactate 100 mL/kg over 3 h (6 h if under 1 year), with 0.9% saline boluses for shock.[18]
• ORS — sodium 75, glucose 75 mmol/L, total osmolarity 245 mOsm/L (reduced-osmolarity formula; CHOICE trial composition).[13]
• Zinc 20 mg/day for 10 to 14 days — WHO-recommended; lower doses (5 to 10 mg) may be equally effective with less vomiting; not supported under 6 months.[14][3]
• Continue feeding and breastfeeding — never stop.
• Ondansetron (single oral dose) reduces vomiting (14% vs 35%), IV rehydration need (14% vs 31%) and, in pooled analyses, hospitalisation (RR 0.53).[4][8]
• Loperamide is contraindicated in young children and not recommended in older children with AGE.
• EHEC (E coli O157:H7) → HUS: triad of microangiopathic haemolytic anaemia + thrombocytopenia + AKI; antibiotics show no proven benefit (meta-analysis: no significant HUS-risk increase — pooled OR 1.15).[20]
• Antibiotics are NOT routine — anti-infectives are exceptional: Shigella, cholera, amoebic dysentery, Giardia.[1]
• Bloody diarrhoea: think Shigella, Campylobacter, EHEC, EIEC, Entamoeba.
• Foul-smelling greasy floating stool: Giardia — treat with metronidazole or tinidazole.
• Rice-water stool, no fever, rapid dehydration: cholera — rehydrate (plan C) and give single-dose azithromycin 20 mg/kg.[15]
• Severe dehydration (plan C): rapid IV Ringer's lactate 100 mL/kg over 3 h (6 h if under 1 year), saline boluses for shock; rapid large-volume regimens offer no advantage over standard volumes.[18][19]
• Metabolic acidosis from bicarbonate loss in stool; hypokalaemia from stool potassium loss.
• Hypernatraemic dehydration: doughy skin, irritability; correct sodium slowly.[1]
• Skin pinch very slow + lethargic + cannot drink = severe dehydration (plan C).[1]
• Hypoglycaemia — easy to miss in malnourished infants; check glucose and treat with IV dextrose.
• Rotavirus vaccine prevents 84% (RV1) / probably 92% (RV5) of severe rotavirus diarrhoea at 1 year in low-mortality countries; lower in high-mortality settings; no excess intussusception.[10]
• Redcurrant-jelly stool with episodic colic and a sausage-shaped mass in a 6 to 36 month-old = intussusception, not AGE.
• Vomiting + acidotic breathing + weight loss in a young child = exclude DKA.
• Vomiting with no wet nappy for many hours and reduced oral intake: a febrile infant = UTI / sepsis until proven otherwise — urinalysis is mandatory.

Exam application bank (NEET-PG / INICET)

One-line answer

Acute gastroenteritis (AGE) = diarrhoea and/or vomiting from GI infection. Rotavirus causes more under-5 diarrhoeal deaths than any other single agent in high-mortality countries; post-vaccine, norovirus is the leading cause of medically attended AGE in US children. WHO treats dehydration stepwise: plan C for severe dehydration = Ringer's lactate 100 mL/kg over 3 h (6 h if under 1 year) with 0.9% saline boluses for shock; hypo-osmolar ORS (245 mOsm/L) is the major treatment; enteral beats IV; continue feeding and breastfeeding; zinc 20 mg/day for 10 to 14 days (WHO); single-dose oral ondansetron reduces vomiting and IV need; EHEC (E coli O157:H7) causes HUS (microangiopathic haemolytic anaemia + thrombocytopenia + AKI) — antibiotics unproven there; antibiotics otherwise only for Shigella, cholera (single-dose azithromycin 20 mg/kg in children) and amoebic dysentery.[10][16][18][13][1][14][4][20][15]

Worked stems (answer without another resource)

Stem 1 — Classic presentation. Map symptoms to mechanism; name the first investigation and first treatment step with dose/route if drug therapy is standard.[3]

Stem 2 — Unstable / complicated. List red flags that force immediate resuscitation, theatre, ICU, antidote, or reperfusion — and what you do in the first 15 minutes.[1]

Stem 3 — Atypical group. Elderly, pregnancy, child, or immunocompromised: how presentation and thresholds change.[1]

Stem 4 — Differential trap. Name the three closest mimics and one discriminator for each.[1]

Stem 5 — Disposition. Who goes home with safety-netting, who is admitted, who needs HDU/ICU/theatre, and what follow-up is mandatory.[11]

Rapid viva checklist

1. Definition + classification
2. Pathophysiology chain
3. Bedside signs / criteria
4. Score with exact components (if any)
5. Emergency bundle
6. Definitive therapy with doses
7. Complications of disease and of treatment
8. Special populations
9. Guideline/trial name if classic
10. Three exam traps

Coverage self-check

If you cannot answer any stem above from this page alone, re-read the matching section — the page is intended to be self-sufficient for final-prof and NEET-PG/INICET questions on Acute Gastroenteritis in Children.

References

1. [1]Guarino A, Ashkenazi S, Gendrel D, et al. European Society for Pediatric Gastroenterology, Hepatology, and Nutrition/European Society for Pediatric Infectious Diseases evidence-based guidelines for the management of acute gastroenteritis in children in Europe: update 2014. Journal of pediatric gastroenterology and nutrition, 2014.PMID 24739189
2. [2]Kotloff KL, Nataro JP, Blackwelder WC, et al. Burden and aetiology of diarrhoeal disease in infants and young children in developing countries (the Global Enteric Multicenter Study, GEMS): a prospective, case-control study. Lancet, 2013.PMID 23680352
3. [3]Lazzerini M, Wanzira H. Oral zinc for treating diarrhoea in children. Cochrane Database of Systematic Reviews, 2016.PMID 27996088
4. [4]Freedman SB, Adler M, Seshadri R, Powell EC. Oral ondansetron for gastroenteritis in a pediatric emergency department. New England Journal of Medicine, 2006.PMID 16625009
5. [5]Collinson S, Tarring N, Bhatnagar S, et al. Probiotics for treating acute infectious diarrhoea. Cochrane Database of Systematic Reviews, 2020.PMID 33295643
6. [6]Hahn S, Kim Y, Garner P Reduced osmolarity oral rehydration solution for treating dehydration due to diarrhoea in children: systematic review. BMJ (Clinical research ed.), 2001.PMID 11451782
7. [7]Fedorowicz Z, Jagannath VA, Carter B Antiemetics for reducing vomiting related to acute gastroenteritis in children and adolescents. The Cochrane database of systematic reviews, 2011.PMID 21901699
8. [8]Tomasik E, Szymanska I, Wysocki J, et al. Systematic review with meta-analysis: ondansetron for vomiting in children with acute gastroenteritis. Alimentary Pharmacology & Therapeutics, 2016.PMID 27401959
9. [9]Kotloff KL, Riddle MS, Platts-Mills JA, Pavlinac P, Zaidi AKM. Shigellosis. Lancet Infectious Diseases, 2018.PMID 29254859
10. [10]Soares-Weiser K, Bergman H, Henschke N, et al. Vaccines for preventing rotavirus diarrhoea: vaccines in use. Cochrane Database of Systematic Reviews, 2019.PMID 31684685
11. [11]Guarino A, Ashkenazi S, Lo Vecchio A, et al. Acute gastroenteritis in children of the world: what needs to be done? Journal of Pediatric Gastroenterology and Nutrition, 2020.PMID 32079974
12. [12]Freedman SB, Vandermeer B, Milne A, Hartling L. Acute infectious pediatric gastroenteritis: beyond oral rehydration therapy. Expert Opinion on Pharmacotherapy, 2007.PMID 17685883
13. [13]CHOICE Study Group Multicenter, randomized, double-blind clinical trial to evaluate the efficacy and safety of a reduced osmolarity oral rehydration salts solution in children with acute watery diarrhea. Pediatrics, 2001.PMID 11335732
14. [14]Dhingra U, Kisenge R, Sudfeld CR, et al. Lower-Dose Zinc for Childhood Diarrhea - A Randomized, Multicenter Trial. New England Journal of Medicine, 2020.PMID 32966722
15. [15]Khan WA, Saha D, Rahman A, et al. Comparison of single-dose azithromycin and 12-dose, 3-day erythromycin for childhood cholera: a randomised, double-blind trial. Lancet, 2002.PMID 12480424
16. [16]Payne DC, Vinje J, Szilagyi PG, et al. Norovirus and medically attended gastroenteritis in U.S. children. New England Journal of Medicine, 2013.PMID 23514289
17. [17]Cortese MM, Parashar UD; Centers for Disease Control and Prevention (CDC) Prevention of rotavirus gastroenteritis among infants and children: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recommendations and Reports, 2009.PMID 19194371
18. [18]Houston KA, Gibb J, Olupot-Olupot P, et al. Gastroenteritis aggressive versus slow treatment for rehydration (GASTRO): a phase II rehydration trial for severe dehydration: WHO plan C versus slow rehydration. BMC Medicine, 2019.PMID 31256761
19. [19]Toaimah FH, Mohammad HM Rapid Intravenous Rehydration Therapy in Children With Acute Gastroenteritis: A Systematic Review. Pediatric Emergency Care, 2016.PMID 26835574
20. [20]Safdar N, Said A, Gangnon RE, Maki DG Risk of hemolytic uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 enteritis: a meta-analysis. JAMA, 2002.PMID 12190370