Acute Diarrhoea & ORS Therapy

Acute diarrhoea remains a leading cause of under-5 mortality in India, and the WHO/UNICEF low-osmolarity ORS + zinc package is among the highest-yield Paediatrics topics in NEET PG. Master dehydration grading (Plan A/B/C), ORS composition, organism-by-age associations, and the narrow set of antibiotic indications.

Definitions & Classification

Diarrhoea = passage of ≥3 loose or watery stools in 24 hours (or a stool consistency change abnormal for the child; for breastfed infants, frequency alone is not diagnostic). It is classified by duration and by mechanism/clinical type.

Type (by duration)	Cut-off	Common causes
Acute watery diarrhoea	< 14 days	Rotavirus, ETEC, V. cholerae, norovirus
Acute bloody diarrhoea (dysentery)	< 14 days, visible blood	Shigella (#1), EHEC, Entamoeba, Campylobacter
Persistent diarrhoea	≥ 14 days	EAEC, post-infectious, malnutrition
Chronic diarrhoea	> 4 weeks	Coeliac, IBD, malabsorption

High-yield: Persistent diarrhoea is defined as ≥14 days; if it begins acutely (infective) it is "persistent", whereas "chronic" (>4 weeks) leans non-infective/malabsorptive. Shigella is the commonest cause of acute bloody diarrhoea (dysentery) worldwide.

Mechanistic types:

• Secretory — toxin-driven (cholera, ETEC), high-volume, persists on fasting, normal osmolar gap. Net Cl⁻/water secretion via cAMP.
• Osmotic — unabsorbed solute (lactose intolerance, magnesium), stops on fasting, high stool osmolar gap (>100).
• Inflammatory/invasive — mucosal invasion (Shigella, EIEC, Salmonella), blood + leucocytes in stool.

Etiology by Age Group

Age / setting	Most likely organism
Infants (overall #1 viral cause worldwide)	Rotavirus
Traveller's diarrhoea	ETEC (heat-labile LT + heat-stable ST toxins)
Bloody diarrhoea, child	Shigella (most common); Shigella flexneri in developing world
Rice-water stools, epidemic	Vibrio cholerae O1/O139
Poultry/eggs, non-typhoidal	Salmonella (Non-Typhoidal)
HUS after bloody diarrhoea	EHEC O157:H7 (Shiga toxin)
Day-care, cruise ships, winter	Norovirus
Pseudoappendicitis, mesenteric adenitis	Yersinia enterocolitica
Antibiotic-associated colitis	Clostridioides difficile
Persistent diarrhoea, immunocompromised	Cryptosporidium, Giardia

High-yield: Rotavirus is the single commonest cause of severe dehydrating diarrhoea in children < 2 yrs; diagnosed by stool ELISA/latex agglutination; prevented by oral live rotavirus vaccine (Rotavac/Rotarix). Peak incidence in cooler/winter months.

Pathophysiology pearls:

• Cholera toxin → ADP-ribosylation of Gs → permanently active adenylate cyclase → ↑cAMP → massive Cl⁻/HCO₃⁻/water secretion.
• ETEC LT mimics cholera toxin (↑cAMP); ST acts via ↑cGMP.
• Shiga toxin (Shigella, EHEC) inhibits 60S ribosomal subunit → cytotoxic; triggers HUS (microangiopathic haemolytic anaemia + thrombocytopenia + AKI).

Assessment of Dehydration (WHO/IMNCI)

The cornerstone of management is classifying dehydration, which dictates the treatment Plan (A/B/C).

Sign	No dehydration	Some dehydration	Severe dehydration
Mental state	Well, alert	Restless, irritable	Lethargic / unconscious
Eyes	Normal	Sunken	Very sunken, dry
Thirst	Drinks normally	Eager, thirsty	Drinks poorly / unable
Skin pinch	Goes back instantly	Goes back slowly	Goes back very slowly (>2 s)
Fluid deficit	< 5%	5–10%	> 10%
WHO Plan	Plan A	Plan B	Plan C

High-yield: Per IMNCI, two or more signs (including at least one key sign — lethargy/unconsciousness, sunken eyes, not able to drink/drinking poorly, very slow skin pinch) define the category. To classify severe, at least one key sign must be present. The two most reliable clinical signs are prolonged skin pinch and altered consciousness/eyes.

Mnemonic for severe dehydration ("the 4 deadly Ds"): Drowsy/unconscious, Deep sunken eyes, Drinks poorly, Delayed skin pinch (>2 s).

Capillary refill > 3 s, absent tears, dry mucous membranes, sunken fontanelle (infants), tachycardia, low urine output and weight loss are supportive. Weight loss best quantifies deficit: 5% (mild), 5–10% (moderate), >10% (severe).

The Treatment Plans

Stepwise IMNCI decision: Assess hydration → classify (A/B/C) → treat dehydration → give zinc → continue feeding → advise on danger signs/return → follow-up.

Plan A — No dehydration (home management)

Four rules of home therapy:

1. More fluids than usual — ORS + home fluids (rice water, soup, buttermilk, breast milk). Avoid sugary drinks/colas.
   • ORS after each loose stool: < 2 yrs: 50–100 mL; 2–10 yrs: 100–200 mL; older/adult: ad libitum.
2. Zinc for 14 days (see below).
3. Continue feeding — never stop breastfeeding; continue age-appropriate diet (no diluting feeds, no "gut rest").
4. When to return — recognise danger signs: blood in stool, repeated vomiting, fever, drinking poorly, no improvement in 3 days, sunken eyes.

Plan B — Some dehydration (ORS, supervised at facility)

• ORS volume = 75 mL/kg over 4 hours (the classic NEET cut-off). If weight unknown, estimate by age.
• Reassess at 4 hours and reclassify. If improved → Plan A; if worsened → Plan C.
• Continue breastfeeding; give zinc.
• Nasogastric ORS (20 mL/kg/hr) if persistent vomiting or unable to drink but not in shock.

High-yield: Plan B ORS dose = 75 mL/kg over the first 4 hours. Vomiting is not a contraindication — give ORS slowly (small sips/spoonfuls every 1–2 min); vomiting usually settles as rehydration proceeds.

Plan C — Severe dehydration (IV, emergency)

Give Ringer Lactate (or normal saline if RL unavailable) IV.

Age	First bolus	Then
< 12 months	30 mL/kg over 1 hour	70 mL/kg over 5 hours
≥ 12 months	30 mL/kg over 30 minutes	70 mL/kg over 2.5 hours

• Total = 100 mL/kg IV. Reassess every 15–30 min; repeat bolus if radial pulse still weak/absent.
• Start ORS (5 mL/kg/hr) as soon as the child can drink (usually within 3–4 hrs).
• Reassess and reclassify after the full IV course.

High-yield: Severe dehydration total IV fluid = 100 mL/kg of Ringer Lactate (30 + 70). Infants get the first 30 mL/kg over 1 hour; older children over 30 minutes. RL is preferred over normal saline (saline lacks bicarbonate precursor/potassium).

ORS — Composition (Low-Osmolarity, WHO 2002)

The reduced-osmolarity ORS replaced the older 311 mOsm/L formula and is now standard.

Component	Low-osmolarity ORS (mmol/L)
Sodium (Na⁺)	75
Glucose (anhydrous)	75
Potassium (K⁺)	20
Chloride (Cl⁻)	65
Citrate (trisodium)	10
Total osmolarity	245 mOsm/L

Mnemonic (Na : Glucose): "75–75" — Na⁺ 75 and glucose 75, total 245.

High-yield: Low-osmolarity ORS (245 mOsm/L, Na 75, glucose 75) reduces stool output, vomiting and the need for unscheduled IV fluids compared with the old 311 mOsm/L solution. Mechanism: Na⁺-glucose co-transport (SGLT1) in the small-bowel enterocyte drives water absorption — intact even in secretory diarrhoea, which is why ORS "works" in cholera.

• The 1:1 molar ratio of Na to glucose (and total glucose ≤ Na or balanced) is essential for optimal co-transport; excess glucose causes osmotic diarrhoea.
• ORS does NOT reduce stool frequency/duration — it prevents/treats dehydration. (Zinc reduces duration & severity.)
• Hypo-osmolar ORS caution: slightly higher risk of transient hyponatraemia, especially in adults with cholera — but benefits outweigh in children.

Zinc Supplementation

High-yield (very frequently asked): Give zinc to every child with diarrhoea for 14 days:

• < 6 months: 10 mg/day
• ≥ 6 months: 20 mg/day

Zinc reduces duration and severity of the current episode and lowers incidence of diarrhoea for 2–3 months afterwards (restores epithelial integrity, immune function, brush-border enzymes).

Feeding & Antibiotics

Feeding: Continue breastfeeding throughout. Resume normal energy-dense diet quickly. Avoid lactose restriction routinely; only consider lactose-free feeds in documented secondary lactose intolerance (persistent diarrhoea worsening with milk).

Antibiotics — used in only a minority of cases:

Indication	Drug of choice
Cholera (severe, confirmed/suspected)	Azithromycin (children); doxycycline/tetracycline (adults)
Shigella dysentery	Ciprofloxacin or Azithromycin (ceftriaxone)
Amoebic dysentery (E. histolytica)	Metronidazole + luminal agent (diloxanide furoate)
Giardiasis	Metronidazole / tinidazole
Cryptosporidiosis	Nitazoxanide
C. difficile	Oral vancomycin / fidaxomicin / metronidazole
Typhoid	Ceftriaxone / azithromycin

High-yield: Routine antibiotics are NOT indicated in acute watery diarrhoea (mostly viral/self-limiting). Antibiotics are reserved for dysentery (bloody stool), suspected cholera with severe dehydration, and identified parasites. In suspected EHEC O157:H7, avoid antibiotics and antimotility agents — they increase the risk of HUS.

Drugs to AVOID in children:

• Antimotility agents (loperamide, diphenoxylate) — risk of ileus, toxic megacolon, masked sequestration; contraindicated < 5 yrs.
• Antiemetics generally avoided (ondansetron sometimes used in ED to enable ORS in older children, but not routine).
• Antisecretory racecadotril (enkephalinase inhibitor) is an adjunct in some settings — reduces stool output, does not replace ORS.

IMNCI Framework (Integrated Management of Neonatal & Childhood Illness)

IMNCI assesses every sick child 0–5 yrs for main symptoms; for diarrhoea it checks: duration, blood in stool, and dehydration. Classification uses a traffic-light colour code:

• Pink (severe) → urgent referral / Plan C.
• Yellow → specific treatment at facility (some dehydration → Plan B; persistent diarrhoea/dysentery → treat).
• Green → home management (Plan A).

A diarrhoea episode is additionally classified as dysentery (blood in stool → antibiotic for Shigella) and persistent diarrhoea (≥14 days → micronutrients, refer if severe).

Complications

• Hypovolaemic shock and AKI (pre-renal) — leading cause of death.
• Electrolyte disturbances: hyponatraemia/hypernatraemia, hypokalaemia (ileus, weakness, arrhythmia), metabolic acidosis (HCO₃ loss).
• Hypernatraemic dehydration — irritability, "doughy" skin, seizures; correct slowly (Na fall < 0.5 mmol/L/hr, < 10–12 mmol/L/day) to avoid cerebral oedema.
• Hypoglycaemia — especially in malnourished infants.
• HUS — after EHEC/Shigella dysentery.
• Persistent diarrhoea, malnutrition, secondary lactose intolerance.
• Paralytic ileus (often hypokalaemia or antimotility drugs).

Key Differentials

• Intussusception — currant-jelly stools, colicky pain, sausage-shaped mass, age 6–18 months; not true diarrhoea.
• Surgical abdomen / acute appendicitis — Yersinia can mimic (pseudoappendicitis).
• Necrotising enterocolitis — neonate, bloody stools, pneumatosis intestinalis.
• UTI / systemic sepsis / otitis media / pneumonia — can present with loose stools in infants ("parenteral diarrhoea").
• Cow's milk protein allergy, coeliac disease, IBD — for persistent/chronic patterns.
• DKA — vomiting/dehydration; check glucose & ketones.

Investigations

• Acute watery diarrhoea is clinical — most need no investigation.
• Stool microscopy/culture: for dysentery, suspected cholera (hanging-drop: darting motility of V. cholerae), outbreaks.
• Stool ELISA/latex: rotavirus.
• Serum electrolytes, urea, creatinine, glucose, ABG: in severe dehydration, altered sensorium, suspected hypernatraemia, or before/while on IV fluids.
• CBC + peripheral smear + LDH + creatinine: if HUS suspected after bloody diarrhoea.

Recently asked / exam angle

• Composition of low-osmolarity ORS — Na 75, glucose 75, total osmolarity 245 mOsm/L (vs old 311). Repeatedly tested.
• Zinc dosing: 10 mg (<6 mo) / 20 mg (≥6 mo) for 14 days — "single-best-answer" favourite.
• Plan B = 75 mL/kg over 4 hrs; Plan C = 100 mL/kg Ringer Lactate (30+70 split; infant first bolus over 1 hr).
• SGLT1 (Na⁺-glucose co-transport) as the molecular basis of ORS efficacy — Physiology/Paeds overlap.
• Mechanism of cholera toxin (Gs ADP-ribosylation → ↑cAMP) and ETEC LT/ST — Microbiology crossover.
• Avoid antibiotics/antimotility in EHEC O157:H7 → HUS risk.
• Commonest cause of acute bloody diarrhoea = Shigella; commonest severe diarrhoea in infants = Rotavirus.
• IMNCI key signs for classifying severe dehydration and the traffic-light classification.
• Drug of choice: cholera in children → azithromycin; amoebiasis → metronidazole + luminal agent.
• Fluid of choice in Plan C → Ringer Lactate.

Rapid revision

1. Low-osmolarity ORS: Na 75, glucose 75, K 20, Cl 65, citrate 10 → 245 mOsm/L.
2. ORS works via SGLT1 Na⁺-glucose co-transport; effective even in secretory diarrhoea/cholera.
3. ORS prevents dehydration but does not reduce stool frequency — zinc reduces duration/severity.
4. Zinc 14 days: 10 mg (<6 mo), 20 mg (≥6 mo).
5. Plan A: more fluids + zinc + continue feeding + know danger signs.
6. Plan B (some dehydration): ORS 75 mL/kg over 4 hours, then reassess.
7. Plan C (severe): 100 mL/kg Ringer Lactate = 30 + 70; infant 1st bolus over 1 hr, older over 30 min.
8. Severe dehydration key signs: lethargy/unconscious, very sunken eyes, drinks poorly, skin pinch >2 s.
9. Rotavirus = commonest severe diarrhoea in infants; Shigella = commonest dysentery.
10. No routine antibiotics in acute watery diarrhoea; treat only dysentery, cholera, parasites.
11. EHEC O157:H7 — avoid antibiotics & antimotility → HUS (haemolytic anaemia + thrombocytopenia + AKI).
12. Avoid loperamide/diphenoxylate in young children; continue breastfeeding throughout.