This lecture, delivered by Dr. Pamela Lee (Department of Paediatrics & Adolescent Medicine), is a clinically-oriented walkthrough of how to approach a child presenting with diarrhoea — from history-taking and clinical assessment of dehydration, through to fluid management, nutritional advice, pharmacological (non-)interventions, antibiotic indications, and discharge planning. It also contextualizes paediatric gastroenteritis (GE) within the global child-mortality landscape. ^[1]

1. Define diarrhoea in children and differentiate acute from chronic causes
2. Identify the commonest aetiologies of acute infective GE (viral, bacterial, protozoal)
3. Perform a systematic history and clinical assessment, including dehydration severity
4. Recognize red-flag features suggesting diagnoses other than GE or progression to shock
5. Know when to investigate (bloods, stool microbiology) — and when NOT to
6. Master fluid management: oral rehydration therapy (ORT) vs IV fluids, including shock management
7. Understand nutritional management principles (no diluted milk, no special formula)
8. Know which pharmacological agents to avoid in children (anti-emetics, anti-diarrhoeals)
9. Identify the specific indications for antibiotics in paediatric GE
10. Counsel parents and carers on home management, red-flag signs, and expected disease course
11. Appreciate the global perspective: diarrhoeal disease and under-5 mortality

Normal stool pattern varies between children - a breastfed neonate may pass 6-8 soft stools per day. The definition therefore combines a pragmatic frequency threshold with change from baseline.

Differential diagnosis of acute-onset bloody stool, fever, and abdominal cramps includes: Campylobacter, Shigella, Salmonella, Clostridium difficile, Yersinia enterocolitica, Vibrio parahaemolyticus, Enteroinvasive E. coli, Enterohemorrhagic E. coli (O157:H7), and initial presentation of inflammatory bowel disease. ^[1]

Why this matters from first principles: Watery stool occurs when the toxin stimulates secretion (secretory mechanism) or the virus destroys absorptive villous cells (e.g., rotavirus) → net water loss into the lumen. Bloody/mucoid stool occurs when the organism invades or directly damages the colonic mucosa, exposing blood vessels and provoking an inflammatory exudate (mucus + PMNs).

Is this truly "diarrhoea"? Characterize: watery vs bloody, presence of mucus. Acute or chronic? ^[1]

Why: Parents may call any loose stool "diarrhoea." You must establish the baseline stool pattern and the nature of the change. The character (watery vs bloody/mucoid) immediately stratifies the likely mechanism and pathogen group.

Number of episodes, frequency, estimated amount as judged by the parents. ^[1]

Why: This quantifies the magnitude of fluid loss. A child passing 10 large watery stools in 6 hours is at far higher risk of dehydration than one with 3 small loose stools over 24 hours.

Vomiting, fever, poor appetite (quantify intake), abdominal pain, irritability. ^[1]

Why:

• Vomiting → additional fluid loss + compromises oral rehydration
• Fever → increases insensible losses + suggests infective cause
• Poor appetite → child not replacing losses
• Irritability → may be an early sign of dehydration or intracranial pathology

Symptoms: dry lips, cool limbs, decreased urine output. ^[1] Risk factors: frequent profuse watery diarrhoea, vomiting, poor fluid intake, concurrent fever. ^[1]

Why: This step directly determines whether the child needs clinic/home management vs. hospital-based rehydration. Each risk factor increases obligatory fluid losses or decreases intake.

Acute diarrhoea DDx: Infective (bacterial vs viral, secretory vs inflammatory), food intolerance, osmotic agents, drugs. Also consider chronic diarrhoea. ^[1]

Why: Not every child with loose stools has GE. Consider osmotic diarrhoea from fruit juices (sorbitol), drug-related (antibiotics), food intolerance (cow's milk protein allergy in infants), or the onset of chronic conditions.

Usual intake, change in content/preparation/utensils, undercooked or raw food, eating out, contact with persons with similar symptoms, nursery attendance, occupation of family members (cooks, kitchen workers, healthcare workers). ^[1]

Why: Identifying the source is crucial for infection control and public health reporting. If the child attends daycare, an outbreak investigation may be triggered.

Setting (child-care centres, institutions, hospitals), family/close contacts, food-borne or water-borne after common exposure, antimicrobial-associated diarrhoea, traveller's diarrhoea, immunocompromised host, history of chronic diarrhoea or underlying GI disease. ^[1]

Did the mother give sufficient fluid? How well tolerated? Any medications given? Already seen a doctor? ^[1]

Why: This avoids duplication, identifies failed interventions (e.g., child vomited all ORS → may need IV), and reveals potentially harmful treatments (e.g., loperamide given by family).

Recurrent diarrhoea, growth pattern, diet, birth history, immunization, family history, social history. ^[1]

Why: Recurrent diarrhoea may suggest immunodeficiency, IBD, coeliac disease, or cow's milk protein allergy. Growth faltering in a child with chronic loose stools is a red flag for malabsorption. Immunization history (rotavirus vaccine) is relevant for risk stratification.

The slide labels Salmonella as the commonest cause, but current CDC guidance identifies diarrhoeagenic E. coli (especially ETEC) most often overall, followed by Campylobacter, Shigella and Salmonella; the distribution varies by destination. Protozoal disease becomes more likely with a prolonged course ^[11].

Rotavirus infects and destroys mature absorptive enterocytes at the villous tips. The resulting villous dysfunction produces malabsorption and secretion, explaining the profuse watery stool. The slide's 25-55% of GE hospitalisations is a pre-vaccine estimate rather than a current universal figure; rotavirus vaccine introduction has substantially changed this epidemiology ^[16].

Characteristics that may suggest a diagnosis other than GE ^[1]

Key differentials to consider when a child presents with diarrhoea and/or vomiting but doesn't fit the GE pattern:

Differential Diagnosis Table Shown in the Lecture [1]

Children younger than 12–18 months commonly present with non-specific symptoms and signs. High fever (≥38 °C if < 3 months; ≥39 °C if ≥ 3 months) may occur in GE but should also raise suspicion of non-enteric infections. ^[1]

Dehydration with plasma Na > 150 mmol/L. ^[1]

'Doughy skin' is not reliable to identify patients with hypernatraemic dehydration. Severity of dehydration is more often underestimated compared with normo-natraemic dehydration. ^[1]

Why dehydration is underestimated: In hypernatraemia, water shifts from the intracellular to the extracellular compartment (osmosis). This relatively preserves the intravascular volume, so signs of dehydration (skin turgor, capillary refill) appear less severe than the actual total body water deficit.

Suspect hypernatraemic dehydration if there are: jittery movements, increased muscle tone, hyper-reflexia, convulsions, drowsiness or coma. ^[1]

Why neurological signs: Hypertonicity draws water from brain cells and can produce irritability, hyperreflexia or seizures. During treatment, an overly rapid fall in sodium can cause cerebral oedema; correction therefore requires frequent biochemical and neurological reassessment.

Do not routinely perform blood biochemical testing. ^[1]

Measure plasma Na, K, urea, creatinine & glucose if: IV fluid therapy is required, symptoms/signs suggest hypernatraemia, unexplained drowsiness in an infant (rule out hypoglycaemia). ^[1]

Measure venous blood acid-base status and chloride concentration if shock is suspected or confirmed. ^[1]

Causes: loss of bicarbonate in diarrhoea (normal anion gap metabolic acidosis), lactic acidosis in hypovolaemic shock (raised anion gap metabolic acidosis). ^[1]

Why this distinction matters: Normal anion gap acidosis from diarrhoea is expected and usually corrects with rehydration. A raised anion gap may indicate lactate from hypoperfusion, but it does not by itself prescribe a fluid volume: assess for clinical shock, treat using the shock pathway and reassess after each intervention.

Most acute GE in children are viral in origin. Even if bacterial, most do not require antimicrobial treatment. Identification of a specific pathogen is not generally required. ^[1]

Continue breastfeeding and other milk feeds. Encourage fluid intake. Discourage fruit juices and carbonated drinks. Offer ORS as supplemental fluid to those at increased risk of dehydration. ^[1]

Why avoid fruit juice: Fruit juices contain high concentrations of fructose and sorbitol, which are poorly absorbed → osmotic diarrhoea, worsening the problem. Carbonated drinks are hyperosmolar and lack electrolytes.

Low-osmolarity ORS ( < 250 mOsm/L) reduces the need for unscheduled IV fluid, and leads to greater reduction in stool output and vomiting compared with high-osmolarity ORS. ^[1]

Why low-osmolarity is better: High-osmolarity ORS in the gut lumen draws water into the lumen by osmosis → can paradoxically worsen diarrhoea. Low-osmolarity ORS allows net water absorption.

At the brush border, rice starch is broken down into glucose. SGLT1 then co-transports sodium and glucose from the intestinal lumen into the enterocyte; water follows into the body. The slide's wording "into the lumen of intestinal villi" reverses the physiological direction.

Why rice-based works well: Rice starch provides glucose molecules slowly (as they are enzymatically released from the polymer) rather than as a sudden osmotic load. This maximizes Na-glucose co-transport (SGLT1) without increasing luminal osmolarity. Evidence shows particular benefit in cholera ^[1].

Use IV fluid if shock is suspected/confirmed; if a child with red flags deteriorates despite ORS; or if persistent vomiting prevents ORS given orally or by NG/OG tube. ^[10] An impaired conscious state or ileus also makes enteral treatment unsafe and requires urgent senior assessment.

Current correction to the lecture slide: give 10 mL/kg of 0.9% sodium chloride rapidly, then reassess. If shock persists, give a second 10 mL/kg, consider causes other than dehydration, and seek paediatric intensive-care advice if shock persists ^[10]. General NICE paediatric IV-fluid guidance likewise uses a 10 mL/kg glucose-free isotonic crystalloid bolus over less than 10 minutes, with reassessment after every bolus ^[17].

The slide's 20 mL/kg + 20 mL/kg sequence is historical and should not be used as the default from these notes. Account for cardiac/renal disease, severe malnutrition, DKA and other special situations, where a standard bolus pathway may be inappropriate.

WHO recommends IV rehydration to correct fluid deficit in 3–6 hours. Attempt early and gradual introduction of ORT during IV therapy. If tolerated, stop IV and complete rehydration with ORT. ^[1]

Obtain urgent expert advice. Use an isotonic solution such as 0.9% sodium chloride (with glucose when indicated) for deficit plus maintenance, usually replace the deficit over 48 hours, monitor sodium frequently and aim for a fall of less than 0.5 mmol/L/hour ^[10].

Why so slow: Rapid reduction in serum Na → osmotic gradient reverses → water rushes into brain cells → cerebral oedema → seizures, permanent brain injury, or death. The 48-hour timeline and < 0.5 mmol/L/hour rate are critical safety guardrails.

Encourage breastfeeding and milk feeds. Replace ongoing loss with ORS 5–10 mL/kg per large watery stool for at-risk groups: children < 1 year (especially < 6 months), low birth weight infants, > 5 diarrhoeal stools in previous 24 hours, > 2 vomits in previous 24 hours. ^[1]

The slide accurately emphasises that most vomiting is self-limiting and that antiemetics are not the core treatment. NICE notes evidence that ondansetron can improve ORS success, but also reports more diarrhoea in some trials; follow the current local paediatric protocol, contraindications and dosing policy ^[10].

Vomiting Pathway and Drug Action Sites [1]

The vomiting reflex is coordinated by the vomiting centre (medulla), which receives input from:

• Higher cortical centres — memory, fear, anticipation, sensory input (pain, smell, sight)
• Chemoreceptor trigger zone (CTZ) — area postrema, floor of 4th ventricle; stimulated by chemotherapy, anaesthetics, opioids
• Stomach / small intestine — intestinal distension, noxious stimuli (GE, surgery, radiotherapy)
• Labyrinths — motion/vestibular input

Drug action sites on this pathway:

• Histamine (H₁) antagonists and muscarinic antagonists — act at vomiting centre/vestibular pathways (promethazine)
• Dopamine (D₂) antagonists — act at CTZ (metoclopramide)
• 5-HT₃ antagonists — act at CTZ and gut afferents (ondansetron)

The slide's claim that ondansetron increases stool because it "retains fluids and toxins" is a hypothesis, not an established mechanism. The clinically relevant point is simply that some trials found more diarrhoea, so any use should be selective and should support - not delay - effective ORS and reassessment ^[10].

Adsorbents (kaolin, smectite), anti-motility agents (loperamide) — no high-level evidence of benefit, NOT recommended. Potentially serious adverse effects: abdominal distension, ileus, drowsiness (loperamide); increased intestinal transit time reduces clearance of pathogens and toxins. ^[1]

"A live microbial food ingredient that, when ingested in sufficient quantities, exerts health benefits on the consumer." ^[1]

Mechanisms:

• Compete with pathogens for binding sites and substrates
• Lower intestinal luminal pH
• Upregulate genes mediating immunity
• Produce trophic short-chain fatty acids promoting mucosal cell growth and differentiation ^[1]

Examples discussed by the lecture: Lactobacillus, Bifidobacterium and Saccharomyces. Probiotic effects are product- and strain-specific, so a generic "probiotic" cannot be assigned the slide's proposed mechanisms or dose. The 2024 WHO guideline suggests against probiotics for acute watery diarrhoea in children up to 10 years (conditional recommendation, low-certainty evidence); there is no WHO recommendation for persistent diarrhoea because of a knowledge gap ^[12]. ORS, feeding and appropriate zinc policy remain the priorities.

Rehydration completed, minimal risk for recurrence of dehydration, uncomplicated disease course. Also consider: reliable carer, understanding of the treatment plan, myths and misunderstandings. ^[1]

Most children with GE can be safely managed at home. Empower parents and carers. ^[1]

Home management advice:

• Continue usual feeds including breastfeeding
• Encourage plenty of fluids, small frequent portions
• Avoid fruit juices and carbonated drinks
• Offer ORS as supplemental fluid

Red-flag symptoms to seek medical attention:

• Appears more unwell, altered responsiveness, irritability, lethargy
• Decreased urine output
• Pale, mottled skin; cold extremities ^[1]

Expected course:

• Diarrhoea: 5–7 days, most stops within 2 weeks
• Vomiting: 1–2 days, most stops within 3 days ^[1]

If symptoms exceed these timelines → return for reassessment.

Access to clean drinking water, sanitation, malnutrition. ^[1]

What the image-heavy slides add: they deliberately contrast children toileting at home with children receiving care amid unsafe water, malnutrition and limited services. The point is not that the biology changes by country, but that exposure, reserve, access to ORS/healthcare and the ability to replace ongoing losses change the outcome. Malnutrition both increases susceptibility and slows mucosal recovery, creating a diarrhoea-malnutrition cycle.

The WHO/UNICEF Integrated Global Action Plan for Pneumonia and Diarrhoea (GAPPD) organises interventions into three pillars:

Handwashing with soap is highlighted as a high-impact, cost-effective intervention across all settings. ^[1]

The GAPPD cover and diagrams shown are from 2013 and used a 2025 target. Their enduring teaching value is the Protect-Prevent-Treat package: breastfeeding and nutrition; vaccination, handwashing, safe water and sanitation; then prompt ORS, feeding, referral and indicated treatment. WHO's 2024 guideline now suggests 5 mg oral zinc daily for up to 14 days for acute watery or persistent diarrhoea in children up to 10 years; national protocols and the child's clinical setting should determine implementation ^[12].

Commonly tested alongside GE because it presents with vomiting and bloody stool ("redcurrant jelly") in a similar age group. ^[8]

Always think of this when EHEC O157:H7 is the cause of bloody diarrhoea. Triad: microangiopathic haemolytic anaemia + thrombocytopaenia + acute kidney injury. Antibiotics may worsen it. ^[1][4]