6-Month-Old with Fever and Diarrhoea - Clinical Approach

1. Initial Assessment: Is This Child Sick or Well?

2. Common Causes to Consider

• Rotavirus is the #1 cause of acute gastroenteritis in children <5 years. Presents with watery, large-volume diarrhoea, often with vomiting and fever. Peak incidence in winter/spring. Incubation: 1-3 days.
• Norovirus: Abrupt onset watery diarrhoea, prominent vomiting.
• Adenovirus: Watery diarrhoea, low-grade fever.

• Salmonella spp., E. coli (STEC), Campylobacter, Shigella

• Urinary tract infection / pyelonephritis
• Pneumonia with diarrhoea as a secondary finding
• Otitis media
• Sepsis/bacteremia
• Intussusception (can present with fever + loose stool + "red currant jelly" stool)

3. Dehydration Assessment (Critical in Infants)

4. Investigations

• Urine dipstick + culture - mandatory in any febrile infant without an obvious source (UTI is the #1 serious bacterial illness in this age group)
• Stool microscopy and culture - if diarrhoea is bloody, severe, or persists >7 days
• FBC + CRP/PCT - if infant is ill-appearing or fever is high (>39°C)
• Blood culture - if sepsis suspected
• Blood glucose, electrolytes - in moderate-severe dehydration
• Stool rotavirus/norovirus antigen - if available, useful for cohorting

5. Management

A. Rehydration (cornerstone of treatment)

• Oral rehydration therapy (ORT) - give 30-50 mL/kg over 4 hours
• Administer 25% of the total volume per hour
• Replace ongoing losses: 10 mL/kg per stool, 2 mL/kg per vomit episode
• Age-appropriate diet should NOT be restricted - continue breastfeeding

• ORT: 60-80 mL/kg over 4 hours; same replacement of ongoing losses
• Observe in ED for 4-8 hours; admit if failing ORT

• IV/IO 0.9% saline 20 mL/kg bolus, repeat as needed until clinical improvement
• Volume >60 mL/kg without improvement - consider septic shock, other diagnoses

B. Antipyretics

• Paracetamol (acetaminophen) 10-15 mg/kg every 4-6 hours for fever/discomfort

C. Antibiotics

• Not routinely indicated for acute gastroenteritis
• Consider in: premature infants, immunocompromised, bloody diarrhoea, bacteremia suspected
• Avoid in STEC (EHEC) diarrhoea - antibiotics increase risk of haemolytic uraemic syndrome (HUS)
• If UTI confirmed: treat with appropriate antibiotic (e.g., oral amoxicillin-clavulanate or cefixime; IV ceftriaxone if septic/systemically unwell)

D. Antimotility Agents

• Contraindicated in young children - loperamide, diphenoxylate/atropine can cause paralytic ileus, CNS depression, and death

E. Probiotics (adjunct)

• Lactobacillus rhamnosus GG (LGG) and Saccharomyces boulardii have some evidence for modest reduction in diarrhoea duration
• ESPGHAN recommends these two strains as adjuncts to ORT
• Use caution in premature/immunocompromised infants

6. Red Flags - Admit / Escalate If:

• Toxic or ill-appearing
• Severe dehydration or shock
• Bloody diarrhoea (risk of HUS, sepsis)
• Failure of ORT after 4-8 hours in ED
• Age <3 months (higher risk serious bacterial illness)
• Suspected meningitis, sepsis, or intussusception
• High fever (>39°C) with no obvious source
• Persistent vomiting preventing oral intake
• Underlying immunodeficiency or chronic illness

7. Parental Education on Discharge

• Signs of worsening dehydration to watch for
• ORT technique and fluid volumes
• When to return: decreased urine output (<1 wet nappy in 8 hours), blood in stool, worsening or not improving in 24-48 hours, high or persistent fever

• Rosen's Emergency Medicine: Concepts and Clinical Practice - Dehydration Assessment, Diarrhoea, ORT sections
• Tintinalli's Emergency Medicine: A Comprehensive Study - Serious Bacterial Illness in Infants

Lactose Intolerance

Definition

Physiology of Lactose Digestion

• Rises in late gestation (peaks at full term)
• Remains high for ~1 month after birth
• Begins to decline thereafter
• By age 5-10 years, enzyme activity drops to ~10% of neonatal levels in most of the world's population

Types of Lactase Deficiency

Global Prevalence (Lactase Nonpersistence)

Pathophysiology

1. Osmotic effect - lactose retains water in the gut lumen → osmotic diarrhoea and abdominal distension
2. Bacterial fermentation - colonic microbiota metabolise lactose → produce H₂, CO₂, and CH₄ (methane) gas → bloating, flatulence, cramping

Clinical Features

• Bloating and abdominal distension
• Flatulence and belching
• Crampy abdominal pain
• Diarrhoea (watery, osmotic - stops with fasting)
• Nausea, occasionally vomiting
• Symptoms typically appear 30 min to 2 hours after lactose ingestion
• Severity depends on the amount of lactose consumed and residual lactase activity

Diagnosis

• Consistent history of symptoms linked to dairy intake
• Resolution of symptoms on a lactose-free diet for 2 weeks = diagnostic

• Patient ingests 25-50 g of lactose
• Exhaled H₂ measured at intervals; rise of >20 ppm above baseline = positive
• Positive in ~90% of patients with malabsorption
• False negatives (5-15%): acidic colonic pH, methane-producing (methanogenic) flora, or absence of H₂-producing bacteria
• False positives: small intestinal bacterial overgrowth (SIBO)
• Avoid test after recent antibiotic use (suppresses gut flora)

• Blood glucose measured fasting and 2 hours after lactose load
• Rise of <20 mg/dL indicates malabsorption
• Less sensitive than breath test; largely superseded

Management

• Reduce or eliminate lactose-containing foods: milk, ice cream, soft cheeses
• Many patients can tolerate small amounts (e.g., ~12 g lactose = 1 cup milk) without symptoms
• Yogurt with live cultures is often better tolerated
• Hard cheeses (cheddar, parmesan) are low in lactose and usually tolerated
• Read food labels - lactose is present in many processed foods

• Lactase tablets (Lactaid, Dairy-Ease) taken with dairy meals - help digest lactose
• Effective for many patients but not universally reliable

• Coeliac disease: gluten-free diet → mucosal recovery → improved lactose tolerance
• Giardiasis: metronidazole or tinidazole
• Tropical sprue: oxytetracycline + folate
• Post-gastroenteritis: temporary (2 weeks) dairy avoidance; lactase activity recovers as the intestinal brush border regenerates

• Patients avoiding dairy are at risk for inadequate calcium and vitamin D intake
• Advise non-dairy calcium sources: broccoli, fortified plant milks (soy, oat, almond), leafy greens, canned fish with bones
• Calcium supplements if dietary intake remains insufficient

Key Clinical Pearls

• Lactose intolerance after gastroenteritis is reported in up to 50-70% of patients; frequency depends on ethnicity and baseline lactase activity
• Advise all patients recovering from acute gastroenteritis to avoid dairy for 2 weeks post-recovery
• Lactose intolerance is frequently confused with or co-exists with IBS - visceral hypersensitivity in IBS may amplify symptoms even at sub-threshold lactose loads
• Secondary causes are more likely if there is weight loss, bloody stool, nocturnal symptoms, or family history of inflammatory bowel disease - investigate accordingly

• Yamada's Textbook of Gastroenterology, 7th ed. - Lactose intolerance and malabsorption
• Basic Medical Biochemistry: A Clinical Approach, 6e (Lippincott) - Lactase nonpersistence/persistence, prevalence table
• Symptom to Diagnosis: An Evidence-Based Guide, 4th ed. - Disease highlights, diagnosis, treatment
• Costanzo Physiology, 7th ed. - Pathophysiology case illustration

Lactose Intolerance in Formula-Fed Babies

Why Formula-Fed Babies Can Get Lactose Intolerance

Types of Lactose Intolerance in Infants

1. Congenital Lactase Deficiency (Rare - Most Severe)

• Cause: Autosomal recessive loss-of-function mutations in the LCT gene (lactase gene). Most reported in Finnish populations.
• Presentation: Symptoms begin immediately when the newborn receives breast milk or any lactose-containing formula - copious watery osmotic diarrhoea, metabolic acidosis, and dehydration from the very first days of life.
• Key point: This is a true genetic disorder, not age-related decline. Lactase is absent or severely reduced from birth.
• Treatment: Complete and permanent removal of lactose from the diet. Lactose-free formula allows normal growth and development.

2. Secondary (Acquired) Lactase Deficiency (Most Common in Infants)

• Cause: Damage to the intestinal brush border by illness or inflammation destroys the lactase-producing enterocytes. The most common triggers in infants are:
  • Acute gastroenteritis (especially rotavirus - very common in infancy)
  • Kwashiorkor / protein-energy malnutrition
  • Parasitic infections (Giardia)
  • Coeliac disease
  • Any condition causing villous atrophy
• Key biochemical fact: Lactase is the first disaccharidase activity lost and the last to recover after intestinal injury - because it is present at the lowest baseline levels compared to sucrase, maltase, and isomaltase.
• Presentation: Infant who was tolerating formula well suddenly develops watery diarrhoea, bloating, and poor weight gain following a gastroenteritis episode or illness.
• Natural course: Reversible - lactase activity recovers as the intestinal brush border regenerates (typically 2-6 weeks).
• Treatment: Temporary switch to lactose-free formula during recovery; resume standard formula once mucosal healing is complete.

3. Developmental / Physiological (Premature Infants)

• Lactase expression begins to rise in the third trimester (peaks at full term). Premature infants have lower lactase activity and may have transient difficulty handling lactose loads, especially in the first weeks of life. This generally resolves as gut maturity develops.

Critical Distinction: Lactose Intolerance vs. Cow's Milk Protein Allergy (CMPA)

Misdiagnosis risk is high - confusing the two leads to nutritional harm from inappropriate dietary restriction or unnecessary use of expensive specialised formulas.

Formula Choices in Lactose Intolerance

Important: Soy formula is not recommended as a first choice for cow's milk protein allergy because 25-40% of CMPA infants also react to soy protein. Use extensively hydrolysed formula instead for true CMPA.

Clinical Approach to a Formula-Fed Baby with Suspected Lactose Intolerance

• When did symptoms start? (From birth → congenital LI; after illness → secondary LI)
• Any recent gastroenteritis?
• Family history of lactose intolerance or atopy?
• Blood or mucus in stools? (Suggests CMPA, not LI)
• Skin rash, wheeze? (Suggests CMPA)

• Growth parameters (weight, length, head circumference)
• Signs of dehydration
• Stool characteristics: watery, frothy, acidic-smelling stools with perianal excoriation = classic for LI

• Stool reducing substances (Clinitest): positive in lactose malabsorption (lactose is a reducing sugar)
• Stool pH <5.5: suggests carbohydrate malabsorption/fermentation
• Stool microscopy/culture: to exclude infection

• Switch to lactose-free formula for 2-4 weeks
• Resolution of symptoms = confirms lactose intolerance
• No improvement = reconsider CMPA → trial extensively hydrolysed formula

• Secondary LI: Reintroduce standard formula after 4-8 weeks (brush border recovery)
• Congenital LI: Lactose-free diet lifelong
• CMPA: Extensively hydrolysed or amino acid formula for minimum 6 months or until 9-12 months of age, then guided reintroduction

Key Clinical Pearls

• True congenital lactase deficiency is rare - a formula-fed baby with sudden-onset symptoms after a GI illness almost certainly has secondary lactase deficiency
• Lactase is uniquely vulnerable - it is the lowest-activity disaccharidase and the last to recover after mucosal damage
• Never give straight cow's milk to infants under 12 months as a formula substitute - it has excess protein/solute load, is lactose-containing, and causes intestinal blood loss
• Post-gastroenteritis LI is temporary - parents need reassurance that standard formula can be resumed once the gut heals
• Perianal excoriation from acidic, fermented stools is a hallmark of lactose intolerance in infants and is a useful bedside clue

• Yamada's Textbook of Gastroenterology, 7th ed. - Congenital lactase deficiency
• Basic Medical Biochemistry: A Clinical Approach, 6e (Lippincott) - Congenital LI, secondary LI, intestinal injury
• Textbook of Family Medicine, 9th ed. - Formula selection in infants, soy and hydrolysed formula guidance
• Harper's Illustrated Biochemistry, 32nd ed. - Congenital disaccharidase deficiencies
• Darma et al., Nutrients 2024 - Lactose intolerance vs. cow's milk allergy in infants: clinical dilemma review (PMID: 38337698)