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Likely diagnosis: Giardiasis (Giardia lamblia infection)
Key clues pointing to this:
  • Chronic (6 week) loose, foul-smelling, non-bloody, non-mucousy stools = malabsorption/steatorrhea pattern, not invasive/inflammatory diarrhea
  • Post-prandial diarrhea + mild abdominal distension = small bowel malabsorption
  • Weight loss (1.5 kg) despite reasonable appetite
  • Well water source (Giardia cysts are chlorine-resistant, classic waterborne route)
  • Outbreak at school (Giardia spreads easily in daycare/school settings via fecal-oral route)
Differentials to consider:
  • Other protozoal: Cryptosporidium
  • Post-infectious/toxin-mediated diarrhea
  • Cow's milk protein intolerance or secondary lactose intolerance (post-infectious)
  • Celiac disease (less likely given acute-ish onset tied to outbreak, but consider if malabsorption doesn't resolve)
  • Toddler's diarrhea (less likely - foul smell, weight loss, and outbreak context argue against it)
Suggested workup:
  • Stool microscopy for ova/cysts x3, or stool Giardia antigen (ELISA)/PCR (more sensitive than microscopy)
  • Stool for reducing substances if lactose intolerance suspected
  • FBC, U&E, albumin, growth chart review
  • Consider stool culture if outbreak suggests other pathogens too
Treatment (if confirmed): Metronidazole (or tinidazole) is first-line for giardiasis in children.
If you can share the actual questions from the scenario, I can answer those specifically.1. Most likely diagnosis: Giardiasis - chronic malabsorptive diarrhea. The pattern fits: foul-smelling, non-bloody/non-mucoid stools for 6 weeks, worse post-prandially, mild weight loss, abdominal distension, well-water exposure, and a school outbreak (classic fecal-oral spread).
2. Organism responsible: Giardia lamblia (also called Giardia duodenalis/intestinalis) - a flagellated protozoan parasite.
3. Investigations:
  • Stool microscopy for ova, cysts and parasites - ideally 3 separate samples (intermittent shedding)
  • Stool Giardia antigen test (ELISA) or stool PCR - more sensitive than microscopy alone
  • Stool for reducing substances (screen for secondary lactose intolerance)
  • FBC, U&E, albumin
  • Growth/weight chart review
  • Consider stool culture to exclude bacterial co-infection given the school outbreak
4. Treatment:
  • First-line: Metronidazole (oral, weight-based dose, typically 5-7 day course)
  • Alternative: single-dose Tinidazole
  • Supportive care: oral rehydration, dietary advice (temporary lactose avoidance if intolerance develops), and hygiene/water safety advice for the family (boil/filter well water) to prevent reinfection
  • Advise school/public health notification given the cluster of cases
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1. Likely diagnosis: Post-infectious (toddler's/post-gastroenteritis) diarrhea, most likely due to secondary lactose intolerance following the acute gastroenteritis - the transient brush-border lactase deficiency causes persistent loose, mucousy stools and poor weight gain after the infection resolves.
(Alternative to keep in mind: post-infectious irritable bowel/toddler's diarrhea if growth is otherwise normal - but poor weight gain here points more toward ongoing malabsorption, i.e. lactose intolerance, rather than simple toddler's diarrhea.)
2. Investigations:
  • Stool for reducing substances (positive supports lactose intolerance)
  • Stool pH (low pH supports carbohydrate malabsorption)
  • Stool microscopy/culture and Giardia antigen (exclude ongoing/secondary infection)
  • FBC, U&E, albumin
  • Growth chart/weight trend
  • Trial of lactose-free diet (both diagnostic and therapeutic)
  • Consider stool elastase or celiac screen (anti-tTG) if symptoms persist beyond expected recovery
Management: temporary lactose-free/reduced-lactose diet with gradual reintroduction over weeks, continue feeding (avoid prolonged restriction), and reassess growth.1. Likely diagnosis: Post-gastroenteritis (secondary) lactose intolerance / post-enteritis syndrome causing ongoing osmotic diarrhea after transient brush-border damage.
2. Investigations:
  • Stool for reducing substances (positive suggests carbohydrate/lactose malabsorption)
  • Stool pH (acidic supports this)
  • Stool microscopy/culture and Giardia antigen (exclude persistent/secondary infection)
  • FBC, U&E, albumin
  • Growth chart - plot weight trend
  • Trial of lactose-free diet (diagnostic and therapeutic)
  • Consider celiac serology (anti-tTG/IgA) if no improvement
3. Important differentials:
  • Secondary lactose intolerance (most likely)
  • Persistent/ongoing infection - Giardia lamblia, Cryptosporidium, or bacterial (e.g. Salmonella carriage)
  • Post-infectious irritable bowel of infancy / toddler's diarrhea
  • Cow's milk protein intolerance (secondary to mucosal injury)
  • Celiac disease (if symptoms persist longer or with failure to thrive)
  • Small intestinal bacterial overgrowth (SIBO)
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