Giardiasis
Giardiasis is infection of the proximal small bowel with the protozoan Giardia lamblia (duodenalis), acquired from cysts in contaminated fresh water or food, causing malabsorptive, foul-smelling, greasy diarrhea with bloating and weight loss over weeks. Diagnosis rests on a stool antigen or nucleic acid test, and treatment is a short course of tinidazole, metronidazole, or nitazoxanide.
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What this article covers
- Overview
Definition: giardiasis is infection of the duodenum and proximal jejunum with the flagellated protozoan Giardia lamblia (also called Giardia duodenalis or Giardia intestinalis), acquired by ingesting cysts shed in contaminated water or food.
- Epidemiology
Leading US parasitic cause of diarrhea: Giardia lamblia is the most common parasitic pathogen identified in the United States and a leading cause of waterborne outbreaks.
- Risk factors
Fresh-water exposure: hikers, campers, and backpackers who drink untreated water from streams, lakes, or wells.
- Pathophysiology
Fecal-oral cyst ingestion: infection begins with ingestion of environmentally resistant Giardia cysts from contaminated water, food, or direct contact.
- Clinical features
Malabsorptive diarrhea: watery, "greasy," floating, foul-smelling stools reflecting fat malabsorption, the most characteristic feature.
- Differential diagnosis
Celiac disease: villous atrophy from gluten sensitivity causing chronic malabsorptive diarrhea, bloating, and weight loss; distinguished by positive tissue transglutaminase IgA and duodenal biopsy…
- Diagnosis
Establish the diagnosis with a positive Giardia-specific stool study; this is a laboratory diagnosis, not a clinical one.
- Management
Treat all symptomatic patients; treatment of asymptomatic carriers is reasonable in select settings (household contacts during an outbreak, day-care or food-handler settings, or to interrupt…
- Complications
Malabsorption and weight loss: the dominant complication, from fat, carbohydrate, and micronutrient malabsorption during active infection.
- Prognosis
Excellent with treatment: symptomatic giardiasis responds well to a short antiparasitic course, with most patients clearing the infection and resolving symptoms.
- Prevention
Treat and filter or boil untreated water before drinking: bring water to a rolling boil for at least 1 minute (3 minutes above about 2,000 meters altitude) or use a filter rated to remove Giardia…
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Diarrhea is three or more unformed stools daily, split by duration into acute (under 14 days, usually infectious), persistent (14 to 30 days, often parasitic), and chronic (over 30 days, usually noninfectious), and by mechanism into osmotic, secretory, inflammatory, malabsorptive, and motility diarrhea. Acute diarrhea is managed with rehydration and tested only when red-flag features are present, while chronic diarrhea is worked up by mechanism using stool studies, celiac serology, fecal calprotectin, and endoscopy.
- Celiac disease
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- Lactose intolerance
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Irritable bowel syndrome is a functional disorder of gut-brain interaction diagnosed clinically by Rome IV criteria, recurrent abdominal pain related to defecation, stool frequency, or stool form, without alarm features. Management is subtyped by stool pattern, with fiber and dietary change first, then IBS-C secretagogues or IBS-D antidiarrheals and antibiotics, and low-dose tricyclics or antispasmodics for pain.