SIGNS AND SYMPTOMS 
History
- Onset 1–2 wk postexposure
- Infection may be asymptomatic (most common).
- Diarrhea of acute onset (90% of symptomatic patients):
- Foul-smelling stools
- Steatorrhea
- Nonbloody
- Self-limiting within 2–4 wk
- More severe in immunocompromised patients and patients with underlying bowel disease
- Flatulence and bloating (70–75%)
- Abdominal cramping (70%)
- Nausea (70%)
- Vomiting (30%)
- Malaise (86%)
- Anorexia (66%)
- Weight loss (60–70%)
- Fever is rare (15%)
- 30–50% of acute cases progress to chronic giardiasis (> 4 wk):
- Infection is more severe and harder to eradicate in immunosuppressed patients.
Pediatric Considerations
- Acute infection:
- Chronic infection:
- Failure to thrive
- Growth retardation and cognitive impairment owing to nutrient malabsorption
Physical Exam
- Abdominal exam is benign.
- Extraintestinal manifestations (10% of patients):
ESSENTIAL WORKUP
- History:
- Possible sources of exposure
- Membership in high-risk group
- Physical exam:
- If gross or occult blood on digital rectal exam, unlikely to be Giardia
DIAGNOSIS TESTS & INTERPRETATION
Lab
- Stool sample for microscopy (ova and parasites):
- 50–70% sensitive if 1 sample
- 85–90% sensitive if 3 samples taken at 2-day intervals (ideal)
- 100% specific
- Ability to detect other parasites as well
- Stool ELISA or immunofluorescent antibody (IFA) assay for Giardia antigen:
- 95% sensitive, 95–100% specific
- Unlike microscopy, cannot rule out other parasites
- Stool polymerase chain reaction (PCR):
- 100% sensitive and 100% specific
- Fecal leukocytes and stool culture unnecessary unless enteroinvasive organisms suspected (fever, bloody stool)
- Serology for anti-Giardia antibodies not helpful in the ED setting
- Electrolytes, BUN/creatinine, glucose:
- If prolonged diarrhea or evidence of dehydration
- CBC:
- Macrocytic anemia in chronic giardiasis
- Nondiagnostic in acute giardiasis
Imaging
Abdominal CT or ultrasound may show bowel wall thickening and flattened duodenal folds (nonspecific findings)
Diagnostic Procedures/Surgery
- Duodenal sampling:
- Entero-Test (patient swallows a weighted string, which is later retrieved and examined for Giardia using microscopy)
- Endoscopy:
- Duodenal aspiration
- Endoscopic duodenal biopsy
DIFFERENTIAL DIAGNOSIS
- Viral gastroenteritis:
- Bacterial infections:
- Staphylococcus
- Escherichia coli
- Shigella
- Salmonella
- Yersinia
- Campylobacter
- Clostridium difficile
- Vibrio cholerae
- Other protozoa:
- Cryptosporidium
- Microsporidia
- Cyclospora
- Isospora
- Entamoeba
- Inflammatory bowel disease
- Irritable bowel syndrome
- Lactase deficiency
- Tropical sprue
- Drugs and toxins:
- Endocrine:
- Addison disease
- Thyroid disorders
- Malignancy:
- Colorectal carcinoma
- Medullary carcinoma of the thyroid
[Outline]
INITIAL STABILIZATION/THERAPY
- ABCs: Airway, breathing, circulation
- IV 0.9% NS if signs of significant dehydration
Pediatric Considerations
- For severe dehydration (> 10%):
- IV bolus with 0.9% NS at 20 mL/kg
- Cardiac monitor
- Blood glucose determination
ED TREATMENT/PROCEDURES
- Oral fluids for mild dehydration
- Correct any serum electrolyte imbalances.
- Stool sample for microscopy
- If stool sample is positive for Giardia: Treat as listed below under medication
- If stool sample negative for Giardia:
- Refer to gastroenterologist for further specialized testing.
- Consider empiric course of metronidazole if high suspicion for Giardia.
MEDICATION
First Line
- Metronidazole or tinidazole are the treatment of choice:
- Metronidazole: 250–500 mg (peds: 15 mg/kg/24h) PO q8h for 5–10 days
- Tinidazole: 2 g (peds [> 3 yr]: 50 mg/kg) PO once
Second Line
Albendazole (78–90% efficacy), quinacrine (90% efficacy), or nitazoxanide (75% efficacy) if 1st-line therapy fails
- Albendazole: 400 mg (peds: 10–15 mg/kg/24h) PO daily for 5–7 days
- Furazolidone: 100 mg (peds: 6–8 mg/kg/24h) PO q6h for 7–10 days (not available in US)
- Nitazoxanide: 500 mg (peds: 100 mg for ages 2–3 yr, 200 mg for ages 4–11 yr) PO BID for 3 days
- Paromomycin: 500 mg (peds: 25–30 mg/kg/24h) PO q8h for 5–10 days
- Quinacrine: 100 mg (peds: 6 mg/kg/24h) PO q8h for 5–7 days (limited availability)
Pediatric Considerations
- Metronidazole is 1st-line therapy (80–95% efficacy)
- Alternatives:
- Furazolidone (80–85% efficacy)
- Nitazoxanide (60–80% efficacy)
- Paromomycin (55–90% efficacy)
Pregnancy Considerations
- Metronidazole contraindicated in 1st trimester
- Albendazole, quinacrine, and tinidazole are contraindicated throughout pregnancy
- Use nitazoxanide instead
- If mild symptoms only, consider deferring treatment until late pregnancy or postpartum
Immunocompromised Considerations
- Immunocompromised patients at risk for disease that is refractory to standard drug regimens:
- Try drug of a different class/mechanism or metronidazole + quinacrine for at least 2 wk
ALERT
- Use furazolidone in older children only:
- Causes hemolytic anemia in infants
- Causes hemolytic anemia in persons with G6PD deficiency
- Avoid quinacrine in G6PD deficiency (causes hemolytic anemia)
- Avoid paromomycin in renal failure
[Outline]
DISPOSITION
Admission Criteria
- Hypotension or tachycardia unresponsive to IV fluids
- Severe electrolyte imbalance
- Children with > 10% dehydration
- Signs of sepsis/toxicity (rare in isolated giardiasis)
- Patients unable to maintain adequate oral hydration:
- Extremes of age, cognitive impairment, significant comorbid illness
Discharge Criteria
- Able to maintain adequate oral hydration
- Dehydration responsive to IV fluids
FOLLOW-UP RECOMMENDATIONS
- Gastroenterology referral for diagnostic endoscopy if symptoms persist for > 4 wk despite drug therapy
- Acquired lactose intolerance may develop and last for weeks to months
- Association with postinfectious fatigue syndrome
[Outline]
Diagnosis is the greatest challenge in this disease:
- Include giardiasis in the differential diagnosis of all patients with diarrhea:
- Giardia occasionally reported in domestic water supply
- Patients may not present with the classic history and risk factors to have giardiasis
- 1 stool sample is frequently insufficient for diagnosis
ICD9
007.1 Giardiasis
ICD10
A07.1 Giardiasis [lambliasis]
[Outline]
- Escobedo AA, Almirall P, Alfonso M, et al. Treatment of intestinal protozoan infections in children. Arch Dis Child. 2009;94:478–482.
- Escobedo AA, Alvarez G, Gonzàlez ME, et al. The treatment of giardiasis in children: Single-dose tinidazole compared with 3 days of nitazoxanide. Ann Trop Med Parasitol. 2008;102:199–207.
- Escobedo AA, Cimerman S. Giardiasis: A pharmacotherapy review. Expert Opin Pharmacother. 2007;8:1885–1902.
- Huang DB, WhiteAC. An updated review on Cryptosporidium and Giardia. Gastroenterol Clin NorthAm. 2006;35:291–314.
- Kiser JD, Paulson CP, Brown C. Clinical inquiries. What's the most effective treatment for giardiasis? J Fam Pract. 2008;57(4):270–272.
- Naess H, Nyland M, Hausken T, et al. Chronic fatigue syndrome after Giardia enteritis: Clinical characteristics, disability, and long-term sickness absence. BMC Gastroenterol. 2012;12:13.
- Yoder JS, GarganoJW, Wallace RM, et al. Giardiasis surveillance–United States, 2009–2010. MMWR Surveill Summ. 2012;61(5):13–23.
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