II. Epidemiology
- Most common Parasitic Infection in world
- Most common Waterborne Illness in United States
- Incidence: 2.5 million cases per year in U.S.
- Childhood Incidence in U.S.: 10% (at some point during childhood)
- Summer rates of Giardia infection are double that of other times of year
III. Pathophysiology
- Characteristics
- Pear-shaped flagellated protozoan
- Low inoculum: <10-25 cysts (even a single oocyst)
- High concentration of shedded oocysts (100 million daily)
- Causative Organisms
- Giardia lamblia
- Giardia intestinalis
- Transmission: Fecal-oral
- Life Cycle
- Stage 1: Cyst transmitted via fecal-oral route
- Stage 2: Disease-causing trophozoite
- Trophozoites attach to wall of Small Intestine
- Trophozoites multiply and some transform to cysts
- Cysts are passed with feces to restart cycle
IV. Precautions
- As with Cryptosporidium, Giardia oocysts can survive in chlorinated pools and hot tubs
V. Risk Factors
- Poor sanitation
- Close contact with source case
- Daycare outbreaks are common
- Sexually-transmitted infection (oral-anal sex)
- Wilderness travel with ingestion of contaminated water
- Exposure to infected animals (zoonosis)
- Beaver
- Cattle
- Dogs
- Rodents
- Bighorn Sheep
VI. Symptoms
- Asymptomatic in 50% of those infected
- Timing
- Characteristics
- Diarrhea without blood or mucus
- Steatorrhea
- Flatulence
- Abdominal Pain
- Belching
- Malabsorption
- Weight loss may be significant
- Less Common findings
- Nausea or Vomiting
- Dehydration
- Fever suggests other diagnosis
VII. Labs
- Stool Ova and Parasite
- Low sensitivity for Giardia cysts (oocysts are excreted intermittently)
- Requires three loose stool samples (85-90% sensitive)
- Recommended even if stool Antigen testing done
- Identifies other concurrent Parasitic Infections
- Stool Giardia Antigen testing
- Test Sensitivity: >90%
- Test Specificity: >95%
- Findings suggestive of other diagnosis
- Fecal Leukocytes not seen in Giardiasis
- Leukocytosis or Eosinophilia not seen in Giardiasis
VIII. Management: Primary Regimens
- Primary options
- Nitazoxanide 500 mg orally twice daily for 3 days or
- Tinidazole 2 grams orally for 1 dose (expensive)
- Alternative options
- Metronidazole 250 mg orally three times daily for 5-7 days
- Furazolidone 100 mg orally four times daily for 7 days
- Albendazole 400 mg orally daily with food for 5 days
- Refractory cases or immunodeficient: Option 1
- Metronidazole (Flagyl) 750 mg orally three times daily for 3 weeks AND
- Add ONE of the following
- Quinacrine 100 mg orally three times daily for 3 weeks OR
- Paromomycin: 10 mg/kg three times daily for 3 weeks
- Refractory cases or immunodeficient: Option 2
- Metronidazole (Flagyl) 250 mg orally three times daily for 5 days AND
- Albendazole 400 mg orally daily with food for 5 days
- Child
- Flagyl is bitter and not well tolerated by children
- Dose: 5 mg/kg/dose (max 250 mg) PO tid for 7 days
- Pregnancy
- Mild cases: Consider delaying until post-delivery
- Moderate to severe cases
- Paromycin 25-35 mg/kg/day in 3 divided doses orally for 5-10 days
- Flagyl has also been used in pregnancy
- Asymptomatic carrier
- Developed country: Treat per above guidelines
- Undeveloped country: Treatment not recommended (High risk of reinfection)
IX. Management: Miscellanous agents
- Albendazole
- Adults or children: 400 mg orally daily for 5 days
- Not FDA approved for Giardiasis
- Quinacrine (70-95% effective) - not available in U.S.
- Adults: 100 mg PO tid for 5 days
- Child: 0.7 mg/kg/dose (max 100/day) PO tid for 7 days
- Furazolidone (Furoxone)
- More tolerable taste for young children
- Less effective in older children than other agents
- Risk of Hemolysis with G6PD Deficiency
- Child: 1.25 mg/kg/dose (max 100 mg) PO qid for 7 days
- Paromomycin (Humatin)
- Oral Aminoglycoside with poor systemic absorption
- Consider when desire no absorption (e.g. pregnancy)
- Adult: 500 mg PO qid for 7-10 days
- Child: 25-35 mg/kg/day divided tid for 7 days
X. Prevention
- See Prevention of Foodborne Illness
- See Prevention of Waterborne Illness
- Avoid swimming in pool for 3 weeks after resolution (asymptomatic shedding persists for 1-3 weeks after resolution)
-
Water Disinfection
- Use only bottled water in endemic areas if possible
- Intermediate halogen resistance to (Iodine, Fluorine)
- Use halogen for longer time before drinking
- Use Iodine purification tablets for >8 hours
- Boil water for 1 minute or heat to 158 F x10 minutes
- Water Filtration
- Ensure adequate sanitation system of water treatment
- Prevention in daycare settings
- Dispose of diapers properly
- Frequent and thorough Hand Washing
XI. References
- Gilbert (2016) Sanford Guide, accessed on IOS, 9/12/2016
- Kucik (2004) Am Fam Physician 69:1161-8 [PubMed]
- Nash (2001) Pediatr Infect Dis J 20:193-6 [PubMed]
- Perkins (2017) Am Fam Physician 95(9):554-60 [PubMed]