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Giardiasis is a topic covered in the 5-Minute Clinical Consult.

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  • Intestinal infection caused by the protozoan parasite Giardia lamblia:
    • G. lamblia is also called Giardia duodenalis and Giardia intestinalis.
  • Infection results from ingestion of cysts, which transform into trophozoites and colonize the small intestine to cause symptoms.
    • Infectious cycle is continued when the trophozoites encyst in the small intestine and are transmitted through water, food, or hands contaminated by feces of an infected person.
  • Most infections result from fecal–oral transmission or ingestion of contaminated water (e.g., swimming).
  • Less commonly acquired through contaminated food


  • Predominant age:
    • All ages but most common in early childhood ages 1 to 9 years and adults 35 to 44 years
  • Predominant gender:
    • Male > female (slightly)
  • Minimal seasonal variability; slight increase in summer and early fall
Pediatric Considerations
  • Most common in early childhood
  • Chronic infection in children can lead to intestinal malabsorption (may also be associated with growth restriction).
  • 5% of patients with traveller’s diarrhea
  • >19,000 cases/year from reportable U.S. states:
    • Giardia is not reportable in Indiana, Kentucky, Mississippi, North Carolina, and Texas.

Etiology and Pathophysiology

Giardia trophozoites colonize the surface of the proximal small intestine: The mechanism of diarrhea is unknown.

No known genetic risk factors

Risk Factors

  • Daycare centers
  • Anal intercourse
  • Wilderness camping
  • Travel to developing countries
  • Children adopted from developing countries
  • Public swimming pools
  • Pets with Giardia infection/diarrhea

General Prevention

  • Hand hygiene
  • Water purification when camping and when traveling to developing countries
  • Properly cook all foods.

Commonly Associated Conditions

Hypogammaglobulinemia, IgA deficiency, and immunosuppression are associated with prolonged course of the disease and treatment failures.

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Stephens, Mark B., et al., editors. "Giardiasis." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2019. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116241/all/Giardiasis.
Giardiasis. In: Stephens MB, Golding J, Baldor RA, et al, eds. 5-Minute Clinical Consult. 27th ed. Wolters Kluwer; 2019. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116241/all/Giardiasis. Accessed April 18, 2019.
Giardiasis. (2019). In Stephens, M. B., Golding, J., Baldor, R. A., & Domino, F. J. (Eds.), 5-Minute Clinical Consult. Available from https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116241/all/Giardiasis
Giardiasis [Internet]. In: Stephens MB, Golding J, Baldor RA, Domino FJ, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2019. [cited 2019 April 18]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116241/all/Giardiasis.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Giardiasis ID - 116241 ED - Stephens,Mark B, ED - Golding,Jeremy, ED - Baldor,Robert A, ED - Domino,Frank J, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116241/all/Giardiasis PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -