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Giardiasis is an illness caused by Giardia lamblia, a one-celled, microscopic parasite that lives in the intestines of people and animals. During the past 15 years, Giardia lamblia has become recognized as one of the most common causes of waterborne disease in humans in the United States. This parasite is found in every region of the United States and throughout the world.

Disease Reporting

What is required?

Health care providers and clinical laboratories are required by law to report cases and suspect cases of Giardiasis to local health departments within one working day of identification. Cases are subject to restriction on school and day-care attendance, food handling, and patient care for the duration of any diarrhea and/or vomiting.

Disease reporting form (pdf) for health-care practitioners

See our disease reporting page for information on how to report and for telephone numbers of local health departments.


For county health departments:

Giardiasis: Investigative guidelines (pdf)
Giardiasis: Case Report Form (pdf)


Giardiasis statistics (pdf) from the 2014 Oregon Communicable Disease Summary from the 2015 Oregon Communicable Disease Summary