An infection of the small intestine caused by the protozoa, Giardia lamblia.
Giardia outbreaks can occur in communities where water supplies become contaminated with raw sewage.
It can be contracted by drinking water from lakes or streams where water-dwelling animals such as beavers and muskrats, or where domestic animals such as sheep, have caused contamination. All travelers are at some risk of acquiring infection, but hikers drinking untreated surface water have the highest risk. The incidence of known cases is approximately 2 out of 10,000 people. It has been on the increase in the last few years. Some infections resolve on their own.