What Is It?
Giardiasis is an intestinal illness caused by infection with the parasite Giardia lamblia, which lives in contaminated water. Although the illness most often occurs in developing countries, giardiasis is also a common cause of waterborne illness in the United States. A person can remain infected with Giardia until the infection is diagnosed and treated. In developing areas of the world, it is common for more than 20% of a country's population to have ongoing Giardia infection. In the United States, only 1 or 2 out of every 10,000 people have Giardia in a typical year, but the infection is found in about 1 out of 3 people who have prolonged diarrhea symptoms if they have recently traveled to a developing country.
As one part of their life cycle, G. lamblia parasites change into cysts. Contagious cysts are found in the feces of infected people or animals. You can become infected with G. lamblia by: