Lack of an association between endemic giardiasis and a drinking water source.

Waterborne outbreaks of giardiasis have been documented in many areas of North America associated with contaminated surface water supplies. The Greater Vancouver Water District (GVWD) administers the distribution of surface waters to 1.4 million people. We wished to determine if endemic giardiasis was associated with this water supply. One hundred and eighty cases, an equal number of laboratory (enteric) controls and 94 neighbourhood (friend) controls were interviewed by questionnaire. The cases and controls were similar in age, sex and community of residence. Risk factors for giardiasis included having a child under six in the house and travel, both in B.C. but outside of the GVWD, and in Africa, the Americas, south of the U.S. or Asia. The cases drank 3.6 cups of water per day, the enteric controls 3.5 and the friend controls 3.7. These amounts are similar to those reported ingested in outbreak studies. Water consumption was not a risk for endemic giardiasis.