Virus may incubate in icy lakes: researchers

*Norwalk affects millions annually

Tom Blackwell, National Post.

Norwalk virus, a gut-wrenching fixture of Canadian winters whose source and seasonal nature have long been a mystery, may originate in drinking water drawn from lakes whose cool winter temperatures keep the microbe nicely preserved, suggests a new study.

University of Toronto researchers, comparing Norwalk outbreaks to river water flow and lake temperatures, theorize that a near-endless "feedback loop" sends the virus from human waste to surface waters, then to water treatment plants that are unable to eliminate the bug, and finally back into household faucets.

The theory, if proven, raises the question of whether tap water should be treated with ultraviolet exposure, virtually the only way to kill the hardy viruses, the researchers say.