The parasite, found worldwide, survives in the gut of both humans and animals. When ingested, it can cause giardiasis, an unpleasant illness that often leads to diarrhea, flatulence, stomach cramps, nausea, fatigue and possibly joint pain. Reports of the disease have risen from roughly 13,000 cases in 1992 to slightly less than 28,000 in 1997, says the CDC which started tracking the disease in 1992. Vermont had the highest incident rate for giardiasis in 1997, with about 42 of every 100,000 people affected, the CDC says. New York had the most cases that year, with nearly 3,400 people reporting giardiasis.
Most people pick up Giardia through contaminated water, experts say.
However, the bug apparently can survive on hard surfaces and on food as well, although foodborne outbreaks occur less frequently. Many people associate Giardia with backcountry hikers drinking untreated water in the wilderness, but Rose says public recreational outbreaks are far more common today. Giardia is called a fecal-oral agent. Outbreaks of giardiasis tend to occur more often in late summer and early fall, but scientists aren't exactly sure why. More rain during the summer months, heavy travel, recreational use of water and the return to school and work all could play a role, Rose says.