Giardiasis in Colorado: an epidemiologic study.

A one-year retrospective laboratory survey in Colorado revealed that 691 (3%) of 22,743 stool examinations for ova and parasites were positive for Giardia lamblia, a higher percentage than that reported from surveys outside of Colorado. The majority of infected residents who were surveyed had experienced an episode of chronic watery diarrhea (median duration 3.8 weeks) with bloating, flatulence, and weight loss (averaging 5.1 kg), and had responded to a course of metronidazole or quinacrine. A statewide telephone survey of 256 cases and matched controls identified: 1) and increased incidence of giardiasis in persons between the ages of 16 and 45, p less than .001, with males and females equally affected; and 2) a higher proportion of cases than controls who visited Colorado mountains (69% vs. 47%), camped out overnight (38% vs. 18%), and drank untreated mountain water (50% vs. 17%), p less than .001. Also identified was a correlation between the seasonal distribution of cases and degree of fecal contamination of mountain streams. These results indicated that G. lamblia is endemic in Colorado and that drinking untreated mountain water is an important cause of endemic ifection.