A descriptive analysis of giardiasis cases reported in Ontario, 1990-1998

Cases of giardiasis in Ontario were described using notifiable disease data from the Ontario Ministry of Health for the years 1990-1998 inclusive. The mean annual age- and sex-adjusted incidence rate was 25.77 cases per 100,0 00 population for the 25,289 cases reported. Children under Five years of a ge had the highest incidence of disease. Males had a higher mean annual inc idence in all age groups. Four deaths occurred among cases. The most freque ntly reported symptoms were loose stools or watery diarrhea (50.1%). A seas onal pattern was noted, peaking in late summer and early autumn. The most f requently reported probable risk settings were the home (40.1%) and travel (39.1%). The study findings suggest that a high proportion of cases occur i n urban areas and spatial analysis showed the highest incidence around Lake Huron and Georgian Bay. Unfiltered water and person-to-person contact are believed to be important sources of infection.