Descriptive analysis of giardiasis in Quebec (Canada) and relation with drinking water source

Background: We analyzed data from the notifiable diseases data base in Queb ec To document the incidence of giardiasis. The objectives were to perform a descriptive analysis of the cases of giardiasis and to verify the relatio n between their incidence and the quality of drinking water. Methods: The Quebec notifiable diseases data-base contained 4273 cases of g iardiasis declared between January 1(st): 1990 and December 31(st): 1995. I ncidence rates were adjusted for age and calculated monthly. The sources an d kinds of treatment of drinking water permitted to elaborate a vulnerabili ty scale for classifying contamination by Giardia sp, into four categories. Incidence of giardiasis was examined in relation with this vulnerability s cale, Other socioeconomic indicators possibly associated with the incidence of giardiasis were also analyzed. Results: Analysis showed that there were few annual variations in the incid ence of giardiasis and that there were no epidemic peaks during the study p eriod. According to age, the incidence follows a bimodal pattern with a pea k for young children and young adults. The incidence rates showed an increa se of the cases at the end of summer and at the beginning of fall, with a h igher relative risk for males. Even if no relation was found between the in cidence of giardiasis and the vulnerability of the drinking water source, i ncidence rates were lower for people living in communities that use the St. Lawrence River as a drinking water source than for those using other sourc es of surface water. Conclusion: This study allowed us to obtain a good description of the cases of giardiasis declared in Quebec and to formulate hypothesis about their c auses. The lower incidence of giardiasis in communities that use the St. La wrence river as their drinking wafer source is possibly related to a lower contamination of this source. However, considering the limits of this work, case-control studies should be considered to understand variables, which i nfluence the incidence of giardiasis in Quebec.