Epidemiology and Infection

Determinants of the geographical distribution of endemic giardiasis in Ontario, Canada: a spatial modelling approach

A. ODOI a1c1, S. W. MARTIN a1, P. MICHEL a3, J. HOLT a4, D. MIDDLETON a5 and J. WILSON a1a2
a1 Department of Population Medicine, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
a2 Division of Enteric, Foodborne and Waterborne Diseases, Population and Public Health Branch, Health Canada, Ontario, Canada
a3 Université de Montreal, CP 5000, St-Hyacinthe, Québec, Canada
a4 Department of Mathematics and Statistics, University of Guelph, Guelph, Ontario, Canada
a5 Ministry of Health and Long-Term Care, Ontario, Canada

Article author query
odoi a   [PubMed][Google Scholar] 
martin sw   [PubMed][Google Scholar] 
michel p   [PubMed][Google Scholar] 
holt j   [PubMed][Google Scholar] 
middleton d   [PubMed][Google Scholar] 
wilson j   [PubMed][Google Scholar] 


Giardiasis surveillance data as well as drinking water, socioeconomic and land-use data were used in spatial regression models to investigate determinants of the geographic distribution of endemic giardiasis in southern Ontario. Higher giardiasis rates were observed in areas using surface water [rate ratio (RR) 2·36, 95% CI 1·38–4·05] and in rural areas (RR 1·79, 95% CI 1·32–2·37). Lower rates were observed in areas using filtered water (RR 0·55, 95% CI 0·42–0·94) and in those with high median income (RR 0·62, 95% CI 0·42–0·92). Chlorination of drinking water, cattle density and intensity of manure application on farmland were not significant determinants. The study shows that waterborne transmission plays an important role in giardiasis distribution in southern Ontario and that well-collected routine surveillance data could be useful for investigation of disease determinants and identification of high-risk communities. This information is useful in guiding decisions on control strategies.

(Accepted March 18 2004)

c1 Author for correspondence. (Email: aodoi@uoguelph.ca)