Abstract
BackgroundGiardia lamblia is the most frequently identified human intestinal parasite in Canada with prevalence estimates of 4–10%. However, infection rates vary by geographical area and localized 'pockets' of high or low infection rates are thought to exist. Water-borne transmission is one of the major routes of infection. Sources of contamination of drinking water include humans, domestic and wild animals. A previous study in southern Ontario, Canada, indicated a bivariate association between giardiasis rates and livestock density and/or manure use on agricultural land; however these variables were not significant when the variable 'rural' was added to the model. In that study, urban areas were defined as those with a minimum of 1,000 persons and a population density of at least 400 persons per Km2; all other areas were considered rural. This paper investigates the presence of local giardiasis clusters and considers the extent to which livestock density and manure application on agricultural land might explain the 'rural' effect. A spatial scan statistic was used to identify spatial clusters and geographical correlation analysis was used to explore associations of giardiasis rates with manure application on agricultural land and livestock density.ResultsSignificant (P < 0.05) high rate spatial clusters were identified in a number of areas. Results also showed significant (P < 0.05) associations between giardiasis rates and both livestock density and manure application on agricultural land. However, the associations were observed in only two regions.ConclusionsThere is evidence that giardiasis clusters in space in southern Ontario. However, there is no strong evidence to suggest that either livestock density or manure application on agricultural land plays an important role in the epidemiology of giardiasis in the study area. Therefore these factors do not seem to explain the higher rates of giardiasis reported in rural areas. The spatial scan statistics methodology used in this study has an important potential use in disease surveillance for confirming or refuting cluster alarms.
Highlights
Infection with Giardia occurs throughout the world, in humans and over 40 other species of animals, with human prevalence ranging from 1 to over 90% depending on location and age of persons sampled [1,2,3]
Geographical correlations of giardiasis rates with livestock density and manure application on agricultural land are explored to assess the extent to which these factors might explain the higher rates of giardiasis reported in rural areas
This paper investigates the presence of clusters of giardiasis in southern Ontario and explores the extent to which livestock density and manure application on agricultural land might explain the 'rural' effect observed in the above study
Summary
Infection with Giardia occurs throughout the world, in humans and over 40 other species of animals, with human prevalence ranging from 1 to over 90% depending on location and age of persons sampled [1,2,3]. The main mode of infection is ingestion of Giardia cysts This may occur by ingestion of contaminated water, food or by hand-to-mouth transfer of cysts, but water-borne transmission is thought to be one of the major routes of infection. Sources of contamination of drinking water include humans, domestic and wild animals. A previous study in southern Ontario, Canada, indicated a bivariate association between giardiasis rates and livestock density and/or manure use on agricultural land; these variables were not significant when the variable 'rural' was added to the model. This paper investigates the presence of local giardiasis clusters and considers the extent to which livestock density and manure application on agricultural land might explain the 'rural' effect. A spatial scan statistic was used to identify spatial clusters and geographical correlation analysis was used to explore associations of giardiasis rates with manure application on agricultural land and livestock density
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