Investigating the association between socioeconomic and agricultural risk factors and the incidence of Salmonella Heidelberg and Salmonella Typhimurium in Ontario in 2015: A multi-level ecological approach.

The incidence of salmonellosis, and other enteric zoonotic diseases, has been associated with various food and environmental exposures and socioeconomic factors. Increasingly, there is interest in exploring differences among serotypes of Salmonella to better inform public health prevention efforts. Consequently, we investigated whether rates of Salmonella Heidelberg and Typhimurium in Ontario communities in 2015 were influenced by household characteristics, agricultural factors, and the presence of meat plants. Data for each reported case of S. Heidelberg and S. Typhimurium in Ontario in 2015 were collected. Expected cases of each serotype were calculated, stratified by age group and sex, according to the underlying population distribution from the Canadian census. Socioeconomic, agricultural census data, and data concerning provincial and federally inspected meat plants were combined with observed and expected case counts. The association between community-level agricultural, meat processing, and socioeconomic variables, serotype, and the rate of salmonellosis in each census subdivision (CSD) was explored using multilevel Poisson models, with random intercepts for CSD and census division (CD). Rates of S. Heidelberg and S. Typhimurium were associated with the proportion of married individuals in a CSD, and were higher in CSDs with the highest quantile of labour participation compared to those in the lowest quantile. There was an interaction effect between cattle, poultry and swine farm density in a CD and serotype, with rates of either serotype decreasing as cattle, poultry, or swine farm density in the encompassing CD increased. The rate of the decrease varied by serotype. Our findings concerning community-level household characteristics may be explained by the influence of family structure and occupation on food consumption patterns and environmental exposures. Rates of S. Heidelberg and S. Typhimurium may be lower in areas with increased animal farm density due to naturally acquired immunity from routine exposure to Salmonella via livestock.