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Open Access Research article

Evaluating risk factors for endemic human Salmonella Enteritidis infections with different phage types in Ontario, Canada using multinomial logistic regression and a case-case study approach

Csaba Varga12*, Dean Middleton34, Ryan Walton34, Rachel Savage3, Mary-Kathryn Tighe3, Vanessa Allen3, Rafiq Ahmed5 and Laura Rosella34

Author affiliations

1 Department of Population Medicine, University of Guelph, Guelph, Ontario, N1G 2W1, Canada

2 Ontario Ministry of Agriculture, Food, and Rural Affairs, Guelph, Ontario, N1G 4Y2, Canada

3 Public Health Ontario, 480 University Ave, Toronto, Ontario, M5G 1V2, Canada

4 Dalla Lana School of Public Health, University of Toronto, 155 College St., Health Sciences Building, 6th Floor, Toronto, Ontario, M5T 3M7, Canada

5 National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Manitoba, Canada

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Citation and License

BMC Public Health 2012, 12:866  doi:10.1186/1471-2458-12-866

Published: 12 October 2012

Abstract

Background

Identifying risk factors for Salmonella Enteritidis (SE) infections in Ontario will assist public health authorities to design effective control and prevention programs to reduce the burden of SE infections. Our research objective was to identify risk factors for acquiring SE infections with various phage types (PT) in Ontario, Canada. We hypothesized that certain PTs (e.g., PT8 and PT13a) have specific risk factors for infection.

Methods

Our study included endemic SE cases with various PTs whose isolates were submitted to the Public Health Laboratory-Toronto from January 20th to August 12th, 2011. Cases were interviewed using a standardized questionnaire that included questions pertaining to demographics, travel history, clinical symptoms, contact with animals, and food exposures. A multinomial logistic regression method using the Generalized Linear Latent and Mixed Model procedure and a case-case study design were used to identify risk factors for acquiring SE infections with various PTs in Ontario, Canada. In the multinomial logistic regression model, the outcome variable had three categories representing human infections caused by SE PT8, PT13a, and all other SE PTs (i.e., non-PT8/non-PT13a) as a referent category to which the other two categories were compared.

Results

In the multivariable model, SE PT8 was positively associated with contact with dogs (OR=2.17, 95% CI 1.01-4.68) and negatively associated with pepper consumption (OR=0.35, 95% CI 0.13-0.94), after adjusting for age categories and gender, and using exposure periods and health regions as random effects to account for clustering.

Conclusions

Our study findings offer interesting hypotheses about the role of phage type-specific risk factors. Multinomial logistic regression analysis and the case-case study approach are novel methodologies to evaluate associations among SE infections with different PTs and various risk factors.