Incidence, distribution, seasonality, and demographic risk factors of Salmonella Enteritidis human infections in Ontario, Canada, 2007-2009.

Csaba Varga,Michele T Guerin,Frank Pollari,David L Pearl,Scott A Mcewen,Jan M Sargeant

doi:10.1186/1471-2334-13-212

Abstract

BackgroundIn Canada, surveillance systems have highlighted the increasing trend of Salmonella enterica serovar Enteritidis (S. Enteritidis) human infections. Our study objectives were to evaluate the epidemiology of S. Enteritidis infections in Ontario using surveillance data from January 1, 2007 through December 31, 2009.MethodsAnnual age-and-sex-adjusted incidence rates (IRs), annual and mean age-adjusted sex-specific IRs, and mean age-and-sex-adjusted IRs by public health unit (PHU), were calculated for laboratory-confirmed S. Enteritidis cases across Ontario using direct standardization. Multivariable Poisson regression with PHU as a random effect was used to estimate incidence rate ratios (IRRs) of S. Enteritidis infections among years, seasons, age groups, and sexes.ResultsThe annual age-and-sex-adjusted IR per 100,000 person-years was 4.4 [95% CI 4.0-4.7] in 2007, and 5.2 [95% CI 4.8-5.6] in both 2008 and 2009. The annual age-adjusted sex-specific IRs per 100,000 person-years ranged from 4.5 to 5.5 for females and 4.2 to 5.2 for males. The mean age-adjusted sex-specific IR was 5.1 [95% CI 4.8-5.4] for females and 4.8 [95% CI 4.5-5.1] for males. High mean age-and-sex-adjusted IRs (6.001-8.10) were identified in three western PHUs, one northern PHU, and in the City of Toronto. Regression results showed a higher IRR of S. Enteritidis infections in 2009 [IRR = 1.18, 95% CI 1.06-1.32; P = 0.003] and 2008 [IRR = 1.17, 95% CI 1.05-1.31; P = 0.005] compared to 2007. Compared to the fall season, a higher IRR of S. Enteritidis infections was observed in the spring [IRR = 1.14, 95% CI 1.01-1.29; P = 0.040]. Children 0–4 years of age (reference category), followed by children 5–9 years of age [IRR = 0.64, 95% CI 0.52-0.78; P < 0.001] had the highest IRRs. Adults ≥ 60 years of age and 40–49 years of age [IRR = 0.31, 95% CI 0.26-0.37; P < 0.001] had the lowest IRRs.ConclusionsThe study findings suggest that there was an increase in the incidence of S. Enteritidis infections in Ontario from 2007 to 2008–2009, and indicate seasonal, demographic, and regional differences, which warrant further public health attention.

Highlights

In Canada, surveillance systems have highlighted the increasing trend of Salmonella enterica serovar Enteritidis
The University of Guelph Ethics Review Board was consulted because our research involved human participants; ethics approval was not required because our data did not contain any personal or health information that could be linked back to the original identifiers
Enteritidis cases were reported into integrated Public Health Information System (iPHIS) in Ontario

Summary

Introduction

In Canada, surveillance systems have highlighted the increasing trend of Salmonella enterica serovar Enteritidis Non-typhoidal salmonellae (NTS) cause an estimated 93.8 million human infections and. Non-typhoidal salmonellae are the second most frequently reported enteric bacterial pathogens in Canada [8,9], the United States of America (US) [10], and Europe [11]; and they are the top foodborne bacteria causing hospitalization and death in Canada [12] and the US [13,14]. In Canada, surveillance systems have highlighted the increasing trend of S. Considering the under-reporting rate of salmonellosis in Canada (an estimated 13 to 37 cases are unreported per reported case), the burden of infections is even higher [16]

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