The epidemiology of travel-related Salmonella Enteritidis in Ontario, Canada, 2010–2011

Abstract

BackgroundIncreases in the number of salmonellosis cases due to Salmonella Enteritidis (SE) in 2010 and 2011 prompted a public health investigation in Ontario, Canada. In this report, we describe the current epidemiology of travel-related (TR) SE, compare demographics, symptoms and phage types (PTs) of TR and domestically-acquired (DA) cases, and estimate the odds of acquiring SE by region of the world visited.MethodsAll incident cases of culture confirmed SE in Ontario obtained from isolates and specimens submitted to public health laboratories were included in this study. Demographic and illness characteristics of TR and DA cases were compared. A national travel survey was used to provide estimates for the number of travellers to various destinations to approximate rates of SE in travellers. Multivariate logistic regression was used to estimate the odds of acquiring SE when travelling to various world regions.ResultsOverall, 51.9% of SE cases were TR during the study period. This ranged from 35.7% TR cases in the summer travel period to 65.1% TR cases in the winter travel period. Compared to DA cases, TR cases were older and were less likely to seek hospital care. For Ontario travellers, the adjusted odds of acquiring SE was the highest for the Caribbean (OR 37.29, 95% CI 17.87-77.82) when compared to Europe. Certain PTs were more commonly associated with travel (e.g., 1, 4, 5b, 7a, Atypical) than with domestic infection. Of the TR cases, 88.9% were associated with travel to the Caribbean and Mexico region, of whom 90.1% reported staying on a resort. Within this region, there were distinct associations between PTs and countries.ConclusionsThere is a large burden of TR illness from SE in Ontario. Accurate classification of cases by travel history is important to better understand the source of infections. The findings emphasize the need to make travellers, especially to the Caribbean, and health professionals who provide advice to travellers, aware of this risk. The findings may be generalized to other jurisdictions with travel behaviours in their residents similar to Ontario residents.

Genetic Diversity and Evolution of Salmonella enterica Serovar Enteritidis Strains with Different Phage Types

“…Phage typing has been found to be useful for the tracking of spatial and temporal distributions of S. Enteritidis. For example, phage type 8 (PT8), PT13a, and PT13 are taken to be most common in North America (5,6), while PT4 has been the dominant phage type in most countries of Western Europe (7)(8)(9). Additionally, PT14b represents a phage type that recently emerged in southern European countries in 2001 (10).…”

“…Additionally, PT14b represents a phage type that recently emerged in southern European countries in 2001 (10). The epidemiology of S. Enteritidis cases associated with international travel revealed distinct relationships between phage types and travel destinations (6,11,12). However, epidemiological comparisons based on phage types alone may not be enough when investigating outbreaks of endemic strains.…”

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

“…Enteritidis, and it was shown in recent Ontario studies that a large proportion of S . Enteritidis cases, especially in the winter and spring, were travel-related [28,56]. …”

“…Previous epidemiological studies have revealed the following individual-level risk factors for S . Enteritidis infections: eating chicken outside of the home [17,18]; eating breaded, stuffed chicken products [19] and raw or undercooked eggs [18,20,21]; another infected person in the home [22]; eating food prepared by an infected food handler [23-26]; contact with birds and reptiles [26]; international travel [18,26-28]; young age [29,30]; and exposures during June and July [31]; although other risk factors might also be important.…”

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

“…These PTs exhibited a seasonal, summer increase and were mostly associated with domestically acquired infections. Conversely, the number of infections with other PTs (4, 1, 6a) increased during the winter months and it was demonstrated that they were largely associated with international travel [5]. …”