Regional, Seasonal, and Antimicrobial Resistance Distributions of Salmonella Typhimurium in Canada: A Multi-Provincial Study

Article excerpt

ABSTRACT

Background: This study was conducted to describe the geographical and seasonal distributions of reported human Salmonella Typhimurium (ST) definitive type 104 (DT104) cases, to compare these characteristics to those of non-DT104 cases, and to investigate specific antimicrobial resistance (AMR) patterns in four Canadian provinces.

Methods: All laboratory-confirmed ST cases originating from passive reporting in Alberta, British Columbia, and Saskatchewan, and every second case in Ontario identified from December 1999 through November 2000 were investigated.

Results: A total of 470 human Salmonella Typhimurium cases were identified during the study period. DT104 was the most common phage type, although its incidence varied by province. The proportion of DT104 cases living in urban Ontario, British Columbia and Saskatchewan did not differ from the general population, but in Alberta, the DT104 cases were more likely to live in rural areas. Overall, DT104 isolates were more often R-type ACSSuT compared to non-DT104 cases, and R-type AKSSuT was often associated with DT208. DT104 cases displayed no seasonality whereas non-DT104 cases were more frequent in the summer than in the winter.

Interpretation: Our results suggest that DT104 and non-DT104 cases vary by province, urban vs. rural residential status and by resistance patterns. Lack of seasonality in the DT104 cases may indicate a lesser influence of the agro-environmental route (i.e., farm - manure - water and direct contact) compared to the agro-food route (i.e., farm - animals - food) for these infections. Strain characterization and integration of surveillance information related to ST from animal, food and humans is warranted.

MeSH terms: Salmonella typhimurium; spatial distribution; drug resistance, microbial

The transmission of many bacterial zoonotic enteric diseases such as salmonellosis, campylobacteriosis, and Shiga toxin-producing Escherichia coli infections involves various interconnected pathways linking the environment, animals, and human populations. For human salmonellosis, the main recognized modes of transmission are contaminated food and water and direct contact with an infected person or animal.1,2

Among the various enteric microbial pathogens transmitted through multiple and dynamic pathways, Salmonella enterica serovar Typhimurium (ST) definitive type 104 (DT104) infections have caused significant public health concern in various countries due to their increased incidence in the last decade and an association with antimicrobial resistance (AMR).3,4 Although substantial research has been conducted to understand the general epidemiology, pathogenesis, and bacteriology of Salmonella and ST infections in Canada and elsewhere, only fragmented information arising from population-based studies and describing geographical and temporal distributions of DT104 in Canada have been published.5-16

The objectives of this study, conducted in four Canadian provinces in 1999-2000, were to describe the geographical and seasonal distributions of reported human ST DT104 cases, to compare these characteristics to those of ST non-DT104 cases, and to investigate specific AMR patterns by province.

METHODS

Data

Every laboratory-confirmed ST case originating from passive reporting in Alberta, British Columbia, and Saskatchewan, and every second case in Ontario (due to higher load of submissions) identified from December 1999 dirough November 2000 were eligible for inclusion. Latitude and longitude coordinates were assigned to each case using the centroid of their residential postal code.17 Cases who resided in the classes "urban core" and "urban fringe" based on the 1996 Statistics Canada classes of urbanicity18 were categorized as urban. Cases who resided in the classes "rural fringe", "urban area outside Consolidated Metropolitan Areas (CMA)" and "rural area outside CMAs" were categorized as rural. …