A descriptive study of human Salmonella serotype typhimurium infections reported in Ontario from 1990 to 1998

Evaluating the Spatial Risk of Bacterial Foodborne Diseases Using Vulnerability Assessment and Geographically Weighted Logistic Regression

Foodborne diseases are an increasing concern to public health; climate and socioeconomic factors influence bacterial foodborne disease outbreaks. We developed an “exposure–sensitivity–adaptability” vulnerability assessment framework to explore the spatial characteristics of multiple climatic and socioeconomic environments, and analyzed the risk of foodborne disease outbreaks in different vulnerable environments of Zhejiang Province, China. Global logistic regression (GLR) and geographically weighted logistic regression (GWLR) models were combined to quantify the influence of selected variables on regional bacterial foodborne diseases and evaluate the potential risk. GLR results suggested that temperature, total precipitation, road density, construction area proportions, and gross domestic product (GDP) were positively correlated with foodborne diseases. GWLR results indicated that the strength and significance of these relationships varied locally, and the predicted risk map revealed that the risk of foodborne diseases caused by Vibrio parahaemolyticus was higher in urban areas (60.6%) than rural areas (20.1%). Finally, distance from the coastline was negatively correlated with predicted regional risks. This study provides a spatial perspective for the relevant departments to prevent and control foodborne diseases.

Divergent geography of Salmonella Wangata and Salmonella Typhimurium epidemiology in New South Wales, Australia

Salmonella enterica serovar Wangata is an important cause of salmonellosis in the state of New South Wales, Australia. Standard surveillance has not identified a common food source and cases have been attributed to an unknown environmental or wildlife reservoir. Investigation of the spatial distribution of cases may provide valuable insights into local risk factors for infection and the potential role of the environment and wildlife.

Using conditional autoregressive analysis, we explored the association between laboratory-confirmed cases of S. Wangata reported to the New South Wales Department of Health and human socio-demographic, climate, land cover and wildlife features. For comparison, a model was also fitted to investigate the association of cases of Salmonella enterica serovar Typhimurium, an established foodborne serotype, with the same features. To determine if cases of S. Wangata were associated with potential wildlife reservoir species, additional variables were included in the S. Wangata model that indicated areas of high suitability for each species.

We found that cases of S. Wangata were associated with warmer temperatures, proximity to wetlands and amphibian species richness. In contrast, cases of S. Typhimurium were associated with human demographic features (proportion of the population comprising children <5 years old), climate (mean annual precipitation and mean annual temperature) and land cover (proportion comprising urban and evergreen broadleaf forest). These findings support the hypothesis that S. Wangata is likely to be associated with an environmental source. Whilst we expected S. Typhimurium to be associated with the human socio-demographic feature, the significance of the land cover features was surprising and might suggest the epidemiology of S. Typhimurium in Australia is more complex than currently understood.

Using environmental health officers' opinions to inform the source attribution of enteric disease: further analysis of the "most likely source of infection"

Background

Policies and programs are needed to mitigate the burden of enteric disease in Canada. Source attribution, a goal of FoodNet Canada, can inform such strategies and can be accomplished with the information provided by expert opinion. This includes environmental health officers’ (EHOs) opinions on the “most likely source of infection” (MLSI) of confirmed cases of enteric disease that are investigated by the Fraser Health Authority in British Columbia, FoodNet Canada’s second sentinel site.

Methods

Exposure data from the MLSI were categorized into ten groups and summarized for five enteric disease groups using endemic cases in the first analysis, and a combination of endemic and international travel cases for the second analysis. An exploratory analysis was also conducted on risk setting information in the MLSI. The final analysis involved using a logistic regression model (Wald test) to describe the inherent biases in the data.

Results

Exposure proportions, by disease group, were similar to those of an analysis of MLSI data from FoodNet Canada’s Ontario sentinel site. Food exposure represented the greatest proportion of overall enteric disease (32.0%), as well as for salmonellosis (45.0%), verotoxigenic E. coli (VTEC) infection (38.1%), and campylobacteriosis (30.0%) cases. The majority of parasitic diseases (41.2%) were attributed to water exposure. Food safety practices and consuming unpasteurized products were more frequently reported for campylobacteriosis (19.7% and 5.4%, respectively) compared to other enteric diseases. More VTEC infection was attributed to domestic travel (4.8%) than the other enteric diseases. Among endemic and international travel-related cases combined, VTEC infection was attributed more to endemic food exposure (35.5%) than international travel (16.1%), but similar proportions of campylobacteriosis were attributed to endemic food exposure (25.1%) and international travel (25.1%). Variations existed in the exposure and risk setting information that EHOs included in the MLSI, and in their propensity to enter food sources over other types of exposures.

Conclusions

Results from the MLSI analysis for exposure, risk setting, and EHO bias, are valid contributions for informing source attribution. Important considerations from this work, including strategies to standardize and improve the quality of MLSI data, will enhance source attribution hypotheses.

A protocol to infect Caenorhabditis elegans with Salmonella typhimurium

In the last decade, C. elegans has emerged as an invertebrate organism to study interactions between hosts and pathogens, including the host defense against gram-negative bacterium Salmonella typhimurium. Salmonella establishes persistent infection in the intestine of C. elegans and results in early death of infected animals. A number of immunity mechanisms have been identified in C. elegans to defend against Salmonella infections. Autophagy, an evolutionarily conserved lysosomal degradation pathway, has been shown to limit the Salmonella replication in C. elegans and in mammals. Here, a protocol is described to infect C. elegans with Salmonella typhimurium, in which the worms are exposed to Salmonella for a limited time, similar to Salmonella infection in humans. Salmonella infection significantly shortens the lifespan of C. elegans. Using the essential autophagy gene bec-1 as an example, we combined this infection method with C. elegans RNAi feeding approach and showed this protocol can be used to examine the function of C. elegans host genes in defense against Salmonella infection. Since C. elegans whole genome RNAi libraries are available, this protocol makes it possible to comprehensively screen for C. elegans genes that protect against Salmonella and other intestinal pathogens using genome-wide RNAi libraries.

Geographical variations in Salmonella incidence in Israel 1997-2006: the effect of rural residency

The overall incidence and serotype distribution of non-typhoid Salmonella (NTS) may vary between different geographical localities. To investigate possible regional differences and the effect of demographic factors, we studied 15 865 episodes of laboratory-confirmed NTS infection in Israel. Using Poisson models we found significant variation in the average annual incidence rate of NTS in 15 administrative sub-districts, which was inversely associated with the percent of rural residency (incidence rate ratio 0.75, 95% confidence interval 0.65–0.86, P<0.001). Variation was also found in the relative incidence of the most prominent serotypes (Enteritidis, Virchow, Typhimurium, Hadar, Infantis), which was affected by rural residency, the percent of non-Jewish population in the sub-district, and the percent of population aged o55 years in the sub-district.Rural residency had a major effect on the epidemiology of salmonellosis in Israel. Future research is required to understand whether decreased incidence in rural areas is an under-detection bias or reflects true differences in NTS illnesses.

Informing source attribution of enteric disease: An analysis of public health inspectors’ opinions on the “most likely source of infection”

Enteric illness continues to place a significant burden on the health of Canadians. To reduce this burden and establish effective prevention and intervention practices, the sources of these infections need to be understood. Multiple methods have been used to examine source attribution. This study presents a unique method for examining source attribution and enteric disease risk factors within a Canadian community. Open text data from 2006 to 2010 were analyzed on the “most likely source of infection” (MLSI) identified by public health inspectors (PHIs), investigating sporadic endemic cases of enteric illness in the Region of Waterloo, Ontario. The MLSI data were classified under nine categories and analyzed using five disease groups consisting of overall enteric disease, campylobacteriosis, salmonellosis, verotoxigenic Escherichia coli (VTEC) infection, and parasitic disease. Food was the most frequently reported MLSI for overall enteric disease (26.1%), salmonellosis (41.1%), and VTEC infection (31.3%). Animal and water exposure were the most frequently reported MLSI for campylobacteriosis (26.2%) and parasitic disease (45.8%), respectively. Food safety practices were more frequently implicated as the source of infection for salmonellosis (17.7%) and campylobacteriosis (12.6%), compared with verotoxigenic Escherichia coli (VTEC) infection (6.3%) and parasitic disease (1.0%). The category unpasteurized was the third most frequent MLSI for campylobacteriosis (12.6%), along with food safety practices (12.6%). The analysis of PHIs’ opinions on the MLSI of enteric disease is a valuable method to inform source attribution. The enhanced Canada's National Integrated Enteric Pathogen Surveillance Program (C-EnterNet) standardized questionnaires provided an important source of data to complete this analysis. The results from this study can be used to generate hypotheses for future studies and inform public health policy and practice at the local, provincial, and national levels to reduce the burden of enteric illness in Canada.

The epidemiology of human salmonellosis in New Zealand, 1997–2008

This study describes the epidemiology of human salmonellosis in New Zealand using notified, hospitalized and fatal cases over a 12-year period (1997–2008). The average annual incidence for notifications was 42·8/100 000 population and 3·6/100 000 population for hospitalizations. Incidence was about twice as high in summer as in winter. Rural areas had higher rates than urban areas (rate ratio 1·23, 95% confidence interval 1·22–1·24 for notifications) and a distinct spring peak. Incidence was highest in the 0–4 years age group (154·2 notifications/100 000 and 11·3 hospitalizations/100 000). Hospitalizations showed higher rates for Māori and Pacific Island populations compared to Europeans, and those living in more deprived areas, whereas notifications showed the reverse, implying that notifications are influenced by health-seeking behaviours.SalmonellaTyphimurium was the dominant serotype followed byS. Enteritidis. For a developed country, salmonellosis rates in New Zealand have remained consistently high suggesting more work is needed to investigate, control and prevent this disease.

Recent trends in the epidemiology of non-typhoidal Salmonella in Israel, 1999-2009

The aim of the present study was to assess the recent trends in the epidemiology of non-typhoid Salmonella in Israel using a sentinel laboratory-based surveillance network. Between 1999 and 2009, 8758 Salmonella stool isolates were reported by five sentinel laboratories. There was a significant decrease in the incidence rate of Salmonella isolates from 70·5/100,000 in 1999 to 21·6/100,000 in 2005 followed by a slight increase to 30·3/100,000 in 2009. Of all Salmonella, 64·3% were isolated from children in the 0-4 years age group. Up to 2008, S. Enteritidis was the most prevalent serotype and in 2009 S. Infantis emerged as the most common Salmonella serotype. The decrease in the incidence of S. Enteritidis and S. Typhimurium and increase in S. Infantis among humans were associated with a similar trend among breeding flocks, which followed significant preventive interventions conducted against S. Enteritidis and S. Typhimurium infections in poultry. Tight surveillance and education of food handlers and consumers should be enhanced to reduce the foodborne transmission of Salmonella in Israel.

Regional, seasonal, and antimicrobial resistance distributions of salmonella typhimurium in Canada: a multi-provincial study

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-DT1 04 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.

Regional, seasonal, and antimicrobial resistance distributions of salmonella typhimurium in Canada: a multi-provincial study

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-DT1 04 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.

Estimated Numbers of Community Cases of Illness Due to Salmonella, Campylobacter and Verotoxigenic Escherichia Coli: Pathogen-specific Community Rates

OBJECTIVE

To estimate the annual number of cases of illness due to verotoxigenic Escherichia coli (VTEC), Salmonella and Campylobacter in the Canadian population, using data from the National Notifiable Disease registry (NND), estimates of under-reporting derived from several National Studies on Acute Gastrointestinal Illness, and the literature.

METHODS

For each of the three pathogens (VTEC, Salmonella and Campylobacter), data were used to estimate the percentage of cases reported at each step in the surveillance system. The number of reported cases in the NND for each pathogen was then divided by these percentages. In cases where the pathogen-specific estimates were unavailable, data on acute gastrointestinal illness were used, accounting for differences between those with bloody and nonbloody diarrhea.

RESULTS

For every case of VTEC, Salmonella and Campylobacter infection reported in the NND, there were an estimated 10 to 47, 13 to 37, and 23 to 49 cases annually in the Canadian population, respectively.

CONCLUSIONS

The authors estimate that a significant number of infections due to VTEC, Salmonella and Campylobacter occur each year in Canada, highlighting the fact that these enteric pathogens still pose a significant health burden. Recognizing the significant amount of under-reporting is essential to designing appropriate interventions and assessing the impact of these pathogens in the population.

Estimating the under-reporting rate for infectious gastrointestinal illness in Ontario

BACKGROUND

In Ontario, infectious gastrointestinal illness (IGI) reporting can be represented by a linear model of several sequential steps required for a case to be captured in the provincial reportable disease surveillance system. Since reportable enteric data are known to represent only a small fraction of the total IGI in the community, the objective of this study was to estimate the under-reporting rate for IGI in Ontario.

METHODS

A distribution of plausible values for the under-reporting rate was estimated by specifying input distributions for the proportions reported at each step in the reporting chain, and multiplying these distributions together using simulation methods. Input distributions (type of distribution and parameters) for the proportion of cases reported at each step of the reporting chain were determined using data from the Public Health Agency of Canada's National Studies on Acute Gastrointestinal Illness (NSAGI) initiative.

RESULTS

For each case of enteric illness reported to the province of Ontario, the estimated number of cases of IGI in the community ranged from 105 to 1,389, with a median of 285, and a mean and standard deviation of 313 and 128, respectively.

CONCLUSIONS

Each case of enteric illness reported to the province of Ontario represents an estimated several hundred cases of IGI in the community. Thus, reportable disease data should be used with caution when estimating the burden of such illness. Program planners and public health personnel may want to consider this fact when developing population-based interventions.

Estimating the under-reporting rate for infectious gastrointestinal illness in Ontario

BACKGROUND

In Ontario, infectious gastrointestinal illness (IGI) reporting can be represented by a linear model of several sequential steps required for a case to be captured in the provincial reportable disease surveillance system. Since reportable enteric data are known to represent only a small fraction of the total IGI in the community, the objective of this study was to estimate the under-reporting rate for IGI in Ontario.

METHODS

A distribution of plausible values for the under-reporting rate was estimated by specifying input distributions for the proportions reported at each step in the reporting chain, and multiplying these distributions together using simulation methods. Input distributions (type of distribution and parameters) for the proportion of cases reported at each step of the reporting chain were determined using data from the Public Health Agency of Canada's National Studies on Acute Gastrointestinal Illness (NSAGI) initiative.

RESULTS

For each case of enteric illness reported to the province of Ontario, the estimated number of cases of IGI in the community ranged from 105 to 1,389, with a median of 285, and a mean and standard deviation of 313 and 128, respectively.

CONCLUSIONS

Each case of enteric illness reported to the province of Ontario represents an estimated several hundred cases of IGI in the community. Thus, reportable disease data should be used with caution when estimating the burden of such illness. Program planners and public health personnel may want to consider this fact when developing population-based interventions.