C-EnterNet 2007 Annual Report

National Integrated Enteric Pathogen Surveillance Program

Executive Summary

C-EnterNet is a multi-partner program facilitated by the Public Health Agency of Canada to detect changes in trends in human enteric disease and in levels of pathogen exposure from food, animal and water sources in Canada. The design is based on a sentinel site surveillance model first adopted in the United States by the Centers for Disease Control (FoodNet) in 1995, to reflect 10% of the population. The system involves enhanced epidemiological and microbiological surveillance of reportable human enteric diseases in selected communities. In addition, the active surveillance of pathogens in retail food, water and food animal operations is designed to be carried out within the same geographical areas. This C-EnterNet Annual Report presents the results from the surveillance data collected from its pilot sentinel site, the Regional Municipality of Waterloo, Ontario, during the year 2007.

A total of 477 human cases of 11 bacterial (6), viral (1) and parasitic (4) enteric diseases were reported to the local public health authority within the pilot sentinel site during 2007. Less than 1% (4) of the cases were outbreak-related, 30% (142) were travel-related and 69% (331) were classified as endemic. Endemic cases include those acquired locally or during travel within Canada. The four most frequently reported diseases (campylobacteriosis, salmonellosis, giardiasis, and amoebiasis) in Sentinel Site 1 in 2007 accounted for 83% of the endemic cases.

The enhanced, systematic and standardized follow-up by the public health inspectors allowed for the documentation of travel status for all cases. Travelling abroad appeared to be a major risk factor for reported acute enteric diseases. The travel-related proportion was higher for shigellosis (82%), amoebiasis (50%), giardiasis (39%) and cryptosporidiosis (37%). Conversely, cases of Hepatitis A appeared to be mainly acquired domestically in 2007. Based on subtyping results, several distinct patterns emerged among the travel-related cases, when compared to the endemic cases. For example, 36% of Salmonella Enteritidis infections were contracted abroad, while cases of S. Typhimurium and S. Heidelberg were primarily of domestic origin (36/39 and 5/5, respectively). The isolates from Campylobacter infections associated with travelling abroad were more frequently resistant to at least one of the eight antibiotics tested compared to the endemic strains (19/24 travel-related vs. 39/68 endemic cases).

The identification of potential risk factors among endemic cases which were identified through follow-up in the C-EnterNet site warrant further investigation. For example, using a private well as the main water source, swimming, contact with household pets, and living on a farm or in a rural area are all potential risk factors for giardiasis and for cryptosporidiosis. Drinking unpasteurized milk appears to be a risk factor for campylobacteriosis, whereas contact with household pets may be a risk factor for salmonellosis.

Food animals are a natural reservoir for several pathogens that cause acute enteric diseases in humans. As observed in other years, these pathogens were found in the local dairy, swine, beef and broiler chicken operations sampled in 2007. A correlation between human strains and strains detected on the farms was occasionally observed. Pathogenic Yersinia enterocolitica were detected on four swine farms; pathogenic Cryptosporidium species were isolated on beef and dairy cattle farms; and Salmonella Enteritidis was detected on broiler chicken farms.

Untreated surface water continues to be a potential exposure route for several enteric pathogens in the pilot site. Giardia and Cryptosporidium occurred frequently in untreated surface water, and several Salmonella serotypes (e.g. Typhimurium, Heidelberg, Thompson), verotoxigenic Escherichia coli (VTEC), C. jejuni and C. coli were occasionally detected in the local watershed. However, even with the use of additional subtyping, strong correlations between the human strains isolated in the sentinel site and strains detected in the untreated surface water were rarely seen.

Pathogens capable of causing human enteric illness (Campylobacter, Salmonella, Listeria) were detected on the three raw meat commodities (pork, chicken and beef) that were sampled at retail emphasizing the need for proper handling and cooking of raw meat. Generally, raw chicken meat was more often contaminated than beef or pork. In the pork samples that were positive for Yersinia, the subtyping data showed that the strains were non-pathogenic. VTEC was detected in a small number of beef samples. Based on the quantitative Most Probable Number (MPN) method, the majority of positive samples had bacterial loads below the limit of detection (<0.3 MPN/g). In some cases, the subtyping results indicated that the subtypes found on the retail meat were similar to those that cause human illness. For example, among Campylobacter strains, MLST pattern 45 was most commonly detected in retail chicken samples (12 out of 51 isolates analyzed) and most commonly detected in endemic human cases (10 out of 50 isolates analyzed). Thirteen other chicken isolates exhibited an MLST pattern that had been detected among human cases. However, the MLST patterns in 26 of the 51 Campylobacter chicken isolates were not common to the MLST patterns from the human strains.

With two calendar years of data, temporal analyses were performed on the human cases, untreated surface water and retail meat data. It was found that endemic VTEC infections decreased in 2007 compared to 2006, whereas endemic salmonellosis increased. Travel-related campylobacteriosis and amoebiasis both increased in 2007. Campylobacter and Yersinia were more frequently isolated from untreated surface water in 2007 compared to 2006, whereas detection of Salmonella in untreated surface water decreased. The prevalences of Campylobacter, Salmonella, VTEC and Listeria on the retail pork, chicken or beef samples were similar between 2007 and 2006 on the retail pork, chicken or beef samples. The prevalence of Yersinia on pork chops increased from 2006 to 2007. Statistically-significant seasonal variations were detected in human endemic campylobacteriosis, salmonellosis, E. coli O157:H7 infections, giardiasis and cryptosporidiosis (all higher in the summer and campylobacteriosis was also higher in the fall), in the detection of Yersinia in untreated surface water (lower in the spring), and in the detection of Campylobacter in retail raw chicken meat (higher in the fall and lower in the winter).

Two years after its implementation in the pilot sentinel site, C-EnterNet's surveillance system provides unique information on the incidence of several enteric diseases in humans, as well as the presence and level of the same pathogens in a number of sources in the community. The system also has demonstrated its utility for the analysis of local temporal variations in pathogens (yearly trends, seasonal cycles) and the identification of important risk factors worth further evaluation. As a consequence, the system provides a clearer understanding of human enteric diseases and their evolution over time within the site, which is fundamental to public health surveillance. In addition, the intensive laboratory analyses combined with the systematic gathering of epidemiological data allows for the exploration of transmission pathways of enteric disease in one community. This relates to source attribution, the second objective of the C-EnterNet program. The use of molecular subtyping has facilitated, in some cases, the identification of a potential link between the source/reservoir and the human cases at the population level. However, more data are needed to provide improved quantitative and reliable source attribution estimates for Canada. This can be achieved through the expansion of this program to five sites across Canada.

In light of recent outbreaks in Canada, collection of surveillance data on enteric illness and the capability to link human illness to exposure sources is fundamental to the understanding of the epidemiology of enteric disease. It is also important for disease detection, outbreak control, and epidemiological knowledge capacity for public health professionals. The results from the C-Enter-Net surveillance system will be used for these purposes, and will directly inform national policy on food and water safety, thereby ensuring our ability to maintain Canada's safe food and water supply in the face of new challenges.