TORONTO — Whole-genome sequencing has changed the ability of public health officials to identify various strains of pathogens that sicken Canadians every year.
“With genetic testing we can definitively link causes and cases of food born illness,” said Stephen Parker of the Public Health Agency of Canada. He manages national food safety surveillance programs and talked about progress in food safety monitoring over the last 10 to 20 years during a Canadian Meat Council conference held in Toronto last fall.
Various agencies track food borne illnesses caused by bacteria like salmonella, listeria and E. coli. Surveillance gathers data from four sentinel sites in British Columbia, Alberta, Ontario and Quebec. Data measures whether food-borne-illness trends are going up or down, as well as determining what food and other sources are making Canadians ill.
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Most of the data comes from FoodNet Canada, which provides detailed information on human illnesses and tracks disease rates and risks.
Among the findings is the persistence of salmonella. There are many types, but in the last 10 years most disease is linked to salmonella enteritidis. Instances of all other serotypes combined have remained about the same, while S. enteriditis (SE) accounts for about 50 percent of reported cases.
However, incidences in 2017-18 seemed to level out.
“In preliminary data, in 2019 we are seeing a decrease in SE but we are seeing a corresponding increase in the other serotypes,” Parker said.
About a quarter of salmonella cases are related to travel but the rest are due to locally acquired infections. There are substantial regional differences with more cases found in British Columbia.
Salmonella causes digestive upsets and many cases are not reported.
“We know for every laboratory confirmed case of salmonella there are 26 cases that go undiagnosed,” he said.
The illness could be mild so people treat themselves. They may go to the doctor but no stool samples are collected to confirm the cause.
Of 3,304 laboratory confirmed cases there were probably 89,900 undiagnosed cases of salmonella, said Parker.
Many of the outbreaks were related to consuming frozen chicken products.
The agency is stepping up retail sampling of commodities like ground beef and chicken breast, frozen raw chicken products, pork sausage, oysters and mussels.
The human illness rates caused by salmonella reflect prevalence seen on farms and retail chicken products.
Comparatively, the number of E. coli related sickness appears to be down. While not all E. coli bacteria cause illness, the types that can cause diarrhea can be transmitted through contaminated water or food, or through contact with animals or infected people.
“The national incidence of E. coli has remained consistently low over the last 10 years,” he said.
“This is a real success story. We have seen a real knock down with fewer E. coli illnesses and less prevalence in retail products,” he said.
Consumer education about food safety has helped.
Consumers know chicken and hamburger should be handled carefully and cooked thoroughly, but many are not aware of the problems associated with frozen raw chicken products, he said.
