Length of Salmonella Outbreak Unusual, Say U of G Food Science Experts

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Prof. Lawrence Goodridge

Two University of Guelph experts in food microbiology say it is unusual for a food recall such as the one that has affected California-grown onions for weeks to drag on for so long.

Prof. Lawrence Goodridge pursues interdisciplinary research on food-borne pathogens and holds the Leung Family Professorship in Food Safety in the Department of Food Science. He said there could be several reasons why salmonella illnesses continue to be reported in Canada despite the source of the problem in California being identified weeks ago.

“This is an unusual outbreak in that it has continued for so long and is increasing in size, even after the source of the outbreak was clearly identified. Usually this situation occurs when a source has not been identified,” he said.

The Public Health Agency of Canada reported this week there have been more than 500 cases of salmonella infection in Canada linked to the onions, including nearly 50 in the first two weeks of September.

The agency issued its first warning about an outbreak of salmonella in late July. In early August, it said the illnesses had been traced to red, white, yellow and sweet yellow onions from Thomson International Inc. of Bakersfield, California.

Goodridge said the shelf life of whole mature onions can be as long as six months. “Since the origin of individual ingredients in foods can be quite difficult to determine, it is also possible that foods containing contaminated onions may also still be circulating,” he said.

Ongoing cases may also reflect inherent delays in reporting food-borne illness, which can take three to five weeks.

That’s because sick people need to first visit a health care professional, which can be delayed. The test can take several days and if there is a positive test, there can then be another delay as the result is communicated to various public health officials.

Prof. Keith Warriner

“Breakdowns at any point is this continuum, which is called the ‘pyramid of surveillance,’ can lead to under-reporting of illnesses, as well as delays in reporting of illnesses,” he said.

Prof. Keith Warriner, who also researches food microbiology and food pathogens with U of G’s Department of Food Science, agreed delays in reporting are likely the key reason why this outbreak appears to be continuing.

“There have been no new cases in the U.S. for 14 days, which would suggest the outbreak is over,” he said.

Both Goodridge and Warriner are available for interviews.

Contact:

Prof. Lawrence Goodridge
goodridl@uoguelph.ca

Prof. Keith Warriner
kwarrine@uoguelph.ca

Prof. Goodridge recently spoke to CBC Radio’s Ontario Morning about the outbreak, as well as to CBC’s The National. Watch the episode here: