Listeriosis Epidemiological Curve

October 3, 2008

The following graph, also known as an epidemiological curve, is up to date as of October 3, 2008.  The graph illustrates the course of the listeriosis outbreak over time.  It shows the week when symptoms of listeriosis began for each of the confirmed cases.  It is important to understand the following contextual points about this graph.

• It is prepared retrospectively and is updated every few days using the information available at the time.  It will not be as current as the daily updates that contain the case count, as information about symptoms takes more time to compile.  

• There is an inherent delay of two to three weeks from the date an illness starts to the date the case is reported to public health authorities.  This delay is the result of the time required for patients to see their physicians and laboratory testing to be completed.

• Under normal circumstances there are two to three reports of cases of listeriosis per week in Canada.  This outbreak was identified following three weeks of higher than expected case reports at the end of July and beginning of August 2008. 

• This outbreak represents one of many different foodborne outbreaks that occur every year.  The Public Health Agency of Canada estimates that every year between 11 and 13 million Canadians suffer from illnesses caused by foodborne bacteria.  While Canada has one of the safest food systems in the world, outbreaks will happen and everyone has a role to play to support food safety.

• The Public Health Agency of Canada and its provincial and local partners remain vigilant.  Since listeriosis can incubate in people for up to 70 days before causing symptoms and considering the inherent delay from symptoms to reporting, it is likely that more cases will be reported over the coming days and weeks.

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