Who was affected by the 2008 Outbreak?

By the end of the 2008 outbreak, listeriosis was confirmed in 57 people and was reported as the underlying or contributing cause of death for 22 of these individuals. Though the majority were in Ontario, illnesses occurred in seven provinces.

These numbers do not adequately describe the human impact of this outbreak, which affected mostly frail, elderly individuals living in long-term care homes. Several people hospitalized because of other diseases, such as cancer that weakened their immune systems that left them susceptible to Listeria infection, also fell ill. Whatever their age or personal circumstances, listeriosis took a terrible toll on their lives and those of their families. Forty percent of those affected in this outbreak died of this serious illness.

Some of the Listeria monocytogenes-contaminated products that caused the outbreak were specifically packaged for the very institutions where these vulnerable people were most likely to be found.

The 2008 outbreak analysis shows that almost 80% of those who developed listeriosis lived in a long-term care home or was admitted to a hospital that had served deli meats taken from large packages contaminated with Listeria monocytogenes.

The following graphs and tables show some of the key characteristics of the listeriosis outbreak. The cases included in the provincial and national analyses are those that meet the national outbreak case definition of a "confirmed"¹ case of listeriosis. The Public Health Agency of Canada (PHAC) defines a case as "a person in the population or study group identified as having a particular disease."²
Case definitions are established for surveillance purposes by PHAC in collaboration with heads of public health of the provinces and territories.

Figure 1, which is called an epidemiological curve, shows that the majority of persons became ill in July and August 2008. In retrospect, the first person who developed listeriosis as part of the outbreak became ill on June 3rd and the last person developed illness on November 22nd.

Infections with the Outbreak Strain of Listeria monocytogenes by Symptom Onset Date or Estimated Date by Symptom Onset Date or Estimated Date

Figure 1 - Confirmed cases of listeriosis by week of illness onset, Canada 2008
Source: Based on data from Public Health Agency of Canada

Development of listeriosis after the three main food recalls took place is not surprising, given the long incubation period and the possible delay of up to 70 days for illness to develop after eating contaminated food. In addition, some people consumed previously frozen deli meat packages they had not thrown away when the recalls were made public. They, unfortunately, consumed contaminated product when they defrosted their reserve (Listeria monocytogenes survives freezing).

Most of the affected people were very old, again unsurprising because so many were residents of long-term care homes. According to an analysis³ of the 56 confirmed cases, the average age was 74 and 68% of those who became ill were female. The youngest person affected was aged 29 and the eldest was 98. The average age of people who died and had listeriosis listed as the underlying or contributing cause of death was 76 years. No pregnant women were identified among confirmed cases.

Among 56 confirmed cases in November 2008, 44 individuals (79%) had been in long-term care homes, hospitalized or had made frequent out-patient visits to a hospital at some point during their incubation period. Of these confirmed cases, four out of five indicated they had eaten deli meats, two reported not eating any deli meats (but were in an institution before becoming ill) and no consumption information was available for the remaining 10 cases. The pattern of illness in the 2008 listeriosis outbreak reflects the distribution of contaminated deli meats primarily to institutions where it was served to vulnerable individuals.

Another quite reasonable assumption by the public, at the time of the outbreak, was the general belief that 'ready-to-eat' meats such as cold cuts are safe to eat without the need for additional preparation. The operators of hospitals and long-term care homes served the ready-to-eat food products - working from the assumption, based on years of experience, that the products were nutritious, easy to chew and safe - without taking extra precautions.

People in these high-risk groups need protection from potentially contaminated foods - something that did not happen in the case of all the Canadians who, in 2008, learned first-hand the serious and frequently fatal consequences of exposure to Listeria monocytogenes.

Next chapter

"The federal, provincial, territorial and municipal governments (and/or Regional Health Boards) have shared responsibility for food safety as a result of the division of powers in Canada's Constitution..."

¹ Confirmed cases: Isolation of Listeria monocytogenes from a normally sterile site, including fetal gastrointestinal contents, with the following PFGE pattern (Scientifically referred as LMACI.0040, LMAAI.0001/.0003 or LMACI.0001, LMAAI.0001); Symptom onset (date of isolation of asymptomatic) on or after June 1, 2008; and, visitor to or resident of Canada.

² http://dsol-smed.phac-aspc.gc.ca/dsol-smed/ndis/glossa_e.html

³ Multi-provincial outbreak of listeriosis - brief epidemiological update, 30 November 2008, Public Health Agency of Canada. Unpublished report produced before the last confirmed case was reported.