The Public Health Agency of Canada estimates that each year roughly one in eight Canadians (or four million people) get sick due to domestically acquired food-borne diseases. This estimate provides the most accurate picture yet of which food-borne bacteria, viruses, and parasites (“pathogens”) are causing the most illnesses in Canada, as well as estimating the number of food-borne illnesses without a known cause.
In general, Canada has a very safe food supply; however, this estimate shows that there is still work to be done to prevent and control food-borne illness in Canada, to focus efforts on pathogens which cause the greatest burden and to better understand food-borne illness without a known cause.
The Public Health Agency of Canada estimates that each year roughly one in eight Canadians (or four million people) get sick with a domestically acquired food-borne illness.
The Agency has estimates for two major groups of food-borne illnesses:
To estimate the total number of food-borne illnesses, the Agency estimated the number of illnesses caused by both known food-borne pathogens and unspecified agents.
|Food-borne agents||Estimated annual number of illnesses
(90% credible interval)
|30 known pathogens||1.6 million (1.2–2.0 million)||40|
|Unspecified agents||2.4 million (1.8–3.0 million)||60|
|Total||4.0 million (3.1–5.0 million)||100|
|Pathogen||Estimated annual number of illnesses
(90% credible interval)
|Norovirus||1,047,733 (679,576 – 1,434,048)||65|
|Clostridium perfringens||176, 963 (95,225 – 270,160)||11|
|Campylobacter spp.||145,350 (95,686 – 212,971)||8|
|Salmonella, nontyphoidal||87,510 (58,832 – 125,525)||5|
The full article entitled “Estimates of the Burden of Food-borne Illness in Canada for 30 Specified Pathogens and Unspecified Agents, circa 2006” is published in the journal Foodborne Pathogens and Diseases.
If you would like a copy of the article in either English or French please contact: enteric.surveillance.entérique@phac-aspc.gc.ca.
Many surveillance systems are used in Canada to provide information about the occurrence of food-borne illness. Most of the Agency’s surveillance systems rely on data from provincial/territorial and local public health ministries/units/authorities. Systems focus on specific pathogens likely to be transmitted through food to detect outbreaks, monitor trends and risk factors.
Each surveillance system plays a role in detecting and preventing food-borne illness and outbreaks.
|Data Source||Description||Geographic Coverage||Timeframe of data used|
|Canadian Notifiable Disease Surveillance System (CNDSS)||Collects the number of laboratory confirmed illnesses reported to local public health units/regions to provincial public health authorities and to the national level on an annual basis.||National||2000-2008|
|National Enteric Surveillance Program (NESP)||Collects detailed case level data from invasive listeriosis cases in participating provinces.||National||2000-2010|
|Enhanced National Listeriosis Surveillance||Collects aggregate counts of laboratory isolates of select enteric pathogens (species and subtype) reported through the provincial laboratories on a weekly basis.||National||2010-2012|
|Provincial Reportable Disease Surveillance System||Collects the number of laboratory confirmed illnesses reported from local public health units/regions to provincial public health authorities only.||Provincial||2000-2010|
|National Studies on Acute Gastrointestinal Illness (NSAGI) Population Surveys||Population surveys asking Canadians about vomiting and diarrhea.||Ontario, British Columbia||2001-2002, 2002-2003, and 2005-2006|
|FoodNet Canada Surveillance||An integrated enteric pathogen surveillance system based on a sentinel site surveillance model that collects information on both cases of infectious gastrointestinal illness and sources of exposure within defined communities. This system provides detailed case information on clinical illness and risk factors.||Waterloo Region, Ontario||2005-2010|
In general, to be captured in a Canadian surveillance system a sick individual must: seek care; have a sample (stool, urine or blood) requested; and submit a sample for testing. In addition, the sample must be tested with a test capable of identifying the causative agent; and finally the positive test result must be reported to the surveillance system (Figure 1). Surveillance systems only capture a small portion of total illnesses given all these necessary steps (i.e. there is under-diagnosis and under-reporting taking place).
Two main methods were used to estimate the number of Canadian food-borne illnesses for the Listing of 30 known pathogens.The first approach:
For each pathogen with surveillance data, we used data from various surveillance systems and corrected for under-reporting and under-diagnosis. We then multiplied the adjusted number by the proportion of illnesses acquired in Canada (that is, not acquired during international travel) and the proportion transmitted by food, to estimate the number of illnesses that are domestically acquired and food-borne (Figure 2).The second approach:
For common pathogens that are not part of standard surveillance, we estimated the number of Canadians who would experience symptoms (e.g. diarrheal illness) and the proportion of those symptoms that is related to the particular pathogen. We then multiplied this number by the proportion of illnesses acquired in Canada and the proportion transmitted by food, to yield an estimated number of illnesses that are domestically acquired and food-borne (Figure 3).
Alternative approaches were used to estimate illnesses where suitable data from surveillance or data on proportion of symptoms attributed to the pathogen were not available.
Then, the estimates for each of the pathogens were added together to arrive at an overall pathogen specific total. An uncertainty model to generate a point estimate and 90% credible interval (i.e. upper and lower limits that account for variability and uncertainty of the data) was used.
Figure 2Figures 2 and 3 - Footnote * First approach: For pathogens where laboratory-confirmed cases were scaled up
Figure 3Figures 2 and 3 - Footnote * Second approach: For pathogens where Canadian population was scaled down
Pathogens for which laboratory-confirmed illnesses were scaled up
National reportable disease data
Provincial reportable disease data
Pathogens for which Canadian population scaled down
Estimating Canadian food-borne illnesses for unspecified agents
Unspecified agents that cause acute gastrointestinal illness fall into four general categories:
To estimate food-borne illnesses from unspecified agents, we used symptom-based data from surveys to estimate the total number of episodes of acute gastrointestinal illnesses (AGI) and then subtracted the number of illnesses accounted for by known AGI pathogens. We then multiplied this number by the proportion of domestically acquired illnesses and of illnesses attributable to food, just as we did for the known agents. Finally, as with the known-pathogens estimate, we used an uncertainty model to generate a point estimate and 90% credible interval (upper and lower limits) (Figure 4).
Food-borne illnesses due to chemicals that cause acute gastrointestinal illness are included in the estimate of illnesses due to unspecified agents. However, chemicals or unspecified agents that do not cause acute gastrointestinal illness are not included in the estimates.
Figure 4Figures 4 - Footnote * Approach for unspecified agents
The Agency’s 2013 estimates of illnesses from food-borne diseases in Canada are more accurate than the estimates published in 2008 of 11 million episodes of food-borne illness each year based on better data and methodologies. The 2008 estimates used values from earlier United States Centers for Disease Control and Prevention estimates applied to a Canadian estimate of the average number of episodes of acute gastrointestinal illness per person occurring each year. In addition, the methodology used for the 2013 estimates is different from that used in 2008. As a result of these differences, no strict side-by-side comparison can be made between the two sets of estimates. The 2013 estimates do not mean that there is less food-borne illness occurring, but rather, that more accurate estimates are now possible.
The 2013 estimates of illnesses from food-borne disease in Canada reflect improvements in methodology since 2008. Perhaps most importantly, these new estimates identify and rank the most important bacteria, viruses and parasites (“pathogens”) responsible for causing food-borne illness. These more specific estimates can further inform policy and regulatory priorities to prevent future illnesses.
The following list highlights the major differences in data and methodology between the new estimates and those published in 2008, and how they affect the estimates of illnesses from food-borne diseases in Canada.
Effects of Difference
Although we cannot compare these estimates to determine trends, we can turn to other data sources for information about trends in some important infections that are transmitted commonly through food.
Data from the Canadian Notifiable Disease Surveillance System (CNDSS) and National Enteric Surveillance Program (NESP) provide the best measures of disease trends. Although these systems include only a portion of the pathogens that make up the estimates, it does allow us to see changes over time for these important food-borne pathogens.
According to these systems some food-borne illnesses have dropped substantially over the past decade, but infections caused by one of the most common pathogens – Salmonella have not declined.
Trends in food-borne illness for 2011 compared to the 1998-2000 baseline period:
Other important pathogens commonly transmitted through food (e.g. norovirus, Clostridium perfringens, Toxoplasma gondii) are not tracked in part because they cause mild symptoms of short duration and because of current limitations in laboratory capacity and techniques. Common prevention measures (e.g. safe food handling) that would decrease illness caused by tracked pathogens would also decrease illness caused by pathogens not currently being tracked.
Canada used similar methodologies as the United States Centre for Disease Control and Prevention (US-CDC) for estimating the burden of food-borne illness in their country.
The overall total estimate (specified and unspecified agents) for Canada is slightly less than the US-CDC estimate with approximately one in eight Canadians compared to the US-CDC estimate of one in six Americans, experiencing food-borne illness per year.
The United States
The United States