ARCHIVED - Anatomy of a Food-Borne Illness Outbreak


An estimated 4 million people suffer food-related illness every year in Canada. The vast majority of these illnesses last a short time and cause minor symptoms such as nausea, vomiting, and diarrhea. Many of these illnesses are sporadic cases, but some are part of outbreaks.

When an outbreak occurs, resources from governments, the health sector and individuals are mobilized to respond. This includes cooperation among health professionals, local health authorities, provincial and territorial ministries of health, as well as the Public Health Agency of Canada (PHAC) and its federal partners, Health Canada and the Canadian Food Inspection Agency.

Learn how a typical outbreak unfolds—from one person getting sick, to identifying the same illness in others across the country, to sharing with Canadians how they can protect their health.

The Role of the Public Health Agency of Canada

The Public Health Agency of Canada plays a leadership role in coordinating the response to national food-borne illness outbreaks, which are outbreaks that occur in more than one province, territory, or country (including Canada). PHAC also provides support to provinces and territories responding to outbreaks within their jurisdictions when assistance is requested. In a national food-borne illness outbreak, PHAC takes the lead in communicating to Canadians about the risks, the response and how they can protect themselves.

Initial Sickness

An individual gets sick, for unknown reasons, suffering from traditional symptoms of food poisoning (nausea, diarrhea, stiff joints, headache). In most cases, the individual does not seek medical attention.

However, in some cases, particularly if the individual is very old, very young, pregnant, has a weakened immune system or has very severe symptoms, he or she will visit a health professional.

The Health Professional

The health professional decides what advice or treatment to give the patient, including whether or not a sample will be sent to a laboratory for analysis. That analysis may help to identify the cause of the infection and improve the advice or treatment the health professional gives the patient.

The basic challenge for the public health system when dealing with a food-borne outbreak is that most people will not need to go to the doctor, and for those that do, not all doctors will take samples. If an outbreak is occurring, many people might be getting sick at the same time, but it will not be clear how many are suffering, what they’re suffering from, and whether the illnesses are connected.

Identifying the Outbreak

To identify an outbreak, public health officials first need to see unusual rates of illness. An example might be if a province that usually sees two cases of a particular type of Salmonella per week is suddenly reporting 10 cases per week. At this point, officials need to determine what is causing the higher rates of illness.

Some outbreaks are identified when a number of people get sick after eating at the same place. Public health officials interview those who got sick and are sometimes able to identify a link to a likely food source. An example would be if a group of people were to become ill after going to the same wedding or eating at the same restaurant.

Confirming the cause of the illness and identifying the genetic fingerprint of the bacteria, virus, or parasite in the laboratory are important steps for linking cases of illness together, and for linking the cases to a food source.

Provincial, territorial and federal labs test samples taken from patients to identify the genetic fingerprint of the bacteria, virus or parasite responsible for the illness. Labs then post the results on PulseNet Canada , a national network that allows microbiologists to track and share genetic fingerprints for comparison across the country. All labs then compare their results with those posted on PulseNet to find matches and identify outbreaks. PulseNet Canada is coordinated by the Public Health Agency of Canada’s National Microbiology Lab in Winnipeg.

Local, provincial, territorial and federal public health officials can also issue notices about food-related outbreaks through the Canadian Network for Public Health Intelligence, a secure web-based alerting system, to keep the rest of the public health community in Canada informed.

The Public Health Agency of Canada will also work with international partners, such as the World Health Organization and the US Centers for Disease Control and Prevention, if the outbreak extends beyond the country’s borders. The Agency supports the International Health Regulations , which are designed to protect against, control and respond to the international spread of diseases.

Taking Action

Solving an outbreak is like having to piece together a picture puzzle, except in most cases officials do not start with all the pieces, and do not know what the picture looks like, how many pieces it has, or where those pieces are.

Coordination of an outbreak investigation is led by local, provincial or federal health authorities depending on how widespread the cases of illness are. For example, an outbreak confined to one town will be handled by local health officials, while one with cases in several cities across a province will be led by provincial officials. The Public Health Agency of Canada takes a lead role when outbreaks span multiple provinces, territories or countries (including Canada).

Public health officials start asking patients, usually with simple questionnaires, what they did, where they went, and what they ate in the previous days and weeks. Once the pieces are put together, and the likely source of the infection is found in a particular food, Health Canada and the Canadian Food Inspection Agency assess the risk and take recall action, if warranted.

Public health authorities will then communicate with the public or those at risk to advise them on how they can protect themselves.

It sometimes can take a number of weeks from the time an individual gets sick to the time a food source is identified and action is taken. In some cases, the source of the outbreak is never found.

Once the outbreak is contained, government and the public health community conduct reviews to learn lessons from the experience and apply them to improve Canada’s health and food safety systems.

For more information on the role of the federal government during a food-borne illness outbreak, check out the Foodborne Illness Outbreak Response Protocol (FIORP) 2010

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