Course:FNH200/Lessons/Lesson 12/Page 12.8

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12.8 Foodborne Diseases

You may have suffered from a bout of foodborne disease or you may know of someone who has been a victim of foodborne disease. We often hear the term food poisoning but foodborne disease is the correct term.

According to the most recent estimate from the Public Health Agency of Canada the number of cases of Foodborne illness that occur in Canada is approximately 4 million cases each year.

A foodborne illness is caused by eating food that has been contaminated in some way. Contamination can be from different causes (etiology): microbiological, parasitic, plant, animal, and chemical.

  • Microbiological agents are responsible for the majority of foodborne disease outbreaks. The specific microbiological agents are discussed in forthcoming sections of this lesson.
  • Parasitic agents refer to parasites such as Trichinella spiralis, Anisakis simplex, tapeworm, and so forth, that are acquired from consumption of infested foods:
    • Trichinella spiralis, associated with consumption of undercooked pork, contaminated water or produce.
    • Anisakiasis caused by Anisakis simplex. Anisakiasis is associated with eating raw fish (sushi, sashimi, lomi lomi, ceviche, sunomono, Dutch green herring, marinated fish and cold-smoked fish) or undercooked fish.
  • Foodborne diseases arising from consumption of plants included consumption of amanita mushrooms, taro leaves, green potatoes, and toxic algae in spirulina (an algae) protein supplement tablets.
  • Illness arising from poisonous animals usually occurred as a result of consumption of shellfish containing paralytic toxins.
  • Chemicals in contaminated foods that cause foodborne disease have included tin in canned foods arising from corrosion inside the metal can, residues of cleaning and sanitizing agents in food, products of rancid fats in foods, and excesses of some ingredients such as monosodium glutamate.

Here are some terms that you need to be familiar with:

  • An incident refers to the occurrence of foodborne illness
  • An outbreak is an incident in which two or more people experience a similar illness after ingestion of the same food and where epidemiological evidence implicates the food as the source of the illness.
  • A single case is a person who has been ill following consumption of food considered to be contaminated on the basis of epidemiological evidence.
  • An outbreak or single cases of unknown etiology refer to situations where epidemiological evidence implicates a common food source but where laboratory analysis fails to identify the etiological agent

Table 12.8 shows the number of cases reported in B.C. for certain types of microorganisms responsible for foodborne diseases.

Table 12.8. Number of reported cases in British Columbia
Microorganism 2000 2004 2006 2014
E. coli O157:H7 166 193 150 56
C. botulinum 4 NA NA NA
Salmonella 710 707 705 1167
Listeria monocytogenes 6 10 13 19
Hepatitis A- Virus 136 76 55 25


Source: B.C. Centre for Disease Control. Annual Summary of reportable diseases. Enteric, Food and Waterborne diseases 2006. NA = Not available.

The numbers in Table 12.8 represent only the "tip of the iceberg" since epidemiological evidence suggests that only 1-4% of all foodborne disease outbreaks are actually reported and documented.

Some of the reasons why only some foodborne disease outbreaks are documented are:

  • many people do not report to a physician when they suspect they are suffering from foodborne disease;
  • actual cases of foodborne disease may be mistakenly diagnosed as having other sources (environmental, unknown sources);
  • many people may attribute a mild case of foodborne illness as being due to the "24-hour flu," a "virus," "eating too much"'
  • sometimes people report that they suspect they are suffering from foodborne illness but the physician does not report the case to local health units or, if reported, the case may not be sufficiently well researched and reported by health units to the provincial health authorities.

Most cases of foodborne illness are only recognized when at least two or more people become sick after eating a meal or food product in common ("outbreak"). Symptoms can arise hours or days following the consumption of the food. The CFIA reports that each year only about 10,000 cases of foodborne illness are reported from which approximately 30 people die. The cost of salmonellosis has been estimated at $850 million per year in hospitalization costs and lost income. If one were to add the costs of foodborne disease caused by other organisms and other agents, the total costs become staggering (in excess of 1.3 billion dollars per year in Canada). Similar foodborne disease trends are reported yearly in the United States, the European Economic Community, Australia and other developed countries.

12.8.1 Microorganisms and Foodborne Diseases

Table 12.9 shows examples of microorganisms that cause foodborne disease. Pathogenic microorganisms can take advantage of situations where safe food handling and storage practices are not followed.

Table 12.9. Examples of microorganisms responsible for foodborne diseases

Microorganism responsible Foodborne disease
E. coli O157H7 E. coli poisoning
Toxin produced by Clostridium perfringens Clostridium food poisoning
Toxin produced by Clostridium botulinum Botulism
Salmonella Salmonellosis
Listeria monocytogenes Listeriosis
Staphylococcus aureus Staph poisoning

The following short descriptions of the microorganisms will provide you with an insight on the major foodborne disease-causing microorganisms, where they are found, conditions and foods implicated in outbreaks, and disease symptoms, as well as means of preventing their growth in foods.

For this course, you do not need to memorize all the details described here or in the readings. However, you should gain an understanding of how such detailed information about the different properties of pathogenic microorganisms can be used to provide guidelines for food handling practices or preservation techniques to ensure better food safety and to decrease the incidence of foodborne illness.

As you read through the descriptions, try also to differentiate between those microorganisms which are responsible for foodborne illness through food intoxications versus those that do so through foodborne infections.

  • In the case of foodborne intoxications, toxic substances are produced in the foods as by-products of the microorganisms prior to consumption, and cause the symptoms of foodborne illness upon ingestion.
  • Foodborne infections result from the ingestion of viable microorganisms in the food at the time of consumption; these pathogenic microorganisms multiply and grow in the host, causing the symptoms of foodborne illness.

Food Intoxications:

Organism Symptoms onset Common foods Prevention
Clostridium botulinum Botulinal toxins are among the most toxic substances known. Estimated LD50 for humans is 1 ng/kg body weight.

Dizziness, double vision, difficult swallowing, respiratory or cardiac paralysis, death (12-36 hrs)

Low acid foods in anaerobic conditions. Improperly home-canned, vacuum-packed, poorly refrigerated foods

Baked potatoes wrapped in foil

Spores have been detected in vegetables such as carrots, potatoes and fruit (contamination with soil), in fresh and processed meats and in honey and corn syrup.

Commercially sterile after processing must receive a "botulinum cook" (12 D)

Use sodium nitrite for cured meats

Properly refrigerate vegetable/fruit juice.

Honey, corn syrup and molasses must not be fed to infants < 1 year of age. Pasteurization of honey does not inactivate the spores.

Organism Symptoms onset Common foods Prevention
Escherichia coli O157:H7(Shiga toxin) Bloody diarrhea, kidney failure and hemolytic uremic syndrome (HUS) in sever cases (12-72 hrs) Undercooked ground meat, raw milk, unpasteurized apple juice/cider, lettuce, spinach, alfalfa sprouts

Contaminated water supply (outbreak in Walkerton, Ontario)

Practice good food sanitation and hand washing.

Properly handle and cook foods.E. coli is killed by normal cooking and pasteurization, as well as ionizing radiation, but is able to survive in acidic conditions (e.g. apple juice). It does not grow well at temperatures below 8°C.

The Kidney Foundation of Canada B.C. branch: E. coli bacteria: What You need to Know

Food Infections:

Organism Symptoms onset Common foods Prevention
Salmonella spp. Nausea, fever, vomiting, abdominal cramps, diarrhea (6-48 hrs) Raw meats and poultry, eggs (about 60% of chickens sold in the retail market are contaminated with Salmonella), milk, dairy products Salmonella are easily killed by heat (normal cooking and pasteurization processes) and ionizing energy, but survive freezing and dehydration. Consequently, frozen and thawed poultry can be just as contaminated as fresh poultry.
Organism Symptoms onset Common foods Prevention
Listeria monocytogenes Flu-like symptoms, meningitis, septicemia, or pneumonia. Birth defects, still birth (1 day- 3 weeks) Raw milk, dairy products, vegetables, fish and meat products The bacteria is capable of growing slowly on foods during storage in the refrigerator, and appears to be fairly tolerant to salt. It is easily killed by proper cooking and pasteurization techniques. Refrigerate raw materials and high-risk foods below 4°C.


Viruses are much smaller than bacteria and require a "living host" (human, animal) in which to grow and reproduce. Viruses do not multiply in food. Viruses are usually transferred from one food to another, from a food worker to a food, or from a contaminated water supply to a food.

Organism Symptoms onset Common foods Prevention
Hepatitis A Fever, nausea, vomiting, abdominal pain, fatigue, swelling of the liver, jaundice (10-50 days) Foods prepared with human contact; contaminated water Wash hands and practice good personal hygiene, avoid raw seafood
Organism Symptoms onset Common foods Prevention
Noravirus Vomiting, diarrhea, headache, fever (24-48 hrs) Sewage, contaminated water, contaminated salad ingredients, raw seafood, infected food workers Use potable water, practice good personal hygiene, cook all seafood

12.8.2 Factors in Foodborne Disease

According to the World Health Organization (WHO), a small number of factors related to food handling are responsible for a large number of foodborne disease outbreaks worldwide. The most common factors and their reasons for contributing to foodborne disease are listed below:

Factor Effect
Preparation of food several hours in advance & improper storage favors growth of pathogenic bacteria and/or formation of toxins
Insufficient cooking or reheating of food not sufficient heat is applied to eliminate/reduce pathogens
Inadequate cooling of foods permits survival of pathogens, allowing them to grow to sufficiently large numbers
Cross-contamination allowing un-contaminated food to become contaminated by improper handling of food
Poor personal hygiene can promote cross-contamination

Why were foods implicated in foodborne disease outbreaks consumed, if they were so heavily contaminated with disease-causing microorganisms?

In some cases the food probably contained millions or billions of such bacteria per gram or millilitre, but the food would have appeared perfectly normal.

It is important to note that most pathogenic bacteria do not alter the colour, odour, flavour or texture of food even though they may be present in large numbers. This is the reason why perishable food must be handled in such a manner that contaminants will be destroyed during cooking or processing and that post-cooking and post-processing contamination must be avoided. In addition, perishable, low acid foods must be handled as though they were contaminated, which means that safe food handling practices must be followed at all times.

Which foods should we be particularly careful about?

Remember the principles we have learned in earlier lessons about factors affecting microbial growth and survival such as pH (acidity), moisture, time-temperature, oxygen.

Think about whether the food has been treated by some process that could decrease or inhibit microbes.

Consider possibility of post-processing contamination that may lead to an unsafe food.

For those who are at risk (e.g. the elderly, the very young, pregnant women and their unborn or newborn babies, and those who are immunocompromised) should be particularly careful about raw meat and fish, milk and eggs, and should avoid deli meats, soft cheeses, uncooked sprouts, liver pate, unpasteurized fruit juices/cider. They should take extra care in washing or peeling fresh fruits and vegetables, or may cook these before eating.

Top 4 places where food can be mishandled and lead to foodborne disease incidents:

  1. Food Service Establishments
  2. Food Processing Establishments
  3. Retail Food Establishments
  4. Homes

Clearly, the food service sector is responsible for the majority of reported foodborne disease incidents and cases. One of the problems in the food service sector is that foods are handled in large quantities. If proper handling procedures are not followed, it is easy for food to become contaminated, for cross contamination to occur, for inadequate cooling to occur, and for inadequate cooking or hot holding temperatures to occur since the food often receives much handling by many people before it reaches the consumer.

Want to learn more?
  • Public health inspectors conduct regular inspections of restaurants, food service establishments, food stores and processors. If you are interested, take a look at the Vancouver/Richmond Restaurant Inspection Reports website for examples of the type of information that inspectors look for.
  • From this website, you can also find a list of closures of food establishments, including the dates and reasons for these closures.

Although the food service sector may be responsible for many incidences of foodborne disease, such incidents were in fact attributed to all sectors of the food industry as well as in homes. It is the responsibility of the food processing industry and the regulatory agencies to ensure that changes in food technology do not lead to undue risks with respect to foodborne illness or other potential hazards. It may be worthwhile, at this point to consider how food is handled in your home.

What can be done to ensure food safety?

The World Health Organization (WHO) and the BC Health Files have developed ten rules for safe food handling, that if followed, can reduce the risk of foodborne disease.

Below are some key points that need to be considered

  • Choose foods processed for safety (i.e. pasteurized products over unpasteurized)
  • Cook foods thoroughly
  • Eat cooked foods immediately
  • Store food promptly and carefully. Perishable and "cold" foods should be kept "cold" below 4°C until ready to cook or eat.
    • Avoid the "Temperature Danger Zone" (TDZ) which is from 4°C to 60°C (40-140°F). Bacteria can grow and/or produce toxins in food if left in the TDZ.
  • Reheat cooked foods thoroughly
  • Avoid cross-contamination. Do not allow any contact between raw food or its traces and cooked food
  • Wash hands repeatedly
  • Keep all kitchen surfaces clean
  • Do not let anyone with diarrhea or infected sores prepare food
  • Wash all fruits and vegetables before eating
  • Finally, if in doubt, throw it out! (Ministry of Health Services, 2001)

12.8.3 The HACCP System: Seven steps to food safety

In the past, food safety programs run by the industry (food processors) and food service establishments, have corrected hazardous conditions after they happened. The HACCP system is designed to anticipate and control problems before they happen. The HACCP systems stands for Hazard Analysis and Critical Control Points. This system is recommended as the best method for ensuring food safety in retail establishments and food processing operations. There are 7 principles in a HACCP system:

  1. Identify Hazards
  2. Determine the critical control points (CCPs)
  3. Establish control measures (critical limits or thres holds)
  4. Establish procedures to monitor CCPs
  5. Establish corrective actions
  6. Keep records
  7. Verify procedures

While each principle is unique, they all work together to form the basic structure of an effective food safety program. (Source: McSwane, D., Rue, N., Linton, r., and Reeves, D.2003. Essentials of Food Safety and Sanitation. Pearson Education Canada Inc., p. 104-121)


The food safety rules described above and the description of the seven steps for HACCP are summarized in the following video:

HACCP: The Hazard Analysis and Critical Control Point System

How important is that we wash our hands?

The following figure dramatically illustrates the importance of washing hands thoroughly after handling raw meats. In this experiment, a previously sanitized hand was rubbed with a cube of raw pork for about 15 seconds. The hand was then pressed gently onto a 9" agar plate and labeled as "soiled hand" (A). Hands were again washed with Hibitane hand sanitizer (4% w/v chlorhexidene gluconate) for 30 seconds and the right hand was gently pressed onto a second agar plate labeled as "washed hand" (B). Both plates were incubated at room temperature for 2 days. The images below show the results/observations after two days:

The importance of washing hands. Right palm soiled with raw pork cubes (photograph courtesy of Eunice Yao, 2000. "Digital Image Analysis of Full-hand Touch Plates: A method of mimicking real soil encountered in food science industry to analyze the efficacy of antimicrobial hand sanitizer and alcohol-based sanitizing gels").

Microbe Video Pt.1

Microbe Video Pt.2

Microbe Video Pt.3