Food Safety: Understanding Foodborne Illness

Most people have been affected by what’s commonly known as food poisoning at some point. Understanding the causes of foodborne illnesses is an important step to help prevent them.

What are foodborne illnesses?

Foodborne illnesses are caused by eating food contaminated with harmful microorganisms. The majority of cases are caused by bacteria. Viruses, parasites, moulds and toxins (chemicals) can also cause foodborne illness.

Foods can become contaminated when food is not handled safely. Some common mistakes include not chilling or cooking foods properly, cross-contamination of cooked with raw foods, and unclean cooking surfaces, utensils, dishes or hands. One of the most common mistakes is leaving foods in the “danger zone” where bacteria grow quickly, between 4°C (40°F) and 60°C (140°F).

What are the symptoms?

The symptoms of foodborne illnesses can range from mild to very serious. They may include:

  • stomach cramps
  • nausea
  • diarrhea
  • vomiting
  • fever
  • headaches

You may feel the affects of food poisoning right after eating a contaminated food or you may not feel sick until a few days or a month later. In most cases, the symptoms don’t last very long. Often people don’t even realize they have a foodborne illness because it can feel like the flu.

Foodborne illnesses, however, can be very serious and even fatal. Some people are more likely to become seriously ill than others. These include infants and young children, pregnant women, senior citizens and people with weakened immune systems, such as those with cancer, liver disease and AIDS. In some cases, foodborne illness can cause long term problems such as kidney damage, arthritis or heart problems.

Which bacteria are to blame?

Scientists have identified hundreds of different foodborne illnesses. Some are rare, while others are much more common. The following five bacteria are common causes of food poisoning. Click on the links below to learn more about the common food sources, symptoms and prevention of each of these:


Common sources

Symptoms may include

Prevention Tips

Campylobacter jejuni

Raw poultry, unpasteurized (raw) milk and untreated water. (Note: dogs, cats and farm animals can also carry this bacteria.)

Fever, headache and muscle pain, followed by diarrhea (often bloody), stomach pain, cramps, nausea and vomiting.

Keep raw meat and poultry separate from ready-to-eat foods. Cook foods to a safe internal temperature. Drink only pasteurized milk and use a safe water supply.

Clostridium botulinum

Improperly prepared home-canned, low-acid foods (e.g. corn, mushrooms, spaghetti sauce, salmon, garlic in oil). Honey may also be contaminated with C. botulinum.

Nausea, vomiting, fatigue, dizziness, headache, double vision, and dryness in the throat and nose. In some cases, these may lead to respiratory failure, paralysis and even death.

Never eat food from cans that are dented, leaking or bulging. Be sure to follow proper canning processes when canning foods at home. Refrigerate all foods that are labelled “keep refrigerated”.  Do not feed honey to children under one year.


Raw or undercooked meats (especially ground meats), raw vegetables and fruit. Untreated water and unpasteurized (raw) milk and unpasteurized apple juice or cider.

Stomach cramps, diarrhea (sometimes bloody) and fever. Some may develop Hemolytic Uremic Syndrome, an unusual type of kidney failure and blood disorder, which can result in death.

Keep your hands, food preparation surfaces and utensils clean. Avoid cross-contamination. Rinse raw vegetables and fruit well. Store and cook foods properly.


Non-dried processed meats (hot dogs and deli meats), unpasteurized (raw) milk and milk products (soft cheeses), raw vegetables, raw or undercooked meat, poultry or fish.

Vomiting, nausea, fever, headache, cramps, diarrhea and constipation. Some may develop meningitis encephalitis (a brain infection) and/or septicaemia (blood poisoning) which can result in death.

Thoroughly cook meat, poultry and fish. Heat hot dogs to steaming hot. Keep leftovers in the refrigerator for a maximum of four days and reheat thoroughly before eating. Wash fresh vegetables and fruit well. Avoid unpasteurized milk and milk products.


Raw or undercooked poultry, meat, fish, and eggs, raw vegetables and fruit, unpasteurized (raw) milk and milk products (soft cheeses), sauces and salad dressings, peanut butter, cocoa and chocolate.

Stomach cramps, diarrhea, fever, vomiting and nausea. Some may experience chronic symptoms, such as reactive arthritis (Reiter's Syndrome) three to four weeks later.

Cook foods to a safe internal temperature. Use a food thermometer to be sure. Use pasteurized egg products instead of raw eggs, in foods such as eggnog, mayonnaise, salad dressing, ice cream and mousses. Wash raw vegetables and fruit well.

What can you do?

Harmful bacteria can infect our food at any point in the food chain, from the farm to when it reaches our plate. The good news is - most cases can be prevented by using safe food handling practices and using a food thermometer to check that your food is cooked properly.

Remember, you usually can’t tell whether foods are contaminated by the way they look, smell, or taste. So the safe rule of thumb is - When in doubt, throw it out!

If you think you have a foodborne illness, report it to your doctor or health department.

Learn more about

Food Safety – True or False

Causes of Food Borne Illness, Canadian Food Inspection Agency.

Food Recalls and Allergy Alerts, Canadian Food Inspection Agency

Food Safety Tips, Canadian Partnership for Consumer Food Safety Education.

Last Update – April 24, 2018

Phone Icon

Dietitians look beyond fads to deliver reliable, life-changing advice. Want to unlock the potential of food? Connect with a dietitian.