University of Rhode Island Food Safety Education

College of the Environment and Life Sciences

Causes and Prevention of Foodborne Illness


CDC estimates that each year roughly 1 in 6 Americans (or 48 million people) get sick, 128,000 are hospitalized, and 3,000 die of foodborne diseases. Symptoms of foodborne illness include upset stomach, abdominal cramps, nausea and vomiting, diarrhea, fever, and dehydration. Symptoms can range from mild to severe and death.

Foodborne illness can affect anyone who eats contaminated food; however, certain populations are more susceptible to becoming ill with a greater severity of illness. These populations include infants and children, the elderly, pregnant women, people taking certain kinds of medications or immune suppressed (e.g. cancer patients, people living with diabetes).

To prevent foodborne illness, it is necessary to understand how food becomes unsafe to eat and what proactive measures can be taken to keep food safe.


The causes of foodborne illness fall into the following 3 categories:

  • Biological hazards include bacteria, viruses, and parasites. Bacteria and viruses are responsible for most foodborne illnesses. Biological hazards are the biggest threat to food safety. This can be inherent in the product or due to mishandling (e.g. time/temperature abuse).
  • Chemical hazards include natural toxins and chemical contaminants. Some natural toxins are associated with the food itself (i.e. certain mushrooms, PSP in molluscan shellfish), some are made by pathogens in the food when it is time/temperature abused (i.e. histamine development in certain seafood species). Some additives, such as sulfites, can be a hazard to certain individuals. Chemical contamination can also occur when products, such as cleaners and sanitizers are not used correctly.
    • Food allergens are also a chemical hazard. Some people are sensitive to proteins in foods. Every food is different. Regulatory authorities have identified 8 food allergens that cause 90% of the allergic reactions. These are milk, eggs, fish, crustacean shellfish (lobster, crab, shrimp), wheat, soy, peanuts, and tree nuts.
  • Physical hazards can include metal shavings from cans, wires from a grill bristle, and plastic pieces or broken glass.
  • Bacteria are single-celled organisms which multiply and increase in number by cell division, under appropriate environmental conditions. The conditions that influence bacterial growth are the food itself, acidity, time, temperature, oxygen, and moisture. Most bacteria need nutrients to survive. They obtain these nutrients from food. Bacteria grow best in food that is neutral to slightly acidic (acidity is measured by pH). Microorganisms have different acidity (pH), temperature, and oxygen requirements for optimal growth. Bacteria need time to grow and they grow rapidly between 41°F and 140°F. Bacterial growth is slowed at temperatures below 41°F and limited at temperatures above 140°F. Some bacteria require oxygen to grow (aerobic), some grow when there is no oxygen (anaerobic), and some can grow with or without oxygen (facultative). Bacteria will grow when food and water is available. If water is bound or tied up with, for example salts or sugars, this water is not available to be used by bacteria. This concept of available water is referred to as water activity (Aw).
    • Some bacteria can be further categorized:
      • Some bacteria are spore formers. The spore provides protection to the organisms during periods of environmental stress. When the conditions are suitable to support bacterial growth, the organism germinates from the spore and continues the growth cycle.
      • Some bacteria produce toxins that cause foodborne illness.
  • Molds are a multi-cellular form of fungi that reproduce by fruiting bodies that break and release thousands of microscopic mold spores, each capable of growing under the right conditions. Molds can send “roots” into the food to provide nourishment to the spore. Molds prefer damp, dark environments for optimal growth. They grow readily on almost any food, as well as walls, ceilings, and other areas of high moisture and humidity. Some molds produce toxins that can cause illness.
  • Viruses are the smallest known organisms. They cannot multiply in food—they need a human host. Viruses are transmitted to food from infected people.
  • Parasites include worms and protozoa. They cannot multiply in food. They can only multiply in a host cell.

Pathogens can cause different types of foodborne illness. Once a contaminated food is eaten, illness can be caused by the pathogens themselves (foodborne infection); caused by toxins produced in the food by pathogens (foodborne intoxication); and caused by toxins produced in the body by pathogens (foodborne toxin-mediated infection).


Follow these 4 simple steps to keep food safe:

  1. CLEAN: Wash hands and food contact surfaces and utensils often, between tasks, and if they have become contaminated. Effective cleaning involves removing soil and debris, scrubbing with hot soapy water and rinsing, using potable/drinking water. Sanitizing involves the use of high heat (e.g. a dishwasher) or chemicals (e.g. chlorine bleach) to reduce or eliminate the number of microorganisms or germs to a safe level.
    • Wash hands with warm water and soap for 20 seconds and dry with a disposable paper towel or clean hand cloth.
      • Alcohol based hand sanitizers are not a replacement for handwashing. They are not effective if the hands are dirty, they are not effective against Norovirus, and they do not eliminate all types of microorganisms.
    • Wash cutting boards, dishes, and utensils after preparing each food item and before you use it for the next food.
      • Use hot, soapy water, rinse with hot water, and air dry or dry with a clean paper towel or clean dish cloth.
      • Or wash in the dishwasher.
    • Wash countertops after preparing each food item and before you use it for the next food.
      • Use paper towels or clean dish cloths to wipe kitchen surfaces or spills.
      • Wash countertops with hot soapy water, rinse with hot water and air dry or dry with a clean paper towel or clean dish cloth.
      • If you choose to sanitize for added protection for bacteria on surfaces, you can use the following:
        • Dilute mixtures of chlorine bleach and water are a cost-effective method of sanitation. Chlorine bleach is a very effective sanitizer. It comes in several concentrations.
        • If bleach is 8.25%:
          •  Measure 1 teaspoon of bleach per 1 gallon of water or 1/8 teaspoon of bleach per 1 pint of water.
          •  Apply to the cleaned countertop and allow to sit for 1-2 minutes and air dry or dry with a clean paper towel.
        • Alternatively, commercial products for sanitizing the home kitchen are available. Follow manufacturer instruction for use.
    • Wash dish cloths often in the washing machine.
    • Store sponge in a place so it can dry after use.
      • To lower the risk of cross-contamination, sanitize the dish sponge often:
    • Replace the dish sponge often.
  2. SEPARATE to prevent cross contamination. Cross contamination is the transfer of harmful bacteria from uncooked food products (e.g. raw meat, fish, and poultry) or unclean people, countertops, and kitchen equipment to ready-to-eat foods (e.g., fruits, vegetables, deli meats/cheeses, and prepared or cooked foods).
    • Prevent cross contamination when grocery shopping.
      • Physically separate raw meat, fish and poultry to prevent their juices from dripping onto other foods. This can be done by:
        • Segregating raw meat, fish and poultry on one side of the shopping cart.
        • Placing raw meat, fish and poultry in separate plastic bags (e.g. one bag for chicken, one bag for fish, etc.).
      • Designate reusable bags for grocery shopping only. Reusable bags for raw meat, fish, or poultry should never be used for ready-to-eat products.
        • Frequently wash bags. Cloth bags should be washed in a washing machine and machine dried or air-dried. Plastic-lined bags should be scrubbed using hot water and soap and air-dried.
        • Separate raw meat, fish and poultry in disposable plastic bags before putting them in a reusable bag
        • Check that both cloth and plastic-lined reusable bags are completely dry before storing them.
    • Prevent cross contamination when storing food in the refrigerator.
      • In the refrigerator, store raw meats, fish, and poultry below ready-to-eat and cooked foods.
      • When thawing frozen raw meat, fish and poultry, put the food in a plastic bag or on a plate on the lowest shelf to prevent juices from dripping onto other foods.
        • After thawing in the refrigerator, food should remain safe and of good quality for a few days before cooking. Food thawed properly in the refrigerator can be refrozen without cooking, although quality may be impacted. Other methods for thawing are explained below (see Chill).
    • Prevent cross contamination when handling, preparing, and serving food.
      • Thoroughly wash your hands before and after handling different food items, after using the bathroom, and anytime they can become contaminate.
      • Use separate cutting boards for meat and produce. Alternatively, prepare produce first, then meat.
      • Wash and rinse cutting board, knives, and preparation area after cutting raw meat, fish or poultry. These items can be sanitized after cleaning.
      • Use a clean serving plate to serve cooked meat. Do not use the plate that held the raw meat, unless it is washed.
      • Throw away any sauce or dip that has been used to marinade raw meat, fish, or poultry. Do not use this extra sauce as a dip for cooked food unless it is boiled first.
  3. COOK food thoroughly and use a thermometer to verify the proper temperature was reached.
    • Cook foods to the safe minimum internal cooking temperature, as indicated in the table below.
    • To determine that the proper temperature was reached, place a food thermometer in the thickest part of the food and allow the thermometer to equilibrate.
      • Make sure it’s not touching bone, fat, or gristle.
      • For whole poultry, insert the thermometer into the innermost part of the thigh and wing and the thickest part of the breast.
      • For combination dishes, place the thermometer in the center or thickest portion of the food. Egg dishes and dishes containing ground meat or poultry should be checked in several places.
    • Clean your food thermometer with hot, soapy water before and after each use!
    • For information on safe cooking temperatures for different foods, please refer to the following chart from USDA
  4. CHILL foods promptly. Cold temperatures slow the growth of harmful bacteria. Cold air must circulate to help keep food safe, so do not over fill the refrigerator. Maintain the refrigerator temperature at 41°F or below. Place an appliance thermometer in the rear portion of the refrigerator, and monitor regularly. Maintain the freezer temperature at 0°F or below.
    • Refrigerate and/or freeze meat, poultry, eggs and other perishables as soon as possible after purchasing.
      • Consider using a cooler with ice or gel packs to transport perishable food.
    • Perishable foods, such as cut fresh fruits or vegetables and cooked food should not sit at room temperature more than two hours before putting them in the refrigerator or freezer (one hour when the temperature is above 90°F).
    • There are three safe ways to thaw food: in the refrigerator (see Separate), in cold water, and in the microwave. Food thawed in cold water or in the microwave should be cooked immediately.
      • Submerging the food in cold water. It is important to place the food in a bag that will prevent the water from entering. Check the water every 30 minutes to make sure it is cold. Cook food prior to refreezing.
      • Microwave thawing. Cook food immediately once thawed because some areas of the food may become warm and begin to cook during the thawing process. Cook food prior to refreezing.
    • Cool leftovers quickly by dividing large amounts into shallow containers for quicker cooling in the refrigerator.

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