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14.1: Foodborne Illness and Food Safety

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    Learning Objectives

    • Identify groups at risk for foodborne illness.
    • Describe the major types of foodborne illness.
    • Identify various causes of food contamination.
    • Describe steps to prevent foodborne illness.
    • Identify federal agencies that regulate food.

    Foodborne illness is a serious threat to health. Sometimes called “food poisoning,” foodborne illness is a common public health problem that can result from exposure to a pathogen or a toxin in food or beverages. Raw foods, such as seafood, produce, and meats, can all be contaminated during harvest (or slaughter for meats), processing, packaging, or during distribution. For all kinds of food, contamination also can occur during preparation and cooking in a home kitchen or in a restaurant. In many developing nations, contaminated water is also a major source of foodborne illness.

    Many people are affected by foodborne illness each year, making food safety a very important issue. The CDC estimates that 48 million Americans get sick from a foodborne illness each year.1 Foodborne illness can range from mild stomach upset to severe symptoms, or even death.

    At-Risk Groups

    No one is immune from consuming contaminated food. But, whether you become seriously ill depends on the microorganism, the amount you have consumed, and your overall health. In addition, some groups have a higher risk than others for developing severe complications to foodborne illness, including:

    • young children
    • elderly people
    • pregnant people
    • people with compromised immune systems from medical conditions, such as diabetes, liver disease, kidney disease, organ transplants, or HIV/AIDS, or from receiving chemotherapy or radiation treatment

    People in all of these groups should handle food carefully, make sure that what they eat has been cooked thoroughly, and avoid taking any chances that could lead to exposure.

    Major Types of Foodborne Illness

    Foodborne illnesses are classified as either food infections or food intoxications. The difference depends on the agent that causes the condition. Microbes, such as bacteria, cause food infections, while toxins, such as the kind produced by molds, cause food intoxications. Different diseases manifest in different ways, so signs and symptoms can vary with the source of contamination. The microbe or toxin enters the body through the gastrointestinal tract and as a result common symptoms include diarrhea, nausea, and abdominal pain. Additional symptoms may include vomiting, dehydration, lightheadedness, and rapid heartbeat. More severe complications can include a high fever, diarrhea that lasts more than three days, prolonged vomiting, bloody stools, and signs of shock.

    One of the biggest misconceptions about foodborne illness is that it is always triggered by the last meal that a person ate. However, it may take several days or more before the onset of symptoms. If you develop a foodborne illness, you should rest and drink plenty of fluids.

    Food Infection

    According to the CDC, more than 250 different foodborne diseases have been identified; most are food infections caused by bacteria, viruses, and parasites.1 The infection then grows inside the body and becomes the source of symptoms. Food infections can be sporadic and often are not reported to physicians. However, occasional outbreaks occur that put communities at risk.

    Bacteria, one of the most common agents of food infection, are single-celled microorganisms (also called microbes) that are too small to be seen with the human eye. Microbes live, die, and reproduce, and like all living creatures, they depend on certain conditions to survive and thrive. In order to reproduce within food, microorganisms require the following conditions:

    • Temperature. Between 40°F and 140°F, which is called the danger zone, microorganisms multiply more rapidly.
    • Water. Many microorganisms require a high moisture content to multiply. Fresh fruits and vegetables have the highest moisture content.
    • Oxygen. Most microorganisms need oxygen to grow and multiply, but a few are anaerobic (do not need oxygen to grow).
    • Acidity (pH) Level. Most microorganisms grow best in a slightly acidic to neutral environment (around 4.6-7.0 on the pH scale).

    Food Intoxication

    Food intoxications are caused by microorganisms that secrete toxins (harmful chemicals) that bind to cells in the body and cause a variety of symptoms. Toxins are categorized as:

    • Enterotoxins. Enterotoxins affect the gastrointestinal system and cause symptoms such as abdominal cramping, diarrhea, and vomiting.
    • Neurotoxins. Neurotoxins affect the nervous system and can cause neurological damage or paralysis. For example, Clostridium botulinum produces botulism toxin which blocks nerve transmissions to muscle cells. Clostridium botulinum can grow in an oxygen-free environment. It can be present in honey, so honey should not be given to infants.

    The Causes of Food Contamination

    Both food infections and food intoxications can create a burden on health systems, when patients require treatment and support, and on food systems, when companies must recall contaminated food or address public concerns. It all begins with the agent that causes the contamination. When a person ingests a food contaminant, it travels to the stomach and intestines. There, it can interfere with the body’s functions and make you sick. In this section, we will focus on several causes of food contamination including bacteria, viruses, parasites, and mold toxins.


    All foods naturally contain small amounts of bacteria. However, poor handling and preparation of food, along with improper cooking or storage can multiply bacteria and cause illness. In addition, bacteria can multiply quickly when cooked food is left out at room temperature for more than a few hours. Most bacteria grow undetected because they do not change the color or texture of food or produce a bad odor. Freezing and refrigeration slow or stop the growth of bacteria, but do not destroy the bacteria completely. The microbes can reactivate when the food is taken out and thawed. Table \(\PageIndex{1}\) lists the symptoms, when symptoms begin, and common food sources for several bacteria that cause foodborne illness.

    Table \(\PageIndex{1}\): Bacteria that Cause Foodborne Illness2
    Bacteria Timeframe for onset of symptoms Symptoms Common food sources
    Salmonella 6 hours - 6 days diarrhea, fever, stomach cramps, vomiting raw or undercooked chicken or turkey; eggs; unpasteurized milk or juice
    Clostridium perfringens 6 - 24 hours diarrhea, stomach cramps beef or poultry; gravies; dried foods
    Campylobacter 2-5 days bloody diarrhea, stomach cramps, fever raw or undercooked poultry, raw milk, contaminated water

    Staphylococcus aureus (Staph)

    30 minutes - 6 hours

    nausea, vomiting, stomach cramps, diarrhea

    foods that are handled without workers washing hands; foods not cooked after handling (such as sliced meats, sandwiches, pastries)
    Listeria monocytogenes 1-4 weeks fever, muscle aches, headache, stiff neck, confusion soft cheeses, raw sprouts, melons, hot dogs, deli meats, smoked seafood, unpasteurized milk
    Escherichia coli (E. coli) 3-4 days severe stomach cramps, bloody diarrhea, vomiting raw or undercooked beef, unpasteurized milk or juice, raw vegetables (such as lettuce or sprouts), contaminated water
    Clostridium botulinum 18-36 hours blurred vision, slurred speech, difficulty swallowing or breathing, muscle weakness and paralysis improperly canned or fermented food, honey
    Vibrio 1-4 days watery diarrhea, nausea, stomach cramps, vomiting, fever, chills raw or undercooked shellfish (particularly oysters)


    Viruses are another type of pathogen that can lead to food infections, however they are less prominent than bacteria.

    The most common form of contamination from handled foods is the norovirus. You can get norovirus from having direct contact with an infected person, consuming contaminated food/water, or touching contaminated surfaces then putting your unwashed hands in your mouth. The norovirus is very contagious (part of the reason for this is that the virus is able to survive on surfaces for weeks); symptoms include vomiting and diarrhea.3

    Hepatitis A is one of the more well-known food-contaminating viruses. Sources include raw shellfish from polluted water, and food handled by an infected person. This virus can go undetected for weeks and, on average, symptoms do not appear until about one month after exposure. At first, symptoms include loss of appetite, nausea, vomiting, and fever. Three to ten days later, additional symptoms can manifest, including jaundice and darkened urine. Severe cases of a hepatitis A can result in liver damage and death.


    Food-contaminating parasites are microscopic organisms that simultaneously derive benefit from and harm their host. The most common parasites that cause foodborne illness are helminths and protozoa.

    • Helminths are multicellular worms (for example, tapeworms and roundworms). Helminths reproduce by releasing eggs; animals may consume the eggs which then develop into larvae that can survive even after the animal is killed. Eating raw or undercooked meat can lead to ingesting the larvae. Thorough cooking destroys the larvae.
    • Protozoa are single-celled organisms. There are several different types of protozoa (for example, Toxoplasma gondii or Giardia). People typically become infected after eating undercooked, contaminated meat or from drinking contaminated water.


    Prions are animal proteins that misfold and become infectious. Prions go on to destroy normal proteins to the point that nerve tissues lose their function leading to neurological disease (known as variant Creutzfeldt-Jakob disease) and eventually death.

    Mold Toxins

    Warm, humid, or damp conditions encourage mold to grow on food. Molds are microscopic fungi that live on animals and plants. Under a microscope, molds look like slender mushrooms. They have stalks with spores that form at the ends. The spores give molds their color and can be transported by air, water, or insects. Spores also enable mold to reproduce. Additionally, molds have root-like threads that may grow deep into food and be difficult to see. The threads are very deep when a food shows heavy mold growth. Foods that contain mold may also have bacteria growing alongside it.

    Some molds, like the kind found in blue cheese, are desirable in foods, while other molds can be dangerous. The spores of some molds can cause allergic reactions and respiratory problems. In the right conditions, a few molds produce mycotoxins, which are natural, poisonous substances that can make you sick if they are consumed. Mycotoxins are contained in and around mold threads, and in some cases, may have spread throughout the food.

    Preventing Foodborne Illness

    Consumers can also take steps to prevent foodborne illness and protect their health. Although you can often detect when mold is present, you can’t see, smell, or taste bacteria or other agents of foodborne disease. Therefore, it is crucial to take measures to protect yourself from disease. The four most important steps for handling, preparing, and serving food are:

    • Clean. Wash hands thoroughly with warm, soapy water for at least twenty seconds before preparing food and every time after handling raw foods. Clean surfaces often and wash utensils after each use. Wash fruits and vegetables (even if you plan to peel them).
    • Separate. Don’t cross-contaminate food during preparation and storage. Use separate cutting boards for produce and for meat, poultry, seafood, and eggs. Store food products separately in the refrigerator.
    • Cook. Heat food to proper temperatures. Use a food thermometer to check the temperature of food while it is cooking. It can be helpful to check the cooking temperature chart at If food is not served immediately after cooking, keep food hot (140oF or above) after it has been cooked.
    • Chill. Refrigerate any leftovers within two hours. Make sure your refrigerator is set to 40oF or below and your freezer is set to 0oF or below. Never thaw or marinate food on the counter; it's best to thaw or marinate foods in the refrigerator to prevent bacteria growth. Know when to keep food and when to throw it out by checking a safe storage time chart such as the one at It is helpful to label leftovers with the date the food was made to help track when the leftovers should be thrown out.

    Food Regulation

    Food regulatory agencies work to protect the consumer and ensure the safety of our food. Food regulation is divided among different agencies, primarily the Food and Drug Administration (FDA) and the United States Department of Agriculture (USDA). It can be confusing to know which agency monitors and manages which regulatory practice. For example, the FDA oversees the safety of eggs when they’re in the shells, while the USDA is in charge of the eggs once they are out of their shells.

    The Food and Drug Administration (FDA)

    The FDA enforces the safety of domestic and imported foods. It also monitors supplements, food labels, claims that corporations make about the benefits of products, and pharmaceutical drugs. Sometimes, the FDA must recall contaminated foods and remove them from the market to protect public health. Recalls are almost always voluntary and often are requested by companies after a problem has been discovered. In rare cases, the FDA will request a recall. But no matter what triggers the removal of a product, the FDA’s role is to oversee the strategy and assess the adequacy and effectiveness of the recall.

    The United States Department of Agriculture (USDA)

    Headed by the Secretary of Agriculture, the USDA develops and executes federal policy on farming and food. This agency supports farmers and ranchers, protects natural resources, promotes trade, and seeks to end hunger in the United States and abroad. The USDA also assures food safety, and in particular oversees the regulation of meat, poultry, and processed egg products.

    The Environmental Protection Agency (EPA)

    A third federal government agency, the Environmental Protection Agency (EPA), also plays a role in the regulation of food. The EPA works to protect human health and the environment. The agency conducts environmental assessment, education, research, and regulation. The EPA also works to prevent pollution and protect natural resources. Two of its many regulatory practices in the area of agriculture include overseeing water quality and the use of pesticides.

    Key Takeaways

    • Groups at risk for foodborne illness include young children, elderly people, pregnant women, and people with compromised immune systems.
    • Foodborne illnesses are classified as either food infections or food intoxications.
    • Causes of food contamination include bacteria, viruses, parasites, and mold toxins.
    • Consumers can take steps to prevent foodborne illness. The four most important steps for handling, preparing, and serving food are clean, separate, cook, and chill.
    • Food regulatory agencies such as the FDA, USDA, and EPA work to protect the consumer and ensure the safety of our food.


    1. Foodborne Germs and Illnesses. Accessed July 15, 2020.
    2. Food Poisoning Symptoms. Accessed July 15, 2020.
    3. Norovirus. Accessed July 16, 2020.
    4. 4 Steps to Food Safety. Accessed July 16, 2020.

    14.1: Foodborne Illness and Food Safety is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by LibreTexts.

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