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Food Poisoning: How Does Food Become Contaminated?

Most people can recognize the symptoms of food poisoning, but do you know how food becomes contaminated in the first place? There are several ways that food can become contaminated. Bacteria can infect food on the farm, in the kitchen, or anywhere in between if people don't take adequate safety precautions.

In this section, we will discuss the sources of food poisoning. We will also explain what you can do to prevent foodborne illnesses.

Types of Food Poisoning

There are two main types of food poisoning: viral and bacterial. Most food poisoning cases today involve bacterial contamination. Bacteria infect food at some point along the chain of distribution. For example, a farmer may plant their crops too close to animal waste, or the sous chef at a local restaurant may prepare food without washing their hands.

When it comes to bacterial foodborne diseases, there are three main kinds of contamination:

  • E. coli
  • Salmonella
  • Listeria

While most food poisoning outbreaks involve bacteria, thousands of Americans develop a viral case of food poisoning yearly. The most common type of viral food poisoning is norovirus. It's common to see this type of food poisoning in cramped places like cruise ships, dormitories, and resorts.

Some of the other less common types of food poisoning include:

  • Vibrio
  • Campylobacter
  • Hepatitis A


Bacteria that live in the intestines of animals are responsible for many food poisoning cases. For example, E. coli (Escherichia coli) typically remains in the discarded portions of the animal and never makes it to the dinner plate.

However, meat and poultry can become contaminated during slaughter if they come into contact with trace amounts of the animal's intestinal contents.

If you wash fresh fruits and vegetables with water contaminated by animal manure or human sewage, they can also become tainted. This is why you must clean all fresh produce before you eat it.

Food Handling

Another common cause of food poisoning is improper and unsafe food handling. Farm workers, cooks, servers, and other food preparers may touch food without washing their hands. For example, if a chef or waiter uses the bathroom and doesn't wash their hands, they may contaminate food with shigella.

Shigella is a foodborne bacteria that causes diarrhea, fever, and stomach cramps. Another illness caused by improper food handling is norovirus. Most people assume this is the familiar stomach flu. The symptoms include the following:

  • Nausea
  • Vomiting
  • Stomach cramps
  • Fever
  • Upset stomach
  • Abdominal pain
  • Fatigue

If you have a weakened immune system or other infectious diseases, your symptoms may be more serious. For instance, some people with severe cases of foodborne illness can develop kidney disease.

If you notice these symptoms, visit your healthcare provider immediately. While your symptoms may resolve in a few days, it's better to be safe than sorry.

Cross Contamination

Some foods are perfectly safe until they come into contact with other infected food products. For example, if you use the same utensil on uncooked shellfish and pasta, the pasta may become tainted.

Cross-contamination with other raw food products can also spread germs that cause illness. To lessen your exposure to food poisoning, avoid certain foods altogether. These include:

  • Soft cheeses
  • Unpasteurized milk
  • Food left at room temperature for more than an hour or two
  • Dairy products past their expiration dates
  • Unrefrigerated deli meats

You can avoid most cases of foodborne illness. If you cook food properly and ensure that all food handlers practice proper hygiene, you should be okay. You also have to use common sense. A helpful rule to follow is that you shouldn't serve the rest of your family food you wouldn't serve your young children.

Food Preparation

In the kitchen, germs can be transferred from one food to another in various ways. For example, you can spread bacteria and other pathogens by using the same knife, cutting board, and other utensils without washing them properly between each usage.

Fully cooked foods can become re-contaminated if they touch other raw foods that contain certain germs. Food can also become dangerous if you rinse it with contaminated water. For more food safety tips, visit's Food Poisoning Prevention page.

Food Storage

Safe food preparation is crucial in avoiding foodborne illnesses. It's also essential that you store foods properly. If you refrigerate foods without covering them, they can become contaminated. The same is true for food not kept refrigerated until you're ready to eat it.

Many bacterial microbes must multiply to cause disease. Under warm and moist conditions, for instance, slightly contaminated food left out overnight can become highly infectious. Prompt refrigeration or freezing typically prevents this growth. High salt, sugar, or acid levels also inhibit bacteria growth.

Heating Food

You can usually destroy bacteria and other things that cause foodborne illness by cooking your food. Heating food to an internal temperature above 160 degrees Fahrenheit or 78 degrees Celsius, even for a few seconds, is enough to kill most bacteria, viruses, or parasites.

Toxins produced by bacteria vary in their sensitivity to heat. For instance, the toxin that causes botulism is inactivated by boiling, whereas the staphylococcal toxin isn't. Botulism is a potentially fatal form of food poisoning that usually causes illness within 18-36 hours of exposure. Staphylococcal usually causes no disease in healthy people.

What To Do if You Develop Food Poisoning Due to Someone's Negligence

If you eat contaminated food at a restaurant and get sick as a result, you need to seek medical help before considering legal help. The same is true if you buy tainted food from a grocery store. Talk to a local products liability attorney who can help you decide what to do next.

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