Key takeaways:
Food poisoning is caused by germs or toxins that contaminate food or water. By definition, food poisoning comes from eating contaminated food — not from contact with another person.
The bacteria and viruses that cause food poisoning can still be contagious. So someone who gets sick from food can potentially spread it to others. This depends on which bacteria or virus is causing the problem.
When someone has symptoms of food poisoning, they won’t know exactly which virus or bacteria is causing it. This can make it hard to know if they’re contagious, so it’s better to avoid possible exposure.
If you have food poisoning, you or someone in your household may wonder if the symptoms are contagious. No one wants to spread illnesses to their friends, family, or co-workers. In many cases, food poisoning isn’t contagious. But there are some exceptions and situations where you can potentially spread it to others.
It can be hard to know whether your specific case is contagious or not. So we’ll go into more detail about how food poisoning spreads and what you can do to keep the people around you safe.
Food poisoning can come from many different microbes. These organisms can contaminate mishandled food or grow in food left at room temperature for too long. For example:
Bacterial infections can develop from eating contaminated food. Many times these bacteria, like E. coli, salmonella, and Campylobacter, grow in undercooked meat. But they can also contaminate plant products. Listeria is another bacteria that commonly lives in soft cheese and deli meats.
Bacterial toxins can also form in food. These toxins can cause symptoms of food poisoning without an actual infection. Bacteria like Staphylococcus aureus and Bacillus can make these toxins.
Viruses can contaminate food as well. Norovirus is a common example — this is the one often associated with outbreaks on cruise ships and day cares. Hepatitis A is another example of a virus that causes food poisoning.
Parasites are another organism that can cause food poisoning. Cyclospora and Giardia are examples.
Food poisoning — by definition — is not contagious. It’s an illness that someone gets from eating contaminated foods. And outbreaks can occur when many people eat the same contaminated food. So, in these outbreaks, the illness isn’t spread from person to person like other infections.
But the bacteria and viruses that cause food poisoning can spread from person to person. This is where it just becomes a matter of terminology. If person A gets sick from E. coli in their hamburger, they have food poisoning. But if they then spread that E. coli to person B, person B has gastroenteritis (“stomach flu”).
So how does food poisoning become contagious? After person A eats the contaminated hamburger, they now have a lot of harmful E. coli in their intestine. And when someone has a lot of vomiting and diarrhea, the bacteria can easily get on their hands. This is especially common right after using the bathroom (which happens a lot with food poisoning). That bacteria can then transfer to the hands of person B through direct contact or shared surfaces. And if person B then puts their hands in their mouth, it can get inside their body.
It’s also worth noting that the bacteria and viruses that cause food poisoning can also cause infections that do not start with food. Norovirus is a good example. This causes outbreaks of stomach flu, which spread like a normal virus.
Here’s the point to remember: It’s safest to assume you’re contagious if you have a case of food poisoning. This is especially true because, based on symptoms alone, it can be impossible to know which bacteria or virus is causing the illness.
Most people recognize the symptoms of food poisoning as soon as they start:
Nausea
Vomiting
Diarrhea
Abdominal pain and cramping
Fever and chills
But even if you know what those telltale symptoms mean, it can be hard to know where they came from. More specifically, you may not know if the cause is from something you ate (food poisoning) or someone else (gastroenteritis).
But looking at your recent history can help. Some clues that your symptoms are food poisoning (rather than a contagious illness) are:
You have an idea of the food that might be to blame. For example, you may have had a noticeably undercooked hamburger or seafood that tasted off.
Other people who ate the same food as you also got sick at the same time.
Your symptoms started all of a sudden. A lot of the causes of food poisoning make you feel sick very quickly, usually within a few hours of a meal. Infections that spread from person to person tend to cause a more gradual onset of symptoms.
Here’s the short answer: You won’t know for sure. It can be impossible to know for certain whether you’re contagious. This is because, most of the time, you don’t find out the exact cause of food poisoning (or whether it was truly food poisoning in the first place). Most cases of food poisoning resolve before someone sees a healthcare provider or gets any formal testing.
If you do see your provider, they might order stool tests to see what is causing the symptoms. These tests include growing bacteria in cultures or examining the stool for signs of parasites. But even these tests don’t always find the cause. At the end of the day, for most cases of food poisoning, it’s hard to know if you’re contagious or not.
The only time food poisoning is not contagious is when the cause is a bacteria toxin (rather than a bacterial infection itself). But, again, there’s no way to know this for sure without formal testing.
Generally, it’s a good idea to stay home if you have symptoms of food poisoning. Most of the time, people don’t need specific treatments for food poisoning. But rest can be helpful (plus, you might not feel like doing anything else). This way, you can avoid spreading infections to other people if you happen to be contagious.
So, if possible, it’s probably best to stay away from other people until you feel better. This is especially true if any of your friends or family are pregnant, immunocompromised, or very young or old. It’s also very important to stay home if you work in the service industry, as you may expose many other people.
Food poisoning — by strict definition — is an illness caused by food contamination. By this definition, it’s not contagious. But any illness that starts with a virus or bacteria and causes vomiting and diarrhea has the potential to spread from person to person.
So, when it comes to food poisoning, the best advice is to play it safe and assume you’re contagious. Practice good hand hygiene and avoid possibly exposing others. When in doubt, check in with your healthcare provider. They might be able to help figure out the cause so you know for sure.
Centers for Disease Control and Prevention. (2022). Food poisoning symptoms.
National Institute of Diabetes and Digestive and Kidney Diseases. (2019). Diagnosis of food poisoning.
National Institute of Diabetes and Digestive and Kidney Diseases. (2019). Symptoms and causes of food poisoning.