What’s the Difference Between Food Poisoning and Stomach Flu?
Key takeaways:
Stomach flu (gastroenteritis) is caused by contagious viruses or bacteria that spread from person to person.
Food poisoning is caused by eating or drinking contaminated food or water. But it can be caused by the same viruses or bacteria that cause stomach flu.
The symptoms of stomach flu and food poisoning are very similar. So, it can sometimes be impossible to know which one you have based on symptoms alone. But there are a few clues that can help.
Table of contents
Many people use the terms “food poisoning” and “stomach flu” interchangeably when someone suddenly develops vomiting and diarrhea. These two illnesses definitely have similar symptoms, but there are differences between them.
Food poisoning is usually caused by bacteria that comes from contaminated food or water. Stomach flu (gastroenteritis, or “gastro” for short) is usually caused by a virus and it spreads from person to person. But there are exceptions to these rules.
Below is a chart to help you quickly understand the main differences between stomach flu and food poisoning. And then, read on to find out more key differences between these two conditions — and when it matters.
Food poisoning | Stomach flu | |
Causes | Bacteria (like Campylobacter, Salmonella, E.coli, and Listeria) or viruses (like Norovirus) | More likely to be caused by a virus (Norovirus is the most common) |
Incubation period | Quick onset, usually within hours after eating contaminated food | Usually about 24 to 48 hours after exposure |
Symptoms | More likely to start with watery or bloody diarrhea | More likely to cause fever and vomiting |
Duration | Depending on the bacteria, it can be anywhere from 24 hours to several weeks | About 1 to 3 days |
Treatment | Fluids for dehydration, antibiotics in some cases | Fluids, anti-nausea medications |
What causes stomach flu?
Stomach flu is a common name for gastroenteritis. This infection comes from germs that spread from person to person. These can be bacteria or viruses. But usually, stomach flu is caused by a virus. Examples include Norovirus, adenovirus, astrovirus, and Rotavirus. These viruses spread among people by coughing or having physical contact.
Despite its name, stomach flu isn’t caused by the influenza virus that causes seasonal flu. The term “flu” came about in the past, before scientists knew what caused infections. And so, it referred to any disease outbreak.
What should you eat after food poisoning? No matter if it’s food poisoning or the stomach flu, these drinks and foods will help you recover.
How do you know if you need IV fluids? Sometimes dehydration can become a serious problem. Here are the reasons to go to the ER for dehydration.
Do you need antibiotics? Many times, antibiotics can do more harm than good for vomiting and diarrhea. But sometimes they’re necessary.
What causes food poisoning?
Food poisoning refers to an illness someone gets from contaminated food. Usually, these illnesses are the result of bacteria or other organisms that can contaminate both animal and plant products. This is more likely to happen to food that’s undercooked, mishandled, or left at room temperature for too long.
Causes of food poisoning include:
Bacterial infections: Organisms like Salmonella, Campylobacter, Listeria, and E. coli can affect the lining of the intestines.
Toxins: Some bacteria make toxic substances that cause the symptoms of food poisoning. Some of these toxins can even survive in food that has been cooked. Examples include Staphylococcus bacteria, Bacillus bacteria, and botulinum.
Parasitic infections: Some other types of organisms, like the parasite Cyclospora, can enter the body in contaminated food.
Viruses: Viruses can contaminate food just like bacteria. Norovirus is a common example.
There’s some overlap between the causes of food poisoning and gastroenteritis. This is because some of the organisms that cause food poisoning can also spread from person to person like a normal infection. For example, Norovirus outbreaks are common and don’t always start with contaminated food. And even if someone gets sick from food poisoning, they can still spread that germ to others.
This is part of the reason it’s hard to know whether someone has food poisoning or the stomach flu. And when it comes to symptoms and treatment, it doesn’t always matter.
What are the symptoms of food poisoning and stomach flu?
Gastroenteritis and food poisoning have similar symptoms. So, it makes sense that someone could confuse the two — or not be sure which one they have. Symptoms to look out for include:
Nausea
Vomiting
Abdominal pain
Fever
Even though the symptoms are very similar, there might be some clues to help you figure out which one you have. Symptoms from food poisoning tend to start quickly. People feel sick all of a sudden, usually a few hours after eating contaminated food. Also, bloody diarrhea is more common with bacteria and food poisoning.
On the other hand, symptoms from gastroenteritis usually develop a little more slowly. The illness might gradually get worse over a day or so. Gastroenteritis may also have other symptoms like congestion, cough, or body aches along with the gastrointestinal symptoms.
But none of these are hard and fast rules.
What are the treatments for food poisoning and stomach flu?
Just like the symptoms, the treatments for food poisoning and gastroenteritis are similar. Many times, people recover at home without any specific treatment. But if your symptoms are more severe, you may need a little extra help getting over the infection. Treatment might include:
IV (intravenous) fluids: This might be helpful if someone is at greater risk of dehydration — like young babies or older adults. They can also help to rehydrate someone who can’t keep anything down.
Antiemetics: These medications help decrease nausea and vomiting. Examples include ondansetron, metoclopramide, or prochlorperazine.
Antibiotics: This might help in some specific cases of bacterial infections. But antibiotics usually aren’t necessary.
Most of the time, food poisoning and gastroenteritis will improve in a day or so. If symptoms last longer than a week or get worse, it’s a good idea to see a healthcare professional.
When should you see a healthcare professional?
Food poisoning and stomach flu usually aren’t severe, but they can both cause complications. There are some situations where these conditions are more serious and need more urgent medical care.
Examples of more severe complications are:
Dehydration: This can happen if someone loses a lot of body fluids through vomiting and diarrhea. And at the same time, is unable to drink anything to stay hydrated.
Kidney failure: This can come from dehydration or direct damage to the kidneys from toxins.
Sepsis: This is when a severe infection starts to affect other organs in the body.
Blood loss: When an infection causes bloody diarrhea, this can lead to a significant amount of blood loss for some people.
Most people won’t have these severe complications. But some groups of people are at a higher risk of problems from gastroenteritis or food poisoning, including those who are:
Immunocompromised: Their bodies might not be able to fight off these infections.
Very young or older: People who are older or very young can have weakened immune systems. They can also become dehydrated more easily.
Pregnant: Some types of food poisoning, like Listeria, can cause complications during pregnancy.
It’s a good idea to see a healthcare professional for vomiting and diarrhea if you:
Are in one of the high-risk categories above
Have abdominal pain that feels more severe than mild cramping
Have frequent, bloody bowel movements
Can’t keep anything down, even small sips of fluids
Experience symptoms for more than 7 days
Feel faint, dizzy, or very weak
Frequently asked questions
It can be. When someone gets food poisoning from certain types of bacteria or viruses, it’s possible that they can then still spread that germ to other people. Other causes of food poisoning — like toxins produced by bacteria — are not contagious. But since it’s hard to know exactly the cause of someone’s symptoms, it’s best to assume that someone with vomiting and diarrhea is contagious.
The first symptoms of food poisoning or the stomach flu can vary based on the person, as well as specific germ causing the problem. With food poisoning, the first symptom may start with diarrhea. With the stomach flu, a fever and/or nausea is often the first symptom, and the diarrhea comes later. But these are not hard and fast rules.
After food poisoning or the stomach flu, the first priority is to get fluids back into your body. In general, it’s better to do this with fluids that have electrolytes — like oral rehydration solutions (like Pedialyte) or soup broth. When you feel ready to try food, stick to bland carbohydrates at first (like rice or toast).
The bottom line
Food poisoning and stomach flu are similar illnesses. When someone has vomiting and diarrhea, it can be hard to know for sure which one they have. But, for most healthy people, the exact virus or bacteria (or where it came from) does not change treatment or recovery. The signs and symptoms to look out for — and reasons to see a healthcare professional — are the same for both.
Why trust our experts?
References
Centers for Disease Control and Prevention. (2024). Symptoms of food poisoning.
FoodSafety.gov. (2023). Bacteria and viruses.
National Institute of Diabetes and Digestive and Kidney Diseases. (2018). Definition & facts for viral gastroenteritis (‘stomach flu’).
National Institute of Diabetes and Digestive and Kidney Diseases. (2018). Symptoms & causes of viral gastroenteritis (“stomach flu”).
National Institute of Diabetes and Digestive and Kidney Diseases. (2019). Symptoms & causes of food poisoning.
National Institute of Diabetes and Digestive and Kidney Diseases. (2019). Treatment for food poisoning.
Stuempfig, N. D., et al. (2023). Viral gastroenteritis. StatPearls.
