Food Poisoning vs. Stomach Flu: Symptoms and Causes

When you're feeling sick to your stomach, it can be difficult to tell whether you have food poisoning or the stomach flu. This is because they share similar symptoms, like vomiting and diarrhea. But these two conditions have completely different causes.

Food poisoning occurs when you eat food contaminated with bacteria, viruses, or parasites, while the stomach flu (medically known as viral gastroenteritis) is usually caused by contact with certain viruses. These illnesses can usually be treated at home but may require medical attention if symptoms become severe or dehydration sets in.

This article explains the differences between food poisoning and the stomach flu, as well as treatment options for each condition.

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Symptoms

The symptoms that occur with food poisoning and the stomach flu overlap quite a bit, so it's important to understand the signs specific to each condition.

The biggest difference between the two illnesses is in the timing. For example, if you develop symptoms within a few hours of eating, it's likely to be food poisoning. On the other hand, stomach flu symptoms typically appear within a day or two after exposure to the virus.

Symptoms of Food Poisoning

The primary symptoms of food poisoning are:

Vomiting
Diarrhea (may be bloody, watery, or mucus-like)
Nausea
Stomach pain and cramping
Fever
Weakness

Symptoms of Stomach Flu (Viral Gastroenteritis)

The primary symptoms of stomach flu include:

Vomiting
Diarrhea
Stomach pain and cramping
Fever
Headache
Muscle aches
Chills

When to Call a Doctor

Watch for symptoms of dehydration, and seek medical attention if you notice any of the following signs:

Vomiting or diarrhea that continues for more than 24 hours
Blood in your vomit
Violent vomiting
Severe abdominal pain
Trouble keeping fluids down
Signs of severe dehydration, which include dark or infrequent urine, dry mouth, dizziness, weakness, confusion, fainting, or high fever

Causes

You can contract food poisoning and the stomach flu from exposure to germs, but in different ways.

Causes of Food Poisoning

Food poisoning is caused by consuming food that's contaminated with germs. This is usually bacteria like E. coli (Eschrichia coli), Staphylococcus aureus, or Salmonella, but it can also include viruses or parasites.

With food poisoning, you'll notice that the illness:

Typically occurs within hours
Can be traced to a particular food source
Affects more than one person
Has more severe symptoms than the stomach flu (such as diarrhea that's bloody and projectile vomiting)

Causes of Stomach Flu

The stomach flu is an infection that attacks your intestines. It's most often caused by viruses like norovirus in adults or rotavirus in children. But it can also be triggered by other viruses, bacteria, parasites, or toxins.

While other illnesses are transmitted through the air, the stomach flu is transmitted via:

Contaminated food or drink
Touching a surface that's been infected
Person-to-person contact with someone who has the infection
Contact with the vomit or stools of someone who has the infection

Diagnosis

A medical diagnosis of food poisoning or the stomach flu isn't always necessary, but there are some exceptions.

If you're a high-risk individual (including older adults, pregnant people, or immunocompromised people), or if your symptoms are severe and long lasting, you should contact a healthcare provider right away for diagnosis and treatment.

Most healthy adults won't need an official diagnosis, though it can be helpful to know so that you can treat your symptoms appropriately and avoid unintentionally transmitting germs.

Diagnosis of Food Poisoning

For food poisoning, many people do not seek medical care and just assume it's food poisoning if they're aware of another person getting sick from the same food or drink source. But if you do see a healthcare provider for a food poisoning diagnosis, you can expect:

A review of your symptoms
Medical history
Physical examination

Additional tests (like blood, urine, or stool tests) may be ordered to identify the potential source of infection. This is especially important in the case of a community outbreak.

Diagnosis of Stomach Flu

Most people are infected with a virus that causes gastroenteritis, since they're very contagious and spread easily. It doesn't always warrant a trip to your healthcare provider's office, but if it does, your appointment will include:

A review of your symptoms
Medical history
Physical examination
Recent whereabouts, as you're more likely to contract the illness in crowded places like daycares or cruise ships

Testing may not be done unless there's a reason to find out the strain of the virus, like a viral outbreak in a hospital setting.

If needed, stool tests can be used to diagnose rotavirus (a common virus that causes the stomach flu), but this isn't routine. Blood tests or imaging tests would only be performed if another disease or condition is suspected.

How Common Are They?

Infections like food poisoning and the stomach flu are common. Each year in the United States, it's estimated that 48 million people get food poisoning, and up to 21 million people get the stomach flu caused by norovirus. While many people quickly recover from these seemingly harmless illnesses, they cause thousands of ER visits and hospitalizations per year in the United States combined.

Treatment

Treating food poisoning and the stomach flu involves similar tactics. Like many viruses, treatment will focus on preventing dehydration and managing symptoms. This can usually be done effectively at home for most people and may include options such as:

Staying hydrated with fluids like water or electrolyte-rich drinks
Slowly incorporating a BRAT diet (banana, rice, apple, and toast) when you're able to keep food down
Getting plenty of rest to help your body heal
Using over-the-counter medications like Pepto-Bismol (bismuth subsalicylate) for an upset stomach, Imodium (loperamide) for mild diarrhea, or Tylenol (acetaminophen) for a fever
Using prescription medications like Zofran (ondansetron) or Reglan (metoclopramide) to treat symptoms of nausea and vomiting, if recommended by your healthcare provider

In certain cases of severe food poisoning, your provider may prescribe antibiotics for infections like shigellosis or an antiparasitic for infections caused by parasites.

High-Risk Individuals

Immediate medical treatment may be required for babies, children, and people with compromised immune systems, who are at high risk for dehydration from vomiting or diarrhea. Some cases of dehydration need to be treated with medications or intravenous (IV) fluids.

Prevention

Food poisoning generally isn't contagious from person to person in the way that the stomach flu is, so prevention tips for both illnesses will vary a bit.

Prevention for Food Poisoning

Food poisoning generally isn't contagious, though some forms can be spread through contact with an infected bodily fluid (like when a person has contaminated feces on their hand and then touches their mouth).

Even though it usually doesn't spread from person to person, there are still steps you can take to prevent food poisoning from occurring in the first place, including:

Wash your hands and work surfaces before, during, and after preparing food.
Separate raw meat, poultry, seafood, and eggs from ready-to-eat foods.
Cook food to the right internal temperature to kill harmful bacteria.
Keep your refrigerator at 40 degrees Fahrenheit or below.
Refrigerate leftovers within two hours of cooking.

Prevention for the Stomach Flu

The stomach flu is very contagious and easily transmitted. A person can be contagious before symptoms start to appear and for days after symptoms have stopped. In fact, germs can stay in your stool for two weeks, so you'll want to take extra hygiene precautions, including:

Wash your hands often and well with soap and water. 
Keep your hands away from your mouth and avoid shaking hands during known virus outbreaks.
Handle and prepare food safely.
Clean and disinfect common surfaces.
Wash laundry thoroughly.
Stay home and away from other people when ill.

Summary

Food poisoning and the stomach flu can come with similar symptoms, like nausea and vomiting, but they're different conditions. While food poisoning is caused by food contaminated by bacteria, virus, parasites, or toxins, the stomach flu is usually caused by norovirus. Both can typically be treated at home with hydration, over-the-counter medications for symptom relief, and rest.

A Word From Verywell

Both food poisoning and the stomach flu are very common. It's important to protect yourself, your loved ones, and your community by practicing good hygiene habits and ensuring foods are prepared and served safely. If you develop either condition, keep a close eye out for signs of severe dehydration, and make sure to see a healthcare provider if you have a weak immune system or are experiencing severe or lingering symptoms.

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