Food Poisoning vs Stomach Flu – Differences, Symptoms, Treatment

Stomach and intestinal upsets are common throughout life. It may occur several times in a year and usually resolves on its own with little to no treatment. However, these disturbances can be serious at times. Most people refer to these upsets as food poisoning or the stomach flu with little understanding of these conditions. Being able to differentiate between these conditions can help prevent complications by early treatment where and when necessary.

Meaning of Food Poisoning

Food poisoning is an illness caused by infectious agents (viruses, bacteria or protozoa) or their toxins which enter the body through consuming contaminated food. Although it specifically refers to a foodborne illness, sometimes these same infections or toxins may enter through contaminated water. However, the term food poisoning is broadly used to refer these conditions that present with the same symptoms.

Food poisoning is a form of gastroenteritis – it may be a viral gastroenteritis, bacterial gastroenteritis or protozoal gastroenteritis.  While gastroenteritis means inflammation of the stomach and small intestine, the condition can also extend to the colon (colitis). Sometimes inflammation of the small and large intestines (enterocolitis) without significant stomach involvement may also be referred to as food poisoning if it occurs with eating contaminated food.

Read more about food poisoning.

Meaning of Stomach Flu

Stomach flu is a common term to describe viral gastroenteritis. Most of the times these infections are caused by noviruses and rotaviruses. Despite being viruses, they are not the same as the influenza virus. Furthermore the infection is not limited to the stomach and may also involve the small and large intestines. Therefore the term stomach flu is a misnomer but medical professionals understand the condition refers to viral gastroenteritis.

However, it is often difficult for patients to differentiate between viral, bacterial and protozoal gastroenteritis. In addition, the viruses that cause the “stomach flu” may not always be contracted through consuming contaminated food or water (as is the case with food poisoning).  These viruses can also be transmitted from person-to-person and adults may have little to no symptoms of some types of stomach flu yet pass the virus to others, including children.

Read more about viral gastroenteritis.

Signs and Symptoms

The signs and symptoms of food poisoning and stomach flu are largely the same although there may be some variation depending on the causative factor. Therefore diagnosis of the exact cause is not always possible by the signs and symptoms. Diagnostic investigations such as a stool analysis and culture as well as blood tests may be required in some cases.


  • Diarrhea – profuse, loose watery stool is present in almost all cases.
  • Bloody stool – usually associated with hemorrhagic viral infections.
  • White ‘rice water’ stool – usually seen with cholera.
  • Mucus in the stool – common in all types.
  • ‘Fishy’ stool odor – usually bacterial like with cholera.

Nausea and Vomiting

  • Nausea – almost always present and persists even with no vomiting or after vomiting subsides.
  • Vomiting – present in most instances but not always and the onset tends to precede diarrhea in many cases.
  • Blood in vomit – rare but may appear as dark coffee grounds (degraded blood) or bright red blood (fresh).

Abdominal Pain

  • Painful abdominal cramps – almost always present.
  • Pain may subside after passing stool or following vomiting.

Other Symptoms

  • Fever – low-grade, high or absent.
  • Malaise – feeling unweel.
  • Fatigue.
  • Muscle pains (myalgia).
  • Headaches.

Neurological symptoms and symptoms of dehydration may also be present.

Incubation Periods

The incubation period is the time from when the infection is acquired till the time the first symptoms become apparent. It varies based on a host of different factors.

  • Within hours to 2 days: Clostridium botulinum, Clostridium perfringens, Listeria, noroviruses and Staphylococcus aureus.
  • From 1 day to 1 week: Campylobacter, Escherichia coli (E. coli), rotavirus, Salmonella, Shigella and Vibrio vulnificus.
  • Longer than 1 week: Giardia lamblia and hepatitis A virus.

Treatment of Food Poisoning and Stomach Flu

Most of the time there is no need for specific medical treatment with viral gastroenteritis. Even bacterial and protozoal infections can at times resolve on its own. The focus of treatment in any type of gastroenteritis is supportive measures like rehydration and bed rest. This helps to prevent complications like dehydration and allows the body to recover from the infection.


Copious amounts of fluids and electrolytes are lost with vomiting and diarrhea. Even sweating as a result of fever may contribute to fluid and electrolyte loss. It can lead to mild, moderate or even severe dehydration, which can be life-threatening if left untreated.

Oral rehydrating solutions (ORS) are the best option for rehydration when a person can drink and hold in liquids. These solutions have the optimal balance of fluids and essential electrolyte to counteract dehydration. However, if oral administration is not possible then IV fluid administration becomes necessary.


Sometimes medical treatment is necessary. This is mainly in the case of some bacterial and protozoal infections. It requires antibiotic therapy, which is usually administered orally but may sometimes be administered intravenously (IV in patients who are unconscious or vomiting profusely.

The entire course of antibiotics must be completed to eradicate the infection as well as prevent recurrence and antibiotic resistance. It is important to note that antibiotics are not effective against viral infections and antivirals are usually not necessary for viral gastroenteritis.

Differences between Food Poisoning and Stomach Flu

There are several differences between food poisoning and stomach flu. However, most of the time it is difficult to identify these differences to distinguish between food poisoning and stomach flu. Irrespective of the cause, rehydration should be commenced immediately and medical attention must be sought as soon as possible.


  • Food poisoning is caused by viruses, bacteria or protozoa (single-celled parasites) or their toxins.
  • Stomach flu is caused by viruses, most frequently the norovirus and rotavirus.


  • Food poisoning is spread through contaminated food and sometimes contaminated water.
  • Stomach flu may be spread through various routes, including contaminated food, water and from person-to-person.


  • Food poisoning may present with no fever, low-grade or high fever.
  • Stomach flu usually causes a low-grade fever.


  • Food poisoning caused by bacteria or protozoa may require antibiotics.
  • Stomach flu usually does not require specific drugs like antivirals and antibiotics are not effective against viruses.

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