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How Do You Know if You Have the Stomach Flu?

Reviewed on 1/12/2021

What is stomach flu?

When you have nausea, vomiting, abdominal pain, and diarrhea, you may wonder if you have stomach flu.
When you have nausea, vomiting, abdominal pain, and diarrhea, you may wonder if you have stomach flu.

When you have nausea, vomiting, abdominal pain, and diarrhea, you are sure to be miserable. You may wonder if you have stomach flu or if something else is making you ill. You are likely to feel better soon, but you may never know the answer to that question. 

The illness known as stomach flu isn't really flu at all. Flu is short for influenza, which is a virus that attacks the respiratory system. A more accurate term for stomach flu is gastroenteritis, which occurs when the linings of the stomach and small intestine become inflamed. Most stomach flu is actually viral gastroenteritis.  

Viral gastroenteritis usually passes fairly quickly and doesn't have lasting effects. For that reason, health experts don't recommend that you seek medical care. Usually, you will be more comfortable at home, and you will be less likely to infect others. 

Occasionally, gastrointestinal illnesses are caused by food poisoning instead of a virus. Both cause stomach pain, nausea, vomiting, and diarrhea, but there are a few differences between the two. If you have body aches, headache, or fever, you are more likely to have stomach flu. Stomach flu is also more likely to cause projectile vomiting. Food poisoning is more apt to cause bloody diarrhea

Sometimes the circumstances around your illness can offer clues. If you've recently been around someone with a similar illness, you probably caught a case of stomach flu. 

If you have eaten food that is easily contaminated, such as seafood, salad greens, dairy products, or undercooked eggs or meat, you may have food poisoning. Of course, if a companion ate the same food and also became ill, that points toward food poisoning. 

Symptoms of stomach flu

The usual symptoms of viral gastroenteritis, or stomach flu, include:

Nausea and vomiting

Often lack of appetite or nausea is the first sign of stomach flu, with vomiting usually following soon after and diarrhea after that. Vomiting typically stops before diarrhea, and you may recover your appetite quickly. 

Cramping and diarrhea

Stomach cramps and audible noises from the intestine often precede watery diarrhea. Severe diarrhea is when you have over ten bowel movements in one day. Generally, viral gastroenteritis doesn't cause pus or blood in the stool

General unwellness

You may have a fever with the stomach flu, but it rarely goes high. You may also have achy muscles and feel generally weak and exhausted. 

Causes of stomach flu

Several viruses can cause stomach flu, including: 

Norovirus

If you have symptoms of stomach flu, it's most likely that you have norovirus. It is transmitted easily and in multiple ways. You can get norovirus from food and from surfaces that are contaminated with the virus. You can also get it from another person. 

Those who have had the virus can spread it for two weeks after they have recovered, making it easy to pass around. Researchers are working on developing a vaccine for norovirus.

Rotavirus

Rotavirus is most common in infants and children, but older people can get it, too. In adults, the illness is usually mild. In children, it may cause severe watery diarrhea and dangerous dehydration

Vaccines are available for rotavirus. Health authorities recommend that children receive their first dose before 15 weeks of age. They should complete the course of two or three doses before they reach eight months of age.

Other viruses

Stomach flu can be caused by three other classes of viruses: adenovirus, sapovirus, and astrovirus. Each of these may account for 2-9% of cases, affecting children more than adults.

Recently a number of novel viruses have been identified in the human gastrointestinal tract. Researchers are unsure whether they cause gastrointestinal illnesses such as diarrhea. Proving that a particular virus is responsible for symptoms isn't an easy task.

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When to see the doctor for stomach flu

Most of the time, you recover quickly from viral gastroenteritis and won't need to see a doctor. Children, older adults, and those with conditions that put them at risk may need medical care, especially if they are dehydrated. 

Signs of dehydration include decreased urination, dry mouth, and dizziness upon standing. With babies, look for a lack of tears and unusual sleepiness or crankiness, along with a low number of wet diapers.  

Other signs that you need to see a doctor include severe abdominal pain, diarrhea lasting more than 48 hours, and blood in the stool.

Diagnosis of stomach flu

Unless you become very ill, you may never get an official diagnosis of your stomach flu. If you do need medical attention, your doctor will probably make a clinical diagnosis based on your signs and symptoms. 

Many clinics and emergency rooms aren't equipped to run tests for viruses. If you are well hydrated and don't have risk factors, you will probably be sent home without testing. 

If you have symptoms that suggest a diagnosis other than viral gastroenteritis, your doctor may order tests. A stool sample can show if you have a bacterial infection instead of a viral one. Computerized tomography (CT) can be used to look for other conditions, such as inflammatory bowel disease (IBD). 

Treatments for stomach flu

Treatment for stomach flu consists of rest and hydration. Drugs such as loperamide may be used to slow down diarrhea. 

Doctors advise those with stomach flu not to restrict their diet but to eat what appeals to them. Some people may find that certain foods make their diarrhea worse. Foods that are sometimes troublesome include {National Institute of Diabetes and Digestive and Kidney Diseases: "Eating, Diet, & Nutrition for Viral Gastroenteritis: 

  • Milk and milk products, which contain lactose
  • Fried foods and other foods high in fat, including most fast food
  • Soft drinks and fruit juices that contain a lot of simple sugars
  • Drinks containing caffeine

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References
American College of Gastroenterology: "Diarrheal Diseases – Acute and Chronic."

Centers for Disease Control and Prevention: "Norovirus."

Centers for Disease Control and Prevention: "Rotavirus."

Merck Manual Consumer Version: "Gastroenteritis."

Merck Manual Professional Version: "Gastroenteritis."

National Institute of Diabetes and Digestive and Kidney Diseases: "Eating, Diet, & Nutrition for Viral Gastroenteritis (“Stomach Flu”)."

National Institute of Diabetes and Digestive and Kidney Diseases: "Treatment of Viral Gastroenteritis (“Stomach Flu”)."

Reliant Medical Group: "Is It a Stomach Virus or Food Poisoning?"

Viruses: "Viruses Causing Gastroenteritis: The Known, The New and Those Beyond."

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