Signs of Stomach Flu and When to See a Doctor

Viral gastroenteritis, commonly known as the stomach flu or a stomach bug, is a highly contagious illness that causes vomiting, diarrhea, abdominal pain, and weakness, among other possible and very uncomfortable symptoms.

For most healthy adults, it is short-lived and without consequence. However, it's important to watch for symptoms of dehydration, especially in children and the elderly, as excessive fluid loss can occur as the result of the stomach flu.

Despite its nickname, the stomach flu is not caused by an influenza virus. Also, it is not a stomach infection but usually an intestinal infection.

Rotavirus, sapoviruses, astroviruses, and adenoviruses are most likely to infect children under 5 years old, but norovirus commonly infects people of all ages. Luckily, there is now an oral vaccine for rotavirus in babies, so infection is not as common as it used to be.

What's certain is that the stomach flu is contagious, as are most other illnesses with diarrhea and vomiting. To understand the risks to yourself and to others, it's important to know the signs of stomach flu.

Stomach Flu - Common Symptoms
Verywell / JR Bee

Frequent Symptoms

Depending on the virus that is causing the infection, the onset after exposure and the duration of illness can vary. Norovirus is the most common cause of viral gastroenteritis. Symptoms usually begin 12 to 48 hours after exposure to the virus, and illness lasts one to three days.

For the other viruses, onset is from two to 10 days after exposure, and illness can last anywhere from a day to two weeks.

Typically, the stomach flu is a "self-limiting" illness, which means it will go away on its own after a few days, though it may linger in some instances. Symptoms of stomach flu may include:

  • Vomiting
  • Abdominal pain or cramps
  • Diarrhea
  • Nausea
  • Fever
  • Chills
  • Weakness
  • Muscle pain
  • Weight loss
  • Decreased appetite

Compared to Food Poisoning

When people talk about "food poisoning," they are often thinking of bacterial infections like Salmonella or E. coli, which are transmitted through meat, eggs, cheese, or produce, causing large outbreaks and food recalls.

In fact, the most common kind of food poisoning in the United States is viral gastroenteritis caused by norovirus. The five most common U.S. foodborne illnesses are:

These germs are less common, but are more likely to lead to hospitalization and long-term health effects:

Unfortunately, there is no good way to know at first which germ is making you sick. Symptom onset can be anywhere from 30 minutes (from Staphylococcus aureus) to 4 weeks (from Listeria), and symptoms can be similar for the different infections.

If your symptoms are severe or last more than three days, your doctor may order a stool culture for bacteria and viruses to see if they can identify the problem. If your test results are positive, your local health department may contact you to determine where you may have been infected.

Bloody diarrhea and fever are not typical signs of viral gastroenteritis, and those signs may indicate an infection with foodborne or waterborne bacteria or parasites, not with a virus.

Complications

Excessive vomiting and diarrhea can lead to dehydration. Infants, children, older adults, and people with weakened immune systems are most at risk of becoming dehydrated from a stomach bug.

Dehydration can usually be prevented or managed, if treated properly. Severe dehydration is an emergency, as it can cause kidney issues (including failure), seizures, low blood volume, coma, and death.

The signs and symptoms of dehydration include:

  • Infrequent urination, with no urination for 12 hours a cause for concern
  • Very dark urine
  • Excessive thirst
  • Dry skin and mouth
  • Dizziness
  • Fatigue/extreme tiredness and lethargy

Children and adults who are dehydrated may have "skin-tenting," in which the skin does not flatten back out immediately if you pinch it.

In babies and small children specifically, also watch for:

  • Excessive irritability
  • No smiling or willingness to play
  • No wet diapers for more than three hours
  • No tears when crying
  • Sunken eyes or soft spot

What to Do at the First Signs of Stomach Flu

Because diarrhea and vomiting can be dehydrating, you should try to stay hydrated as much as possible, even sipping an oral rehydration drink and water enough to make sure that you are urinating frequently and that your urine is not dark. Follow instructions on the bottle, including restrictions on age. Babies should get breast milk or formula.

At the first signs of stomach flu, you should assume that the cause is infectious and work to prevent the spread of the stomach infection to others. Your stool and vomit may contain viruses for up to two weeks after you recover.

This means thorough handwashing with soap for at least 20 seconds:

  • After using the bathroom
  • After changing diapers of a sick child
  • After touching any stool or vomit or objects touched by the sick person
  • Before preparing any food
  • Before touching any shared objects

People who are actively vomiting or have diarrhea should not go to work, daycare, or school. Babies who still use diapers should not use swimming pools for at least a week after diarrhea resolves.

Clean surfaces that may have come into contact with stool or vomit with a solution of 5 to 25 tablespoons of bleach per 1 gallon of water. Clean any potentially infected clothing or linen with the longest possible laundry cycle and machine dry them.

When to See a Doctor

If you have a fever greater than 101.3 F degrees (38.5 C) for more than 24 hours, cannot keep liquids down for more than 24 hours, or show signs of dehydration, call your healthcare provider. They can prescribe medications to decrease vomiting and may recommend treatment with intravenous (IV) fluids.

Seek immediate medical attention for the following symptoms:

  • Vomiting blood
  • Bloody or black, tar-like stools
  • Large amounts of mucus in the stool
  • Confusion
  • Feeling lightheaded or fainting when standing
  • Severe abdominal pain
  • Severe dehydration
  • Persistent vomiting lasting two days or longer
  • Diarrhea that lasts more than three days

In addition, children with the following symptoms should be seen immediately:

  • Unusually sleepy or difficult to wake up
  • Lethargy or severe irritability
  • Fever of 102 degrees F or higher

Frequently Asked Questions

How long does the stomach flu last?

It depends on the virus causing the symptoms. The most common cause of viral gastroenteritis is norovirus, and most people have a resolution of norovirus symptoms in less than 48 hours.

What can I eat with the stomach flu?

You can eat normally with the stomach flu, which includes formula and breastmilk for babies. You may find that you tolerate a bland diet better while sick with the stomach flu. Some people have worse diarrhea if they consume caffeine, sugary drinks, spicy foods, dairy products, or alcohol. The important thing is to stay hydrated by drinking water, broth, and non-sugary drinks.

How do I avoid getting the stomach flu if my family has it?

Make sure to wash your hands well with soap and water for at least 20 seconds before eating or putting your hands near your face. Don't have infected people prepare your food. Clean your hands after touching common objects, and make sure to sanitize objects with bleach.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institutes of Health. Viral gastroenteritis. Last reviewed May 2018.

  2. Bányai K, Estes MK, Martella V, Parashar UD. Viral gastroenteritis. Lancet. 2018;392(10142):175-186. doi:10.1016/S0140-6736(18)31128-0

  3. U.S. Centers for Disease Control and Prevention. Burden of foodborne illness: Findings. Updated November 5, 2018.

  4. U.S. Centers for Disease Control and Prevention. Foodborne germs and illnesses. Updated March 18, 2020.

  5. U.S. Centers for Disease Control and Prevention. Food poisoning symptoms. Updated March 9. 2021.

  6. Hartman S, Brown E, Loomis E, Russell HA. Gastroenteritis in children. AFP. 2019;99(3):159-165.

  7. Fleisher GR, O'Ryan MG. Patient education: Acute diarrhea in children (Beyond the Basics). UpToDate. Updated June 29, 2020.

  8. UpToDate. Patient education: Diarrhea in adolescents and adults (The Basics). Updated July 10, 2019.

Additional Reading