Gastroenteritis (Stomach Flu)

Reviewed on 7/22/2022

What to Know About Gastroenteritis (Stomach Flu)

Women sick in bed with stomach flu
Picture of a sick woman in bed with stomach flu by iStock

Gastroenteritis, commonly referred to as the "stomach flu, is a condition that causes irritation and inflammation of the stomach and intestines (the gastrointestinal tract).

  • The most common symptoms of gastroenteritis are:
  • Many people also refer to gastroenteritis as "stomach flu." This can sometimes be confusing because influenza (flu) symptoms include:
    • headache,
    • muscle aches and pains, and
    • respiratory symptoms.
    • Influenza does not involve the gastrointestinal tract.
  • The term stomach flu presumes a viral infection, even though there may be other causes of infection.
  • Viral infections are the most common cause of gastroenteritis; but bacteria, parasites, and food-borne illnesses (such as from shellfish that has been contaminated by sewage or from consuming raw or undercooked shellfish from contaminated water) can also be the offending agents. Many people who experience vomiting and diarrhea that develops from these types of infections or irritations think they have "food poisoning," when they actually may have a food-borne illness.
  • Travelers to foreign countries may experience "traveler's diarrhea" from contaminated food and unclean water.
  • The severity of infectious gastroenteritis depends on the immune system's ability to resist the infection. Electrolytes (these include essential chemicals like sodium, potassium, and chloride) may be lost in vomit and diarrhea fluid.
  • Most people recover easily from a short episode of vomiting and diarrhea by drinking clear fluids to replace the fluid that was lost and then gradually progressing to a normal diet. But for others, especially infants and the elderly, the loss of bodily fluid with gastroenteritis can cause dehydration, which can be a life-threatening illness unless it is treated and fluids in the body are replaced.
  • The most recent data from the CDC show that deaths from gastroenteritis have increased dramatically. In 2007, 17,000 people died from gastroenteritis, overwhelmingly, these people were older and the most common infections were Clostridium difficile and Norovirus.
  • There were an estimated 179 million cases of gastroenteritis in the United States in 2010 and more than 80% of those who were ill never sought medical care. Only 1% required hospital admission.

How Do You Get the Stomach Flu? Is It Contagious?

Viruses and bacteria can be contagious and can spread through the consumption of contaminated food or water. In up to 50% of diarrheal outbreaks, however, no specific agent is found.

Gastroenteritis or stomach flu can spread from person to person due to improper hand-washing following a bowel movement or handling a soiled diaper.

What Are the Signs and Symptoms of the Stomach Flu? Can It Be Serious?

By definition, gastroenteritis affects both the stomach and the intestines, resulting in vomiting and diarrhea.

Common Stomach Flu (Gastroenteritis) Symptoms and Signs in Children and Adults

  • Low-grade fever, usually less than 100 F (37.7 C)
  • Nausea with or without vomiting
  • Mild-to-moderate diarrhea (Dehydration also can intensify the symptoms of nausea and vomiting.)
  • Crampy painful abdominal bloating (The cramps may come in cycles, increasing in severity until a loose bowel movement occurs and the pain resolves somewhat leaving a dull ache.)

More Serious Signs and Symptoms of the Stomach Flu (Gastroenteritis) in Children and Adults

  • Blood in vomit or stool (this is never normal and the affected individual should seek immediate medical care)
  • Vomiting more than 48 hours
  • Fever higher than 101 F (40 C)
  • Swollen abdomen
  • Increasingly severe abdominal pain
  • Dehydration—weakness, lightheadedness, decreased urination, dry skin, dry mouth, and lack of sweat and tears are characteristic symptoms of dehydration.
  • If symptoms continue or worsen, call a healthcare professional.

Diarrhea is one of the leading causes of infant sickness and death. Worldwide, diarrhea accounts for 3-5 million deaths yearly for all age groups. In general, most adults and children recover after they are appropriately rehydrated.

How Long Does the Stomach Flu Last?

Gastroenteritis caused by viruses may last 1-2 days. However, some bacterial cases can continue for months.

Are Stomach Flu and Food Poisoning the Same Thing?

  • Stomach flu (gastroenteritis) is almost always caused by an infection. The infection can enter the body in different ways. Drinking contaminated water is a common cause and sometimes the infection may enter the body because of poor personal hygiene (not washing your hands after using the toilet).
  • Food poisoning may be one cause of gastroenteritis, and that infection may be caused by a bacteria, virus, or parasite. Depending on the circumstances, food may be contaminated by how long it has been stored, cleaned, prepared, and how long it has been left out to be served.

If there is an outbreak in which many people have the signs and symptoms of vomiting and diarrhea, and the type of infection is found, health agencies try to find the source of the infection to prevent further illnesses and outbreaks. In some instances, it may be related to only one restaurant or cruise ship, but for other infectious outbreaks, the Centers for Disease Control and Prevention has to do significant detective work to find the root cause that infected the food chain.

What Causes the Stomach Flu?

Gastroenteritis has many causes. Viruses and bacteria are the most common.

Viruses (Norovirus, Rotavirus, Adenoviruses, Parvoviruses, and Astroviruses)

Norovirus - Fifty to seventy percent of cases of gastroenteritis in adults are caused by noroviruses (genus Norovirus, family Caliciviridae). This virus is highly contagious and spreads rapidly. Norovirus is the most common cause of gastroenteritis in the United States.

  • Noroviruses can be transmitted by
    • consuming contaminated food and liquids,
    • touching objects contaminated with Norovirus and then placing the hands or fingers in the mouth,
    • direct contact with an infected individual (for example, exposure to Norovirus when caring for or sharing foods, drinks, eating utensils with an affected individual, and
    • exposure to infected individuals and objects in daycare centers and nursing homes.
  • Norovirus is often in the news when cruise ship passengers contract the virus causing gastroenteritis epidemic on board the ship.

Rotavirus - According to the CDC, "Rotavirus was also the leading cause of severe diarrhea in U.S. infants and young children before rotavirus vaccine was introduced for 2006. Prior to that, almost all children in the United States were infected with rotavirus before their 5th birthday. Each year in the United States in the pre-vaccine period, rotavirus was responsible for more than 400,000 doctor visits; more than 200,000 emergency room visits; 55,000 to 70,000 hospitalizations; and 20 to 60 deaths in children younger than 5 years of age."

Other viruses that cause gastrointestinal symptoms include:

Adenoviruses - This virus most commonly causes respiratory illness; however, other illnesses may be caused by adenoviruses and include gastroenteritis, bladder infections, and skin rashes.

Parvoviruses - The human bocavirus (HBoV), which can cause gastroenteritis belongs to the family Parvoviridae.

Astroviruses - Astrovirus infection is the third most frequent cause of gastroenteritis in infants.

Parasites and Protozoans (Giardia, Cryptosporidium)

These tiny organisms are less frequently responsible for intestinal irritation. A person may become infected with one of these by drinking contaminated water. Swimming pools are common places to come in contact with these parasites. Common parasites include

  • Giardia is the most frequent cause of waterborne diarrhea, causing giardiasis. Often, people become infected after swallowing water that has been contaminated by animal feces (poop). This may occur by drinking infected water from rivers or lakes but giardia may also be found in swimming pools, wells, and cisterns.
  • Cryptosporidium (Crypto) is a parasite that lives in the intestine of affected individuals or animals. The infected individual or animal sheds the Cryptosporidium parasite in the stool. Crypto may also be found in food, water, soil, or contaminated surfaces (swallowing contaminated water, beverages, uncooked food, unwashed fruits, and vegetables) or on contaminated surfaces (touching contaminated bathroom fixtures, toys, diaper pails, changing tables, changing diapers, caring for an infected individual or handling an infected cow or calf). Those at risk for serious disease are individuals with weakened immune systems.

Bacteria (Clostridium difficile, Salmonella, Shigella, and Campylobacter, and E coli)

Bacteria may cause gastroenteritis directly by infecting the lining of the stomach and intestine. Some bacteria such as Staphylococcus aureus produce a toxin that is the cause of the symptoms. Staph is a common cause of food poisoning.

Escherichia coli infection can cause significant complications. E. coli O157:H7 (one type of the bacteria) can cause complications in approximately 10% of affected individuals (for example, kidney failure in children [hemolytic-uremic syndrome or HUS], bloody diarrhea, and thrombotic thrombocytopenic purpura [TTP] in the elderly.

Salmonella, Shigella and Campylobacter

Salmonella, Shigella and Campylobacter are also common causes of illness.

  • Salmonella is contracted by ingesting the bacteria in contaminated food or water, and by handling poultry or reptiles such as turtles that carry the germs.
  • Campylobacter occurs by the consumption of raw or undercooked poultry and meat and through cross-contamination with other foods. Infants may acquire the infection by contact with poultry packages in shopping carts. Campylobacter is also associated with unpasteurized milk or contaminated water. The infection can be spread to humans by contact with infected stool of an ill pet (for example, cats or dogs). It is generally not passed from human to human.
  • Shigella bacteria generally spreads from an infected person to another person. Shigella are present in diarrheal stools of infected individuals while they are ill, and for up to one to two weeks after contracting the infection. Shigella infection also may be contracted by eating contaminated food, drinking contaminated water, or swimming or playing in contaminated water (for example, wading pools, shallow play fountains). Shigella can also spread among men who have sex with male partners.

Clostridium difficile

Clostridium difficile (C difficile) bacteria may overgrow in the large intestine after a person has been on antibiotics for an infection. Although almost any antibiotic can lead to this condition, the most common antibiotics that pose a potential risk for C difficile include:

Other risk factors for C difficile infection include hospitalization, individuals 65 years of age or older, and pre-existing chronic medical conditions.

The CDC lists C. Difficile as one of the most common causes of death due to gastroenteritis and suggest that new strains of the bacteria have become more aggressive and dangerous.

What Are Other Common Causes of the Stomach Flu?

Gastroenteritis that is not contagious to others can be caused by:

  • chemical toxins (usually found in seafood), 
  • food allergies,
  • heavy metals,
  • antibiotics, and
  • other medications.

What Exams and Tests Diagnose the Causes of Stomach Flu?

Gastroenteritis is often self-limiting, and the care is supportive designed to control symptoms and prevent dehydration. Tests may not be needed. The health care professional often may make the diagnosis based on history of symptoms and physical examination.

If the symptoms persist for a prolonged period of time blood and stool tests may be appropriate to determine the cause of the vomiting and diarrhea.

Patient History and Physical Examination

Taking a thorough history and physical examination is very helpful in making the diagnosis.

Questions asked by the health care professional may include:

  1. Have any other family members or friends had similar exposure or symptoms?
  2. What is the duration, frequency, and description of the patient's bowel movements, and is vomiting present?
  3. Can the patient tolerate any fluids by mouth?

These questions help determine the potential risk of dehydration. Other questions to help assess hydration also may include the amount and frequency of urination, weight loss, lightheadedness, and fainting (syncope).

Other information in the medical history that may be helpful in the diagnosis of gastroenteritis include:

  • Travel history: Travel may suggest E. coli bacterial infection or a parasite infection acquired from something the patient ate or drank. Norovirus infections tend to occur when many people are confined to a close space (for example, cruise ship).
  • Exposure to contaminated water: Swimming in contaminated water or drinking from suspicious fresh water such as mountain streams or wells may indicate infection with Giardia - an organism found in water.
  • Diet change, food preparation habits, and storage: When the disease occurs following exposure to undercooked or improperly stored or prepared food (for example foods at picnics and BBQs that should be refrigerated to avoid contamination), food poisoning must be considered. In general, symptoms caused by bacteria or their toxins will become apparent after the following amount of time:
    • Staphylococcus aureus in 2 to 6 hours
    • Clostridium 8 to 10 hours
    • Salmonella in 12 to 72 hours
  • Medications: If the patient has used antibiotics recently, they may have antibiotic-associated irritation of the gastrointestinal tract, caused by Clostridium difficile infection.
  • Toxins and poisons: Gastrointestinal symptoms can occur following exposure to a variety of toxins and poisons, which can occur in association with job-related or recreational activities.

Physical examination will look for other causes of vomiting and/or diarrhea unrelated to gastroenteritis. If there are specific tender areas in the abdomen, the doctor may want to determine if the patient has one of the following, or any other conditions that may be the cause of the patient’s symptoms:

Other noninfectious gastrointestinal diseases such as Crohn's disease, ulcerative colitis, or microscopic colitis also must be considered. The doctor will feel the abdomen for masses. A rectal examination may be considered, where the physician inspects the anus for any abnormalities and then inserts a finger into the rectum to feel for any masses. Stool obtained during this test may be tested for the presence of blood.

The doctor may order other laboratory tests, including:

Stool samples may be collected and tested for white blood cells, red blood cells and different types of infections.

If warranted based on the patient's presentation and situation, stool cultures may be taken to try and grow the organism that might have caused the infection. The results may not affect treatment, even if the culture is positive, since most infections resolve by themselves.

When Should You Call a Doctor If You Have the Stomach Flu?

Treatment of gastroenteritis includes self-care and home remedies that are aimed at keeping the patient well hydrated to avoid dehydration.

Medical treatment may be necessary if the patient becomes dehydrated and needs intravenous (IV) fluids at the doctor's office or emergency department to replenish lost fluids.

  • Sometimes antibiotics may be prescribed to treat some infections (for example, C. diff).
  • Antiemetic medications can be used to treat nausea and vomiting.
  • Antidiarrheal medication to decrease the frequency and amount of diarrhea is sometimes recommended depending upon the cause of diarrhea.
  • Vomiting blood or having bloody or black bowel movements are not normal, and emergency care should be sought, however; some medications such as iron or bismuth subsalicylate (Pepto-Bismol) can turn stool black in color.
  • Fever, increasing severity of abdominal pain, and persistent symptoms should not be ignored, and seeking medical care should be considered.

What Diet, Foods, or Drinks Help Relieve Stomach Flu Symptoms?

  • In general, clear fluids (anything you can see through), may be tolerated in small amounts. Think of it as adding just an ounce or less to the normal saliva that the patient is already swallowing. However, giving too much fluid at one time may cause increased nausea due to a distended stomach, which causes additional irritation.
  • Clear fluids do not include carbonated beverages, but flat colas or ginger ale (with no fizz) are often well tolerated.
  • Coke syrup also may be helpful in settling the stomach.
  • Jell-O and popsicles may be "solid food" alternatives to clear fluids in children who aren't interested in clear fluids.
  • After an infection or irritation of the digestive tract, the person may not be able to eat a regular diet. Some people may be unable to tolerate dairy products for several weeks after the disease has run its course. The diet should be advanced slowly from bland non-dairy soups and grain products to a solid meal.
  • Gradually transition to the BRAT Diet.

What Natural Home Remedies Treat Dehydration from the Stomach Flu?

The treatment of gastroenteritis is aimed at maintaining hydration while the vomiting and diarrhea resolve, often spontaneously. Home remedies that address keeping fluid in the body are key to recovery. Since most causes of gastroenteritis are due to viruses, replacing the fluid lost because of vomiting and diarrhea allows the body to recuperate and fight the infection itself.

Oral rehydration therapy using balanced electrolyte solutions such as Pedialyte or Gatorade/Powerade may be all that is needed to replenish the fluid supply in an infant or child. Plain water is not recommended because it can dilute the electrolytes in the body and cause complications such as seizures due to low sodium.

Although adults and adolescents have a larger electrolyte reserve than children, electrolyte imbalance and dehydration may still occur as fluid is lost through vomiting and diarrhea. Severe symptoms and dehydration usually develop as complications of medication use or chronic diseases such as diabetes or kidney failure; however, symptoms may occur in healthy people. Clear fluids are appropriate for the first 24 hours to maintain adequate hydration. After 24 hours of fluid without vomiting, the diet can be progressed to other foods, for example, the BRAT diet, as tolerated.

The key to oral rehydration is small frequent feedings. If offered free access to a bottle, infants may drink quickly to quench their thirst and then vomit because of a distended, full stomach. Instead, it may be best to limit the amount of fluid given at one time. There are a variety of regimens that are used and they follow a basic format:

  • Offer 1/3 of an ounce (5 to 10 cc) of fluid at one time, wait for 5 to 10 minutes, then repeat.
  • If this amount is tolerated without vomiting, increase the amount of fluid to 2/3 of an ounce (10 to 20 cc). Wait and repeat.
  • If tolerated, increase the fluid offered to 1 ounce (30 cc) at a time.
  • If vomiting occurs, go back to the 1/3 of an ounce (5 to 10 cc) and restart.
  • Once the child is tolerating significant fluids by mouth, a more solid diet can be offered.

The important thing to remember is that the goal is to provide fluid to the child and not necessarily calories. In the short term, hydration is more important than nutrition.

For infants and children, fluid status can be monitored by:

  • whether they are urinating,
  • if they have saliva in their mouths,
  • tears in their eyes, and
  • sweat in their armpits or groin.

If the child's baseline weight is known, dehydration can be measured by comparing weight.

Medical care should be accessed immediately if the child is listless, floppy, or does not seem to be acting normally.

The critical step is replacing fluids when the person is nauseous and doesn't want to drink (hydrate). This is especially difficult with infants and children. Small frequent offerings of clear fluids, sometimes only a mouthful at a time, may be enough to replenish the body's fluid stores and prevent admission to the hospital for intravenous (IV) fluid administration.

What Medications or Antibiotics Treat and Cure the Stomach Flu?

Antibiotics are usually not prescribed until a bacteria or parasite has been identified as the cause of the infection. Antibiotics may be given for certain bacteria, specifically Campylobacter, Shigella, and Vibrio cholerae, if properly identified through laboratory tests. Otherwise, using any antibiotic or the wrong antibiotic can worsen some infections or make them last longer.

Antibiotics are not used to treat viral infections.

Some infections, such as Salmonella, are not treated with antibiotics. With supportive care comprising of fluids and rest, the body is able to fight off and rid itself of the infection without antibiotics.

For adults, the doctor may prescribe medications to stop the vomiting (antiemetics) such as:

Sometimes these medications are prescribed as a suppository.

Zofran is an effective anti-nausea medication used for infants and children.

Antidiarrheal medications are not usually recommended if the infection is associated with a toxin that causes the diarrhea. The most common antidiarrheal agents for people older than 3 years of age include over-the-counter (OTC) medications such as:

Can You Prevent From Getting the Stomach Flu?

With most infections, the key is to block the spread of the organism. To prevent from getting the stomach flu:

  • Always wash your hands.
  • Eat properly prepared and stored food.
  • Bleach soiled laundry.
  • Vaccinations for Vibrio cholerae, and rotavirus have been developed. Rotavirus vaccination is recommended for infants in the U.S. Vaccines for V. cholerae may be administered to individuals traveling to at-risk areas.
  • Food handlers should not return to work until their symptoms have resolved. Salmonella infections are a special case; those who work in the medical profession or who are food handlers need to have negative stool cultures for Salmonella before being allowed to return to work.

What Do Stomach Flu (Gastroenteritis Infections) Look Like (Pictures)?

<em>Cryptococcus colitis</em> (shown at the arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.
Cryptococcus colitis (shown at the arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.

Pathological changes seen in intestinal lumen with pseudomembranous colitis (indicated by arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.
Pathological changes seen in intestinal lumen with pseudomembranous colitis (indicated by arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.
<em>Strongyloides stercoralis</em> parasite (highlighted by arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.
Strongyloides stercoralis parasite (highlighted by arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University. 

<em>Giardia lamblia</em> (indicated by the arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.
Giardia lamblia (indicated by the arrows). Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.

Normal stain of stool sample looking for ova, parasites, and leukocytes. Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University.
Normal stain of stool sample looking for ova, parasites, and leukocytes. Image courtesy of Alexis Carter, MD, Department of Pathology and Laboratory Medicine, East Carolina University. 
Reviewed on 7/22/2022
Foodborne Germs and Illnesses. CDC. Updated: Oct 23, 2019.

Tintinalli J, et al. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th edition. .

Wikswo ME, Hall AJ. Outbreaks of acute gastroenteritis transmitted by person-to-person contact--United States, 2009-2010. MMWR Surveill Summ. 2012 Dec 14. 61(9):1-12.