Cold, Flu, & Cough Health Center

Is It a Stomach Flu or Influenza?

Sometimes people mistake symptoms of stomach flu, or gastroenteritis, for the viral infection we commonly call "flu." But the "stomach flu" is not the flu. It is a gastrointestinal illness caused by a number of factors including bacteria, viruses and parasites. The flu, which causes fever, congestion, muscle aches, and fatigue, is caused by viruses only. 

How Does Stomach Flu Differ From Influenza?

Stomach flu actually refers to gastroenteritis or irritation and inflammation of the stomach and intestines (the gastrointestinal tract). Gastroenteritis may be caused by a virus, bacteria, parasites in spoiled food or unclean water, or another trigger such as lactose intolerance, which causes a reaction to dairy products.

Influenza (flu), on the other hand, is a viral infection that mimics a cold except that it starts forcefully with symptoms of fatigue, fever, and respiratory congestion. While more than 100 different virus types can cause a common cold, only influenza virus types A, B, and C cause flu. More severe cases of influenza can lead to life-threatening illnesses such as pneumonia.

In addition, while antibiotics can treat a bacterial infection that may cause gastroenteritis, antibiotics cannot treat influenza because flu is caused by a virus.

What Are the Symptoms of Stomach Flu?

Symptoms of gastroenteritis or stomach flu include: 

• Abdominal cramps
• Stomach pain
• Nausea
• Vomiting
• Diarrhea

You may also have fever, headache, and swollen lymph glands, depending on the type of bug that causes it.

In severe cases of gastroenteritis, loss of bodily fluid can result in dehydration, a life-threatening condition that needs medical attention. Signs of dehydration include:

• Sunken eyes
• Light-headedness
• Increased thirst
• Dry or sticky mucous membranes in the mouth
• Lack of normal elasticity of the skin
• Decreased urine output
• Decreased tears

You can avoid dehydration by continuing to drink fluids. When you are able to keep food down, bland foods -- like toast, rice, bananas, and applesauce -- should be tried first. However, experts now recommend returning to a normal diet within 24 hours, if possible.  

What Causes a Stomach Flu?

There are many causes of gastroenteritis, including bacteria, viruses, parasites, dairy products, and poor hygiene. 

Bacteria that cause gastroenteritis include:

• E. coli
• Campylobacter
• Shigella
• Salmonella

Viruses are responsible for 30% to 40% of gastroenteritis cases in children, and may include:

• Norovirus or Norwalk-like virus
• Adenovirus
• Rotavirus
• Calicivirus
• Astrovirus

Stomach viruses are notorious for spreading rapidly because of poor hand washing.

While not as common, parasites such as giardia and cryptosporidium can cause severe diarrhea and dehydration. Water-borne parasites are common in underdeveloped parts of the world that have unsanitary water supplies. It is recommended that travelers drink bottled water to avoid water-borne parasites.

Some foods may irritate your stomach and also cause gastroenteritis. Reaction to dairy products in someone with lactose intolerance is the most common example. Severe reactions to seafood is another example.

A lack of good hygiene can result in a stomach flu. For instance, improper hand washing after using the bathroom or after changing a baby's diaper can spread the infectious bug from person to person. Many doctors call stomach flu "a family affair" because it is so highly contagious and usually goes through all members of a family.