context: Sometimes people mistake symptoms of stomach flu, or gastroenteritis, for the viral infection we commonly call "flu." But they're not the same. Stomach flu happens when your stomach and intestines (also called the gastrointestinal or GI tract) are inflamed and irritated. Causes range from bacteria, viruses, and parasites to food reactions and unclean water. The flu comes with symptoms like fever, congestion, muscle aches, and fatigue. The cause is the influenza virus. More severe cases can lead to life-threatening illnesses like pneumonia. Antibiotics are sometimes used to treat bacterial gastroenteritis, but they don't work against flu viruses. They can include: Cramps in your belly or sides Stomach pain Nausea Vomiting Diarrhea You may also have a fever, headache, and swollen lymph glands, depending on the type of germ that causes it. In severe cases, days of throwing up and having diarrhea (or both) can cause your body to lose a lot of moisture. If you lose too much, you may need medical attention. Sometimes it can be life threatening. Signs to watch for include: Sunken eyes Lightheadedness Being more thirsty Dry or sticky mouth Lack of normal elasticity of the skin Peeing less Fewer tears You can avoid it by drinking plenty of liquids. When you can keep food down again, try bland things like toast, rice, bananas, and applesauce first. Go back to a normal diet within 24 hours if you can. Many things cause gastroenteritis, including bacteria, viruses, parasites, dairy products, and poor hygiene. Bacteria that cause gastroenteritis include: E. coli Campylobacter Shigella Salmonella Viruses cause close to half of all gastroenteritis cases in adults and even more in children. Some of them may include: Norovirus or Norwalk-like virus Adenovirus Rotavirus Cytomegalovirus Herpes simplex virus Viral hepatitis Stomach viruses spread fast because people don't wash their hands well after using the bathroom or changing a baby's diaper. Wash long enough to sing " Happy Birthday" twice. Many doctors call stomach flu "a family affair" because it's so highly contagious it can affect every member of a family. While they're not as common, parasites like giardia, cryptosporidium, and E. hystolica (the cause of dysentery) can cause severe diarrhea and dehydration. They're often found in parts of the world where the water isn't clean. Travelers should drink bottled water to avoid them. Some foods may irritate your stomach and also cause gastroenteritis. The way someone who can't digest dairy (or is lactose intolerant) reacts to dairy products is a good example. Severe reactions to seafood are another example. Those high on the list are pregnant women, infants, people who aren't eating well, people whose immune systems are weakened, and older adults. How severe your case is depends on how well your body can resist the infection. If you have symptoms of stomach flu and are weak and dizzy, you may be dehydrated. Call your doctor if you have these symptoms. Blood in your vomit or poop Dehydration -- you can't pee, or there's very little when you do go, you're very thirsty, can't make tears, and your mouth is always dry Fever of 100.4 degrees F or higher in an infant or 102.2 degrees F or higher in an older child or adult Swollen tummy or pain in the right lower part of the belly Vomiting that lasts more than 48 hours If you can't keep fluids down and you're losing them from fever, vomiting, and diarrhea, get emergency medical help. Tell friends and family that if you pass out, someone should call 911.