How Long Your Stomach Flu Is Really Contagious

The stomach flu is an infection of the intestines that can be caused by a variety of germs. Loose, watery diarrhea and vomiting are the most common symptoms of the stomach flu, though headache, fever, muscle aches, and abdominal cramps may also occur (via Centers for Disease Control and Prevention). Symptoms typically begin a day or two after infection and last for one to 10 days, depending on its cause.

Although colloquially referred to as the stomach flu, the infection is actually not related to the flu — the respiratory illness caused by the influenza virus — at all. The medical term for stomach flu is gastroenteritis, which means the inflammation of the stomach and intestines.

Many germs can cause gastroenteritis, including viruses like noroviruses and rotaviruses; bacteria, such as Salmonella and Shigella; and parasites, such as Giardia. In most instances, the stomach flu will clear up on its own, though drinking fluids, eating bland food, and getting plenty of rest will help (via Mayo Clinic). Infants, young children, older adults, and immunocompromised individuals are at a higher risk of dehydration from the stomach flu and may require treatment at a medical center or hospital to prevent or correct dehydration.

The stomach flu is very common. Each year in the United States, there are 19 to 21 million cases of norovirus, the most common cause of viral gastroenteritis, according to the National Institute of Diabetes and Digestive and Kidney Diseases. The illness is spread by eating food or drinking beverages contaminated with germs, touching contaminated surfaces and then touching your mouth, nose, or eyes, or shaking hands with a sick person. Being in close contact with someone who is infected, including sharing food or utensils, caring for them, or being in close proximity while they are vomiting can also cause the stomach flu to spread.

How long a person with gastroenteritis is contagious depends on the cause of the infection, though generally, it is most likely to spread to others from the time when the first symptoms appear to several days after they've ended (via Healthline). However, it's possible for people with rotavirus to infect others even before symptoms begin, and studies show norovirus can still be contagious for two weeks or longer after the sick person feels better.

To prevent the spread of the stomach flu, it's important to wash your hands regularly or use hand sanitizer if soap and water aren't available, avoid shaking hands during outbreaks, disinfect contaminated surfaces, and ensure food is stored, cooked, and served properly and in a hygienic manner. If you're sick, try to stay away from others to avoid spreading the infection.