Noroviruses cause more cases of stomach flu or gastroenteritis in adults than any other virus, according to Dr. James M. Steckelberg of the Mayo Clinic. If you have norovirus, you are contagious from the time you begin feeling ill until at least three days after you recover, the National Center for Immunization and Respiratory Diseases says.
In children, rotaviruses are the most common cause of stomach flu symptoms, Dr. Steckelberg says. If you have rotavirus, you're contagious for up to two days before you start having symptoms and for up to 10 days after you recover, according to the Immunization Action Coalition, which provides information about vaccine-preventable diseases.
You can catch these viruses from an infected person through direct contact, such as kissing or shaking hands, or by sharing eating utensils. You can also catch them if an infected person doesn't wash his hands after using the bathroom and then touches food you later eat or surfaces that you touch.
Many of these viruses are spread by the fecal-oral route, meaning fecal matter gets on the hands of someone who uses the bathroom or changes a diaper. That person then touches something that another person touches. The second person touches his mouth or eats food with the germs on his hands and ingests the virus, then gets sick.
The best way to prevent catching the viruses that cause stomach flu is to wash your hands frequently, especially before eating and after using the bathroom. Hand-washing interrupts transmission via the fecal-oral route.
Also, avoid direct contact with people you know are sick, and don't eat food prepared by them. Also, avoid preparing food for others when you are sick.
A vaccine to prevent illness from rotavirus in young children became available 2006. A second vaccine was approved in 2008. Infants take the vaccine in a series of doses at either 2, 4 and 6 months or 2 and 4 months depending on the vaccine used. The Immunization Action Coalition says children older than 15 weeks should not get the vaccine. Check with your child's pediatrician about whether and when your child should be vaccinated.