Hi and sorry you are ill. There is no such thing as "stomach flu" meaning the influenza virus does not cause flu in the stomach. It is considered gastroenteritis. The symptoms of diarrhea, vomiting, low grade fever up to 100 degrees and possible cramps are caused by many things, virus or bacterial. However, the most common cause is a virus called Norovirus. It is spead from person to person by fecal oral contamination.