According to WebMD, the stomach flu, also referred to as gastroenteritis, is a highly contagious illness caused by several viruses that include norovirus, rotavirus and adenovirus. The illness is passed from person to person through infected stool, and the viruses can remain on surfaces for months at a time.
Mayo Clinic explains that individuals with viral gastroenteritis can be contagious for as long as two weeks, depending on the specific virus. Individuals with norovirus, the most common form of stomach flu, are contagious the moment they begin to experience symptoms and for at least three days following recovery. Individuals suffering from rotavirus are contagious prior to developing symptoms and are typically capable of spreading the virus for up to two weeks after recovery.