Norovirus is a very contagious viral illness that causes a sudden onset of vomiting and diarrhea, which can last for approximately 1-3 days.  Norovirus is more commonly known as the "stomach flu", but is not related to influenza.  Norovirus is often spread through direct contact with someone who is infected with norovirus, contact with contaminated surfaces, or consuming food and water contaminated with the virus.