Few illnesses come on as abruptly as norovirus. One moment you may feel completely fine, and the next you’re dealing with intense nausea, vomiting, and diarrhea. If symptoms develop suddenly and spread quickly among family members, coworkers, or classmates, norovirus is often the cause. Commonly referred to as the “stomach flu,” norovirus is not related to influenza. Instead, it’s a highly contagious virus that affects the stomach and intestines, causing inflammation known as ...