When someone talks about having “the stomach flu,” they are probably describing acute-onset gastroenteritis caused by one of the noroviruses.
The Centers for Disease Control and Prevention (CDC) estimates that noroviruses cause nearly 21 million cases of acute gastroenteritis annually, making noroviruses the leading cause of gastroenteritis in adults in the United States. Norovirus is highly contagious and transmitted by infected individuals at an enormous rate. According to CDC estimates, this translates into about 2,500 reported norovirus outbreaks in the United States each year. Norovirus outbreaks have been reported in many settings, including healthcare facilities, restaurants and catered events, schools, and childcare centers. Cruise ships account for a small percentage (1%) of reported norovirus outbreaks overall. Norovirus outbreaks occur throughout the year but are most common from November to April. The most common symptoms are sudden onset of vomiting and watery diarrhea, although stomach cramps and pain also often occur. Some people experience fever and body aches. Symptoms usually start 12 to 48 hours after being exposed and typically last about 1 to 3 days.