Excerpt:

Norovirus is a highly contagious virus that causes acute gastroenteritis, an inflammation of the stomach and intestines. It is the leading cause of food-borne illness worldwide, causing hundreds of millions of cases each year.

Although infections are often brief, typically lasting 24 to 72 hours, symptoms can be intense. Sudden onset vomiting, watery diarrhea, nausea, stomach cramps and sometimes low-grade fever or body aches are common. Most healthy adults recover quickly, but young children, older adults and people who become dehydrated can experience serious complications.

One reason norovirus spreads so efficiently is its extremely low infectious dose: fewer than 20 viral particles may be enough to cause illness. By comparison, many other viruses require far higher doses to trigger infection.

In practical terms, microscopic contamination on food, surfaces or hands can be enough to make someone sick. The virus spreads primarily through the fecal–oral route, via contaminated food or water, direct person-to-person contact or touching contaminated surfaces and then the mouth.

Norovirus is also remarkably resilient. It can survive on surfaces for days, withstand freezing temperatures and resist many common disinfectants. It is not reliably killed by alcohol-based hand sanitizers, making thorough hand-washing with soap and water essential. Adding to the challenge, infected individuals can spread the virus before symptoms appear and may continue shedding it for days after recovery.

These characteristics of high infectivity, environmental persistence, and the ability to spread before and after symptoms appear make norovirus particularly difficult to control, especially in settings where large numbers of people live, eat and interact in close proximity.