Noroviruses are members of a group of viruses called caliciviruses. 

Often (incorrectly) referred to as the "stomach flu," the virus causes your stomach, intestines or both to become inflamed, leading to the sudden onset of severe pain, nausea, diarrhea and vomiting. Norovirus infections occur most frequently in closed and crowded environments such as hospitals, nursing homes, child care centers, schools and cruise ships.

Noroviruses are highly contagious, with infection spread through contaminated food or water, shared utensils (think buffet lines...), and contaminated common surfaces (doorknobs, handrails, etc..). You can also be infected through close contact with an infected person.

According to the CDC:

"Just a very small amount - as few as 18 viral particles - of norovirus on your food or your hands can make you sick. That means the amount of virus particles that fit on the head of a pin would be enough to infect more than 1000 people."

Diarrhea, abdominal pain and vomiting typically begin 12 to 48 hours after exposure. Norovirus symptoms last one to three days, and most people recover completely without treatment. However, for some people - especially infants, older adults and people with underlying disease - vomiting and diarrhea can be severely dehydrating and require medical attention.

If you are headed to the Winter Olympics in PyeongChang, S. Korea, you would do well to become fanatical about hand washing and avoiding touching communal surfaces. Hand sanitizer should be with you at all times. This will be a highly transient environment with visitors from around the world gathering in common spaces. Be cautious.

You should also consider purchasing disinfectant for use within your hotel room as an extra precaution.