You do not have to travel all the way to the Winter Olympics to get infected. A professor of infectious disease at the Medical College of Wisconsin is tracking it from her lab. It has soared from zero in November, to 14 cases in just the past week.
She hopes no Olympic athlete will get infected in South Korea.
"That would be very bad because they get very sick and dehydrated," said Dr. Silvia Munoz-Price, Medical College of Wisconsin.
Getting sick from it spreads through feces. Symptoms include nausea, fever and violent vomiting.
If you get it you will feel better in about three days.
To stop the spread, Munoz-Price says, "Wash your hands, wash your hands, wash your hands."