The Olympic organizing committee says another 42 cases of norovirus have been reported at the Olympics, bringing the total to 128 in the past week. Most of the cases, 97 in all, are people staying at a youth center in Pyeongchang that housed security personnel for the games.

About 1,200 people there were sequestered, forcing the military to step in to help with security. Those who have tested negative for norovirus have been released from quarantine and returned to work.

Eight of the new cases have been reported in Pyeongchang or in Gangneung, the seaside city where ice sports will be held. The sick people have been quarantined and officials are trying to figure out how they got the virus.

What is norovirus?

Norovirus is a very infectious bug that causes symptoms including diarrhea, nausea, muscle pain and vomiting. It’s more common in winter but can be seen any time of year. Symptoms usually appear one to two days after infection and typically last for another two or three days.

How does norovirus spread?

Norovirus is spread by contaminated water and food, though the virus can also be transmitted if people touch dirty surfaces or are in close contact with people already sickened by the disease. Previous large outbreaks have been reported in restaurants, on cruise ships, or in building complexes where people share a common water source. It also spreads quickly in public places including hospitals, schools, and nursing homes. Frequent hand-washing and cleaning of surfaces can help curb the spread of the germ.

How is norovirus treated?

There is no specific medical treatment for norovirus; most medical professionals advise patients with symptoms not to come into a hospital to avoid spreading the virus. Doctors say drinking plenty of fluids to avoid dehydration. Adults can take drugs to treat diarrhea and nausea, but doctors or pharmacists should be consulted before these medicines are given to children. Anyone who has signs of severe dehydration, such as persistent dizziness, or who doesn’t improve within a few days, should seek medical attention.