PYEONGCHANG, Korea, Republic Of — The Olympic Games, says Dr. Bob McCormack, is where the viruses of the world come to meet.

The medical director for the Canadian Olympic Committee has been preaching that to Canada's team of 225 athletes as an outbreak of norovirus threatens to derail the Pyeongchang Olympics.

"They've trained eight to 12 years for this one moment in time when they can prove and perform, and of course it's a tragedy if they get derailed by injury or illness," McCormack said. "A lot of focus has been on injury coming into the Games, but an illness can derail you the same way."

The number of confirmed cases grew to 128 by Thursday evening, with 42 new cases that day. None of the cases are athletes, and the COC said no Canadian staff members have been affected.

Sometimes called the winter vomiting bug, norovirus is characterized by nausea, abdominal pain, vomiting and diarrhea. It's the same nasty bug that felled a dozen Canadian athletes and staff, including decathlete Damian Warner and sprinter Aaron Brown, at last summer's world track and field championships. Some 30 athletes, all staying in the same downtown London hotel, became ill at that meet.

The bug can cut a swath through any large gathering where people are housed in close quarters, in some cases striking hundreds of vacationers on a single cruise ship.

"It's highly contagious," McCormack said.

He praised Pyeongchang's organizing committee's swift response, and said they're working with South Korea's Centers for Disease Control and Prevention and the World Health Organization, as they race to get ahead of the outbreak.

"They've taken a very pro-active approach in saying 'We're going to have heightened surveillance, we're going to have aggressive quarantine, to make sure it doesn't get out of control,'" McCormack said.

Venue walls are plastered with posters about the importance of hand washing. Venue restaurant staff wear surgical masks and gloves. Bottles of hand sanitizer are everywhere. At the main media village in Gangneung, cleaning staff announced they would start swabbing down bathrooms with chlorine bleach daily.

Health concerns come hand in hand with any Games, said McCormack, who's been part of Canada's medical staff at 10 Olympics. In 2016, fear of the Zika virus kept numerous high-profile athletes away, including golfer Jason Day and Canadian tennis player Milos Raonic.

McCormack said history shows that six to eight per cent of athletes are likely to fall ill at a Games. Intense training, he added, can weaken an athlete's immune system.

"We tell the athletes 'You've got to be extra careful in terms of using the hand sanitizer and washing your hands, getting proper sleep, keeping your immune system healthy,'" McCormack said. "When something like this happens, people are maybe a little bit more focused about washing their hands, about putting the Purel on their hands every time they go in and out of the dressing room, about being careful with kissing and body contact, not sharing towels . . . but we sometimes let it slide."

Long track speedskater Laurent Dubreuil said Canadians athletes aren't overly concerned about the bug.

"It's the usual stuff, wash your hands, don't hug people. Isolate people if they show signs," Dubreuil said. "We are crossing our fingers. If we are careful by washing our hands and using Purel, we are going to put the odds in our favour. . . I hope it does not happen to anyone on our team, or anyone in general."

Maxim Noreau, a defenceman on Canada's men's hockey team, said they had a briefing Thursday about norovirus.

"Especially at the meal hall, how that's kind of a concern right now. Just to be vigilant, obviously washing your hands and stuff like that," Noreau said. "But at this point there's only so much that we can control too. I think we have a good staff supporting us and taking care of us, making sure we stay healthy. So we've just got to trust them and eat what we're told, I guess."

Hong Jeong-ik from South Korea's Centers for Disease Control and Prevention said Thursday the number of cases is likely to continue to rise.

Some 1,200 security personnel was quarantined after several dozen became ill, and 900 military personnel had to be brought in to replace them. The security personnel staying at the Horeb Youth Center remain the most affected with 97 confirmed cases, including 34 new cases Thursday.