With the opening ceremony set for Friday, an outbreak of the highly infectious gastrointestinal bug norovirus already has a solid lead at the 2018 Olympic Winter Games in South Korea.

In just a few days, official case counts have nearly quadrupled, according to multiple reports from The New York Times. The tally was 32 just two days ago but quickly climbed to 86. Then another 42 cases were confirmed by Thursday night, bringing the total to 128 around the Olympic sites.

Officials at the games first announced the outbreak of the virus—also called the “winter vomiting bug”—on Tuesday. Security personnel were the first to test positive, and about 1,200 of the security staff were sequestered in their rooms at the time. About 1,100 people, some non-security personnel, were still in quarantine on Thursday. South Korea deployed 900 military personnel to make up for the quarantined security workers.

But the infection has now spread beyond the security staff to Olympics Organizing Committee staff, venue personnel, and even cafeteria workers. Hong Jeong-ik from South Korea’s Centers for Disease Control told the Times that officials were testing food and water to try to identify the source of the infection. “We still haven’t figured out the source yet. It’s going to take some time,” he said.

No athletes are known to have been infected.

Norovirus is a particularly tenacious and pernicious bug. It’s generally spread by the fecal-oral route—which can be direct or via food, beverages, surfaces, or air. Viruses can linger on contaminated surfaces for up to two weeks and survive heating, cooling, and some disinfectants. They can also be easily aerosolized, such as by a toilet flush. As few as just 18 of the wee germs can ignite a gut infection, which sheds billions of viral copies in feces and vomit. Infected people tend to be sick for one to three days with diarrhea, vomiting, and abdominal cramps. Viral shedding can continue after symptoms clear.

Officials are pushing for everyone to wash their hands often and use hand sanitizer, although that’s less effective against norovirus. They’re also telling everyone to only eat cooked food and boil water before drinking it.

So far, athletes at the games seem undeterred, including Mitchell Whitmore, an American speed skater at his third Olympics. “If Michael Jordan can play through the flu, I can race with the virus,” Whitmore told the Times. “If I break my leg, I’m still racing.”