Olympic officials are scrambling to contain an outbreak of the norovirus that has sickened dozens of security guards days ahead of the official kickoff of the 2018 Pyeongchang Winter Games.

Around 1,200 security staff members have been kept in their rooms while they wait to be tested for the highly contagious virus, Olympic representatives said during a news conference on Tuesday. To make up for the personnel shortage, South Korea has deployed 900 members of its military.

At least 41 security guards have tested positive for the virus, which causes stomach pain and diarrhea, according to South Korea’s national news agency Yonhap.

The Olympics will begin on Friday and run through Feb. 25.

The outbreak appears to be centered on security staff members lodging near Olympic sites, but the precise source is unclear.