Just a few days away from opening, the 2018 Winter Games in PyeongChang are already taking a hit—and it's a big one! Norovirus has struck at least 41 security guards with complaints of vomiting and diarrhea. This highly contagious collection of viruses are some of the most difficult to combat and prevent.

That's because Norvirus is quickly and easily transmitted (if proper precautions are not taken), lives longer on surfaces than most other viruses, and it can reinfect its victims.

Facts that did not escape Olympic officials who pulled all 1,200 active security guards from duty to be tested for the virus. They also had to replace them—with 900 South Korean military troops.