The Kansas City Health Department directed 10 people to quarantine after the Chiefs identified the infected person and other attendees who potentially came into contact with the individual.
"I want to remind everyone that COVID-19 is anywhere and everywhere," Kansas City health director Dr. Rex Archer said in a statement Thursday. "While we're all tired of it, frustrated and even angry at how it has altered and stricken our lives and livelihoods, we must continue to think of those who have not and will not survive it."
The Chiefs added that the individual entered the stadium in agreement with mask mandates and was seated in the lower level of the stadium.
The reigning Super Bowl champions kicked off the 2020 season in front of 15,895 fans. While the Chiefs and Jacksonville Jaguars were the only teams to play with people in the stands in Week 1, four other clubs are set to open their stadiums with limited capacities in Week 2.