The team explained how the health and safety and contract tracing protocols set up at Arrowhead Stadium limited the potential exposure to others inside the venue:
"The individual and the individual's group were seated in the lower level of the stadium. By design, the stadium's COVID protocol plan limited potential exposure to a single seating zone within the stadium. All staff with known interactions with the positive case were required to wear personal protective equipment (PPE), including a mask. Additionally, the protocols in place at the stadium require all attendees to be wearing masks inside the stadium."
Unlike MLB, the NFL hasn't set a uniform policy banning fans from games. Instead, the league has allowed teams to set their own limits based on guidelines from state and local officials.
The Chiefs said in August they were planning to fill Arrowhead Stadium to around 22 percent of its total capacity for Week 1. All fans would be required to wear face masks, and the venue is divided into specified zones that prevent access to the entire concourse.
Kansas City said it used "parking and ticket scanning data, as well as video record review" to determine that the fan who tested positive and the others in their party "entered the stadium in compliance with mask mandates."
The reigning Super Bowl champions were far from the only team to welcome in fans for Week 1, and some colleges have sold a small percentage of tickets for their games this season as well.
As the year goes on, franchises may look to relax whatever restrictions they initially put in place while still falling within local health guidelines.
The Chiefs' next home game is Oct. 4 against the New England Patriots.
According to CNN, officials have confirmed more than 6.6 million cases of COVID-19 in the United States, with 197,364 people dead from the disease.