A fan who attended the NFL’s season-opening game last week at Arrowhead Stadium in Kansas City, Mo., tested positive for the novel coronavirus the following day, leading the Kansas City Health Department to direct 10 people to quarantine for potential exposure to the virus.

The positive test and quarantines were announced Thursday by the city’s health department. The account was confirmed by the Kansas City Chiefs, who hosted the Houston Texans in the game Sept. 10.

“Compliance with the protocols remains a key component to making this plan effective,” the Chiefs said in a written statement. “We appreciate the professionalism and diligence of the Health Department and will continue to support its efforts in this matter and throughout the season.”

The Chiefs and Jacksonville Jaguars were the only NFL teams to have fans in attendance at home games during the season’s opening week. The Chiefs had an announced crowd of 15,895 for their 34-20 victory over the Texans. Other home teams played in stadiums without fans during the Week 1 games.

The NFL is allowing fans as permitted under state and local guidelines. The Cleveland Browns, Indianapolis Colts, Dallas Cowboys and Miami Dolphins are expected to have fans at their Week 2 home games.

According to the Chiefs, the fan who tested positive and other members of that fan’s group at the game were seated in the stadium’s lower level and were wearing masks, as required, when entering the stadium. The Chiefs said they reviewed video and used contact-tracing methods that included parking and ticket-scanning data.

“This process allowed the team to identify the other guests sitting with this individual, the service staff with whom this individual may have come in contact with, as well as any other ticket holders near this person at the time of entry into the stadium,” the Chiefs said in their statement. “Within hours of being notified, the Chiefs were able to pinpoint the names of the other members of the party as well as detailed information about the path and location of entry, and this information was provided to the Health Department.”

All fans who attend NFL games this season are required to wear masks. At the Chiefs-Texans game, fans were required to enter the stadium through designated entrances and were subject to distancing measures and other protocols within the stadium. Fans sat mostly in small groups, even in the stadium’s upper reaches. The seven rows of seats closest to the field were covered by tarps and unused, under a leaguewide directive. Some fans tailgated in the parking lots before the game, as was permitted.

The Chiefs said their protocols for fans were designed to limit “potential exposure to a single seating zone within the stadium.” The team also said it has “worked in close cooperation with Dr. Rex Archer and the Kansas City Health Department to provide all of the relevant information available.”

The Chiefs previously said they were operating with the stadium at about 22 percent capacity for the opener.

“I want to remind everyone that COVID-19 is anywhere and everywhere,” Archer, the Kansas City health director, said in a written statement. “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 city health department said that the Chiefs and those identified as contacts of the fan who tested positive “responded swiftly to investigators’ questions and provided crucial information, so all exposures could be identified.”

Under the NFL’s protocols, all players, all coaches and certain team staff members are tested daily, except for game days. All players and coaches were available for the Week 1 games under the testing protocols. In the most recent testing results announced Wednesday by the league and the NFL Players Association, there were two new confirmed positive tests by players and five new confirmed positives among other personnel in testing from Sept. 6 to Saturday. That was among a total of 40,479 tests administered, according to the league and NFLPA.