Study suggests NFL crowds may have led to coronavirus spikes – San Francisco Chronicle

As spectators return to sports venues across the nation — including A’s and Giants home games earlier this month, and Warriors home games starting April 23 — they convene amid scarce data measuring the impact of such crowds on the coronavirus pandemic.

But new academic research suggests a connection between large gatherings of NFL fans and an increase in coronavirus cases where games were played in front of crowds last season.

Santa Clara County public health officials did not allow the 49ers to host spectators at Levi’s Stadium in 2020, unlike several NFL teams. The Dallas Cowboys, for instance, averaged 27,378 fans for eight home games, including more than 30,000 four times; and the Tampa Bay Buccaneers had six crowds exceeding 15,000, plus 24,835 for the Super Bowl, on Feb. 7.

The study — led by Justin Kurland, director of research at the National Center for Spectator Sports Safety and Security at the University of Southern Mississippi — found more than twice as many coronavirus cases in counties where teams hosted at least 20,000 fans, compared with counties with other teams. The case rate per 100,000 residents also was twice as high, according to the study, and neighboring counties had similarly high case counts in the three weeks after games.

Hillsborough County in Florida, where the Bucs play, experienced a spike in cases between two and three weeks after several games, according to the study. Kurland and his colleagues cited a similar pattern across nearly every NFL team allowing more than 5,000 spectators at games last season.

The study, one of the most ambitious efforts to gauge the effect of crowds at sporting events, was submitted to Lancet, a scientific journal, for peer review. The findings were not presented as proof that NFL games caused the spikes in coronavirus cases but rather as “compelling evidence,” per the study.

The authors’ stated interpretations of the data included advising “a more moderate, phased-in approach” for crowds at large-scale sporting events, until reaching sufficient herd immunity.

Dr. John Swartzberg, a UC Berkeley infectious-disease expert, acknowledged an observational study like this does not prove cause. Swartzbergwasn’t surprised by the findings, given the key factors in coronavirus spread: how close people are together, how loud they are and the prevalence of the disease in the community.

“In situations where the prevalence is significant and people are crowded together in stadiums, particularly without masks, we are asking for trouble,” Swartzberg said.

Alex Piquero, chair of the sociology department at the University of Miami, also was involved in the study. Piquero said the results — tracking case counts in counties where fans were allowed (plus adjacent counties) and where they weren’t — echoed the warnings of public health officials.

“We’re not saying the NFL should not have opened, but there was a way to do it in a very measured way,” Piquero said. “So our lesson for the upcoming season is slow and steady. Have a small number of people and space them out.”

That’s not what NFL Commissioner Roger Goodell envisions. He said March 30 that he expects to have full stadiums for games in the 2021 season.

Piquero’s comment also offered a relevant reminder for major-league baseball teams. The A’s and Giants have had fewer than 9,000 spectators at every home game to date, except for Opening Night on April 1 in Oakland (10,436). San Francisco public health officials are requiring fans at Oracle Park to test negative for the virus or offer proof of full vaccination.

This stands in striking contrast to teams such as the Texas Rangers and Houston Astros. The Rangers hosted four crowds of more than 26,000 people last week, including 38,238 for their home opener April 5. The Astros had nearly 22,000 fans for each of their three home games last week against the A’s.

Photos and television coverage of those games, and the Rangers’ home opener, showed many people sitting shoulder to shoulder while ignoring MLB guidelines to wear face coverings.

“I condemn what happened with the Rangers — a lot of people didn’t have masks, they were yelling and the incidence of disease was significant there,” Swartzberg said. “That was irresponsible.”

Swartzberg sees the logic in San Francisco’s plan to spread out about 8,900 fans at Giants games, while requiring negative tests or vaccination. He’s also skeptical fans really will be dispersed, really will keep their masks on and really will be fully vaccinated (the Giants are not checking all spectators).

NFL officials, asked by The Chronicle about the study’s findings, pointed to a report (also not yet peer-reviewed) from researchers at Georgia Tech and Harvard. That found attendance at NFL and NCAA college football games didn’t cause “a significant increase” in local COVID-19 cases.

“With the expert guidance of local, state and federal public health officials … we hosted fans safely and responsibly during the 2020 NFL season,” Jeff Miller, the league’s executive vice president of communications, public affairs and policy, said in an emailed statement.

The NFL was quick to downplay the findings of the Kurland-Piquero group. Still, its research examined case rates in multiple counties to account for fans who might have traveled farther to attend games, and for a longer time frame to account for the virus’ incubation period.

Major League Baseball did not allow fans during its 2020 season, though about 11,000 spectators attended National League Championship Series and World Series games in October in Arlington, Texas. A spokesman for the Tarrant County public health department did not respond to a request for comment on the impact those crowds might have had on virus cases in the area.

Baseball Commissioner Rob Manfred, speaking during a recent appearance on ESPN’s “Baseball Tonight,” essentially deferred to local public health officials regarding big crowds at Rangers games this month. Manfred noted the mask mandate implemented by MLB and the Rangers — part of guidelines developed by the league after offseason consultation with health experts — even though enforcement clearly was spotty.

In Florida, public health officials discovered mixed results when they studied cases in Hillsborough County in the weeks following the Super Bowl. They found “low numbers” of cases directly associated with official Super Bowl events, the report said, though the county’s percentage of statewide cases increased slightly in February and its positivity rate was higher.

Kurland and Piquero, among five authors of the recent study, understood the complexity of pinpointing the cause behind virus spikes. They also insisted the evidence suggests teams start with small crowds (about 5,000) and gauge the impact before welcoming more people.

“That’s by far a more reasoned and evidence-based approach, rolling fans back into stadiums,” Kurland said, “rather than saying, ‘We’re tired of all this, let’s come back.’”

Ron Kroichick is a San Francisco Chronicle staff writer. Email: rkroichick@sfchronicle.com Twitter: @ronkroichick

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