Ecstatic fans cheering and hugging at the Champion's League game between Atalanta and Valencia in February boosted the spread of the coronavirus, the mayor of the worst-hit Italian city said on Tuesday.
Bergamo, in the northern Lombardy region, is now Italy's worst-hit province, with nearly 6 728 infections.
Its football team Atalanta had been having a stellar season, with a historic Champions League qualification. Its game against Spanish rival Valencia on 19 February at the San Siro stadium in Milan had been feverishly awaited by fans.
Atalanta pulled off a stunning 4-1 victory - each goal met with shouts of glee, fans clutching at each other in excitement.
Bergamo Mayor Giorgio Gori told foreign journalists the match was "among the sad explanations" for the high infection rate in the city and wider province.
"Some 40 000 Bergamo inhabitants went to Milan to watch the game. Others watched it from their homes, in families, in groups, at the bar," he said.
"It's clear that evening was a situation in which the virus was widely spread," he added.
But Gori said he didn't think it was "the starting point". Instead he believed Bergamo's troubles began when a patient at the Fenaroli Hospital in Alzano was admitted with coronavirus but it went undetected, allowing him to infect others.
Two weeks after the historic match in Milan the curve of the number of those infected in Bergamo began to rise steeply and the town has become the epicentre for the pandemic in Europe.
Some 4 178 people have died so far in Lombardy, out of a total of over 6 820 in Italy.
Gori said he thought the statistics failed to represent the real toll on Bergamo and the surrounding region because "there are certainly many elderly people who died at home, without it having been possible to take them to hospital".
"These people are not included in the official statistics. No tests have been done on them either before or after death".
Spanish club Valencia have said that 35 percent of their team and staff have tested positive for coronavirus, following the trip to Milan.
Atalanta on Tuesday confirmed that goalkeeper Marco Sportiello, who played in Valencia on 10 March as the Italian club qualified for the Champions League quarter-finals, had become their first player to test positive for Covid-19.
"Marco is currently asymptomatic," the team said in a statement. "The preventive quarantine, to which Marco and all the members of the first team had been subjected, will end on 27 March."