Vienna, Austria(CNN) Henrik Lerfeldt has fond memories of Kitzloch, a popular restaurant and bar in the Austrian ski resort town of Ischgl, where he partied several nights while on vacation three weeks ago.

The 56-year-old Dane, who spoke to CNN from self-quarantine at his home 50 miles from Copenhagen last week, said that his time in Kitzloch in the Austrian province of Tyrol was the way "after-ski" is supposed to be. "Lots of people, lots of drinks, and nice waiters happy to serve you more."

Four days after his return home, Lerfeldt tested positive for the coronavirus, or Covid-19, as did one of his friends he was traveling with. But they are just two among hundreds of people from all over Europe whose infections are traced back to Ischgl, some of them directly to Kitzloch, according to European authorities.

Authorities closed down Kitzloch in Ischgl, Austria, on March 9.

Kitzloch declined to comment when contacted by CNN for comment. Its owner, Bernhard Zangerl, told German news site t-online on March 16 that his employees must have also contracted the virus from someone, and the site reports Zangerl as saying it was audacious to try to pin this on one company.

Despite an official warning from the Icelandic government on March 4 that a group of its nationals had contracted coronavirus in Ischgl, Austrian authorities allowed ski tourism -- and the partying that goes with it -- to continue for another nine days before fully quarantining the resort on March 13. Bars in Ischgl were closed on March 10.

Even after a bartender tested positive for the virus, the medical authority of Tyrol -- where ski tourism is one of the biggest economic drivers -- reiterated in a press release on March 8 that there was "no reason to worry." CNN has reached out to Franz Katzgraber, the director of Tyrol's medical authority, for further comment and not received a response.

Ischgl and its neighboring villages draw around 500,000 visitors each winter, with high-profile celebrities and politicians such as Paris Hilton, Naomi Campbell and Bill Clinton among them in previous years.

After a string of rebuttals that the town and bar were linked to the spread of the virus, Austrian authorities have since conceded that they were.

In a statement emailed to CNN last week, the provincial government denied it had dragged its feet, saying it acted in a timely and efficient manner. "With the measures taken, the authorities were able to contain the continuation of the chain of infections," Bernhard Tilg, Tyrol's provincial councilor responsible for health, care facilities, science, and research, said in the statement.

In a statement to CNN on Tuesday, the public prosecutor's office in Innsbruck said it had commissioned the Tyrol Criminal Police Office to conduct "investigations on suspicion of negligent endangerment of people by communicable diseases." The prosecutor's office added that it was looking into the possibility that a catering company did not report an employee's positive coronavirus test at the end of February.

Health experts say alarm bells were missed

The assistant to the director of health at the Icelandic health directorate told CNN that the country's chief epidemiologist Thorolfur Gudnason informed Austrian authorities on March 4 that several Icelandic tourists were infected with the virus while in Ischgl. Gudnason used Europe's official Early Warning and Response System, the directorate confirmed in an email.

On March 5, the day after Iceland notified Austria that Icelandic tourists had contracted Covid-19, Reykjavik added Ischgl to its list of risk zones for Covid-19 transmission, putting the risk of infection in the village on par with China, South Korea, Italy and Iran.

Jan Pravsgaard Christensen, a professor of immunology of infectious diseases, at the University of Copenhagen, told CNN that Iceland's listing should have immediately raised alarm bells.

"Considering that it is a place where people are in close contact in bars, restaurants, and so on, once they know of ... people infected in the same area, they should have initiated a quarantine very quickly," he said.

However, regional authorities in Tyrol downplayed the risk. In a first official reaction to Iceland's listing, Katzgraber said in a March 5 press release that it was "unlikely" there was contagion in Tyrol.

Based on a statement by a single traveler who said that a sick tourist who had visited Italy shared the same flight home to Iceland, Katzgraber said in the same press release that the group of Icelandic tourists likely contracted the virus after they left Austria, giving no evidence.

Oral beer pong and sharing whistles

On March 7 -- three days after Iceland's warning -- a 36-year-old bartender at Kitzloch tested positive. Twenty-two of the bartender's contacts were quarantined, 15 of whom have since tested positive for Covid-19, the provincial government confirmed in press releases.

The outbreak had spread far beyond the Tyrol.

The most recent available Danish government figures show that out of more than 1,400 cases in Denmark, 298 contracted the virus in Austria. In comparison, only 61 cases are linked to travel to Italy, so far the hardest-hit country in Europe.

As of March 20, Icelandic authorities are aware of eight people who got infected with coronavirus in Ischgl specifically, the health authority told CNN.

"At first, we didn't understand how this many cases could have happened," Christensen, who had been briefed by experts working on Iceland's response to the pandemic, said. But a clearer picture emerged when officials worked out what was going on in some of Ischgl's tightly packed bars and clubs.

"We realized that they exchanged saliva because they were playing beer pong," using their mouths, he said, although he did not single out any specific bars where the game took place. The game involved spitting ping pong balls out of their mouths into beer glasses, and those balls were then reused by other people.

Lerfeldt reported that Kitzloch bartenders, including the 36-year-old who later tested positive for coronavirus, blew on a brass whistle to get people to move out of their way as they took shots to customers. Several customers also blew the whistle for fun, Lerfeldt said. "I can see why people would want to whistle it -- and nobody knew he was sick," Lerfeldt said.

Monika Redlberger-Fritz, head of the influenza department at the Medical University of Vienna, told CNN that the way the virus spread in Ischgl means there was likely at least one person who infected a large number of other people.

"That means that there was at least one patient who had a very high viral load, and while most people will infect two to three others on average, these people can transmit the disease to 40, 50, or 80 people." Redlberger-Fritz said that this may have cut the lead time for authorities to react by several days.

Anita Luckner-Hornischer, an official with Tyrol's medical authority, said in a press release on March 8 that "a transmission of the virus onto the guests of the bar is, from a medical point of view, rather unlikely." She gave no evidence.

Authorities closed down Kitzloch on March 9 and said there was no increased risk of transmission.

By March 10, Günther Platter, the provincial governor of Tyrol, said at a press conference that all new cases confirmed in the province that day -- 16 in total -- were tied to a single bar and one of its barkeepers. Local authorities later confirmed the bar to be Kitzloch, the small but bustling bar where Lerfeldt said he and his friends partied for five nights.

"We have found that the risk of infection is very high in the bars. All cases go back to one bar," Platter said at the press conference.

Hundreds of cases traced back to Ischgl

At least four countries have now reported links to Ischgl, showing how the tiny village, home to no more than 1,600 permanent residents, became a major vector in spreading Covid-19.

Alongside Denmark and Iceland, Germany has traced about 300 cases back to Ischgl, more than 80 of them in Hamburg and 200 in the small city of Aalen, according to German media. CNN has been unable to independently verify these figures.

The count is so high that Aalen set up a new email address specifically for people who have visited Ischgl to get in touch with authorities. In a virtual press conference on March 17, the health minister of the German state Baden-Württemberg said, according to German state news agency DPA: "Our problem isn't called Iran, it's Ischgl."

Norway also confirmed that, as of March 20, 862 out of its 1,742 cases were contracted abroad, and said it traced 549 of them back to Austria, according to the Norwegian Institute of Public Health.

Kitzloch has a capacity for 100 people and, when Lerfeldt was there, was packed with patrons from Denmark, Sweden, Norway and Germany, he said.

When the national government announced a lockdown of the area on the afternoon of March 13 -- nine days after Iceland's notification -- the remaining tourists were asked to leave the village and return home without stopping.

Most returned straight to their respective home countries, Tilg, the provincial councilor responsible for health, care facilities and research, told Austrian public broadcaster ORF, but hotel owners in the provincial capital of Innsbruck confirmed to local media that hundreds of Ischgl tourists who were stranded that Friday afternoon checked into their establishments to wait for flights Saturday.

"The authorities acted correctly in every aspect," Tilg reiterated several times in the ORF interview on March 16, and rejected all criticisms in an email to CNN.

Tilg blamed the spread of the virus in Tyrol -- which accounts for about a quarter of Austria's more than 4,400 coronavirus cases as of March 23 -- on tourists who either carried it into the province or did not follow regional authorities' advice to return home immediately.

Europe is now the epicenter of the coronavirus outbreak and the European Union has closed its borders to all non-essential travel as it attempts to slow its spread. The Austrian government put Ischgl under full quarantine on March 13. Five days later, on March 18, local officials extended these measures and ordered all 279 communities in Tyrol to isolate themselves.

While Lerfeldt and his friends say they have fully recovered, Christensen said that it is impossible to determine the number of people who were infected by Ischgl's ski tourists once they returned home, to countries all over Europe.