About 70 young people were exposed to the coronavirus during a party at a ski resort in Kuopio on 19 September. So far 21 have been diagnosed with Covid-19, health officials said on Monday.
As of Friday, 12 infections had been traced to the festivities.
The latest cases have emerged among people who were already under quarantine. There is so far no evidence of onward transmission to others who did not attend the party.
On Monday, one case was still under investigation in Kuopio that may be linked to the same cluster.
The city of Kuopio’s chief infectious disease doctor, Raija Savolainen, stressed the importance of those who may have been exposed remaining in quarantine.
“A negative test result during a quarantine period does not mean that the quarantine ends,” Savolainen told Yle.
Most aged 17-20
According to the local newspaper Savon Sanomat, those who attended were mostly aged 17-20 and stayed in two rented cabins.
About 50 of them were mainly in one lodge, with about 20 in another nearby cabin and plenty of visits back and forth. Some may have also been to bars and restaurants in the resort area.
Most of those who took part live in Kuopio or nearby Nilsiä, but some were from Siilinjärvi, Mikkeli, Kajaani, Helsinki and elsewhere.
Tahko is in eastern Finland, some 500km from Helsinki. The downhill ski season has not yet begun, but the centre plans to offer cross-country skiing on artificial snow beginning at the end of next week.