STOCKHOLM, Aug 6 (Reuters) - The spread of COVID-19 in Sweden has continued to accelerate with infection rates no longer considered low, the country"s health authority said on Friday, blaming increased travel abroad and packed dance floors in busy night club venues in Stockholm. There were 3,451 new cases of COVID-19 in Sweden last week, a 30% increase compared to the week before, the authority said, adding that at 59 cases per 100,000 people the spread of the infection was no longer at a low level. "We see a lot of cases with people who have been infected abroad in popular travel destinations in Europe," state epidemiologist Anders Tegnell said in a statement, adding that 17% of new cases were linked to such tourism. Under Tegnell"s watch, Sweden has relied mainly on voluntary measures to stem the spread of infections, though curbs on opening hours for restaurants and limits on crowds at venues such as shopping malls had been implemented until recently. In July, the government pressed ahead with a planned easing of pandemic restrictions but warned that new variants of the virus demanded vigilance and urged people to adhere to social distancing recommendations. "We have also received reports of congestion at several holiday resorts in Sweden, including on Gotland, but also at dance venues in, for example, Stockholm," Tegnell said. He said the vaccine rollout continued according to plan, with just over 79% of adults having had at least one dose and just over 53% of adults having had two shots. (This story has been refiled to fix typo in headline)