1. WHO announces COVID-19 outbreak a pandemic.https://www.euro.who.int/en/health-topics/health-emergencies/coronavirus-covid-19/news/news/2020/3/who-announces-covid-19-outbreak-a-pandemic; 2019 [accessed 13 September 2020].
2. Cluster of coronavirus disease associated with fitness dance classes, South Korea;Jang;Emerg Infect Dis,2020
3. Yonhap. New Virus Cases Spike on Steady Rise in Club-Linked Infections, Another Looming Cluster. The Korea Herald May 27, 2020.http://www.koreaherald.com/view.php?ud=20200527000242&ACE_SEARCH=1
4. Coronavirus disease outbreak in call center, South Korea;Park;Emerg Infect Dis,2020
5. A pilot research project coordinated by the European Choral Association – Europa Cantat in the frame of the multi-annual Cultural Cooperation Project “VOICE – Vision on Innovation for Choral Music in Europe” with the support of the EU.https://europeanchoralassociation.org/wp-content/uploads/2019/01/singingeurope_report.pdf. 2019 [accessed 13 September 2020].