Singing Is a Risk Factor for Severe Acute Respiratory Syndrome Coronavirus 2 Infection: A Case-Control Study of Karaoke-Related Coronavirus Disease 2019 Outbreaks in 2 Cities in Hokkaido, Japan, Linked by Whole Genome Analysis

BACKGROUND: Singing in an indoor space may increase the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We conducted a case-control study of karaoke-related coronavirus disease 2019 (COVID-19) outbreaks to reveal the risk factors for SARS-CoV-2 infection among individuals who participate in karaoke. METHODS: Cases were defined as people who enjoyed karaoke at a bar and who tested positive for SARS-CoV-2 by reverse-transcription polymerase chain reaction between 16 May and 3 July 2020. Controls were defined as people who enjoyed karaoke at the same bar during the same period as the cases and tested negative. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. ORs of key variables adjusted for each other were also estimated (aOR). RESULTS: We identified 81 cases, the majority of whom were active elderly individuals (median age, 75 years). Six cases died (case fatality ratio, 7%). Among the cases, 68 (84%) were guests, 18 of whom had visited ≧2 karaoke bars. A genome analysis conducted in 30 cases showed 6 types of isolates within 4 single-nucleotide variation difference. The case-control study revealed that singing (aOR, 11.0 [95% CI, 1.2–101.0]), not wearing a mask (aOR, 3.7 [95% CI, 1.2–11.2]), and additional hour spent per visit (aOR, 1.7 [95% CI, 1.1–2.7]) were associated with COVID-19 infection. CONCLUSIONS: A karaoke-related COVID-19 outbreak that occurred in 2 different cities was confirmed by the results of genome analysis. Singing in less-ventilated, indoor and crowded environments increases the risk of acquiring SARS-CoV-2 infection. Wearing a mask and staying for only a short time can reduce the risk of infection during karaoke.