COVID-19 outbreak among physicians at a Canadian curling bonspiel: a descriptive observational study

BACKGROUND: Transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is known to occur among individuals who congregate in large groups, especially during indoor activities. Our objective was to provide a detailed clinical description of an outbreak of coronavirus disease 2019 (COVID-19) that occurred after a sporting and social event during the early days of the pandemic. METHODS: We conducted a descriptive study of a curling bonspiel in Edmonton held on Mar. 11–14, 2020. We used standardized interviews between Apr. 17 and May 5, 2020, to collect demographic data, travel history, symptoms (type, onset and duration), self-reported testing results for SARS-CoV-2 ribonucleic acid (RNA) using reverse transcription polymerase chain reaction (RT-PCR), and clinical outcomes. We also obtained results of convalescent SARS-CoV-2 immunoglobulin G serology. RESULTS: All 73 curlers (55 active health care workers) who participated in the bonspiel were interviewed for the study. Convalescent SARS-CoV-2 immunoglobulin G serology was completed in 62 (85%) participants. Of the 73 participants (55 [75%] male, median age 51 [range 26–79] yr, 58 [79%] physicians), 40 curlers (55%) tested positive for SARS-CoV-2 RNA by RT-PCR; an additional 16 participants developed symptoms but had negative swabs or were not tested (14 were probable cases), for a 74% attack rate (confirmed or probable cases). Anosmia with ageusia or dysgeusia occurred in 39 of 54 (72%) confirmed or probable cases. The clinical course was mild in most participants (1 emergency visit, no hospital admissions). Transmission likely occurred from multiple individuals with minor nonspecific symptoms during the event, possibly during shared meals. INTERPRETATION: The 74% attack rate (confirmed or probable cases) highlights the infectivity of SARS-CoV-2 during sporting and social events. This reinforces the need for public health measures (masking, physical distancing and limiting the size of social gatherings) during future waves of COVID-19 in Canada.