Societal COVID-19 epidemic counter measures and activities associated with SARS-CoV-2 infection in an adult unvaccinated population - a case-control study in Denmark, June 2021

Measures to restrict physical inter-personal contact in the community have been widely implemented during the COVID-19 pandemic. We studied determinants for infection with SARS-CoV-2 with the aim of testing the efficiency of such measures. We conducted a national matched case-control study among unvaccinated persons aged 18-49 years. Cases were selected among those testing positive for SARS-CoV-2 by RT-PCR over a five-day period in June 2021. Controls were selected from the national population register and were individually matched on age, sex and municipality of residence and had not previously tested positive. Cases and controls were interviewed via telephone about contact with other persons and exposures in the community. We included 500 cases and 529 controls and determined odds ratios (ORs) and 95% confidence intervals (95%CIs) by conditional logistical regression with adjustment for household size and immigration status. We found having had contact with another individual with a known infection as the main determinant for SARS-CoV-2 infection. Reporting close contact with an infected person who either had or did not have symptoms resulted in ORs of 20 (95%CI:9.8-39) and 8.5 (95%CI 4.5-16) respectively. In contrast, community exposures were generally not associated with disease; several exposures were negatively associated. Exceptions were: attending fitness centers, OR=1.4 (95%CI:1.0-2.0) and consumption of alcohol in restaurants or cafes, OR=2.3 (95%CI:1.3-4.2). For reference, we provide a timeline of non-pharmaceutical interventions in place in Denmark from February 2020 to March 2022. Fitness centers and alcohol consumption were mildly associated with infection, in agreement with findings of our similar study conducted six month earlier (Epidemiology & Infection 2021;150:e9.). Transmission of disease through involvement in community activities appeared to occur only rarely, suggesting that community restrictions in place were efficient. Instead, transmission appeared to primarily take place in a confined space via contact to known persons.