Background The risk factors for SARS-CoV-2 transmission are not well characterised. We sought to identify potential risk factors for transmission and actionable information that can be used to prevent SARS-CoV-2. Methods Individuals tested for SARS-CoV-2 at four accredited laboratories were invited. In addition, participants were recruited through a media campaign. Self-reported SARS-CoV-2 test results were compared with laboratory results, demographic data and behavioural facts were collected

more »

... sing a digital platform. In a cross-sectional design positive cases were compared with negative and untested control groups. Findings Approximately 14 days after a countrywide lockdown in Norway, 116,678 participants were included. Median age was 46 years, 44% had children in preschool or in school; 18% were practicing health professionals. International flights, contact with infected individuals, and gatherings of more than 50 people, were associated with increased risk of testing positive. Health professionals who treated COVID-19 patients were at higher risk of testing positive than those who did not. Having undergone light infections, the last six months was strongly associated with lower odds ratio of SARS-CoV-2 positivity. Contact with children, use of hand sanitiser and use of protective gloves in private were also associated with lower odds ratio of testing positive for SARS-CoV-2. Interpretation Further research is needed to explore if being a parent or looking after children is associated with lower risk of SARS-CoV-2 positivity in the next phases of the pandemic. Immunological research should be done to determine the effects of prior trivial infections on SARS-CoV-2 infection. We confirm that large gatherings during the pandemic should be avoided and those who are infected, or under suspicion thereof, posed very high risks to others in this population. Registration: Trial registration: ClinicalTrials.gov: NTC 04320732, March 25, 2020.