Background

There are conflicting findings about the associations between smoking, obstructive lung disease and COVID-19. 

Objectives

To assess risk factors for COVID-19, by comparing PCR positive (PCR+) cases with PCR negative (PCR-) controls using a test-negative case-control study design, including population controls.

Methods

This observational, multicenter test-negative case-control study included SARS-CoV-2 RT- PCR (Real-time ?polymerase chain reaction) positive and negative participants from south-eastern Norway between February and December 2020. The study included the first and second pandemic waves in Norway, dominated by the alpha virus. A self-reported questionnaire about possible risk factors was completed by the participants 3-5 months after the first PCR test. We applied univariate and multiple regression analysis.

Results

400 PCR+ cases and 719 PCR- controls were included. The mean age of PCR+ cases and PCR- controls was 48±15 years and 47±14 years, respectively. Only six percent of participants were hospitalized. Male participants were represented in 49% of PCR+ and 34% of PCR- participants. Asthma was present in 64 (16%) of the PCR+ compared to 135 (19%) of the PCR- participants. Male gender was positively associated with risk for COVID-19 (OR 1.9, 95% CI; 1.4 to 2.6). For smoking the OR was 0.5, 95% CI 0.3 to 0.8. Non-statistically significant negative associations were observed between asthma and COVID-19 (OR 0.83, 95% CI; 0.6 to 1.2) and between COPD and COVID-19 (OR 0.41, 0.13 to 1.11).

Conclusions

Male gender was positively associated with COVID-19 infection in this test-negative study. Smoking was negatively associated with COVID-19 and no association was detected between asthma or COPD and COVID-19.