ABSTRACT
BACKGROUND: Since patients with chronic inflammatory rheumatic joint diseases may be more prone to infections, we wished to investigate the incidence of COVID-19 in this group, and explore the possible significance of factors related to the rheumatic disease, the patient or the treatment. MATERIAL AND METHOD: Altogether 27 907 patients registered in the Norwegian Arthritis Registry (NorArthritis) were linked to the Norwegian Surveillance System for Communicable Diseases and the Norwegian Intensive Care and Pandemic Registry in order to find the incidence of COVID-19 in 2020, and the proportion of patients who were hospitalised. A standardised incidence ratio (SIR) was calculated by comparing with sex and age-specific incidence in the general population. Logistic regression analysis was used to investigate whether diagnosis, age, sex, disease activity, comorbidity or drug therapy had any bearing on the incidence. RESULTS: A total of 185 of the patients in NorArthritis tested positive for COVID-19, of whom 10 % were hospitalised. The incidence was lower than in the general population (SIR 0.84; 95 % confidence interval (CI): 0.72-0.97, P = 0.02). Young age and low disease activity were associated with higher incidence of infection. The other factors had no significant effect. INTERPRETATION: The fact that the incidence of COVID-19 was lower than in the general population, and that within the group it was lower in those with moderate/high disease activity and greater age, is most likely attributable to patients of advanced age with chronic active disease having protected themselves against infection to a greater degree.