Background: Early evidence from China suggested that blood groups may be involved in susceptibility to COVID-19. Several subsequent studies which reported controversial results. Objectives: We conducted a retrospective matched case-control study that aims to investigate the association between blood groups and the risk and/or severity of COVID-19.
Methods: We compared the blood groups distribution of 474 patients admitted to the hospital for COVID-19 between March 2020 and March 2021, to that of a positive control group of outpatients infected with COVID-19 and matched them for sex and age, as well as to the distribution in the general population. Results: 318 HC+ pairs with available blood group information were matched. The proportion of group A-Rh+ in hospitalized patients (HC+) was 39.9% (CI 35.2% - 44.7%), compared to 44.8% (CI 39.8%-49.9%) and 32.3% in the positive out-patient…
