At-home sampling to meet geographical challenges for serological assessment of SARS-CoV-2 exposure in a rural region of northern Sweden, March to May 2021: a retrospective cohort study

BACKGROUND: The current SARS-CoV-2 pandemic has highlighted a need for easy and safe blood sampling in combination with accurate serological methodology. Venipuncture for testing is usually performed by trained staff at healthcare centres. Long travel distances to healthcare centres in rural regions may introduce a bias of testing towards relatively large communities with closer access. Rural regions are therefore often not represented in population-based data. AIM: The aim of this retrospective cohort study was to develop and implement a strategy for at-home testing in a rural region of Sweden during spring 2021, and to evaluate its role to provide equal health care for its inhabitants. METHODS: We developed a sensitive method to measure antibodies to the S-protein of SARS-CoV-2 and optimised this assay for clinical use together with a strategy of at-home capillary blood sampling. RESULTS: We demonstrated that our ELISA gave comparable results after analysis of capillary blood or serum from SARS-CoV-2-experienced individuals. We demonstrated stability of the assay under conditions that reflected temperature and humidity during winter or summer. By assessment of capillary blood samples from 4,122 individuals, we could show both feasibility of the strategy and that implementation shifted the geographical spread of testing in favour of rural areas. CONCLUSION: Implementation of at-home sampling enabled citizens living in remote rural areas access to centralised and sensitive laboratory antibody tests. The strategy for testing used here could therefore enable disease control authorities to get rapid access to information concerning immunity to infectious diseases, even across vast geographical distance.