Characterizing Post-COVID Syndrome in Outpatient and Inpatient Setting in Sweden Using Diagnosis Codes - A Nationwide Observational Cohort and Matched Cohort Study

Background: Increasing reports highlight long-term complications following COVID-19 (post-COVID syndrome (PCS)), however, the incidence, risk factors and clinical features are still unclear. To enable diagnosis the ICD codes Z861A, U089 and U099 were introduced in 2020/2021.Methods: PCS incidence was determined from all SARS-CoV-2 laboratory-verified test-positive individuals cross-linked with the Patient Registry, diagnoses registered at healthcare visits at least 3 months post-COVID-19 were described, and risk factors for PCS determined using logistic regression. Identification of enriched diagnoses/diseases was performed using a matched cohort study (MCS) design with control individuals for PCS patients that were COVID-negative (matched on age, sex, county of residence) or COVID-positive (+ disease severity).Findings: 1,057,174 individuals tested positive for SARS-CoV-2 from February 1st 2020 to May 25th 2021 with 6,389 PCS patients. The matched control individuals to PCS patients were: 23,795 COVID-negative and 25,556 COVID-positive individuals. The strongest risk factor for PCS in the COVID-19 cohort was disease severity (e.g., mechanical ventilation vs no contact with outpatient or inpatient clinics: OR 114·7 (95% CI 105·1-125·3), and frequent diagnoses were dyspnea (13·4%), malaise/fatigue (8%) and abnormal findings on pulmonary diagnostic imaging.Interpretation: Severity of COVID-19 associates with receiving a PCS diagnosis and dyspnea, malaise/fatigue and abnormal findings on pulmonary diagnostic imaging were the most common diagnoses associated with PCS. Funding: ALF-funding; MIMS; Kempe- PA Hedlund’s Foundation. Research Council Sweden & Norway; Horizon Europe; Academy of Finland.Declaration of Interest: None.Ethical Approval: The study received ethical approval from the Swedish Ethical Review Authority (DNR 2020-02150).