Exploring predictors of post-COVID-19 condition among 810 851 individuals in Sweden

BACKGROUND: Long-term effects of COVID-19 can place burden on individuals, healthcare, and society. We aimed to evaluate the importance of a wide range of potential risk factors for being diagnosed with post-COVID-19 condition (PCC). METHODS: We used data from national and regional registers and databases for all adult residents in the two largest regions in Sweden. Individuals with a first COVID-19 between 1 August 2020 and 9 February 2022 were included and followed until PCC diagnosis, censoring (death or migration), or 30 November 2023. Using Cox proportional hazards models and backwards stepwise selection, we evaluated a large set of risk factors including sociodemographic data, comorbidities, healthcare contact behaviors, COVID-19-related factors, as well as PCC in family and cohabitants (as proxies for genetics and shared environment). RESULTS: We include 810,851 individuals (age range 18-106 years and 53.3% women), of whom 1.4% are diagnosed with PCC during follow-up. Female sex, older age, being born outside Sweden, higher educational attainment, essential workers, having comorbidities such as thromboembolic disease, asthma, fibromyalgia, depression/anxiety, and stress-related disorders, being infected earlier in the study period, experiencing severe acute COVID-19, not being vaccinated before COVID-19, and having a relative or a cohabitant with PCC are associated with an increased risk of being diagnosed with PCC. CONCLUSIONS: In this large population-based cohort study, our exploratory analysis reveals several risk factors for being diagnosed with PCC. Our findings can serve as a basis for future targeting of preventive measures against PCC.