(SLB-064) Risk factors associated with post-COVID-19 condition among 810,851 individuals in Sweden: population-based cohort study

Background: Long-term effects of COVID-19 can place a burden on individuals, healthcare, and society. However, large population-based studies on risk factors for post-COVID-19 condition (PCC) are still limited.

Objectives: To evaluate the importance of a wide range of potential risk factors for being diagnosed with PCC.

Methods: Register-based cohort study including all adults with a COVID-19 infection in the two largest regions in Sweden, from 1 August 2020 to 30 November 2023. Data were obtained from national and regional registers.
The outcome was a valid clinical diagnosis of PCC, defined as ICD-10-SE code U09.9 in primary and secondary care as the main or secondary diagnosis, recorded no earlier than 28 days after the first COVID-19 infection.
A large set of potential risk factors reflecting personal sociodemographic data, health conditions, healthcare contact behaviors, COVID-19-related factors, area-level socioeconomic status (SES), as well as PCC in family and cohabitants (as proxies for genetic and shared environmental factors) were evaluated.
Cox proportional hazard models, with calendar time as the underlying time scale, were used to estimate hazard ratio (HR) with a 95% confidence interval (95%CI) for each risk factor. Backwards stepwise selection was performed starting from this full model (including all potential risk factors) to determine the more important ones. The significance level for the removal of a factor was p≥0.1 and for addition back into the model p≤0.05. The backwards stepwise selection was also done separately in subgroups for each stratum of variants of concern (VOC) period and severity of the acute infection.

Results: The study included 810,851 individuals, of whom 1.4% were diagnosed with PCC during follow-up. Female sex, older age, being born outside Sweden, higher educational attainment, essential worker (e.g., healthcare worker, bus driver), having comorbidities such as thromboembolic disease, asthma, fibromyalgia, 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 were associated with an increased risk of being diagnosed with PCC.

Conclusions: In this large population-based cohort study, our exploratory analysis revealed several risk factors for being diagnosed with PCC. Our findings are important for advancing the understanding of this patient group and may help guide future studies exploring causal associations and underlying mechanisms of PCC. Additionally, these insights could support policymakers in designing targeted preventive measures against PCC.