Respiratory symptoms up to 18 months after COVID-19 – a longitudinal observational study

Abstract Background This study aimed to identify, analyse and compare adults with and without respiratory symptoms over time after COVID-19 and identify predictors of persistent respiratory symptoms, in hospitalised and non-hospitalised patients. Methods Participants were recruited at the Post COVID-19 clinic at Karolinska University hospital, Sweden, between May 2020 until December 2022, with longitudinal data collected until February 2025. Data from medical records and two clinical follow-up visits were analysed. Participants were categorised based on presence or absence of self-reported respiratory symptoms. Clinical outcomes included physical function, patient-reported outcomes, lung function and other clinically relevant parameters. Results A total of 963 out of 1976 participants were included, of whom 760 (79%) were identified with respiratory symptoms and 203 (21%) were not at first follow-up visit. The respiratory symptom group showed poorer physical function and worse patient-reported outcomes at the first follow-up (adjusted p < 0.05). Lung function was generally preserved, although diffusing lung capacity for carbon monoxide (DLCO) was lower in the respiratory symptom group (79% vs 84%, adjusted p < 0.05). Both groups improved over time, and the magnitude of change did not differ significantly between groups. However, participants in the respiratory symptom group remained more impaired across several outcomes at follow-up. Presence of respiratory symptoms at the first follow-up visit was the strongest independent predictor of belonging to the respiratory symptom group at second follow-up visit (OR 5.31, 95% CI 2.74–10.89). Conclusions Respiratory symptoms after acute COVID-19 were highly prevalent and were associated with poorer clinical outcomes, despite similar recovery over time. Further research is needed to better clarify underlying mechanisms and to guide targeted rehabilitation strategies.