Background: Some individuals have a persistence of symptoms following both COVID-19 (post-acute COVID-19 syndrome; PACS) and other viral infections. This study used prospectively collected data from an international trial to compare symptoms following COVID-19 and non-COVID-19 respiratory illness, to identify factors associated with the risk of PACS, and to explore symptom patterns before and after COVID-19 and non-COVID-19 respiratory illnesses.

Methods: Data from a multicentre randomised controlled trial (BRACE trial) involving healthcare workers across four countries were analysed. Symptom data were prospectively collected over 12 months, allowing detailed characterisation of symptom patterns. Participants with COVID-19 and non-COVID-19 respiratory illness episodes were compared, focussing on symptom severity, duration (including PACS using NICE and WHO definitions), and pre-existing symptoms.

Findings: Compared to those with a non-COVID-19 illness, participants with COVID-19 had significantly more severe illness (OR 7·4, 95%CI 5·6-9·7). Symptom duration meeting PACS definitions occurred in a higher proportion of COVID-19 cases than non-COVID-19 respiratory controls using both the NICE definition (2·5% vs 0·5%, OR 6·6, 95%CI 2·4-18·3) and the WHO definition (8·8% vs 3·7%, OR 2·5, 95%CI 1·4-4·3). When considering only participants with COVID-19, age 40-59 years (aOR 2·8, 95%CI 1·3-6·2), chronic respiratory disease (aOR 5·5, 95%CI 1·3-23·1), and pre-existing symptoms (aOR 3·0, 95%CI 1·4-6·3) were associated with an increased risk of developing PACS. Symptoms associated with PACS were also reported by participants in the months preceding their COVID-19 or non-COVID-19 respiratory illnesses (32% fatigue and muscle ache, 11% intermittent cough and shortness of breath).

Interpretation: Healthcare workers with COVID-19 were more likely to have severe and longer-lasting symptoms than those with a non-COVID-19 respiratory illness, with a higher proportion meeting the WHO or NICE definitions of PACS. Age, chronic respiratory disease, and pre-existing symptoms increased the risk of developing PACS following COVID-19.