Background Post COVID-19 conditions, also known as long COVID, are of public health concern, but little is known about their underlying risk factors.

Aims To investigate associations of air pollution exposure with long COVID among Swedish young adults.

Methods We used data from the BAMSE (Children, Allergy, Environment, Stockholm, Epidemiology [in Swedish]) cohort. From October 2021 to February 2022 participants answered a web-questionnaire focusing on persistent symptoms following acute SARS-CoV-2 infection. Long COVID was defined as symptoms after confirmed infection with SARS-CoV-2 lasting for two months or longer. Ambient air pollution levels (particulate matter?2.5 ?m [PM_2.5], ?10 ?m [PM₁₀], black carbon [BC] and nitrogen oxides [NO_x]) at individual-level addresses were estimated using dispersion modelling.

Results A total of 753 participants with SARS-CoV-2 infection were included of whom 116 (15.4%) reported having long COVID. The most common symptoms were altered smell/taste (n=80, 10.6%), dyspnea (n=36, 4.8%) and fatigue (n=34, 4.5%). Median annual PM_2.5 exposure in 2019 (pre-pandemic) was 6.39 (interquartile range [IQR] 6.06-6.71) ?g/m³. Adjusted Odds Ratios (95% confidence intervals) of PM_2.5 per IQR increase were 1.28 (1.02-1.60) for long COVID, 1.65 (1.09-2.50) for dyspnea symptoms specifically and 1.29 (0.97-1.70) for altered smell/taste. Positive associations with long COVID were found for the other air pollutants and remained consistent across sensitivity analyses. Associations tended to be stronger among participants with asthma, and those having had COVID during 2020 (versus 2021).

Conclusion Ambient long-term PM_2.5 exposure may affect the risk of long COVID in young adults.