Association between short-term exposure to air pollution and COVID-19: a case-crossover cohort study.

Authors

Andreas Tornevi, Christer Janson, Andreas Palm, Magnus Svartengren, Juan Wang, Andrei Malinovschi, Josef D Järhult, Mathias Holm, Sven-Erik Dahlen, Lars Modig, Bertil Forsberg, Össur Ingi Emilsson

Published in

BMJ open respiratory research. Volume 13. Issue 1. Aug 17, 2026. Epub Aug 17, 2026.

Abstract

To investigate associations between short-term fluctuations in urban background air pollution and the incidence of COVID-19 across three Swedish cities using detailed individual-level data.
A case-crossover analysis was conducted using individual-level data from a prospective cohort of adults across three Swedish cities (Stockholm, Gothenburg and Uppsala), including 3999 confirmed COVID-19 cases. Subjects were classified as cases on the date of their first positive PCR test, which occurred between 7 March 2020 and 26 January 2022. Exposure data for daily levels of PM2.5, PM10 and NO₂ were obtained from urban background monitoring stations. Lag-specific and cumulative associations were examined using distributed lag models and distributed lag non-linear models, adjusting for meteorological variables.
A significant association was observed between elevated PM2.5 levels and testing positive for COVID-19 on the same day (lag 0), with an OR of 1.084 (95% CI 1.011 to 1.162) per IQR (3.3 µg/m³) increase. Similar lag 0 effects were found across the three cities. For PM10, the most consistent associations were observed at lag 3. For NO₂, significant effects at lag 0 emerged only after excluding the final COVID-19 wave. Subgroup analyses showed similar effects among individuals with pre-existing respiratory conditions, though results were less consistent.
Our findings suggest that short-term fluctuations in air pollution, particularly for PM2.5, are associated with the timing of confirmed COVID-19 cases. A possible explanation for the short lag association is that air pollution exacerbates symptoms, prompting individuals to seek testing, rather than directly facilitating new infections.

PMID:
42608143
Bibliographic data and abstract were imported from PubMed on 18 Aug 2026.

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