tetano
Editor, Senior Moderator
BMJ Open Respir Res
. 2026 Aug 17;13(1):e003279.
doi: 10.1136/bmjresp-2025-003279.
Association between short-term exposure to air pollution and COVID-19: a case-crossover cohort study
Andreas Tornevi[SUP] 1 [/SUP], Christer Janson[SUP] 2 [/SUP], Andreas Palm[SUP] 2 [/SUP], Magnus Svartengren[SUP] 3 [/SUP], Juan Wang[SUP] 2 4 [/SUP], Andrei Malinovschi[SUP] 4 [/SUP], Josef D Järhult[SUP] 5 [/SUP], Mathias Holm[SUP] 6 [/SUP], Sven-Erik Dahlen[SUP] 7 8 [/SUP], Lars Modig[SUP] 9 [/SUP], Bertil Forsberg[SUP] 9 [/SUP], Össur Ingi Emilsson[SUP] 2 10 [/SUP]
Affiliations
Objective: 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.
Methods: 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 NO[SUB]2[/SUB] 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.
Results: 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 NO[SUB]2[/SUB], 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.
Conclusions: 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.
Keywords: COVID-19; Viral infection.
. 2026 Aug 17;13(1):e003279.
doi: 10.1136/bmjresp-2025-003279.
Association between short-term exposure to air pollution and COVID-19: a case-crossover cohort study
Andreas Tornevi[SUP] 1 [/SUP], Christer Janson[SUP] 2 [/SUP], Andreas Palm[SUP] 2 [/SUP], Magnus Svartengren[SUP] 3 [/SUP], Juan Wang[SUP] 2 4 [/SUP], Andrei Malinovschi[SUP] 4 [/SUP], Josef D Järhult[SUP] 5 [/SUP], Mathias Holm[SUP] 6 [/SUP], Sven-Erik Dahlen[SUP] 7 8 [/SUP], Lars Modig[SUP] 9 [/SUP], Bertil Forsberg[SUP] 9 [/SUP], Össur Ingi Emilsson[SUP] 2 10 [/SUP]
Affiliations
- PMID: 42608143
- DOI: 10.1136/bmjresp-2025-003279
Objective: 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.
Methods: 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 NO[SUB]2[/SUB] 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.
Results: 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 NO[SUB]2[/SUB], 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.
Conclusions: 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.
Keywords: COVID-19; Viral infection.