{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T15:25:40Z","timestamp":1786980340590,"version":"build-2736575974"},"reference-count":28,"publisher":"BMJ","issue":"1","license":[{"start":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T00:00:00Z","timestamp":1786924800000},"content-version":"unspecified","delay-in-days":16,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004359","name":"Vetenskapsr\u00e5det","doi-asserted-by":"publisher","award":["2022-06377_VR"],"award-info":[{"award-number":["2022-06377_VR"]}],"id":[{"id":"10.13039\/501100004359","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Open Resp Res"],"accepted":{"date-parts":[[2026,7,31]]},"published-print":{"date-parts":[[2026,8]]},"abstract":"<jats:sec>\n                    <jats:title>Objective<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      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\n                      <jats:sub>2<\/jats:sub>\n                      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.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      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\u2009\u00b5g\/m\u00b3) increase. Similar lag 0 effects were found across the three cities. For PM10, the most consistent associations were observed at lag 3. For NO\n                      <jats:sub>2<\/jats:sub>\n                      , 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.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmjresp-2025-003279","type":"journal-article","created":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T14:35:11Z","timestamp":1786977311000},"page":"e003279","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Association between short-term exposure to air pollution and COVID-19: a case-crossover cohort study"],"prefix":"10.1136","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8608-0168","authenticated-orcid":false,"given":"Andreas","family":"Tornevi","sequence":"first","affiliation":[{"name":"Department of Epidemiology and Global Health, Umea University, Ume\u00e5, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5093-6980","authenticated-orcid":false,"given":"Christer","family":"Janson","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Respiratory, allergy and sleep research, Uppsala University, Uppsala, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andreas","family":"Palm","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Respiratory, allergy and sleep research, Uppsala University, Uppsala, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8165-7236","authenticated-orcid":false,"given":"Magnus","family":"Svartengren","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Occupational and Environmental Medicine, Uppsala University, Uppsala, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4435-097X","authenticated-orcid":false,"given":"Juan","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Respiratory, allergy and sleep research, Uppsala University, Uppsala, Sweden"},{"name":"Department of Medical Sciences, Clinical physiology, Uppsala University, Uppsala, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4098-7765","authenticated-orcid":false,"given":"Andrei","family":"Malinovschi","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Clinical physiology, Uppsala University, Uppsala, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Josef D","family":"J\u00e4rhult","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Zoonosis Science Center, Uppsala University, Uppsala, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mathias","family":"Holm","sequence":"additional","affiliation":[{"name":"Department of Occupational and Environmental Medicine, School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sven-Erik","family":"Dahlen","sequence":"additional","affiliation":[{"name":"Department of Respiratory Medicine and Allergy, Karolinska University Hospital, Stockholm, Sweden"},{"name":"Clinical Lung and Allergy Research Unit, Department of Medicine Huddinge, Karolinska Institutet and University Hospital, Stockholm, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lars","family":"Modig","sequence":"additional","affiliation":[{"name":"Department of Epidemiology and Global Health, Umea University, Ume\u00e5, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bertil","family":"Forsberg","sequence":"additional","affiliation":[{"name":"Department of Epidemiology and Global Health, Umea University, Ume\u00e5, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7199-8491","authenticated-orcid":false,"given":"\u00d6ssur Ingi","family":"Emilsson","sequence":"additional","affiliation":[{"name":"Department of Medical Sciences, Respiratory, allergy and sleep research, Uppsala University, Uppsala, Sweden"},{"name":"Faculty of medicine, University of Iceland, Reykjav\u00edk, Island"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,8,17]]},"reference":[{"key":"2026081707350707000_13.1.e003279.1","unstructured":"WHO, global air quality guidelines: particulate matter (PM2. 5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. 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