The impact of poor air quality on hospital attendance of multimorbid patients.

Background: Air pollution can severely affect human health. It can contribute to the deterioration of different clinical conditions, leading to increased healthcare utilisation and death. Despite the breadth of evidence on the negative impacts of air pollution on individual long-term conditions, it is currently unclear how air pollution exposure can affect individuals that have different combinations of long-term conditions, and whether it can contribute to hospital attendance. We conducted a systematic review of the literature to understand the impact of air pollution exposure on the hospital attendance of multimorbid patients. Methods: We searched six major databases (Medline via Ovid, Embase via Ovid, Web of Science, CINAHL, Global Health, and Scopus) using grouped MeSH terms, including "air pollution", "multimorbidity", "association" and "hospitalisation" with no time restrictions. Articles published in English that evaluated the impact of various air pollutants (PM2.5, PM10, SO2, NO2, O3, and CO) on hospital attendance were included. The review is registered with The International Prospective Register of Systematic Reviews (CRD42022369757) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: Nineteen studies met the inclusion criteria. We categorised them into four clinical groups ("cardiovascular," "respiratory," "neurodegenerative and mental health," and "dependence and hepatic diseases") based on the primary diagnosed condition of patients in these studies. Although PM2.5 was the most studied air pollutant in relation to hospital attendance, NO2 lead to an increase in hospital attendance of multi-morbid patients after a relatively short exposure period (2 days), when compared to PM2.5 (5 days). We found that factors relating to Climatic conditions (e.g., temperature), Air Pollutants, Demographic factors (e.g., age, biological sex) and Chronic long-term conditions (the "CADC" effect) can influence the likelihood of hospital attendance amongst multi-morbid individuals in the same group. Conclusion: Exposure to air pollutants increased the likelihood of hospital attendance among multimorbid patients. Future research is required to understand the CADC effect particularly among those from lower socio-economic backgrounds. Systematic review registration: International prospective register of systematic reviews (CRD42022369757).