Long-term PM2.5 exposure may lead to more severe COVID-19
Long-term exposure to particulate matter ≤2.5 μm (PM2.5) results in increased admission to hospital for COVID-19, according to a recent study.
“If the associations observed in this study are indeed causal, appropriate measures to prevent SARS-CoV-2 infection among patients residing in high PM2.5 exposure areas or public health efforts to decrease PM2.5 levels could lessen COVID-19 morbidity as well as its burden on the healthcare system,” the researchers said.
The study estimated the 10-year (2009–2018) PM2.5 exposure at the residential zip code of COVID-19 patients diagnosed at the University of Cincinnati healthcare system between 13 March 2020 and 30 September 2020. The researchers used logistic regression to determine the odds ratio (OR) and 95 percent confidence interval (CI) for COVID-19 hospitalizations associated with PM2.5, with adjustments for socioeconomic characteristics and comorbidities.
Of the 14,783 patients with COVID-19 included in the analysis, 13.6 percent were hospitalized. The geometric mean PM2.5 was 10.48 μg/m3. [Respirology 2021;26:1181-1187]
The adjusted analysis revealed that each 1-μg/m3 increase in 10-year annual average PM2.5 correlated with 18-percent more hospitalization (OR, 1.18, 95 percent CI, 1.11–1.26). Similarly, an increase of 1 μg/m3 in PM2.5 estimated for the year 2018 resulted in 14-percent higher hospital admissions (OR, 1.14, 95 percent CI, 1.08–1.21).
Individual-level studies supported the current findings and showed the association of PM2.5 exposure with respiratory infections and related outcomes. For instance, both long- and short-term exposure to PM2.5 in children correlated with hospitalization and healthcare use for respiratory syncytial virus bronchiolitis, especially during infancy. [Environ Res 2009;109:321-317; Am J Respir Crit Care Med 2018;198:759-766]
Similar results were noted in older adults for influenza with regard to short-term PM2.5 exposure. [Am J Respir Crit Care Med 2018;198:759-766]
Several mechanisms could explain how long-term exposure to PM2.5 might lead to COVID-19 hospitalization.
“PM2.5 suspended in the air may play a role in SARS-CoV-2 transmission and infection by carrying the virus, but also by impairing bronchial immunity and epithelial cell integrity to enhance the bronchial attachment and replication of SARS-CoV-2,” the researchers said. “Moreover, PM2.5 particles can penetrate the respiratory tract and reach the alveoli to deliver the virus to its target type II alveolar cells.” [Infect Control Hosp Epidemiol 2020;41:1011-1015]
PM2.5 could injure the lungs through inflammation and free radical peroxidation, which could then worsen COVID-19. These particles were found to stimulate the release of proinflammatory cytokines from activated alveolar macrophages and cytokine-producing genes. They could also induce the production of free radicals that might oxidize alveolar cells due to the presence of metal and other transition elements. [J Thorac Dis 2016;8:E69-74]
“Excessive free radicals production reduces cellular antioxidant capacity and leads to lipid peroxidation as well as increase in intracellular calcium concentrations which can further induce cellular damage,” the researchers explained.
“Future studies should include study samples that are nationally representative and a better resolution of PM2.5 exposure at patients' residential address to confirm these findings,” they noted.