A team led by Yale School of Public Health (YSPH) researchers has found a significant connection between long-term exposure to common air pollutants and hospital readmissions among people who have had a stroke. The finding suggests the need to reevaluate air pollution regulations in the U.S.

The study found a significant association between long-term exposure to common air pollutants, even at levels below national air quality limits, and higher all-cause 30-day readmissions after ischemic stroke.

The researchers published their findings in an article in Stroke, “Associations Between Long-Term Air Pollutant Exposure and 30-Day All-Cause Hospital Readmissions in US Stroke Patients.” Authors are Phoebe Tran, who earned a PhD at YSPH and is now with the University of Tennessee; Joshua Warren, associate professor of biostatistics at YSPH; Erica C. Leifheit, research scientist in Chronic Disease Epidemiology at YSPH; Dr. Larry B. Goldstein of the University of Kentucky; and Judith H. Lichtman, professor and chair of the Department of Chronic Disease Epidemiology at YSPH.

The study focused on average annual carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), particulate matter 2.5 (PM2.5), and sulfur dioxide (SO2) exposure and 30-day all-cause hospital readmission among people 65 and older who were hospitalized for ischemic stroke in 2014-2015.

Of 448,148 stroke patients, 12.5% were readmitted within 30 days. The results of the study showed that each one standard deviation increase in average annual CO, NO2, PM2.5, and SO2 exposure was associated with a 1.1%, 3.6%, 1.2%, and 2.0% increased risk of 30-day readmission, which are the adjusted values reported in the paper.

Whether air quality improvements lead to reductions in post-stroke readmissions requires further research, the authors concluded.