Air Pollution Exposure May Up Risk for Hospital Readmission for Stroke

Patients who had a stroke in areas with higher long-term levels of air pollutants were at increased risk for 30-day readmission, even though pollutant levels were below national limits, according to study findings published in the journal Stroke.

Previous studies have linked exposure to air pollutants with increased stroke rates and stroke-related morbidity and mortality. The relationship between air pollutants with 30-day readmission risk remains unclear.

Researchers from the Yale School of Public Health sourced data for this study from Medicare files and the Environmental Protection Agency (EPA) Air Quality System. Patients covered by Medicare fee-for-service between 2014-2015 who had an ischemic stroke were evaluated for 30-day readmission risk on the basis of exposure to average annual carbon monoxide (CO), nitrogen dioxide (NO₂), ozone (O₃), particulate matter 2.5 (PM_2.5), and sulfur dioxide (SO₂) levels in their county.

A total of 448,148 patients were discharged with ischemic stroke during the study period and they were mostly White (84.7%); women (53.5%); and a mean age, 79.2. Stratified by hospital performance, 110,377 were discharged from a low, 201,156 from an intermediate, and 136,615 from a high readmission center.

All patients were discharged from hospitals with county-wide air pollutant levels below national levels for all pollutants, except for tropospheric NO₂, which has no EPA standard.

After adjusting for patient and hospital characteristics as well as ambient temperature, risk for 30-day readmission increased with every one standard deviation increase in annual:

• NO₂ (adjusted hazard ratio [aHR], 1.036; 95% CI, 1.029-1.044);
• SO₂ (aHR, 1.020; 95% CI, 1.011-1.030);
• PM_2.5 (aHR, 1.012; 95% CI, 1.002-1.023); and
• CO (aHR, 1.011; 95% CI, 1.004-1.019) levels.

However, there was no annual increase in O₃ levels (aHR, 0.993; 95% CI, 0.985-1.000).

Results were relatively consistent when stratified by hospital performance.

Study limitations included the lack of data about hospital capacity and the generalization of air pollutant data county-wide. 

“Long-term exposure to common air pollutants, even at levels below national limits, was associated with higher all-cause 30-day readmissions after IS [ischemic stroke],” the researchers noted.

They concluded, “[O]ur study expands knowledge of the association between air quality and readmissions to patients with IS and highlights the need for further research in this area.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.