Particulate Matter Pollution Of Different Particle Sizes And Stroke Hospitalizations:Estimating The Associations And Related Economic Losses In Guangzhou,China

Background:Stroke is a leading cause of death and disability among adults in China.Numerous epidemiological studies have reported associations between exposure to air pollution and the risk of morbidity and mortality from stroke.However,the effect of particulate matter of different particle sizes on distinct stroke subtypes remains uncertain.Moreover,the majority of existing studies have employed regional average concentrations as air pollutant proxy for all subjects,and evidence based on individual fine-scale exposure assessment is scarce.Objective:The purpose of this study was to investigate the effect of short-term exposure to ambient particulate matter（PM）of different particle sizes on the risk of hospital admission for stroke and its major subtypes in Guangzhou.Furthermore,we aimed to identify potential effect modification between PM exposure and stroke hospitalization,and evaluate the excess hospitalization admissions from stroke and related economic costs due to PM pollution.The findings of the study are expected to provide substantial theoretical support for the formulation of pertinent environmental and health policies.Methods:This study utilized hospitalization records of stroke patients admitted to 67 hospitals in Guangzhou between January 1,2014 and December 31,2018.PM exposure data at a 1 km×1 km resolution,including submicron particulate matter（PM₁）,fine particulate matter(PM_2.5)and inhalable particulate matter(PM₁₀),were derived from China High Air Pollutants（CHAP）dataset.The air pollution exposure for each patient was estimated based on their residential address and the date of hospital admission.An individual-level time-stratified case-crossover（TSCC）approach,in combination with a conditional logistic regression model,was employed to examine the associations between short-term exposure to size-specific particles and the risk of stroke hospitalization.Restricted cubic spline functions were used to smooth exposure-response curves.We performed subgroup analyses by sex（male,female）,age（<75,≥75 years）,and season（warm,cold）,and used two-sample z-tests to evaluate potential effect differences between subgroups.To check the robustness of our findings,we conducted several sensitivity analyses by building two-pollutant models and altering given parameter specifications.A time-series analysis was used to validate the main results of the TSCC design.Meanwhile,involving different guidelines as the reference,the attributable number and related economic cost of stroke hospitalization due to exceeding PM pollution in Guangzhou were estimated employing a cost of illness approach.Results:1.During the study period,a total of 178,586 stroke cases were admitted to the hospital,including 141,709（79.4%）hospital admissions from ischemic stroke and 25,255（14.1%）hospital admissions from hemorrhagic stroke.The median cost of hospitalization was 11814.6 Yuan,and the median length of stay was 10 days.From2014 to 2018,the average daily concentrations of PM₁,PM_2.5and PM₁₀in Guangzhou were 26.2μg/m³,36.1μg/m³,and 55.7μg/m³,respectively.Approximately 96.2%and60.5%of the days exceeded the daily PM_2.5and PM₁₀standards of the World Health Organization air quality guidelines 2021.2.Short-term exposure to size-specific PM was significantly associated with an increased risk of hospital admissions for total stroke and ischemic stroke but not with hemorrhagic stroke.PM₁exhibited relatively stronger effects on stroke than PM_2.5and PM₁₀.Specifically,a 10-μg/m³increase in PM₁,PM_2.5and PM₁₀exposure at lag 03-day was associated with a 1.6%[95%confidence interval（CI）:0.8%–2.4%],0.7%（95%CI:0.3%–1.1%）and 0.7%（95%CI:0.4%–1.0%）increase in odds of hospitalization from total stroke,and 2.3%（95%CI:1.4%–3.3%）,1.0%（95%CI:0.5%–1.4%）and0.9%（95%CI:0.6%–1.3%）from ischemic stroke,respectively.3.There was an almost linear exposure-response curve between PM exposure and hospital admission for total stroke and ischemic stroke.The curves were relatively flat at low concentrations and became steeper at high concentrations.4.Stratified analysis revealed no significant differences in the effects of PM exposure on stroke hospitalization among age and sex subgroups.Significant effects of PM exposure on stroke were observed only during cold months.5.Our sensitivity analyses confirmed the robustness of the observed effects of particles after adjusting for gaseous pollutants or model parameters.Furthermore,the results of the time-series analysis supported the reliability of our main findings.6.Over the study period,ambient PM₁,PM_2.5,and PM₁₀pollution were responsible for approximately 38.4 thousand,30.9 thousand,and 50.5 thousand stroke hospitalizations,respectively,in Guangzhou.The associated economic losses were estimated at 976 million Yuan,786 million Yuan,and 1.286 billion Yuan,respectively,equivalent to 0.105‰,0.085‰,and 0.138‰of the local GDP.Conclusion:Short-term exposure to size-specific PM was significantly associated with increased risks of hospitalization for total stroke and ischemic stroke,and posed a considerable number of excess hospitalization admissions and economic losses.A greater magnitude of associations was observed for PM₁compared with PM_2.5and PM₁₀.People were more susceptible to the adverse effects of particulate air pollution during the cold season.The findings of this study underscore the importance of continued efforts to reduce the burden of stroke by controlling PM pollution,especially PM with smaller particle sizes.