Daily changes in fine particulate matter are associated with acute myocardial infarction hospitalizations: an individual-level time-stratified case-crossover study in Zhongshan, China
Background Acute myocardial infarction (AMI) imposes a substantial and growing burden globally. Short-term exposure to ambient fine particulate matter (PM2.5) has been linked to AMI mortality, yet most studies have focused on absolute pollutant concentrations. The association between daily changes in PM2.5 and AMI hospitalizations remains poorly understood. Methods We conducted an individual-level time-stratified case-crossover study in Zhongshan, China, from 2020 to 2024. A total of 1,795 AMI hospitalizations were identified from a tertiary hospital, with 5,877 control days matched by day of week within the same calendar month. Daily PM2.5 exposure was assigned based on residential address using the China High Air Pollutants (CHAP) dataset at 1 km resolution. Conditional logistic regression models were fitted to estimate the association between a 10 μg/m3 increase in PM2.5 (both absolute concentration and day-to-day change) and AMI hospitalization, adjusting for temperature, relative humidity, and public holidays. Subgroup analyses were performed by age, sex, season, AMI subtype, and comorbidities. Results A 10 μg/m3 increase in PM2.5 from the previous day to the admission day (lag0–lag1) was associated with a 7.89% (95% CI: 0.86%–15.40%) higher odds of AMI hospitalization. Associations were found among females (22.58%), adults aged >65 years (22.16%), cold-season admissions (10.85%), and patients with ST-segment elevation myocardial infarction (17.90%), with age identified as a significant effect modifier (P for interaction < 0.05). Results remained robust after adjustment for co-pollutants (except for nitrogen dioxide) and alternative degrees of freedom (df) for temperature and relative humidity. Conclusion Daily increments in ambient PM2.5 concentration were independently associated with an increased risk of AMI hospitalization, particularly among females, older adults, and patients with ST-segment elevation myocardial infarction. These findings suggested that day-to-day PM2.5 variability may warrant consideration in future cardiovascular prevention frameworks.