Short-term effects of ozone air pollution on hospital admissions for myocardial infarction: A time-stratified case-crossover study in Taipei

This study was undertaken to determine whether there was a correlation between ambient ozone (O-3) levels and number of hospital admissions for myocardial infarction (MI) in Taipei, Taiwan. Hospital admissions for MI and ambient air pollution data for Taipei were obtained for the period from 2006 to 2010. The relative risk (RR) of hospital admissions for MI was estimated using a time-stratified case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased RR for a number of MI admissions was significantly associated with higher O-3 levels both on warm days (>23 degrees C) and on cool days (<23 degrees C). This observation was accompanied by an interquartile range elevation correlated with a 7% (95% CI = 2%-12%) and 17% (95% CI = 11%-25%) rise in number of MI admissions, respectively. In the two-pollutant models, no significant associations between ambient O-3 concentrations and number of MI admissions were observed on warm days. However, on cool days, correlation between ambient O-3 after inclusion of each of the other five pollutants, particulate matter (PM10 or PM2.5), sulfur dioxide (SO2), nitrogen dioxide (NO2) or carbon monoxide (CO), and number of MI admissions remained significant. This study provides evidence that higher levels of ambient O-3 increase the RR of number of hospital admissions for MI.