Susceptibility Factors to Ozone-Related Mortality-A Population-Based Case-Crossover Analysis

Abstract

ISEE-0133 Background and Objective: Acute effects of ozone on mortality have been extensively documented in clinical and epidemiological research. However, few studies have focused on subgroups of the population especially vulnerable to these effects. The objective of the study is to estimate the association between cause-specific mortality and exposure to ozone, and to evaluate whether individual socio-demographic or chronic conditions present greater susceptibility to adverse effects of ozone. Methods: A case-crossover analysis was conducted in 10 Italian cities to evaluate individual effect modifiers of the ozone-mortality association. Data on mortality and air pollution exposure were collected for the period 2001-2005 (April to September), for 129,026 deceased subjects. Individual information was retrieved on cause of death, socio-demographic characteristics, chronic conditions from previous hospital admissions, and place of death. Results: We estimated a 1.54% (95% confidence interval, CI, 0.92-2.15) increase in total mortality for 10 ug/m3 increase in ozone (8-hour, lag 0-5). The association had a prolonged lag for total, cardiac and respiratory mortality (lag 0-5), while there was a suggestion of a delayed effect on mortality from cerebrovascular causes (lag 3-5). No important confounding effect of PM10 or NO2 was found. In the subgroup analysis, the effect was more pronounced among the elderly over 85 years of age (3.51%, 95% CI 2.41-4.62), women (2.25%, 95% CI 1.37-3.14), and for people who died outside the hospital (2.10%, 95% CI 1.05-3.17), especially diabetics (5.53%, 95% CI 1.39-9.84). Conclusion: A strong effect of ozone on mortality has been found in Italian cities. Greater vulnerability was confirmed for women and elderly; other subgroups of the population emerged as especially affected, in particular chronically ill house-bound and diabetics.