Long-Term Exposure to Low Level Air Pollution in Sydney and Mortality and Hospital Admission Using the '45 and Up' Cohort: Methodological Challenges

摘要

We used the '45 and Up' cohort study of older (45+ years) residents of New South Wales, Australia, to investigate the health efffects of long term air pollution exposure. Individual level data was collected on 267,153 subjects via baseline questionnaire mostly completed in 2008 and these data were linked to routinely collected death registrations data (up to 2015) and hospital admissions data (up to 2014) via personal identifiers (including age, sex, residential address). Neighbourhood level socio-economic status data was liked to study subjects residential address. Subjects residential address was used to estimated annual average NO2 exposure using a satellite based land use regression model for 2007 for all study subjects, while Chemical Transport Model data blended with fixed site monitor data for 2010/11 was used to estimate annual average PM2.5 exposure for subjects in the Sydney metropolitan area. We implemented Cox proportional hazards models to assess the associations between air pollution exposure and all-cause mortality, and respiratory hospital admissions while adjusting for individual level socio-demographic and behavioral factors, as well as area-level factors. Annual average PM2.5 and NO2 exposure was 4.5 μg/m3 and 17.5 μg/m3 respectively. Covariate adjusted models found that mortality and respiratory hospital admissions were associated with PM2.5 and NO2 (mortality Hazard Ratios (HR)=1.06 (95% CI: 1.00-1.11), asthma admissions HR=1.08 (95% CI: 0.89 -1.30), bronchitis admissions HR=1.32 (95%CI: 0.96 -1.80) per 1 u.g/m3 increase in PM2.5 respectively). Increasing model complexity generally reduced the magnitude of the HR point estimates and the strength of the associations but may have resulted in over control for covariate effects. Even at the relatively low level long term air pollution exposures generally seen in Sydney, and with limited follow up, air pollution exposure within our cohort had a detrimental effect on mortality and hospitalisation.