Confounding and Effect Modification in the Short-Term Effects of Ambient Particles on Total Mortality: Results from 29 European Cities within the APHEA2 Project

Abstract

We present the results of the Air Pollution and Health: A European Approach 2 (APHEA2) project on short-term effects of ambient particles on mortality with emphasis on effect modification. We used daily measurements for particulate matter less than 10 microm in aerodynamic diameter (PM10) and/or black smoke from 29 European cities. We considered confounding from other pollutants as well as meteorologic and chronologic variables. We investigated several variables describing the cities' pollution, climate, population, and geography as potential effect modifiers. For the individual city analysis, generalized additive models extending Poisson regression, using a smoother to control for seasonal patterns, were applied. To provide quantitative summaries of the results and explain remaining heterogeneity, we applied second-stage regression models. The estimated increase in the daily number of deaths for all ages for a 10 microg/m3 increase in daily PM10 or black smoke concentrations was 0.6% [95% confidence interval (CI) = 0.4-0.8%], whereas for the elderly it was slightly higher. We found important effect modification for several of the variables studied. Thus, in a city with low average NO2, the estimated increase in daily mortality for an increase of 10 microg/m3 in PM10 was 0.19 (95% CI = 0.00-0.41), whereas in a city with high average NO2 it was 0.80% (95% CI = 0.67-0.93%); in a relatively cold climate the corresponding effect was 0.29% (95% CI = 0.16-0.42), whereas in a warm climate it was 0.82% (95% CI = 0.69-0.96); in a city with low standardized mortality rate it was 0.80% (95% CI = 0.65-0.95%), and in one with a high rate it was 0.43% (95% CI = 0.24-0.62). Our results confirm those previously reported on the effects of ambient particles on mortality. Furthermore, they show that the heterogeneity found in the effect parameters among cities reflects real effect modification, which is explained by specific city characteristics.

Daily mortality and particulate matter in different size classes in Erfurt, Germany

“…The association between PM and all-cause mortality has been consistently observed (Pope and Dockery, 1999;Samet et al, 2000;Katsouyanni et al, 2001;Health Effects Institute, 2003). A 10 mg/m 3 increase in the concentration of PM 10 was associated with an increase in mortality by 0.27% in the US (Dominici et al, 2002) or by 0.6% in Europe (Katsouyanni et al, 2002), respectively.…”

“…Elevated concentrations of particulate matter (PM) have been linked with increased acute mortality worldwide (Pope and Dockery, 1999;Samet et al, 2000;Katsouyanni et al, 2001;Health Effects Institute, 2003). Evidence suggests that increased PM concentrations mainly affect the cardiovascular and respiratory systems (Peters et al, 1997a(Peters et al, , 1999Gold et al, 2000;Ibald-Mulli et al, 2001;Brook et al, 2002;Devlin et al, 2003;Schulz et al, 2005) and are especially associated with increased cardiovascular hospital admissions (Schwartz, 1999;Zanobetti et al, 2000;Le Tertre et al, 2002;D'Ippoliti et al, 2003;von Klot et al, 2005;Dominici et al, 2006) or increased cardiovascular mortality (Clancy et al, 2002;Forastiere et al, 2005;Zeka et al, 2005;Ostro et al, 2006).…”

Associations between ambient air pollution and daily emergency department attendances for cardiovascular disease in the elderly (65+ years), Sydney, Australia

“…We used routinely collected data for both the exposures and outcomes. We constructed daily time series of hospital ED attendances, air pollutants and meteorological factors for the Sydney metropolitan region following the APHEA2 protocol (Atkinson et al, 2001;Katsouyanni et al, 2001;Le Tertre et al, 2002).…”

“…We followed the APHEA2 protocol (Atkinson et al, 2001;Katsouyanni et al, 2001) to produce same day (lag0) and lagged (lag1, lag2, lag3 days) Sydney average pollutant concentrations for particulate matter (BSP, PM 10 , PM 2.5 F 24-h averages), NO 2 (1-h average), O 3 (1-h average), CO (8-h average) and SO 2 (24-h average) and for daily average temperature and daily average relative humidity.…”

Ambient particle source apportionment and daily hospital admissions among children and elderly in Copenhagen

“…Associations between air pollution and cardiovascular and respiratory morbidity and mortality in adults are well established (Spix et al, 1998;Atkinson et al, 2001;Katsouyanni et al, 2001;A Le Tertre et al, 2002;Brunekreef and Holgate, 2002;Englert, 2004;Brunekreef and Forsberg, 2005;Dominici et al, 2006). For respiratory symptoms in children, the results are more mixed and suggest different impacts, and dose-response relationships may be different from those seen in adults (Schwartz, 2004).…”