| Short-Term Effects of Carbon Monoxide on Mortality: An Analysis within the APHEA Project Evangelia Samoli,1 Giota Touloumi,1 Joel Schwartz,2 Hugh Ross Anderson,3 Christian Schindler,4 Bertil Forsberg,5 Maria Angela Vigotti,6 Judith Vonk,7 Mitja Kosˇnik,8 Jiri Skorkovsky,9 and Klea Katsouyanni1 1Department of Hygiene and Epidemiology, University of Athens Medical School, Athens, Greece; 2Harvard School of Public Health, Boston, Massachusetts, USA; 3Community Health Sciences, St. George's, University of London, London, United Kingdom; 4Institute of Social and Preventive Medicine, University of Basel, Basel, Switzerland; 5Department of Public Health and Clinical Medicine, Umea University, Umea, Sweden; 6Universita degli studi di Pisa, Pisa, Italy; 7Department of Epidemiology and Statistics, University of Groningen, Groningen, the Netherlands; 8Institute of Public Health, Department of Environmental Health, Ljubljana, Slovenia; 9Institute of Hygiene, Teplice, Czech Republic Abstract
Objectives: We investigated the short-term effects of carbon monoxide on total and cardiovascular mortality in 19 European cities participating in the APHEA-2 (Air Pollution and Health: A European Approach) project. Methods: We examined the association using hierarchical models implemented in two stages. In the first stage, data from each city were analyzed separately, whereas in the second stage the city-specific air pollution estimates were regressed on city-specific covariates to obtain overall estimates and to explore sources of possible heterogeneity. We evaluated the sensitivity of our results by applying different degrees of smoothing for seasonality control in the city-specific analysis. Results: We found significant associations of CO with total and cardiovascular mortality. A 1-mg/m3 increase in the 2-day mean of CO levels was associated with a 1.20% [95% confidence interval (CI) , 0.63–1.77%] increase in total deaths and a 1.25% (95% CI, 0.30–2.21%) increase in cardiovascular deaths. There was indication of confounding with black smoke and nitrogen dioxide, but the pollutant-adjusted effect of CO on mortality remained at least marginally statistically significant. The effect of CO on total and cardiovascular mortality was observed mainly in western and southern European cities and was larger when the standardized mortality rate was lower. Conclusions: The results of this large study are consistent with an independent effect of CO on mortality. The heterogeneity found in the effect estimates among cities may be explained partly by specific city characteristics. Key words: air pollution, carbon monoxide, heterogeneity, modeling, mortality. Environ Health Perspect 115:1578–1583 (2007) . doi:10.1289/ehp.10375 available via http://dx.doi.org/ [Online 16 August 2007]
Address correspondence to E. Samoli, Department of Hygiene and Epidemiology, University of Athens Medical School, 75 Mikras Asias St., 115 27 Athens, Greece. Telephone: 30-210-7462085. Fax: 30-210-7462205. E-mail: esamoli@med. uoa.gr This work was funded through two grants from the European Commission Environment and Climate Programme (contract numbers ENV4-CT97-0534 and QLK4-CT-2001-30055) . The authors declare they have no competing financial interests. Received 18 April 2007 ; accepted 15 August 2007.
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