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      Short-Term Effects of PM 10 and NO 2 on Respiratory Health among Children with Asthma or Asthma-like Symptoms: A Systematic Review and Meta-Analysis


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          Our goal was to quantify the short-term effects of particulate matter with aerodynamic diameter ≤ 10 μm (PM 10) and nitrogen dioxide (NO 2) on respiratory health of asthmatic children from published panel studies, and to investigate the influence of study and population characteristics as effect modifiers.

          Data extraction

          After a systematic literature review, we extracted quantitative estimates of the association of PM 10 and/or NO 2 with respiratory symptoms and peak expiratory flow (PEF). Combined effect estimates for an increase of 10 μg/m 3 were calculated by random effects meta-analysis for all studies and for different strata defined by study characteristics. The effect of publication bias was investigated with Egger’s and Begg’s tests and “trim-and-fill” analyses.

          Data synthesis

          We identified 36 studies; 14 were part of the European Pollution Effects on Asthmatic Children in Europe (PEACE) study. Adverse associations of PM 10 with asthma symptoms were statistically significant [odds ratio (OR) = 1.028; 95% confidence interval (CI), 1.006–1.051]. There were also associations, although not statistically significant, of PM 10 with cough (OR = 1.012; 95% CI, 0.997–1.026) and on PEF (decrease of −0.082 L/min; 95% CI, −0.214 to 0.050). NO 2 had statistically significant associations with asthma symptoms in the overall analysis considering all possible lags (OR = 1.031; 95% CI, 1.001–1.062), but not when we evaluated only the 0–1 lag. We found no publication bias, although it appeared when excluding the PEACE studies. When we applied the trim-and-fill method to the data set without the PEACE studies, the results were similar to the overall estimates from all studies. There was an indication for stronger PM 10 associations for studies conducted in summer, outside of Europe, with longer lags, and in locations with higher NO 2 concentrations.


          We found clear evidence of effects of PM 10 on the occurrence of asthma symptom episodes, and to a lesser extent on cough and PEF. The results for NO 2 are more difficult to interpret because they depend on the lag times examined. There was an indication of effect modification by several study conditions.

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          Most cited references 31

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          Confounding and effect modification in the short-term effects of ambient particles on total mortality: results from 29 European cities within the APHEA2 project.

          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.
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            Acute effects of particulate air pollution on respiratory admissions: results from APHEA 2 project. Air Pollution and Health: a European Approach.

            The APHEA 2 project investigated short-term health effects of particles in eight European cities. In each city associations between particles with an aerodynamic diameter of less than 10 microm (PM(10)) and black smoke and daily counts of emergency hospital admissions for asthma (0-14 and 15-64 yr), chronic obstructive pulmonary disease (COPD), and all-respiratory disease (65+ yr) controlling for environmental factors and temporal patterns were investigated. Summary PM(10) effect estimates (percentage change in mean number of daily admissions per 10 microg/m(3) increase) were asthma (0-14 yr) 1.2% (95% CI: 0.2, 2.3), asthma (15-64 yr) 1.1% (0.3, 1.8), and COPD plus asthma and all-respiratory (65+ yr) 1.0% (0.4, 1.5) and 0.9% (0.6, 1.3). The combined estimates for Black Smoke tended to be smaller and less precisely estimated than for PM(10). Variability in the sizes of the PM(10) effect estimates between cities was also investigated. In the 65+ groups PM(10) estimates were positively associated with annual mean concentrations of ozone in the cities. For asthma admissions (0-14 yr) a number of city-specific factors, including smoking prevalence, explained some of their variability. This study confirms that particle concentrations in European cities are positively associated with increased numbers of admissions for respiratory diseases and that some of the variation in PM(10) effect estimates between cities can be explained by city characteristics.
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              Approaches to heterogeneity in meta-analysis.

               D Petitti (2001)
              This paper reviews publications from January 1999 to March 2001 on reproductive health topics that were self-identified as meta-analysis or were indexed as meta-analysis in MEDLINE. It sought to assess whether tests of statistical heterogeneity were done, whether the results were reported, and how a finding of significance for a test of statistical heterogeneity was handled and the results interpreted. The review identified some concerns. Tests of statistical heterogeneity were not done universally even though virtually all writers on the topic emphasize their importance. Even when done, results of these tests were not universally reported. Although the consensus appears to be that heterogeneity tests are conservative for meta-analysis of studies and a probability value of 0.10 is preferred, many meta-analyses used the conventional value of 0.05 without providing a reason. The rationale for the choice of a random or fixed effects model was not generally evident. The review also provided some positive models and some recommendations for assessing, reporting and exploring heterogeneity are made considering these models and the published recommendations of experts. Copyright 2001 John Wiley & Sons, Ltd.

                Author and article information

                Environ Health Perspect
                Environmental Health Perspectives
                National Institute of Environmental Health Sciences
                April 2010
                12 November 2009
                : 118
                : 4
                : 449-457
                [1 ] Institute of Epidemiology, Ulm University, Ulm, Germany
                [2 ] Department of Epidemiology, Local Health Authority Rome E, Rome, Italy
                Author notes
                Address correspondence to G. Weinmayr, Institute of Epidemiology, Ulm University, Helmholtzstr. 22, D-89081 Ulm, Germany. Telephone: 49-731-50-31071. Fax: 49-731-50-31069. E-mail: gudrun.weinmayr@ 123456uni-ulm.de

                S.K.W. is now deceased.

                The authors declare they have no competing financial interests.

                This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.

                Public health

                pm, air pollution, children, no2, asthma, short-term effects


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