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      Effect of outdoor air pollution on asthma exacerbations in children and adults: Systematic review and multilevel meta-analysis

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          Abstract

          Background

          Several observational studies have suggested that outdoor air pollution may induce or aggravate asthma. However, epidemiological results are inconclusive due to the presence of numerous moderators which influence this association. The goal of this study was to assess the relationship between outdoor air pollutants and moderate or severe asthma exacerbations in children and adults through a systematic review and multilevel meta-analysis.

          Material and methods

          We searched studies published in English on PubMed, Scopus, and Google Scholar between January 2000 and October 2016. Studies following a case-crossover design with records of emergency departments and/or hospital admissions as a surrogate of moderate or severe asthma exacerbations were selected. A multilevel meta-analysis was employed, taking into account the potential clustering effects within studies examining more than one lag. Odds ratios (ORs) and 95% confidence intervals were estimated. A subgroup analysis in children aged 0 to 18 years and a sensitivity analysis based on the quality of the included studies as defined in the Newcastle-Ottawa Scale were performed. Publication bias was evaluated through visual inspection of funnel plots and by a complementary search of grey literature. (Prospero Registration number CRD42015032323).

          Results

          Database searches retrieved 208 records, and finally 22 studies were selected for quantitative analysis. All pollutants except SO 2 and PM 10 showed a significant association with asthma exacerbations (NO 2: 1.024; 95% CI: 1.005,1.043, SO 2: 1.039; 95% CI: 0.988,1.094), PM 10: 1.024; 95% CI: 0.995,1.053, PM 2.5: 1.028; 95% CI: 1.009,1.047, CO: 1.045; 95% CI: 1.005,1.086, O 3: 1.032; 95% CI: 1.005,1.060. In children, the association was significant for NO 2, SO 2 and PM 2.5.

          Conclusion

          This meta-analysis provides evidence of the association between selected air pollutants and asthma exacerbations for different lags.

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          Most cited references58

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          Preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement and publication bias.

          Publication bias is a major problem in evidence based medicine. As well as positive outcome studies being preferentially published or followed by full text publication authors are also more likely to publish positive results in English-language journals. This unequal distribution of trials leads to a selection bias in evidence l level studies, like systematic reviews, meta-analysis or health technology assessments followed by a systematic failure of interpretation and in clinical decisions. Publication bias in a systematic review occurs mostly during the selection process and a transparent selection process is necessary to avoid such bias. For systematic reviews/meta-analysis the PRISMA-statement (formerly known as QUOROM) is recommended, as it gives the reader for a better understanding of the selection process. In the future the use of trial registration for minimizing publication bias, mechanisms to allow easier access to the scientific literature and improvement in the peer review process are recommended to overcome publication bias. The use of checklists like PRISMA is likely to improve the reporting quality of a systematic review and provides substantial transparency in the selection process of papers in a systematic review. Copyright © 2010 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
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            Association between Air Pollutants and Asthma Emergency Room Visits and Hospital Admissions in Time Series Studies: A Systematic Review and Meta-Analysis

            Background Air pollution constitutes a significant stimulus of asthma exacerbations; however, the impacts of exposure to major air pollutants on asthma-related hospital admissions and emergency room visits (ERVs) have not been fully determined. Objective We sought to quantify the associations between short-term exposure to air pollutants [ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particulate matter ≤10μm (PM10) and PM2.5] and the asthma-related emergency room visits (ERV) and hospitalizations. Methods Systematic computerized searches without language limitation were performed. Pooled relative risks (RRs) and 95% confidence intervals (95%CIs) were estimated using the random-effect models. Sensitivity analyses and subgroup analyses were also performed. Results After screening of 246 studies, 87 were included in our analyses. Air pollutants were associated with significantly increased risks of asthma ERVs and hospitalizations [O3: RR(95%CI), 1.009 (1.006, 1.011); I2 = 87.8%, population-attributable fraction (PAF) (95%CI): 0.8 (0.6, 1.1); CO: RR(95%CI), 1.045 (1.029, 1.061); I2 = 85.7%, PAF (95%CI): 4.3 (2.8, 5.7); NO2: RR(95%CI), 1.018 (1.014, 1.022); I2 = 87.6%, PAF (95%CI): 1.8 (1.4, 2.2); SO2: RR(95%CI), 1.011 (1.007, 1.015); I2 = 77.1%, PAF (95%CI): 1.1 (0.7, 1.5); PM10: RR(95%CI), 1.010 (1.008, 1.013); I2 = 69.1%, PAF (95%CI): 1.1 (0.8, 1.3); PM2.5: RR(95%CI), 1.023 (1.015, 1.031); I2 = 82.8%, PAF (95%CI): 2.3 (1.5, 3.1)]. Sensitivity analyses yielded compatible findings as compared with the overall analyses without publication bias. Stronger associations were found in hospitalized males, children and elderly patients in warm seasons with lag of 2 days or greater. Conclusion Short-term exposures to air pollutants account for increased risks of asthma-related ERVs and hospitalizations that constitute a considerable healthcare utilization and socioeconomic burden.
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              How important are comprehensive literature searches and the assessment of trial quality in systematic reviews? Empirical study.

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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                20 March 2017
                2017
                : 12
                : 3
                : e0174050
                Affiliations
                [1 ]Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
                [2 ]Universidad Tecnológica Nacional, Facultad Regional San Nicolás, San Nicolás, Argentina
                [3 ]Comisión de Investigaciones Científicas (CIC), La Plata, Argentina
                [4 ]Hospital Interzonal General de Agudos “San Felipe”, San Nicolás, Argentina
                The Ohio State University, UNITED STATES
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                • Conceptualization: PO NQ.

                • Formal analysis: PO NQ.

                • Funding acquisition: PO NQ.

                • Investigation: PO NQ JR BB JV.

                • Methodology: PO NQ.

                • Project administration: PO NQ.

                • Software: PO.

                • Supervision: PO.

                • Visualization: PO.

                • Writing – original draft: PO NQ.

                • Writing – review & editing: PO NQ JR BB JV.

                Author information
                http://orcid.org/0000-0001-8911-663X
                Article
                PONE-D-16-35682
                10.1371/journal.pone.0174050
                5358780
                28319180
                6602c5c0-c45e-46a2-9fbc-d150b8052af1
                © 2017 Orellano et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 5 September 2016
                : 2 March 2017
                Page count
                Figures: 2, Tables: 2, Pages: 15
                Funding
                This study did not receive any specific funding, but was supported by the research budget of the Universidad Tecnológica Nacional, Facultad Regional San Nicolas. PO is supported by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and NQ by the Comisión de Investigaciones Científicas (CIC).
                Categories
                Research Article
                Medicine and Health Sciences
                Pulmonology
                Asthma
                Engineering and Technology
                Environmental Engineering
                Pollution
                Air Pollution
                Physical Sciences
                Chemistry
                Environmental Chemistry
                Pollutants
                Ecology and Environmental Sciences
                Environmental Chemistry
                Pollutants
                Research and Analysis Methods
                Mathematical and Statistical Techniques
                Statistical Methods
                Meta-Analysis
                Physical Sciences
                Mathematics
                Statistics (Mathematics)
                Statistical Methods
                Meta-Analysis
                Earth Sciences
                Geography
                Cartography
                Latitude
                Medicine and Health Sciences
                Critical Care and Emergency Medicine
                Research and Analysis Methods
                Database and Informatics Methods
                Database Searching
                Physical Sciences
                Materials Science
                Materials by Structure
                Mixtures
                Particulates
                Custom metadata
                All relevant data are within the paper and its Supporting Information files.

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