Indoor Environmental Exposures and Exacerbation of Asthma
Indoor Environmental Exposures and Exacerbation of Asthma
We examined publications since 2000 relating indoor exposures and exacerbation of asthma in conjunction with prior evidence (IOM 2000) and provide conclusions about the current strength of evidence. We used a set of previously defined categories for strength of evidence (IOM 2000): a) sufficient evidence of causal relationship, b) sufficient evidence of an association, c) limited or suggestive evidence of an association, d) inadequate or insufficient evidence to determine whether or not an association exists, and e) limited or suggestive evidence of no association (for category descriptions, see Supplemental Material, Table S1 http://ehp.niehs.nih.gov/wp-content/uploads/123/1/ehp.1307922.s001.508.pdf).
In this review we considered the evidence that specific indoor environmental exposures might cause exacerbation of asthma. Eligible outcome measures, all among asthmatics, included frequency or severity of respiratory symptoms, illness-related school absences, urgent care or emergency department visits, hospitalization, unscheduled health care visits, amount or frequency of medicine for asthma control or prevention, airway inflammation assessed by fraction of exhaled nitric oxide (FeNO), and asthma-related quality of life.
Potentially modifiable biological and chemical exposures resulting from indoor sources were considered for inclusion as potential causes of asthma morbidity. Infectious agents and outdoor-generated pollutants that penetrate buildings were excluded. Studies on new onset of asthma, asthma prevalence, or experimental biologic markers of asthma were excluded.
Only studies of human health effects were included. Eligible study designs were controlled (experimental) exposure studies, environmental intervention studies, and a variety of observational designs: prospective or retrospective (longitudinal) cohort, case–control, and cross-sectional. Case studies and case series were ineligible. Detailed inclusion and exclusion criteria are described in the Supplemental Material, http://ehp.niehs.nih.gov/wp-content/uploads/123/1/ehp.1307922.s001.508.pdf "Study inclusion criteria."
PubMed searches were performed in May and August 2011 and updated in August 2013. Search terms focused primarily on the indoor environmental risk factors considered in the IOM 2000 review. We added the category tag "major" to identify articles that included the IOM risk factor as a main topic and the broader category tag "mesh" to identify articles that included the IOM risk factors as a subject, but not necessarily as a main topic. This search strategy was designed to exclude editorials, letters, commentaries, clinical trials (phases 1–4) that would assess drug development and efficacy, and studies focusing on genetic predisposition or polymorphisms associated with asthma development. In addition, this search was restricted to findings published in English during the past 13 years. For further details regarding the search strategy, see Supplemental Material, http://ehp.niehs.nih.gov/wp-content/uploads/123/1/ehp.1307922.s001.508.pdf "Literature search strategy."
In total, the searches yielded 2,570 articles. After application of inclusion and exclusion criteria to the abstracts, we identified 162 articles of preliminary interest. We further excluded 99 studies after reviewing the full articles. Six additional peer-reviewed articles from reference lists or researchers' files were included. Finally, 69 articles were selected for this review article. We considered recent findings in conjunction with evidence cited in the IOM (2000).
Methods
We examined publications since 2000 relating indoor exposures and exacerbation of asthma in conjunction with prior evidence (IOM 2000) and provide conclusions about the current strength of evidence. We used a set of previously defined categories for strength of evidence (IOM 2000): a) sufficient evidence of causal relationship, b) sufficient evidence of an association, c) limited or suggestive evidence of an association, d) inadequate or insufficient evidence to determine whether or not an association exists, and e) limited or suggestive evidence of no association (for category descriptions, see Supplemental Material, Table S1 http://ehp.niehs.nih.gov/wp-content/uploads/123/1/ehp.1307922.s001.508.pdf).
Specific Priorities, Inclusions, and Exclusions
In this review we considered the evidence that specific indoor environmental exposures might cause exacerbation of asthma. Eligible outcome measures, all among asthmatics, included frequency or severity of respiratory symptoms, illness-related school absences, urgent care or emergency department visits, hospitalization, unscheduled health care visits, amount or frequency of medicine for asthma control or prevention, airway inflammation assessed by fraction of exhaled nitric oxide (FeNO), and asthma-related quality of life.
Potentially modifiable biological and chemical exposures resulting from indoor sources were considered for inclusion as potential causes of asthma morbidity. Infectious agents and outdoor-generated pollutants that penetrate buildings were excluded. Studies on new onset of asthma, asthma prevalence, or experimental biologic markers of asthma were excluded.
Only studies of human health effects were included. Eligible study designs were controlled (experimental) exposure studies, environmental intervention studies, and a variety of observational designs: prospective or retrospective (longitudinal) cohort, case–control, and cross-sectional. Case studies and case series were ineligible. Detailed inclusion and exclusion criteria are described in the Supplemental Material, http://ehp.niehs.nih.gov/wp-content/uploads/123/1/ehp.1307922.s001.508.pdf "Study inclusion criteria."
Literature Search
PubMed searches were performed in May and August 2011 and updated in August 2013. Search terms focused primarily on the indoor environmental risk factors considered in the IOM 2000 review. We added the category tag "major" to identify articles that included the IOM risk factor as a main topic and the broader category tag "mesh" to identify articles that included the IOM risk factors as a subject, but not necessarily as a main topic. This search strategy was designed to exclude editorials, letters, commentaries, clinical trials (phases 1–4) that would assess drug development and efficacy, and studies focusing on genetic predisposition or polymorphisms associated with asthma development. In addition, this search was restricted to findings published in English during the past 13 years. For further details regarding the search strategy, see Supplemental Material, http://ehp.niehs.nih.gov/wp-content/uploads/123/1/ehp.1307922.s001.508.pdf "Literature search strategy."
In total, the searches yielded 2,570 articles. After application of inclusion and exclusion criteria to the abstracts, we identified 162 articles of preliminary interest. We further excluded 99 studies after reviewing the full articles. Six additional peer-reviewed articles from reference lists or researchers' files were included. Finally, 69 articles were selected for this review article. We considered recent findings in conjunction with evidence cited in the IOM (2000).
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