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Reduced Asthma Incidence in Children following Decreased Nitrogen Dioxide Levels in Southern California
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A1019 - Reduced Asthma Incidence in Children following Decreased Nitrogen Dioxide Levels in Southern California
Author Block: E. Garcia, K. T. Berhane, T. Islam, R. McConnell, R. Urman, Z. Chen, F. D. Gilliland; Department of Preventive Medicine, University of Southern California, Los Angeles, CA, United States.
Introduction: Air pollution has been linked with adverse pulmonary effects in children, including airway inflammation, decreased lung function, and asthma exacerbation. Whether air pollution affects the development of pediatric asthma, however, remains unclear. We examined how asthma incidence rates changed with decreasing community-level annual average air pollution concentrations, specifically nitrogen dioxide (NO2), during a 20-year period across three adolescent cohorts in the Southern California Children’s Health Study (CHS).
Methods: Questionnaire-based reports of incident asthma (N=525) were identified among subjects in three prospective CHS cohorts followed from approximately 4th grade through high school graduation (1993-1999, 1996-2002, and 2006-2012). NO2 was continuously monitored in the nine communities in which subjects resided at baseline. Multilevel Poisson regression with an offset term was used to estimate the association between asthma incidence during follow up and community-level annual average NO2 concentrations in baseline year for each cohort (e.g., 1993, 1996, and 2006). A random effect for cohort nested within town was included in the model. Exposure was defined as change from the community-specific 1993 NO2 concentration and effect estimates were scaled to the mean change in community-level NO2 concentrations from 1993 to 2006. Both unadjusted and models adjusted for baseline age, sex, ethnicity and race are reported. We assessed effect measure modification by a variety of factors.
Results: The three cohorts included 4,140 children (mean baseline age: 9.5 years; 2,179 [53%] female; 2,273 [55%] White; 1,686 [41%] Hispanic) with no history of physician-diagnosed asthma at baseline. The observed community-level annual average NO2 concentrations in 1993 ranged from 8.0 to 41.7 ppb in the nine communities and reductions between 1993 and 2006 ranged from 0.8 to 14.1 ppb. The incidence rate ratio (RR) for asthma associated with a mean reduction of 6.2 ppb for NO2 was 0.76 (95% Confidence Interval (CI): 0.64-0.90) and 0.75 (CI: 0.63-0.88) in the unadjusted and adjusted models, respectively. We observed no evidence of effect measure modification by sex, race, ethnicity, parental educational attainment, or use of Spanish, versus English, language baseline questionnaire.
Conclusion: Reductions in community-level concentrations of NO2 from 1993 to 2006, observed in communities with a mean baseline concentration of 24 ppb—well below the US EPA annual standard, were statistically significantly associated with reduced risk of asthma in children.
Author Block: E. Garcia, K. T. Berhane, T. Islam, R. McConnell, R. Urman, Z. Chen, F. D. Gilliland; Department of Preventive Medicine, University of Southern California, Los Angeles, CA, United States.
Introduction: Air pollution has been linked with adverse pulmonary effects in children, including airway inflammation, decreased lung function, and asthma exacerbation. Whether air pollution affects the development of pediatric asthma, however, remains unclear. We examined how asthma incidence rates changed with decreasing community-level annual average air pollution concentrations, specifically nitrogen dioxide (NO2), during a 20-year period across three adolescent cohorts in the Southern California Children’s Health Study (CHS).
Methods: Questionnaire-based reports of incident asthma (N=525) were identified among subjects in three prospective CHS cohorts followed from approximately 4th grade through high school graduation (1993-1999, 1996-2002, and 2006-2012). NO2 was continuously monitored in the nine communities in which subjects resided at baseline. Multilevel Poisson regression with an offset term was used to estimate the association between asthma incidence during follow up and community-level annual average NO2 concentrations in baseline year for each cohort (e.g., 1993, 1996, and 2006). A random effect for cohort nested within town was included in the model. Exposure was defined as change from the community-specific 1993 NO2 concentration and effect estimates were scaled to the mean change in community-level NO2 concentrations from 1993 to 2006. Both unadjusted and models adjusted for baseline age, sex, ethnicity and race are reported. We assessed effect measure modification by a variety of factors.
Results: The three cohorts included 4,140 children (mean baseline age: 9.5 years; 2,179 [53%] female; 2,273 [55%] White; 1,686 [41%] Hispanic) with no history of physician-diagnosed asthma at baseline. The observed community-level annual average NO2 concentrations in 1993 ranged from 8.0 to 41.7 ppb in the nine communities and reductions between 1993 and 2006 ranged from 0.8 to 14.1 ppb. The incidence rate ratio (RR) for asthma associated with a mean reduction of 6.2 ppb for NO2 was 0.76 (95% Confidence Interval (CI): 0.64-0.90) and 0.75 (CI: 0.63-0.88) in the unadjusted and adjusted models, respectively. We observed no evidence of effect measure modification by sex, race, ethnicity, parental educational attainment, or use of Spanish, versus English, language baseline questionnaire.
Conclusion: Reductions in community-level concentrations of NO2 from 1993 to 2006, observed in communities with a mean baseline concentration of 24 ppb—well below the US EPA annual standard, were statistically significantly associated with reduced risk of asthma in children.
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