Association of Changes in Air Quality With Incident Asthma in Children in California, 1993-2014

Abstract

<div class="section"> <a class="named-anchor" id="ab-joi190043-1"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e298">Question</h5> <p id="d793427e300">What is the association between reductions in regional air pollutant concentration and incidence of childhood asthma? </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-2"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e303">Findings</h5> <p id="d793427e305">In this longitudinal study that included 4140 children, each 4.3–parts-per-billion decrease in nitrogen dioxide was associated with a reduction of 0.83 cases per 100 person-years in asthma incidence; each 8.1-μg/m ³ decrease in particulate matter less than 2.5 μm was associated with a reduction of 1.53 cases per 100 person-years in asthma incidence. There were no statistically significant associations with change in ozone and particulate matter less than 10 μm. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-3"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e311">Meaning</h5> <p id="d793427e313">Declines in nitrogen dioxide and particulate matter less than 2.5 μm may be associated with decreased childhood asthma incidence. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-4"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e317">Importance</h5> <p id="d793427e319">Exposure to air pollutants is a well-established cause of asthma exacerbation in children; whether air pollutants play a role in the development of childhood asthma, however, remains uncertain. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-5"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e322">Objective</h5> <p id="d793427e324">To examine whether decreasing regional air pollutants were associated with reduced incidence of childhood asthma. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-6"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e327">Design, Setting, and Participants</h5> <p id="d793427e329">A multilevel longitudinal cohort drawn from 3 waves of the Southern California Children’s Health Study over a period of air pollution decline. Each cohort was followed up from 4th to 12th grade (8 years): 1993-2001, 1996-2004, and 2006-2014. Final follow-up for these data was June 2014. Population-based recruitment was from public elementary schools. A total of 4140 children with no history of asthma and residing in 1 of 9 Children’s Health Study communities at baseline were included. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-7"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e332">Exposures</h5> <p id="d793427e334">Annual mean community-level ozone, nitrogen dioxide, and particulate matter less than 10 μm (PM ₁₀) and less than 2.5 μm (PM _2.5) in the baseline year for each of 3 cohorts. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-8"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e343">Main Outcomes and Measures</h5> <p id="d793427e345">Prospectively identified incident asthma, collected via questionnaires during follow-up.</p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-9"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e348">Results</h5> <p id="d793427e350">Among the 4140 children included in this study (mean [SD] age at baseline, 9.5 [0.6] years; 52.6% female [n = 2 179]; 58.6% white [n = 2273]; and 42.2% Hispanic [n = 1686]), 525 incident asthma cases were identified. For nitrogen dioxide, the incidence rate ratio (IRR) for asthma was 0.80 (95% CI, 0.71-0.90) for a median reduction of 4.3 parts per billion, with an absolute incidence rate decrease of 0.83 cases per 100 person-years. For PM _2.5, the IRR was 0.81 (95% CI, 0.67-0.98) for a median reduction of 8.1 μg/m ³, with an absolute incidence rate decrease of 1.53 cases per 100 person-years. For ozone, the IRR for asthma was 0.85 (95% CI, 0.71-1.02) for a median reduction of 8.9 parts per billion, with an absolute incidence rate decrease of 0.78 cases per 100 person-years. For PM ₁₀, the IRR was 0.93 (95% CI, 0.82-1.07) for a median reduction of 4.0 μg/m ³, with an absolute incidence rate decrease of 0.46 cases per 100 person-years. </p> </div><div class="section"> <a class="named-anchor" id="ab-joi190043-10"> <!-- named anchor --> </a> <h5 class="section-title" id="d793427e365">Conclusions and Relevance</h5> <p id="d793427e367">Among children in Southern California, decreases in ambient nitrogen dioxide and PM _2.5 between 1993 and 2014 were significantly associated with lower asthma incidence. There were no statistically significant associations for ozone or PM ₁₀. </p> </div><p class="first" id="d793427e376">This study uses Southern California Children’s Health Study data to examine associations between changes in regional air pollution (ozone, nitrogen dioxide, and particulate matter &lt;10 μm and &lt;2.5 μm) and changes in childhood asthma incidence across 3 child cohorts. </p>