Association of Changes in Air Quality With Bronchitic Symptoms in Children in California, 1993-2012

Abstract

Importance: Childhood bronchitic symptoms are significant public and clinical health problems that produce a substantial burden of disease. Ambient air pollutants are important determinants of bronchitis occurrence.

Objective: To determine whether improvements in ambient air quality in Southern California were associated with reductions in bronchitic symptoms in children.

Design, setting, and participants: A longitudinal study involving 4602 children (age range, 5-18 years) from 3 cohorts was conducted during the 1993-2001, 1996-2004, and 2003-2012 years in 8 Southern California communities. A multilevel logistic model was used to estimate the association of changes in pollution levels with bronchitic symptoms.

Exposures: Average concentrations of nitrogen dioxide, ozone, particulate matter with an aerodynamic diameter of less than 10 µm (PM10) and less than 2.5 µm (PM2.5).

Main outcomes and measures: Annual age-specific prevalence of bronchitic symptoms during the previous 12 months based on the parent's or child's report of a daily cough for 3 months in a row, congestion or phlegm other than when accompanied by a cold, or bronchitis.

Results: The 3 cohorts included a total of 4602 children (mean age at baseline, 8.0 years; 2268 girls [49.3%]; 2081 Hispanic white [45.2%]) who had data from 2 or more annual questionnaires. Among these children, 892 (19.4%) had asthma at age 10 years. For nitrogen dioxide, the odds ratio (OR) for bronchitic symptoms among children with asthma at age 10 years was 0.79 (95% CI, 0.67-0.94) for a median reduction of 4.9 ppb, with absolute decrease in prevalence of 10.1%. For ozone, the OR was 0.66 (95% CI, 0.50-0.86) for a median reduction of 3.6 ppb, with an absolute decrease in prevalence of 16.3%. For PM10, the OR was 0.61 (95% CI, 0.48-0.78) for a median reduction of 5.8 µg/m3, with an absolute decrease in prevalence of 18.7%. For PM2.5, the OR was 0.68 (95% CI, 0.53-0.86) for a median reduction of 6.8 µg/m3, with absolute decrease in prevalence of 15.4%. Among children without asthma (n = 3710), the ORs were 0.84 (95% CI, 0.76-0.92) for nitrogen dioxide; 0.85 (95% CI, 0.74-0.97) for ozone, 0.80 (95% CI, 0.70-0.92) for PM10, and 0.79 (95% CI, 0.69-0.91) for PM2.5; with absolute decrease in prevalence of 1.8% for nitrogen dioxide, 1.7% for ozone, 2.2% for PM10, and 2.3% for PM2.5. The associations were similar or slightly stronger at age 15 years.

Conclusions and relevance: Decreases in ambient pollution levels were associated with statistically significant decreases in bronchitic symptoms in children. Although the study design does not establish causality, the findings support potential benefit of air pollution reduction on asthma control.

Figure 1. Annual mean air pollutant levels during the follow-up period of the CHS study (1994–2011) by community^a

a. Plots depict data for 1994–2011, even though the models use 1992–2011 exposure data to examine associations with 1993–2012 data on bronchitic symptoms. This is because data for 1992 and 1993 were not complete and had to be substituted with 1994 data in some cases. For PM10 mean pollutant concentrations from 1994 were used for Alpine, Riverside and Upland for 1992 and 1993 due to missing data. Similarly, PM2.5 mean pollutant concentrations from 1994 were used for 1992 and 1993, for all eight communities, due to missing data.

Figure 2. Predicted change in bronchitic symptom prevalence at age 10 versus the change in mean air pollutants over the study period by community^a,b

a. ALP = Alpine, LKE= Lake Elsinore, LGB=Long Beach, MRL=Mira Loma, RIV=Riverside, SDM=San Dimas, SMA = Santa Maria, UPL=Upland b. Plots depict (along with y=0 and x=0 line for reference) the predicted changes from the longitudinal model in prevalence of bronchitic symptoms at age 10 (across the 1993–2001 and 2003–2012 cohorts) as functions of the changes in mean exposures levels, comparing high to low mean pollution levels for the 1992–2000, 1995–2003 and the 2002–2011 averaging periods. The estimates used in the plots are based on longitudinal models with adjustments for gender, race/ethnicity, and a spline function of age with knots (breakpoints) at 10 and 15 years of age.