The influence of socioeconomic markers on the association between fine particulate matter and hospital admissions for respiratory conditions among children

Abstract

Objectives: We evaluated the influence of socioeconomic status (SES) on hospital admissions for respiratory conditions associated with ambient particulate matter that is 2.5 micrometers or less in aerodynamic diameter (PM2.5) in children aged 1 to 9 years in 12 California counties, from 2000 to 2005.

Methods: We linked daily hospital admissions for respiratory conditions (acute respiratory infections, pneumonia, and asthma) to meteorological, air pollution, and census data.

Results: In San Diego, San Bernardino, Riverside, and Los Angeles counties, the admission rates for children associated with PM2.5 ranged from 1.03 to 1.07 for combined respiratory conditions and 1.03 to 1.08 for asthma in regions with lower SES. We observed 2 distinct patterns of the influence of the composite SES Townsend index. In lower-SES South Coast areas, PM2.5-associated hospital admission rates for all respiratory outcomes were predominantly positive whereas results in the Central Valley were variable, often tending toward the null.

Conclusions: These distinct patterns could be attributed to the heterogeneity of regional confounders as well as the seasonal variation of emission sources of PM2.5. Composite SES is one potential factor for increasing susceptibility to air pollution.

FIGURE 1—

Multivariate models by county for (a) hospital admissions of combined respiratory conditions, (b) hospital admissions of acute respiratory infections, (c) hospital admissions of pneumonia, and (d) hospital admissions of asthma: California, 2000–2005. Note. CI = confidence interval. Models included day of week, smoothing splines of 1-day lag temperature (3 df), smoothing splines of time (2 df/y), binary Townsend index, and 3-day lag PM2.5 per 10 μg/m³.

FIGURE 2—

Interaction models for (a) hospital admissions of combined respiratory conditions, (b) hospital admissions of acute respiratory infections, (c) hospital admissions of pneumonia, and (d) hospital admissions of asthma: California, 2000–2005. Note. CI = confidence interval; SES = socioeconomic status. Models included day of week, smoothing splines of 1-day lag temperature (3 df), smoothing. Lower SES defined as upper half of Townsend index score. Higher SES defined as lower half of Townsend index score.