Short-term associations between ambient air pollutants and pediatric asthma emergency department visits

Abstract

Rationale: Certain outdoor air pollutants cause asthma exacerbations in children. To advance understanding of these relationships, further characterization of the dose-response and pollutant lag effects are needed, as are investigations of pollutant species beyond the commonly measured criteria pollutants.

Objectives: Investigate short-term associations between ambient air pollutant concentrations and emergency department visits for pediatric asthma.

Methods: Daily counts of emergency department visits for asthma or wheeze among children aged 5 to 17 years were collected from 41 Metropolitan Atlanta hospitals during 1993-2004 (n = 91,386 visits). Ambient concentrations of gaseous pollutants and speciated particulate matter were available from stationary monitors during this time period. Rate ratios for the warm season (May to October) and cold season (November to April) were estimated using Poisson generalized linear models in the framework of a case-crossover analysis.

Measurements and main results: Both ozone and primary pollutants from traffic sources were associated with emergency department visits for asthma or wheeze; evidence for independent effects of ozone and primary pollutants from traffic sources were observed in multipollutant models. These associations tended to be of the highest magnitude for concentrations on the day of the emergency department visit and were present at relatively low ambient concentrations.

Conclusions: Even at relatively low ambient concentrations, ozone and primary pollutants from traffic sources independently contributed to the burden of emergency department visits for pediatric asthma.

Figure 1.

Loess dose–response estimates (solid line) and twice-standard error estimates (dashed lines) from generalized additive models for associations between 3-day moving average air pollutant concentrations and emergency department visits for pediatric asthma. The reference (denominator) for the rate ratio is the estimated rate at the 5th percentile of the pollutant concentration. Estimates are only presented for the 5th percentile through the 95th percentile of pollutant concentrations because of instability in the dose–response estimates at the distribution tails.

Figure 2.

Constrained cubic polynomial distributed lag models. The rate ratio and 95% confidence interval displayed for each pollutant correspond to an interquartile range increase in the cumulative ambient pollutant concentration during the 8-day period of interest (lags 0–7). Point estimates and 95% confidence intervals are also presented graphically for the lag-specific rate ratios. To enhance the stability of the distributed lag estimates, the cubic polynomial was fit to lags 0–13; however, the rate ratios and 95% confidence intervals presented in the Figure correspond to the effects of lags 0–7 only.

Figure 3.

Warm season rate ratios and 95% confidence intervals for interquartile range increases in 3-day moving average ambient air pollutant concentrations for single-pollutant and two-pollutant models. CO = carbon monoxide; EC = PM_2.5 elemental carbon; NO2 = nitrogen dioxide; O3 = ozone; PM_2.5 = particulate matter less than 2.5 μm in aerodynamic diameter; SO4 = PM_2.5 sulfate. *Time period limited to August 1, 1998, to December 31, 2004.