The Response of Children with Asthma to Ambient Particulate Is Modified by Tobacco Smoke Exposure

Rationale: Ambient particulate matter concentrations have been positively associated with urinary leukotriene E-4 (LTE4) levels and albuterol usage in children with asthma but interactions with environmental tobacco smoke (ETS) exposure have not been demonstrated despite obvious exposure to both pollutants in an urban setting. Objectives: To assess the health effects of concurrent ETS and ambient particulate matter exposure in children with asthma. Methods: Albuterol usage and LTE4 levels were monitored in 82 urban schoolchildren with asthma over three consecutive fall to spring school periods. Concentrations of morning maximum ambient particulate matter <2.5 mu m in aerodynamic diameter (mmPM(2.5)) and urine cotinine levels were also measured daily. Measurements and Main Results: Albuterol usage and LTE4 were related to mmPM(2.5) concentrations on days when urine cotinine levels were low (<10 ng/ml/mg creatinine); on these days, mean albuterol usage and LTE4 increased up to 5 or 6% per 10 mu g/m(3) increase in mmPM(2.5). In contrast, no significant relationship was observed when cotinine was high, although mean albuterol usage and LTE4 levels were greater in this case. Model fits for LTE4 levels as a function of mmPM(2.5) concentrations were improved when mmPM(2.5) concentrations were logged, suggesting a nonlinear dose-response relationship between particulate matter exposure concentrations and airway mediators of asthma, for which the relationship tends to flatten at higher concentrations. Conclusions: This study suggests that ETS modifies the acute effects of low-level ambient PM2.5 exposure on childhood asthma. This negative interaction, the smaller effect of particulate matter exposure in children exposed to higher ETS, may be related to a nonlinear dose-response relationship between asthma mediators and particulate exposures.