Effects of ambient air pollution on symptoms of asthma in Seattle-area children enrolled in the CAMP study

We observed a panel of 133 children (5-13 years of age) with asthma residin g in the greater Seattle, Washington, area for an average of 58 days (range 28-112 days) during screening for enrollment in the Childhood Asthma Manag ement Program (CAMP) study. Daily self-reports of asthma symp toms were obt ained from study diaries and compared with ambient air pollution levels in marginal repeated measures logistic regression models. We defined days with asthma symptoms as any day a child reported at least one mild asthma episo de. All analyses were controlled for subject-specific variables [age, race, sex, baseline height, and FEV1 PC20 concentration (methacholine provocativ e concentration required to produce a 20% decrease in forced expiratory vol ume in 1 sec)] and potential rime-dependent confounders (day of week, seaso n, and temperature). Because of variable observation periods for participan ts, we estimated both between- and within-subject air pollutant effects. Ou r primary interest was in the within-subject effects: the effect of air pol lutant excursions from typical levels in each child's observation period on the odds of asthma symptoms. In single-pollutant models, the population av erage estimates indicated a 30% [95% confidence interval (CI), 11-52%] incr ease for a 1-ppm increment in carbon monoxide lagged I day, an 18% (95% CI, 5-33%) increase for a 10-mug/m(3) increment in same-day particulate matter < 1.0 <mu>m (PM1.0), and an 11% (95% CI, 3-20%) increase for a 10-mug/m(3) increment in particulate matter < 10 <mu>m (PM10) lagged 1 day. Conditiona l on the previous day's asthma symptoms, we estimated 25% (95% CI, 10-42%), 14% (95% CI, 4-26%), and 10% (95% CI, 3-16%) increases in the odds of asth ma symptoms associated with increases in CO, PM1.0, and PM10, respectively. We did not find any association between sulfur dioxide (SO2) and the odds of asthma symptoms. In multipollutant models, the separate pollutant effect s were smaller. The overall effect of an increase in both CO and PM1.0 was a 31% (95% CI, 11-55%) increase in the odds of symptoms of asthma. We concl ude that there is an association between change in shea-term air pollution levels, as indexed by PM and CO, and the occurrence of asthma symptoms amon g children in Seattle. Although PM effects on asthma have been found in oth er studies, it is likely that CO is a marker for vehicle exhaust and other combustion by-products that aggravate asthma.