Of the 2240 children in the sampling frame who were 6 to 12 years of age, had physician-diagnosed asthma according to International Classification of Diseases, Ninth Revision, billing codes, and resided in a 9-county area surrounding Cincinnati, we screened 1694 (76%) for eligibility between May 31, 2001, and March 27, 2003. Of these children, 353 (21%) were eligible to participate (). Of the 353 eligible children and their families, 225 (64%) agreed to participate in the trial. There were no significant differences in children's age, gender, asthma severity, or race, parents' education, marital status, household income, or health insurance, or number of cigarettes smoked in or around the house per day for families that chose to participate versus those that chose not to participate.
Enrollment, random assignment, and retention of Cincinnati Asthma Prevention study participants.
Of the 225 families that agreed to participate, 110 (49%) were assigned randomly to the intervention group and 115 (51%) to the control group. At baseline, the mean age of the children was 8.6 years (range: 5.3–11.7 years); 62% of the children were male. Children were exposed to a geometric mean of 13 cigarettes per day. Numbers of unscheduled asthma visits and airborne particle levels were significantly greater in the control group. Some other measures of asthma severity tended to be greater in the control group, but these differences were not statistically significant ( and ). Of the 225 children enrolled in the trial, 215 (95%) completed the study ().
Baseline Characteristics of Study Population According to Group Assignment
Baseline Exposure to Environmental Tobacco Smoke and Indoor Airborne Particles According to Group Assignment
In unadjusted analyses, there were fewer unscheduled asthma visits at follow-up assessment in the intervention group (189 vs 274 visits; P = .046). This difference persisted after adjustment for baseline differences in the multivariate analyses. With adjustment for baseline differences, there was a significant difference in the rate of decrease in the number of unscheduled asthma visits among children in the intervention group, compared with the control group (). The adjusted mean number of unscheduled visits for the intervention group decreased by 8.9% per month, compared with a decrease of 0.9% per month in the control group. With adjustment for baseline differences, there were 185 unscheduled asthma visits among children in the intervention group, compared with 227 unscheduled asthma visits among children in the control group, a reduction of 42 visits (95% confidence interval: 1.25–82.75 visits; P = .043). This is equivalent to a reduction of 18.5% (95% confidence interval: 1%–36%) in the number of unscheduled asthma visits during the study ().
FIGURE 2 Mean numbers of unscheduled asthma visits in the previous 3 months, reported at quarterly intervals during the trial, according to group assignment, with adjustment for differences in the numbers of unscheduled asthma visits at baseline. The solid line (more ...)
Numbers of Unscheduled Asthma Visits, Asthma Symptoms, Reported Exposure to Tobacco Smoke, and Exhaled Nitric-Oxide Levels According to Group Assignment
In a secondary analysis, developed a priori, we examined the effect of HEPA air cleaners among 141 (68%) of 207 families with functioning monitors who used 1 or both air cleaners >70% of the time. With adjustment for baseline differences in unscheduled asthma visits, the rate of reduction in the number of unscheduled asthma visits over time was significantly greater in the intervention group, compared with the control group (P = .006). The number of unscheduled asthma visits for the intervention group decreased by 12.7% per month, compared with an increase of 0.7% per month in the control group.
There was a significant difference in the reductions in the numbers of airborne particles of >0.3 μm according to group assignment (P = .026) (). The absolute mean reduction in levels of airborne particles of >0.3 μm during the trial was 1.1 × 106 particles per ft3 for the intervention group, which was equivalent to a 25% reduction in airborne particle levels. In contrast, there was a reduction of only 0.3 × 106 particles per ft3 (5%) for the control group. There was no significant difference in levels of airborne particles of >5 μm according to group assignment ().
Exposures to Tobacco and Indoor Particles, According to Group Assignment, During Study
There were no significant differences between groups with respect to severity of asthma symptoms, medication use, exhaled nitric-oxide levels, air nicotine levels, serum cotinine levels, or hair cotinine levels during the trial (). There were no significant group-season (P = .328) or group-allergy severity (P = .583) interactions for unscheduled asthma visits.
To validate parents' reports of unscheduled visits, we examined the rate of agreement of parent-reported unscheduled asthma visits by using medical billing records from the Cincinnati Children's Hospital Medical Center. We found that 87% of parent-reported unscheduled asthma visits (714 of 824 visits) were in agreement with billing records for each 3-month interval.