The goal was to test the effects of high-efficiency, particulate-arresting (HEPA) air cleaners on unscheduled asthma visits and symptoms among children with asthma exposed to secondhand smoke.


We enrolled 225 eligible children who were 6 to 12 years of age, had physician-diagnosed asthma, and were exposed to ≥5 cigarettes per day. We conducted a double-blind, randomized trial. Children were assigned randomly to receive 2 active or inactive HEPA air cleaners.


Of 225 enrolled children, 110 (49%) were assigned to the intervention group and 115 (51%) to the control group; 215 (95%) completed the trial. During the trial, there were 42 fewer unscheduled asthma visits among children in the intervention group (18.5% [95% confidence interval: 1.25%–82.75%]; P = .043), compared with those in the control group, after adjustment for baseline differences. There was a significant difference in the reductions of levels of particles of >0.3 μm according to group assignment; there was a 25% reduction in particle levels in the intervention group, compared with a 5% reduction in the control group (P = .026). There were no significant differences in parent-reported asthma symptoms, exhaled nitric-oxide levels, air nicotine levels, or cotinine levels according to group assignment.


These results hold promise for using HEPA air cleaners as part of a multifaceted strategy to reduce asthma morbidity, but further research is necessary before they can be recommended routinely for the medical management of asthma.

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