Childhood asthma and household exposures to nitrogen dioxide and fine particles: a triple-crossover randomized intervention trial.

Objective: Triple-crossover randomized controlled intervention trial to test whether reduced exposure to household NO or fine particles results in reduced symptoms among children with persistent asthma.

Methods: Children ( = 126) aged 5-11 years with persistent asthma living in homes with gas stoves and levels of NO 15 ppb or greater recruited in Connecticut and Massachusetts (2015-2019) participated in an intervention involving three air cleaners configured for: (1) NO reduction: particle filtration and NO scrubbing; (2) particle filtration: HEPA filter and NO scrubbing; (3) control: particle filtration and NO scrubbing. Air cleaners were randomly assigned for 5-week treatment periods using a three-arm crossover design. Outcome was number of asthma symptom-days during final 14 days of treatment. Treatment effects were assessed using repeated measures, linear mixed models.

Results: Measured NO was lower (by 4 ppb,  < .0001) for NO-reducing compared to control or particle-reducing treatments. NO-reducing treatment did not reduce asthma morbidity compared to control. In analysis controlling for measured NO, there were 1.8 (95% CI -0.3 to 3.9,  = .10) fewer symptom days out of 14 in the particle-reducing treatment compared to control.

Conclusions: It remains unknown if using an air cleaner alone can achieve levels of NO reduction large enough to observe reductions in asthma symptoms. We observed that in small, urban homes with gas stoves, modest reductions in asthma symptoms occurred using air cleaners that remove fine particles. An intervention targeting exposures to both NO and fine particles is complicated and further research is warranted.

Registration Number: NCT02258893.