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

Abstract

Objective

Triple-crossover randomized controlled intervention trial to test whether reduced exposure to household NO₂ or fine particles results in reduced symptoms among children with persistent asthma.

Methods

Children (n = 126) aged 5–11 years with persistent asthma living in homes with gas stoves and levels of NO₂ 15 ppb or greater recruited in Connecticut and Massachusetts (2015–2019) participated in an intervention involving three air cleaners configured for: (1) NO₂ reduction: sham particle filtration and real NO₂ scrubbing; (2) particle filtration: HEPA filter and sham NO₂ scrubbing; (3) control: sham particle filtration and sham NO₂ 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 NO₂ was lower (by 4 ppb, p < .0001) for NO₂-reducing compared to control or particle-reducing treatments. NO₂-reducing treatment did not reduce asthma morbidity compared to control. In analysis controlling for measured NO₂, there were 1.8 (95% CI −0.3 to 3.9, p = .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 NO₂ 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 NO₂ and fine particles is complicated and further research is warranted.

Registration Number

NCT02258893.

Keywords:

• Children
• asthma symptoms
• persistent asthma
• household NO₂
• gas stoves
• air cleaner
• RCT

Acknowledgements

We gratefully acknowledge our Harvard colleagues Stephen T. Ferguson and J. M. Wolfson for their engineering and laboratory expertise in the development phase of this project; and the support and encouragement provided during the trial by our Data Safety Monitoring Board: Drs. George O’Connor, Meyer Kattan and Judith Goldberg.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported by the National Institutes of Health/National Institute of Environmental Health Sciences (NIH/NIEHS) under Grant R01ES023505-05; and the Connecticut Department of Public Health (CTDPH) under Contract RFP# 2016–0087.