Association of Indoor Nitrogen Dioxide Exposure With Respiratory Symptoms in Children With Asthma

Abstract

Belanger K, Gent JF, Triche EW, Bracken MB, Leaderer BP. Am J Respir Crit Care Med. 2006;173:297–303 PURPOSE OF THE STUDY. Chronic exposure to indoor nitrogen dioxide (NO2) may be a public health concern. The primary source of residential NO2 is gas-fueled cooking appliances. The authors’ objective was to examine associations of indoor NO2 exposure with respiratory symptoms among children with known asthma. STUDY POPULATION. Subjects were 728 children younger than 12 years with physician-diagnosed asthma living in Connecticut and southwest Massachusetts. All children had active asthma and had lived at the same address for at least 2 months before NO2 sampling. METHODS. At enrollment, a research assistant visited the home and recorded family ethnicity, housing characteristics (multifamily versus single family, number of rooms, water leaks, visible mold), presence of smoking in the home, and the use of household appliances fueled by natural gas. Mothers were also asked about number of days of respiratory symptoms experienced by the child and medications used for each month of the previous year. NO2 was measured in each home by using a Palmes tube placed in the main living area for 10 to 14 days after the enrollment visit. RESULTS. The mean concentration of indoor NO2 was 8.6 ppb in homes with electric ranges and 25.9 ppb in homes with gas stoves. The mean NO2 level measured in multifamily homes was 22.9 ppb, and the mean NO2 level in single-family homes was 10.2 ppb. Measured NO2 (>20 ppb) was associated with ethnicity: white families were least likely to have high exposures, and Hispanic families were the most likely. Among children living in multifamily housing, exposure to gas stoves and high levels of NO2 were associated with wheezing, shortness of breath, and chest tightness. For children in single-family homes, neither exposure to gas stoves nor to measured NO2 was associated with any respiratory symptom. CONCLUSIONS. The authors concluded that there is an association between exposure to high levels of indoor NO2 and respiratory symptoms in children with physician-diagnosed asthma. This association, however, was limited to children who lived in multifamily homes, probably because of the smaller size (and air volume) of the apartments. The authors also suggested a strong association of NO2 exposure with housing characteristics, lower socioeconomic status, and ethnicity. REVIEWER COMMENTS. This study demonstrated an association between increased NO2 levels and asthma symptoms of children in multifamily homes. The important potential confounders in the analysis should have been adequately dealt with in the logistic regression analysis used. The biological basis of the association is poorly understood, and the value of intervention to reduce exposure is speculative. Additional studies will be needed to clarify and confirm the association.