Chauhan AJ, Inskip HM, Linaker CH. Lancet. 2003;361:1939–1944
Purpose of the Study.
Nitrogen dioxide (NO2) exposure has been linked to respiratory tract illness. This study examined the relationship between the level of personal exposure to NO2 and the severity of asthma exacerbations caused by respiratory viral infections.
The subjects were 114 asthmatic children, 8 to 11 years of age (63 male subjects and 51 female subjects).
The cohort of 114 children collected daily upper and lower respiratory tract symptom scores and peak expiratory flow (PEF) values for up to 13 months. During this time, NO2 collection tubes were worn on the children’s outer clothing, placed in the subjects’ bedrooms at night, and changed weekly. Symptom scores determined the likelihood of an upper respiratory tract infection and prompted the collection of nasal aspirates, for assessment of the presence of common respiratory viruses and atypical bacteria with reverse transcription-polymerase chain reaction assays. NO2 exposure levels were divided into tertiles of low (<7.5 μg/m3), medium (7.5–14 μg/m3), and high (>14 μg/m3). Exposure levels in the week before or after an upper respiratory tract infection were analyzed in relation to the severity of asthma in the week after an infection.
Two hundred nineteen episodes of upper respiratory tract infection occurred among 99 subjects. Lower respiratory tract symptom scores were increased and PEF values were decreased with increasing personal exposure to NO2 in the week before infection for all upper respiratory tract infections combined and for piconavirus and respiratory syncytial virus individually. There was no significant change in lower respiratory tract symptom scores or PEF values with high NO2 exposure in the week after infection.
Higher levels of NO2 exposure in the week before the beginning of a respiratory tract infection were associated with increases in the severity of resulting asthma exacerbations.
NO2 exposure may be derived from indoor sources, such as gas-burning stoves or wood-burning fireplaces. The levels of NO2 in this study were well within the standards for air quality safety. NO2 exposure itself, in the range experienced by the study cohort, was not associated with adverse symptom scores or lower PEF values. The highest levels of exposure were associated with worsening of asthma symptoms and decreased PEF values in the presence of upper respiratory tract infection. The results should be interpreted with caution, however, because there were no control aspirates from subjects with stable symptom scores and PEF values.