Respiratory viruses are considered to be one of the main triggers of asthma exacerbations in children. Exposure to nitrogen dioxide (NO₂), a common environmental pollutant, has been linked to respiratory symptoms in both children and adults. Whether high individual exposure to NO₂ increases the severity of asthma exacerbations caused by common viruses remains unclear.

This prospective study looked at 114 asthmatic children, all living in non-smoking homes, between the ages of 8 and 11 years. Participants recorded upper and lower respiratory tract symptoms and peak flow measurements for up to 13 months. In addition, weekly personal NO₂ exposure was measured with the aid of diffusion tubes kept on clothing during the day. At the onset of a respiratory tract illness nasal aspirates were taken which were subsequently screened for common viruses plus atypical bacteria. For all viruses together and respiratory syncytial virus alone, significant increases in respiratory tract symptoms were associated with a greater exposure to NO₂ in the week before infection. In terms of reduction in peak flow, there was an association with greater NO₂ exposure in the week before infection with picornavirus alone.

This study concluded that high personal exposure to NO₂ may be associated with an increase in the severity of virus induced asthma exacerbations. These findings should make the medical, scientific, and political communities aware of potential health and financial benefits when air pollution measures are employed.