The effects of allergens in outdoor air on both atopic and nonatopic subjects with airway disease

BACKGROUND

Reports on air pollution and asthma exacerbations have been inconsistent, although effects of airborne allergen can be spectacular. With no generalized test for allergen in air, it is not known how far allergen is responsible for nonepidemic exacerbations of the disease.

METHODS

Two hundred and ninety-seven patients using bronchodilators aged 18-64 years attending a London practice provided serum samples and were asked to report any acute respiratory events over the coming months. Small particles with a mean aerodynamic diameter <10 microm (PM(10)) were collected using a high volume sampler on the roof of the practice. The ability of airborne particles to bind IgE from the patients was compared for particles sampled on the weekend before their reported exacerbation with particles sampled on the weekend 2 weeks before or after.

RESULTS

Exacerbations were associated with a 25% increase in IgE binding to particles collected on the previous weekend compared with the control weekends (95% confidence interval: 10-43%; P = 0.00089). This increase was not higher in patients with positive skin tests or in those sensitized to grass or tree pollens.

CONCLUSIONS

Airborne allergen is an important cause of exacerbations even in those with 'intrinsic' asthma. It is important to identify the allergens responsible, as some of these may be controllable. Interpretation of associations of asthma exacerbations with other air pollutants is difficult in the light of these findings.