Changes in indoor allergen and fungal levels predict changes in asthma activity among young adults.

Background: Exposures to allergens are thought to be important risk factors for asthma. We conducted a longitudinal study of indoor allergen and fungal levels in Melbourne homes between 1996 and 1998 to examine the effect of changes in allergen exposure upon asthma and associated outcomes.

Methods: Participants were visited at home in 1996 (n=485) and 1998 (n=360), when dust and air samples were collected from their bedrooms and assayed for Der p 1, Fel d 1, ergosterol and fungal propagules. Subjects then attended the lung function laboratory to complete a questionnaire, spirometry, methacholine challenge and skin prick testing. The associations between the change in allergen levels and change in clinical outcomes were examined using multiple logistic and linear regression.

Results: Participants whose Cladosporium fungal exposure doubled had 52% greater odds of having had an attack of asthma in the last 12 months. A doubling of fungal exposure was also associated with 53% greater odds of developing atopy. A doubling of Fel d 1 floor levels was associated with 73% increased odds of doctor-diagnosed asthma. A doubling of Der p 1 levels in bed dust was associated with a 64% greater odds of persistent bronchial hyper-reactivity.

Conclusions: These findings provide evidence that changes in indoor levels of fungi and house dust mites can affect the risk of development and persistence of asthma and atopy in adults. Further studies are required to establish any benefit of sustained reductions in indoor allergen exposures, and to determine whether these effects are truly 'allergic' or because of immune stimulation in the airway through other less specific mechanisms.