House dust mite avoidance measures improve peak flow and symptoms in patients with allergy but without asthma: a possible delay in the manifestation of clinical asthma?

Asthma caused by allergy to house dust mite is a growing problem. Patients with allergy who do not have asthma (yet) might develop asthma depending on exposure to precipitating factors. We sought to determine whether house dust mite avoidance measures have an effect on the development of asthma. Patients with allergy (n = 29) who had no diagnosis of asthma (FEV1 of 99.1% +/- 10.6% of predicted, peak flow variability of 5.21% +/- 3.41%, reversibility of FEV1 after 400 microg salbutamol of 3.92% +/- 3.75% according to the reference values) were randomly allocated (subjects blinded) to a treatment (n = 16) and a placebo group (n = 13). House dust mite avoidance treatment consisted of applying Acarosan (Allergopharma, J. Ganzer KG, Hamburg, Germany) (the placebo group used water) to the floors (living room, bedroom), and the use of covers for mattresses and bedding that were impermeable to house dust mite (the placebo group used cotton covers for mattresses only). We tested whether the intervention had an effect on peak flow parameters and asthma symptom scores during 6 weeks of treatment. Significant improvements were seen in the treatment group in symptom scores (Borg score) for disturbed sleep, breathlessness, wheeze, and overall symptom score. Slight but statistically significant improvements in peak flow (morning, evening, and variability) were seen in the treatment group also. No significant changes were seen in the placebo group. Although this study is not long enough to study the development of asthma, the results indicates that house dust mite avoidance measures had an effect on peak flow parameters and asthma symptoms in patients with allergy but without asthma. These findings might implicate that a shift in developing clinically manifest asthma could be achieved with house dust mite avoidance measures. To give a better answer to whether preventing the development of asthma is possible, larger studies with a longer follow-up period are necessary.