Effectiveness of measures depends on stage of asthma

EDITOR—In their meta-analysis G⊘tzsche et al concluded that measures to control house dust mites are not clinically effective in patients with asthma who are sensitive to mites.1 In the accompanying editorial Strachan commented that this was probably because several control measures used in the included studies did not result in a (relevant) reduction in concentrations of house dust mite allergens. Improvements in clinical condition are consequently not to be expected. Some studies in the meta-analysis found clinical effects while others did not.1 This may not be a result of effectively reducing allergen concentrations but of measuring different groups of asthmatic patients in different stages of disease. We believe that early treatment of mild asthma might have more impact than treating mild to moderate asthma.

We investigated the (clinical) effects of a combined allergen avoidance strategy (use of covers on mattresses and bedding that are impenetrable to house dust mites and use of benzyl benzoate (Acarosan) on living room and bedroom floors) in two groups of subjects allergic to house dust mites. One group had some early signs of asthma2 but no diagnosis and the other had a confirmed diagnosis of mild asthma.3 In the subjects without diagnosed asthma, peak flow rates and symptom scores stabilised during follow up (figure (top)), suggesting that the onset of asthma may have been delayed. The subjects with mild asthma showed no clinical effects during the same follow up (figure (bottom)), although allergen concentrations were reduced, especially on mattresses (10-fold, P=0.0001).3

We hypothesise that allergen avoidance has more impact as an early preventive measure than as treatment of mild asthma. In …