Increased ventilation rate as way to reduce the exposure to house dust mites and improve the health of asthmatic children - an intervention design

International field studies have documented that indoor air quality is unsatisfactory in many buildings. The overall hypothesis of this project is that improving the indoor environment in dwellings can improve health and reduce suffering from indoor related diseases such as allergy and asthma that have shown a marked increase in incidence all around the world during last decades.The purpose of this study is to investigate the effect of increased ventilation and expected lower exposure to house dust mites on symptoms and medication intake among asthmatic children. This will be done by installing balanced mechanical ventilation systems in 80 single-family houses. Half of the houses will be equipped with an effective ventilation system increasing air change rates from normal to approximately 3 h-1. A fake ventilation system will be installed in the other half of the houses. Primary subjects for the intervention are children with verified asthma and allergy to house dust mites. Children will be exposed to titration of medication prior to the study and randomly distributed to groups with fake or controlled ventilation system. The intervention will last for nine months in each house and will be blinded to both participants and paediatricians. Several physical and chemical parameters will be monitored including: air change rate, concentrations of different sizes of particles, air temperature, relative humidity, carbon dioxide concentration, number of house dust mites, and relevant allergens concentration. Health outcomes will be evaluated in cooperation with paediatricians by means of clinical examinations, measurements of biomarkers, medication intake and questionnaires.