A PILOT-STUDY OF THE EFFECT OF MECHANICAL VENTILATION AND HEAT-EXCHANGE ON HOUSE-DUST MITES AND DER-P-1 IN NEW-ZEALAND HOMES

We have examined the effect of reducing relative humidity (RH), with i nbuilt mechanical ventilation and heat-exchange (MVHE) units, on house -dust-mite (HDM) counts and allergen levels, in a pilot study of 10 We llington dwellings. Recent international prevalence studies in adults and children have confirmed a high prevalence of asthma in New Zealand . Sensitivity to HDM is common among the general population, and HDM i s the major allergen associated with asthma. Recent studies of allerge n levels have confirmed high concentrations of Der p 1 in the domestic environment. While humidity was significantly reduced in those dwelli ngs fitted with ventilation units, no systematic effect on mites or De r p 1 was observed during the study period. When the reductions in hum idity were examined in the context of the time spent below the critica l equilibrium humidity (CEH), the intervention led to RH values below the CEH for only 39% of the total of 24-h periods for which measuremen ts were made. Reducing RH by means of MVHE in New Zealand domestic dwe llings does not lower humidity sufficiently, or long enough, to have a ny measurable effect on HDM populations.