Effect of electric heating carpet on house dust mites.

An electric heating carpet (EHC) that had been especially modified to produce a steady surface temperature of 45 to 50 degrees C was set up in the bedroom of an asthmatic patient, and the density of floor dust mites in this room was compared monthly for 2 years with that in two non-EHC control rooms. When the EHC was used during the mite-growing summer season, the monthly variation in mite density in the EHC room was almost parallel to that in the non-EHC rooms, with a preponderance of floor mites in the non-EHC rooms. In contrast, when the EHC was used during the winter season, the density of floor mites in the EHC room increased as compared with that in the non-EHC rooms, and the ratio of mite density in the EHC room to that in the non-EHC rooms was transiently reversed during this period.