Background: It has been hypothesized that changes in heating systems and insulation of homes in developed countries have generated an indoor climate favorable to organisms that excrete allergens inducing sensitization and allergic disease. The purpose of this study was to determine the influence of the installation of highly insulated windows and central heating systems on indoor climate, and mite-allergen (Der f 1) and mold spore concentrations.
Methods: The bedrooms of 98 apartments were examined before and 7 months (mean) after installation of insulated windows and central heating systems. The air-exchange rate, temperature, and humidity were measured. In settled dust on carpets and mattresses, the number of colony-forming mold spores and the Der f 1 concentration were determined. The inhabitants completed a questionnaire about their lifestyles and housing conditions.
Results: The air-exchange rate decreased from geometric mean 0.73 to 0.52 per hour (P=0.029). Temperature (mean 13.4 vs 17.5 degrees C, P<0.001), and absolute humidity (mean 4.6 g vs 6.2 g H2O/kg air, P<0.001) increased. Relative humidity remained nearly unchanged (mean 47.6 vs 49.1%). Der f 1 concentrations on carpets (geometric mean 0.65 vs 1.28 microg/g dust, P < 0.001) and mattresses (geometric mean 1.56 vs 2.40 microg/g, P=0.002) increased. Among the fungi that were analyzed, only the thermotolerant species Aspergillus fumigatus increased (geometric mean 20 vs. 60 colony-forming units/g carpet dust, P = 0.02).
Conclusions: The findings of this study suggest that the installation of insulated windows and central heating systems is associated with an increase of Der f 1 concentrations in carpet and mattress dust and of A. fumigatus in carpet dust in apartment bedrooms.