The abundance of house dust mites (Pyroglyphidae) in different home textiles in Europe, in relation to outdoor climates, heating and ventilation

In Europe, house dust mites of the family Pyroglyphidae are abundant producers of allergens in dwellings. Their prevalence in dwellings as well as their distribution among different types of home textiles vary in different localities in Europe. The main limiting factor for mite population growth is water activity. Water activity is closely related to relative humidity in the mite niche. Relative humidity in the mite niche is influenced by outdoor temperature and absolute air humidity, heating and ventilation. The mean January outdoor air temperature was determined. Based on outdoor temperatures and absolute air humidities, the length of heating season and length of mite population growth season for different home textiles were defined. These variables were validated with published data on mite abundance in mattresses and on floors in climatically distinct areas in Finland, Denmark, United Kingdom, The Netherlands, France, Switzerland, Italy and Poland. Length of mite population growth season - abbreviated to mite season - can be shortened by effective ventilation. Therefore, minimal required ventilation rates, to keep the relative humidity in the mite niche below the hygienic moisture limit for mite population growth, in European countries, were collected. No significant correlation was demonstrated between length of heating season and mite numbers in any of the home textiles. Between mean January outdoor air temperature and mite numbers in mattresses; and between length of mite season and mite numbers in mattresses, significant correlations were seen (Spearman rank correlation test, p <0.05). On floors, none of the climatic variables showed a significant correlation with mite numbers. Minimal required ventilation rates were found in Denmark and the Netherlands, only. In contrast to length of heating season, mean January outdoor air temperature and length of mite season in mattresses can predict the overall abundance of house dust mites in mattresses in a climatic area. To predict the overall mite burden on floors, the influence of outdoor climate should be examined in combination with soil and constructional factors. To shorten the length of the mite population growth season minimal required ventilation rates have to be known