House dust mite allergen levels in carpeted sleeping accommodation are higher in private houses than public places

Objective: To compare mite allergen levels in carpeted sleeping accommodation in private dwellings and public places. Methods: The concentration of Dermatophagoides pteronyssinus Group 1 allergen in house dust was measured in mattresses and bedroom floors in 12 homes, 5 hotels, 11 child care centres and a university hall of residence. Indoor temperature and relative humidity were also measured. A questionnaire clarified details regarding the age of the building, age of the carpet, method and frequency of cleaning, frequency of room use and use of air-conditioning. Results: Median allergen levels in mattresses and carpets in private homes (21.1 and 20.6 mug/g dust, respectively) were significantly higher than in public places (2.5 and 3.1 mug/g, respectively; P < 0.0001). Mean relative humidity was significantly higher in private houses (68.5%; 95% CI 67.2-69.3%) than in public places (56.4%; 95% CI 52.7-60.1%; P < 0.0001). Conclusions: Carpeted sleeping accommodation in public places has lower house dust mite allergen levels than private houses. Lower levels of relative humidity may be an important component of the explanation.