To investigate the year-to-year variation of mite antigen density (Der p I, Der f1) in dust from mattresses and the relevance of residential factors for antigen load, information derived from an epidemiologic study including two surveys carried out in the households of a cohort of elementary school children (n= 1291) was analysed.
When considering residences with measurements taken in both years in question (n= 1050), rank-correlation indicated a predominance of stability for both antigens (Der p I: rs= 0-82, p=0.0001; Der f I: rs=0.72, P= 0.0001), Using multiple regression analyses, significant associations between antigen concentrations and a variety of residential factors were found. Use of a blanket of animal hair, use of a cover or underblanket, wet spots in the bedroom, higher relative humidity and a low storey level were significantly associated with increased concentrations of Der p I, whereas inverse relationships between this antigen and room temperature, number of persons per m2 as well as use of underfloor heating were seen. Regarding Der f I, older mattresses, use of a cover or underblanket, higher weight of sampled dust, high educational level and higher ratio of inhabitants per m2 were significantly associated with increased concentrations of the antigen. On the other hand, lower Der f I concentrations were found when interior sprung mattresses were used and when the mattress was ‘treated regularly’.
In conclusion, two measurements, 1 year apart from each other, show that stability of mite antigen concentrations predominated. Our data suggest that allergic patients should be advised against living in lower storeys and damp homes and to use a newer or encased mattress and to give preference to a residence with underfloor heating.