THE MELBOURNE HOUSE-DUST MITE STUDY - LONG-TERM EFFICACY OF HOUSE-DUST MITE REDUCTION STRATEGIES

Background: Asthma severity among mite-sensitized individuals appears to be related to the degree of mite allergen exposure. Objectives: The objective of this study was to assess the longterm effectiveness of m ite avoidance measures in the homes of asthmatic children in Melbourne , Australia. Methods: The concentration of house dust mite allergen (D er p 1) was measured on the child's mattress surfaces and bedroom floo rs in 85 homes on 10 occasions over a 16-month period. After the first three visits, all mattresses were covered with a semipermeable encase ment, and carpeted bedroom floors were randomly allocated to regular a pplications of a placebo or an ''anti-mite'' shampoo.Results: The conc entration of Der p 1 recovered was initially high in the carpeted bedr ooms (n = 66) (41.1, 95% confidence interval, 30.7 to 55.0 mu g Der p 1 per gm) and mattresses (n = 85) (39.6, 27.2 to 57.7). During the ini tial observation period the concentration of mite allergen fell in the treatment, placebo, and parental control groups. During the seven tre atment periods, no differences were seen between the Der p 1 concentra tions in the groups using the ''anti-mite'' shampoo, placebo shampoo, or the parental control group (e.g., at visit 4; 12.6, 8.2 to 19.5; 14 .8, 8.6 to 25.1; and 12.0, 8.1 to 17.7 mu g/gm, respectively). In cont rast, the concentration of Der p 1 in samples from uncarpeted floors a nd mattress encasements was low (4.1, 2.1 to 8.0 mu g/gm and 4.2, 2.6 to 6.5 mu g/gm, respectively) and insufficient dust for analysis was f requently obtained from these sites. Conclusions: There was no additio nal benefit from the use of an ''anti-mite'' shampoo. The absence of c arpets and the use of mattress encasements was a useful long-term stra tegy for mite allergen avoidance.