House-dust mite content in mattresses in relation to residential characteristics and symptoms in atopic and nonatopic children living in northern Norway

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Abstract
The occurrence of house-dust mites (HDMs) was investigated in the mattresses of 19 children previously found to be skin prick test (SPT) positive to HDM and in 19 nonatopic children derived from an extensive survey of 424 schoolchildren, all living in northern Norway. Domestic mites were counted and identified microscopically. Mite counts ranging from 10 to 1800 mites per gram mattress dust were found in 10 of the 19 HDM-sensitized children compared to none in the control group, corresponding to an odds ratio of more than 20. Of the 540 domestic mites found, 70 were identified by species. Dermatophagoides pteronyssinus (Dpt) was the only HDM species identified (64 mites), while five were storage mites and one was a Tarsonemus species. Positive radioallergosorbent tests (RAST) to Dpt were demonstrated in 9/10 children with and in 5/9 without mite infestation compared to none in the control group. Elevated IgE levels were also found more frequently in children with mite-infested mattresses than in those without. IgE levels were within normal levels in all 19 children in the control group. Latent atopy was found in four children, three with and one without mite infestation. There was no correlation between the concentration of mites and the degree of sensitization. Poor ventilation, increased humidity, and water leak(s) were associated with the presence of domestic mites in mattresses. As HDM growth is highly dependent on humidity and microhabitat, it should be possible to avoid HDM exposure and allergy in this region.