House dust mite exposure in asthmatic and healthy children: the difference is carpeting

To determine whether house dust mite (HDM) exposure in living rooms and bedrooms is higher in asthmatic children than in those of age and sex matched healthy children, living in the same area.

Types of floor-coverings were recorded and dust samples were collected by vacuum cleaning the total area of living rooms and bedrooms; Der p I and Der p II per gram fine dust concentrations were assessed. Twenty-five asthmatic children (RAST HDM > or = class 3, age 6-12 years) and 25 healthy children participated in the study.

The frequency of cleaning and prevalence of smooth floor-coverings in bedrooms of asthmatic children were significantly higher. There were no differences in living rooms in this respect. The amount of fine dust/m2 floor space was significantly lower in bedrooms of asthmatic children. Concentrations of HDM were low and no differences in Der p I and Der p II concentrations were observed between the two groups (asthmatic children: Der p I living room: 1.1 (0.04-59.4 micrograms/g), bedroom: 0.5 (below detection--19.3 micrograms/g); nonasthmatic children: Der p I living room: 1.4 (below detection--27.5 micrograms/g), bedroom: 0.9 (below detection--68.8 micrograms/g. Smooth floor coverings contained significantly less fine dust, Der p I, and Der p II than carpeted floors.

Low HDM concentrations are a general finding in Dutch dwellings in the present generation of children. We observed a higher cleaning frequency, and more smooth floor coverings in bedrooms of asthmatic children than of healthy children, yet HDM concentrations were not significantly different. The latter can be explained by the observation that only 40% of the asthmatic children had smooth floor coverings in their bedrooms. Smooth floor coverings contain less fine dust and lower concentrations of Der p I and Der p II than carpeted floors.