A randomized trial of dehumidification in the control of house dust mite

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Abstract
House dust mites (HDM) are sensitive to humidity. Few studies have adequately examined the potential of dehumidification in reducing HDM numbers. The study examined the effect of portable domestic dehumidifiers, and a behavioural programme to reduce humidity, on HDM counts and HDM allergen levels. A randomized controlled trial was undertaken. A total of 76 homes were allocated to three groups that received a portable domestic dehumidifier, a behavioural programme, or no intervention. Humidity, temperature, HDM counts (trap and vacuum samples), HDM allergen, and other details of the home environment were measured on four occasions over a period of 1 year. Interventions and measurements were concerned predominantly with one bedroom. There was a reduction in relative humidity in the dehumidifier group, but not the behavioural group. A decline in HDM trap counts was observed for all three groups. Change scores did not indicate that the dehumidifier group had a greater decline than the other groups. A secondary analysis examining presence or absence of HDM showed a shift from households having HDM at baseline to households not having HDM in the final round for some trap measures. Change score analysis indicated that this shift was greater in the dehumidifier group compared with other groups. The dehumidifier group did not show a greater decline in HDM allergen than that seen in the other two groups. Neither the dehumidifier nor the behavioural intervention had a major effect on HDM counts or allergen levels. However, the study did have a number of limitations relating to size, timing of intervention, and running of the dehumidifiers. The secondary data analysis may indicate some effect of dehumidification, but clearly this effect was small. There is a need for more information on the effects of reducing ambient humidity on the distribution of HDM within their habitats.

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