Year-round housedust mite levels on the highveld

Objective. To determine the levels of the allergen DerP1, attributable to t he house-dust mite (HDM) Dermatophagoides pteronyssinus. Design. A four-season study conducted during 1994/95, sampling mattresses a nd carpets in the main bedrooms of suburban homes. Setting. Thirty randomly selected homes in the Edenvale area, occupied by b oth black and white families living under similar socio-economic conditions in comparable environments. Results. All homes tested positive for the allergen, and in 20% HDM levels exceeded levels recognised as 'safe' in terms of respiratory allergy, i.e. 2 mu g/g of dust. Once mites were established in a home, they remained for months thereafter. The considerable seasonal variation recorded in HDM leve ls could not readily be explained. Conclusion. The HDM is extremely sensitive to minimal variations in microcl imate. Its year-round presence is of concern on the Highveld. Infestation l evels below 2 mu g/g of dust, until recently considered the critical point for sensitisation, may be significant triggers of symptoms.