Objective. To determine the levels of the allergen DerPl, attnbutable to the house-dust mite (HDM) Dermatophagoides pteronyssinus.Design. A four-season study conducted during 1994/95, sampling mattresses and carpets in the main bedrooms of suburban homes.Setting. Thirty randomly selected homes in the Edenvale area, occupied by both 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 ug/g of dust. Once mites were established in a home, they remained for months thereafter. The considerable seasonal variation recorded in HDM levels could not readily be explained.Conclusion. The HDM is extremely sensitive to minimal variations in microclimate. Its year-round presence is of concern on the Highveld. Infestation levels below 2 JIg/g of dust, until recently considered the critical point for sensitisation, may be significant triggers of symptoms
