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Year-round housedust mite levels on the Highveld
A Cadman1, R Prescott, P C Potter
1Bernard Price Institute, University of the Witwatersrand, Johannesburg.
Objective:
To determine the levels of the allergen DerPI, attributable 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 micrograms/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.
Conclusions:
The HDM is extremely sensitive to minimal variations in microclimate. Its year-round presence is of concern on the Highveld. Infestation levels below 2 micrograms/g of dust, until recently considered the critical point for sensitisation, may be significant triggers of symptoms.