Clinical significance of aero-allergen identification in the western Cape

Positive identification and documentation of the seasonal variation of aero-allergens and the immune responses to them has important implications for the timing of allergen avoidance measures and the selection of patients suitable for immunotherapy. The relative abundance of aero-allergens in the Cape Peninsula during 1984-1987 was measured by continuous volumetric air sampling, using a Burkard spore trap. Mould spore counts of greater than 3,000 spores/m3 were found throughout the year and were only exceeded by pollen grains in the months of September and October (range 4,800-7,400 spores/m3). Gramineae and Compositae spores were found perennially in significant numbers. Pollen from allergenic trees peaked at fixed times each year: oak in August; plane in September and pine between August and October. Grasses found on the Peninsula include sweet vernal, Bermuda grass, rye grass, common reed, Johnson grass, brome grass, canary grass, annual meadow and kikuyu. In vivo skin tests in 209 children with known allergic disease were positive to Dermatophygoides pteronyssimus (73%), South African grasses (38%), tree pollens (22.4%), flower and weed pollens (19.6%), cat (27%), dog (12%) and feathers (18.6%). One-third of the 1,372 children screened at Red Cross War Memorial Children's Hospital Allergy Service had positive specific IgE responses to environmental allergens. Investigation of 62 children possibly allergic to grass using the radio-allergosorbent test revealed positive results in 25 (41%). Of these, 92% were positive to Timothy grass, a grass not occurring in the Cape Peninsula. Knowledge of cross-reactivity profiles for local allergens minimises the number of tests required in allergy diagnosis.