Microgeographic factors and patterns of aeroallergen sensitisation.

OBJECTIVE: To examine patterns of airborne allergen (aeroallergen) sensitisation in the Greater Sydney area (Sydney), and their relationships with climate, coastal proximity and environment (urban v regional).

DESIGN, SETTING, PARTICIPANTS: Retrospective cross-sectional study of patients who underwent aeroallergen skin prick testing at three Sydney allergy clinics, January 2001 - October 2014.

MAIN OUTCOME MEASUREMENTS: Proportions of patients sensitised to specific aeroallergen types; relationships between sensitisation patterns and climate and geography.

RESULTS: Of 1421 patients who met the selection criteria (mean age, 28.3 years [SD, 21.3]; 53.3% were female), 1092 (76.8%) were sensitised to at least one aeroallergen. Those living less than 15 km from the coast were less commonly sensitised to cockroach (< 15 km, 15.1%; 15-30 km, 40.0%; > 30 km, 39.7%; P < 0.001) and grass aeroallergens (< 15 km, 36.5%; 15-30 km, 52.2%; > 30 km, 58.1%; P < 0.001) than patients further inland; the same applied to mould, weed and tree aeroallergens. Subtropical grass sensitisation was more common in temperate/warm summer climates (about 50%) than in temperate/hot summer (27.1%) or subtropical climates (15%) (P < 0.001), and less common in urban (36.7%) than in regional areas (54%; P = 0.014). 72.4% of grass-sensitised patients were co-sensitised to both temperate and subtropical grasses. A selected ten-aeroallergen skin prick test panel identified 98.5% of atopic patients in this Sydney sample.

CONCLUSIONS: Environmental and geographic factors are associated with different patterns of allergic sensitisation in Sydney. Extensive co-sensitisation to subtropical and temperate grasses has implications for immunotherapy in Australia, where most currently available therapies are based on formulations directed at temperate grasses only.