• Andrew W Kam, Winnie Wy Tong, Jenna M Christensen, Constance H Katelaris, Janet Rimmer, and Richard J Harvey.
• University of New South Wales, Sydney, NSW andrew.kam@hotmail.com.
• Med. J. Aust. 2016 Oct 3; 205 (7): 310-5.

ObjectiveTo 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, ParticipantsRetrospective cross-sectional study of patients who underwent aeroallergen skin prick testing at three Sydney allergy clinics, January 2001 - October 2014.Main Outcome MeasurementsProportions of patients sensitised to specific aeroallergen types; relationships between sensitisation patterns and climate and geography.ResultsOf 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.ConclusionsEnvironmental 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.

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