The effect of local cropping activities and weather on the airborne concentration of allergenic Alternaria spores in rural Australia

Atopy to the fungus Alternaria is strongly associated with respiratory disease. The prevalences of asthma and of allergy to Alternaria are high amongst children living in rural towns of south-eastern Australia. In such towns, airborne allergenic spores have been proposed to arise from nearby crops, but this has not been tested and crops are unlikely to be the only sources of Alternaria. We sought to identify sources and factors that influence concentrations of spores of Alternaria detected in rural towns, Over two years, we sampled spores in two towns (Wagga Wagga and Moree, New South Wales, Australia), in nearby wheat and cotton crops during harvesting and control periods, in a cotton gin and a grain shed. Alternaria was present in both towns throughout the study, and above the crops, at the gin and grain shed. Daily and annual concentrations were amongst the highest recorded worldwide and peaks persisted for six months in Wagga Wagga and ten months in Moree. Crop maturation affected the spore load in the air more than the actual days of harvest, Regression analysis showed that the overall spore concentrations above towns correlated with those above crops. Variables of rainfall and maximum temperature correlated with concentrations in both towns, and additionally wind direction in Wagga Wagga. In conclusion, crops and produce handling released spores into the air that reached nearby rural towns, with peaks in spore concentrations following warm temperatures and recent rainfall.