Background: Many people in the subtropical Northern Rivers area of New South Wales, Australia, blame the pollen of Tibouchina tree, which flowers at the same time as ragweed, Bahia grass and Bermuda grass, for hayfever and asthma exacerbations during fall between March and May.
Objectives: To determine whether Tibouchina pollen is allergenic. To determine whether airborne ragweed pollen is present in this region for sufficient length of time and concentration to cause fall respiratory symptoms, and to determine if Bahia grass and Bermuda grass are associated with fall respiratory symptoms.
Methods: Pollen and Alternaria spores were monitored using a Burkard 7-day spore trap. Two hundred and six volunteers in the Northern Rivers area filled in questionnaires before skin prick tests (SPT) were performed with a panel of skin testing extracts.
Results: One hundred fifty-three (74.3%) subjects were atopic and reacted to one or more aeroallergens. Seventy were SPT positive to ragweed, OR 3.36 (CI 1.03 to 12.15) and 11 to Tibouchina (OR incalculable). Fifty of the 70 ragweed-positive subjects had fall hayfever or exacerbations of hayfever and/or asthma, OR 23.4 (CI 8.90 to 64.00). Eleven subjects were SPT positive to Tibouchina extract. There was a statistical association between Bermuda grass and hayfever, but not asthma OR 13.44 (CI 1.85 to 27.04).
Conclusions: Ragweed pollen was present for a sufficient length of time and concentration to sensitize and provoke fall hayfever and asthma exacerbations. Tibouchina pollen is an aeroallergen causing mild-to-moderate allergic symptoms in a few people. There is an association between Bahia grass and asthma in children, and between Bermuda grass and allergic rhinitis in adults.