Association between grass, tree and weed pollen and asthma health outcomes in Adelaide, South Australia: a time series regression analysis

OBJECTIVES: We aim to establish daily risk estimates of the relationships between grass, tree and weed pollen and asthma health outcomes. DESIGN: Time series regression analysis of exposure and health outcomes using interaction by month to determine risk estimates all year round. SETTING: Metropolitan Adelaide, South Australia. PARTICIPANTS: Health outcomes for asthma are based on 15 years of hospital admissions, 13 years emergency presentations and ambulance callouts. In adults (≥18 years), there were 10 381 hospitalisations, 26 098 emergency department (ED) presentations and 11 799 ambulance callouts and in children (0–17 years), 22 114, 39 813 and 3774, respectively. OUTCOME MEASURES: The cumulative effect of 7 day lags was calculated as the sum of the coefficients and reported as incidence rate ratio (IRR) related to an increase in 10 grains of pollen/m(3). RESULTS: In relation to grass pollen, children and adults were disparate in their timing of health effects. Asthma outcomes in children were positively related to grass pollen in May, and for adults in October. Positive associations with weed pollen in children was seen from February to May across all health outcomes. For adults, weed pollen-related health outcomes were restricted to February. Adults were not affected by tree pollen, while children’s asthma morbidity was associated with tree pollen in August and September. In children, IRRs ranged from 1.14 (95% CI 1.06 to 1.21) for ED presentations for tree pollen in August to 1.98 (95% CI 1.06 to 3.72) for weed pollen in February. In adults, IRRs ranged from 1.28 (95% CI 1.01 to 1.62) for weed pollen in February to 1.31 (95% CI 1.08 to 1.57) for grass pollen in October. CONCLUSION: Monthly risk assessment indicated that most pollen-related asthma health outcomes in children occur in the colder part of the year, while adults are affected in the warm season. The findings indicate a need for year-round pollen monitoring and related health campaigns to provide effective public health prevention.