Melbourne School of Population and Global Health - Theses
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ItemThe role of short-term grass pollen exposure in allergic disease and lung health( 2023-02)Background: Australia has one of the highest prevalence of allergic diseases. Although the mortality rate is low, allergic conditions are associated with significant burden. Environmental risk factors of allergic diseases include exposure to aeroallergens such as pollen. In Australia, temperate grass pollen is the primary seasonal aeroallergen. Research Gaps: Although it is well-established that temperate grass pollen can trigger asthma hospitalisations, its relationship with lung function and airway inflammation at a community level is understudied. Furthermore, no study to date has considered the short-term associations between pollen exposure and food allergy. Studies on selective populations have shown that eczema can be exacerbated with increasing ambient pollen exposure, but population-based studies are lacking. Moreover, the evidence on the potential effect modification by individual and environmental factors on the associations is scarce. Aim: I investigated the associations between short-term grass pollen exposure and lung function, airway inflammation, food allergy and eczema across different age groups within the community and identified potential effect modifiers of these associations. Methods: My doctoral research utilised a systematic review methodology and original data from large population-based cohorts: HealthNuts, The Melbourne Atopy Cohort Study (MACS) and the Tasmanian Longitudinal Health Study (TAHS). Grass pollen exposure was assessed either using daily concentrations or the season as a proxy measure of exposure. Where daily pollen data were available, exposure was investigated on the day of exposure (lag 0) and up to three days before (lag 3). Statistical modelling was performed accounting for the distribution of the model residuals, the functional form for the associations between the exposure and outcomes, and confounders. Interactions with individual and environmental factors were explored using likelihood ratio tests. Results: Research Question 1 – The systematic review showed that outdoor pollen exposure is an important risk factor for type-2 inflammation in the upper and lower airways in people with ever asthma and/or seasonal allergic rhinitis, but the evidence on lung function was limited (Chapter 3). Research Question 2 – Increasing grass pollen concentrations were associated with reversible obstructive lung function deficits in children with allergic disease, the greatest risk of exacerbation in food allergic children (Chapter 5). Research Question 3 – There was evidence of a relationship between increasing grass pollen concentrations, and subsequent airway inflammation (1-2 days after the exposure) and lung function deficits (2-3 days after the exposure). Adults and individuals with co-existing allergic diseases were especially vulnerable. (Chapter 6). Research Question 4 – Peak grass pollen season was associated with lower pre- and post-bronchodilator lung function in smokers with allergic respiratory disease, those exposed to higher traffic-related air pollution, with co-existing allergic diseases or with poor adherence to inhaled corticosteroids (Chapter 7). Research Question 5 – Persistent grass pollen exposure over 4 days was associated with increased odds of food skin-prick test reactivity and eczema flares in children, but the impact was greater if peanut allergy was already present (Chapter 8). Conclusions: My work has significant public health and clinical implications. Notably, there was evidence of association between ambient grass pollen exposure, and subsequent lung function impairment and airway inflammation in both children and adults, mainly on the large and medium-small sized airways. There was also an association with post-bronchodilator measures in middle-aged adults, implying that the pathology in this age group may be distinct from classic, reversible asthma. Furthermore, the negative health impacts of short-term grass pollen exposure may extend to non-respiratory allergic diseases such as food allergy and eczema. Lastly, I identified high-risk groups who were more vulnerable to grass pollen, which were adults, smokers with allergic respiratory disease, those exposed to higher traffic-related air pollution, with allergic co-morbidities or with poor adherence to inhaled corticosteroids.