Childhood health outcomes associated with air pollution in early life: investigating the role of exposure intensity and duration
Creators: name: Ziou, Myriam
Publisher: name: University of Tasmania
Year: 2024

description: <b>Background</b> <br>Particulate air pollution is a major cause of morbidity and mortality, and young children are particularly vulnerable to its adverse effects. Increasing knowledge has been gained in the last decades on the consequences of exposure to background ambient levels of fine particulate matter (PM<sub>2.5</sub>) on children’s health. However, the evidence on the effects, especially long-term, of emissions from extreme air pollution events, such as landscape fires, is not as robust. <br>In the aftermath of a fire lasting six weeks in the Hazelwood open-cut brown coal mine in the summer of 2014 in Victoria, the Latrobe Early Life Follow-up (ELF) Study was set up to investigate its long-term health consequences in children exposed to the smoke during pregnancy or infancy. This pollution event affected a population of nearly 75,000 and provided a natural experiment allowing to contrast exposure in early life to air pollution to an episodic extreme event and to otherwise low levels of day-to-day air pollution. The extreme event also provided the opportunity to compare outcomes associated with prenatal and early postnatal exposure windows. <br><b><i>Aims of the thesis </i></b><br>1. To review and pool together the existing literature on the relationship between exposure to particulate matter and the occurrence of upper respiratory tract infections (URTIs) in children (Chapter Two) <br>2. To determine if exposure to particulate matter in early life from a coal mine fire and/or from ambient sources are associated with increased hospital care utilisation (Chapter Three) <br>3. To determine if exposure to particulate matter in early life from a coal mine fire and/or from ambient sources are associated with primary and pharmaceutical care (Chapter Four) <br>4. To determine if exposure to particulate matter in early life from a coal mine fire and/or from ambient sources are associated with subclinical markers of allergic sensitisation (Chapter Five) <br><b><i>Methods</i></b> <br>To address Aim One, a systematic review and meta-analysis on exposure to outdoor particulate air pollution and URTIs in childhood and adolescence was undertaken. Published relevant articles were extracted from six databases, and the studies respecting prespecified inclusion and exclusion criteria were assessed for quality and risk of bias using a combination of validated tools. Meta-analyses were performed for the comparable short-term studies of time-series or case-crossover designs, while the remainder of studies were summarised in a narrative analysis. <br>To address Aim Two and Aim Three, the deidentified ELF data linkage cohort was utilised to investigate the relationship between exposure <i>in utero</i> and during infancy to PM<sub>2.5</sub> emissions from the Hazelwood mine fire and/or from chronic background sources, and healthcare utilisation following the event. Exposure estimates for cumulative fire-related PM<sub>2.5</sub> were obtained from a prognostic meteorological and pollutant dispersion model, while annual ambient PM<sub>2.5</sub> concentrations were estimated by a satellite-based land-use regression model. Both exposures were assigned at the birth address. For Aim Two, logistic regression was used to estimate associations with hospital admissions and emergency department (ED) presentations in the first year of life (exposure <i>in utero</i>) or the year after the fire (exposure &lt;1 year old). Continuous exposure-response was estimated with multiple regression, while exposure groups were compared with inverse probability weighting using propensity scores. For Aim Three, quasi-Poisson models were used to estimate associations with general practitioner (GP) attendances and prescribed medications dispensed before age two (exposure <i>in utero</i>) or in the two years after the fire (exposure &lt;2 years old). <br>To address Aim Four, the relationship between exposure <i>in utero</i> and during infancy to PM<sub>2.5</sub> emissions from the fire and/or from chronic background sources and subsequent allergic sensitisation was examined in the prospective identified ELF cohort. Exposure estimates for fire-related PM<sub>2.5</sub> were obtained from a prognostic meteorological and pollutant dispersion model and based on reported movements during the event, while annual ambient PM<sub>2.5</sub> concentrations were estimated at the birth address using a satellite-based land-use regression model. Total immunoglobulin E (IgE) and specific IgE for seven aeroallergens were measured seven years after the fire. Logistic regression was used to estimate associations with sensitisation to dust, cat, fungi, and grass, while linear regression was used to estimate associations with total IgE levels. <br><b><i>Results</i></b> <br>The systematic review and meta-analysis (Chapter Two) of 34 studies found some evidence of a link between particulate air pollution and URTIs. The meta-analyses showed there were short-term associations between health services utilisation for URTIs and both PM<sub>2.5</sub> and PM<sub>10</sub>, albeit slightly stronger for PM<sub>10</sub>. The narrative review found mixed results for both those pollutants, but the four studies investigating total suspended particles found a positive relationship with symptoms or medical visits. However, there was a large heterogeneity across methods and results, and evidence on long-term associations was overall scarce. <br>In Chapter Three, exposure <i>in utero</i> to fire-related PM<sub>2.5</sub> was associated with increased ED presentations for allergies or skin rash, while children exposed during infancy were at higher risk of visiting the ED for respiratory and/or infectious outcomes. Longer term exposure to higher levels of ambient PM<sub>2.5</sub> in early life was associated with increased ED presentations and hospital admissions for infectious outcomes, as well as overall ED presentations. <br>In Chapter Four, there was evidence of an association between exposure <i>in utero</i> to fire-related PM<sub>2.5</sub> emissions and systemic steroids dispensed, while exposure during infancy was linked to an increase in antibiotics dispensing, as well as a temporary increase in GP attendances and a delayed increase in steroid skin creams dispensing. Longer term exposure to ambient PM<sub>2.5</sub> in early life was also associated with increased GP attendances and antibiotics dispensed. <br>In Chapter Five, no association was found between exposure to fire-related PM<sub>2.5</sub> at any stage and markers of allergic sensitisation. Conversely, children whose residence at birth were in areas with higher levels of ambient PM<sub>2.5</sub> had an increased chance of being sensitised to dust seven years after the fire. <br><b><i>Conclusions</i></b> <br>This thesis provided deeper understanding of the long-term associations between exposure in the prenatal and early postnatal periods to both high levels of air pollution from an extreme medium-term event and modest levels from background ambient sources, and health outcomes of a range of severity. In both cases, there was evidence of increased allergic and infectious outcomes. The findings of this work highlight the urgent need, at all political levels, to elaborate efficient and appropriate plans to respond to air quality hazards, while collaborative efforts must also be made to constantly decrease ambient levels of air pollution, even when within the current Australian and international guidelines