Ambient air quality and the risk of acute myocardial infarction hospitalizations in Lautoka city, Fiji.
Thesis DisciplineHealth Sciences
Degree GrantorUniversity of Canterbury
Degree NameMaster of Health Sciences
Background: Air pollution is a known risk factor for heart disease. Results from epidemiological studies from major Western cities suggest that increase in air pollution leads to an increased risk of hospitalisation due to acute myocardial infarction; the increased risk is attributed to the ambient air quality. However, there is limited evidence of the association between air quality and risk of heart disease related hospitalisations in the Pacific. This thesis has addressed the gap in the evidence by conducting a meta-analysis of observational epidemiological studies on the association between air quality and hospitalisation due to acute myocardial infarction or due to significant ischaemia and developed a predictive model based on air quality of Lautoka city and the estimates from the meta analysis. The goal of this thesis is to assess the ambient air quality in Lautoka Central Business District (CBD) and model the risk of hospitalisation due to acute myocardial infarction to the wider population of Lautoka who commute daily into the city centre.
Methods: Ambient air quality was measured for a period of three months from 15th August 2018 to 15th November 2018. These included particulate matter with an aerodynamic diameter less than 10 microns (PM₁₀), particulate matter with an aerodynamic diameter less than 2.5 microns (PM₂.₅), sulphur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO) and ozone (O₃). Air quality data for the Lautoka central business district was analysed and compared with the guideline values set by the World Health Organization. Comparisons were made for the daily mean concentrations as well as mean concentrations during hours of the day over a 24-hour period. A systematic review and metaanalysis of published studies on the association between ambient air quality and risk of hospitalization due to myocardial infarction was conducted which yielded 20 case-cross over studies. On the basis of the ambient air quality data and extrapolation of pooled estimates from the meta-analysis, a predictive model was constructed for those days that would be expected to have high levels of myocardial infarction or acute heart disease related hospitalisations.
Results: Particulate Matter (PM₁₀ and PM₂.₅) were the only air pollutants that showed substantial concentrations. The daily mean concentrations observed in the Lautoka CBD for PM₁₀ and PM₂.₅ was 64.15μg/m³ and 9.34 μg/m³ respectively. The daily (24hr) mean concentrations for PM₁₀ exceeded the WHO guideline value of 50 μg/m³ from Tuesdays to Fridays and the concentrations showed an increasing trend from Mondays to Fridays. Both pollutants exhibited high concentrations during the peak traffic hours (6am-9am in the morning and 4pm to 7pm in the afternoon. Among the 137, 846 AMI hospitalizations the meta-analytic odds in the overall analyses; fixed effects model, OR = 1.04(95%CI = 1.03 – 1.04), random effects model OR = 1.07 (95%CI: 1.05 – 1.10). Both models were significant when analysing exposure to common air pollutants and risk of AMI hospitalization. In the subgroup analysis for short-term exposure to increments of at least 5-10μg/m³ of PM₂.₅, the effect estimate in the (1) fixed effects model, OR = 1.04(95%CI = 1.03-1.05), (2) random effects model, OR = 1.05(95% CI: 1.03-1.07) respectively. Again, both models were significant when analysing short-term (lag 3hrs -1 day) exposure to PM₂.₅ and risk of AMI hospitalization.
Conclusion: On the basis of the pooled estimates from the meta-analysis and the air quality data, exposure to common air pollutants may increase the risk of AMI hospitalizations among the daily commuters to Lautoka CBD as well as to the wider Lautoka city populace. Importantly, low concentrations of PM₂.₅ was associated with the risk of increased AMI hospitalizations. Furthermore, the risk of AMI hospitalisation is highest on Thursdays and Fridays and 1-24 hrs after exposure to high pollutant levels during peak traffic hours on these days.