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Geographical epidemiology: air quality and public health

Geographical epidemiology: air quality and public health

Establishing links between environmental exposures and health outcomes using individual level data is notoriously difficult. There are problems of obtaining measures of dose levels for individuals as well as handling what are often long latency times between exposure and diagnosis. Ecological study designs at the small area level provide one way of studying the effects of environmental exposures on different health outcomes. Whilst such studies are unlikely to yield reliable estimates of risk linked to incremental shifts in the environmental variable (and suffer from problems such as the modifiable areal units problem, and aggregation and specification bias) they can be useful for the purposes of formulating hypotheses that may then be examined by other, medically more rigorous, methods.

In collaboration with Dr Ravi Maheswaran of the Sheffield School for Health and Related Research and other colleagues at Sheffield, we have been investigating whether mortality rates and hospital admissions for coronary heart disease and stroke are higher in areas of Sheffield with higher outdoor pollution levels for nitrogen oxides, carbon monoxide and particulate matter (PM10) whilst controlling for the confounding effects of age, sex, deprivation and smoking prevalence. The work has been funded by the Trent Regional Health Authority and the Colt Foundation. Demographic and socio-economic data were obtained at the small area (enumeration district) level. Sheffield air pollution estimates were derived from the Indic Air-Viro model for a lattice grid (figure 1) and then translated to the ED framework using areal interpolation under different assumptions (figure 2). Health outcome data was for the period 1994-9. The research is making extensive use of GIS technology and spatial data analysis and Poisson spatial modelling techniques in WinBUGS.

[Information about this project continued below.]

Diagram as described adjacent

Figure 1 (above). Mean annual nitrogen oxide (NOx) pollution for the period 1994-99 for the city of Sheffield. The line of high values cutting the north east quadrant of the map follows the M1 motorway. The cluster of high values in the middle is the city centre.

Figure 2 (below). Average NOx pollution value for each Census enumeration district obtained from different areal interpolation techniques.

Diagram as described adjacent

In the case of coronary heart disease mortality, results are consistent with an excess risk in areas with high outdoor NOx, a proxy for traffic-related pollution, although residual confounding cannot be ruled out. If causality were assumed, 6% of coronary heart disease deaths would have been attributable to outdoor NOx. In the case of strokes, results are consistent with an excess risk of stroke mortality, and to a lesser extent hospital admissions, associated with chronic exposure to outdoor air pollution. If causality were assumed, 11% of stroke deaths would have been attributable to outdoor air pollution.

Air pollution is a potentially modifiable risk factor so that this work has implications for policy makers.

Currently there are no PhD students working in the area of geographical epidemiology. However Matthew Wang is evaluating Community Health Centres (CHCs) in Jinan province, P.R.China. Jinan was the first city to introduce CHCs and in collaboration with the Jinan Health Bureau he is undertaking an evaluation of people's response to these centres which in many respects follow the model of GP practices in the UK's National Health Service. Also Neeraj Garg Baruah, currently (2011) a first year student is planning to undertake research using agent based modelling to analyse the spread of an infectious disease at the small area level.


Recent publications include:

  • 'Inference from ecological models: estimating the relative risk of stroke from air pollution exposure using small area data.' Spatial and Spatio-Temporal Epidemiology, 2010, 1, 123-131. (with G.Li, R.Maheswaran, M.Blangiardo, J.Law, N.Best, S.Richardson.)
  • 'Outdoor NOx and stroke mortality - adjusting for small area level smoking prevalence using a Bayesian approach.' Statistical Methods in Medical Research 2006, 15, 499-516 (with R.Maheswaran, P.Brindley, J.Law, T.Pearson, N.Best).
  • 'Analysing the relationship between smoking and coronary heart disease at the small area level.' Geographical Analysis, 2006, 38, 140-159. (with J.Law, R.Maheswaran, and T.Pearson).
  • 'Outdoor air pollution and stroke in Sheffield, United Kingdom - a small area level geographical study.' Stroke, 2005, 36, 239-243. (with R Maheswaran, T.Pearson, M.Campbell, P.Brindley, S.Wise, J.Law).
  • 'Outdoor air pollution, mortality and hospital admissions from coronary heart disease in Sheffield, United Kingdom - a small-area level ecological study.' European Heart Journal. (with R. Mahesawaran, P.Brindley, J.Law, T.Pearson, P.Fryers, S.Wise and M.Campbell). 2005, 26, 2543-2549.
  • 'The effect of alternative representations of population location in the area interpolation of air pollution exposure.' Computers, Environmental and Urban Systems, 2005, 29, 455-469. (with P.Brindley, S.Wise, and R.Maheswaran).
  • 'Using modelled outdoor air pollution data for health surveillance.' In R.Maheswaran and M.Craglia (eds) GIS in Public Health Practice, Taylor and Francis, London, 2004, 125-149 (with P.Brindley, R.Maheswaran, T.Pearson, S.Wise).