17 th EPIET Epidemiology Course Menorca, September / October 2011 Environmental Epidemiology

1. 17th EPIET Epidemiology CourseMenorca, September / October 2011 Environmental Epidemiology (Introduction)‏ Helen Maguire HPA London region with acknowledgement of previous work of Amandine COCHET French institute for public health surveillance Environmental health department and colleagues at HPA CRCE London

2. Objectives To provide a basic knowledge about • Challenges and issues relating to environmental epidemiology • Concept of low risk but large impact • Methods of investigation 2

3. What is the environment ? Restrictive definition: environment = air + water + soil • all the physical, chemical and biological factors external to a person, and all the related behaviours (WHO)‏ • the sum of all external conditions affecting the life, development and survival of an organism (US-EPA)‏ • everything that is not me (Einstein)‏ • Involuntary exposure

4. High risks of adverse health outcome resulting from exposure • Occupational environment - aromatic amines and bladder cancer - asbestos fibres and mesothelioma - cadmium and kidney diseases - benzene and leukaemia - pesticides and infertility - organic solvents and neurological disorders etc ... • General environment …

5. December 1952 - London

6. December 1952 - London

7. 1932-1968 - Minamata

8. 1932-1968 - Minamata

9. December 1984 - Bhopal

10. December 1984 - Bhopal

11. 1986 - Tchernobyl

12. Thyroid cancer in children

13. 2003 - Paris

14. 2005 - Katrina

16. Buncefield Explosion • Plume stretched • for 70 miles • across southern England

18. Nature of risks in general environment • Anthropogenic activities • London fog 1952, Minamata 1953, Bhopal 1984, Tchernobyl 1986, Buncefield fire England 2005, • Natural origin • Heat waves, • Hurricanes… • Mixed origin • UV and melanoma

19. The 2 most FAQ in environmental health ? E D • What is the environment’s Health impact = Considering environmental factor E, how many cases of disease D is it expected to generate? • What is the Burden of disease attributable to the environment = Considering disease D, what percentage is due to environmental factor E?

21. does this space time dsitribution = a cluster?

22. ..sometimes there is no doubt about a common exposure

23. Some challenges in environmental epidemiology E D ?

24. Characteristics of exposure in environmental epidemiology E D • Multiple pollutants (RF) • Multiple routes of exposure • 1 RF n D • Low levels of exposure • Long duration of exposure • Changes over time

25. Characteristics of health outcomes in environmental epidemiology E D • Multifactorial diseases : n RF 1 D • Rare disease • Long latent periods

26. Buncefiled oil depot explosion and fire East of England 2005 attendance at A&E after the fire

27. … presenting complaints

28. Characteristics of environmental risks E D

29. High risks • High RR • benzidine / bladder cancer RR = 500 • tobacco (>25cig/d) / lung cancer RR = 30 • Usually severe and often specific health outcomes • “Well defined” populations • in space, in time, sociodemographic,

30. Lowrisks • Urban air pollution and short-term respiratory diseases • RR = 1.1 - 1.5 • Magnetic fields and children leukaemia • RR = 1.3 • …

31. Small relative risks do not mean small health impacts Relative risk ratio measure Attributable risk (AR) % 100 * (Incidence in exposed – Incidence unexposed) ______________________________ Incidence in exposed • PAR%= p * ( RR -1) / [ 1+ p * ( RR - 1) ]if the relation is causal, it estimates the proportion (amount) of disease that we can attribute to the exposure

32. example calculation of AR and AR%

33. attributable risk for smoking and lung cancer death (Doll and Hill 1956)

34. Further challenges: misclassification Theoretical baseline situation E0 = non exposed, E1=low exposure, E2=high exposure * Incidence : x /100.000, ** RR : true Relative Risk

35. Heterogeneity in the population’s sensitivity to the exposure 50% 50% * (S) : “normal” sensitivity (s) : lowsensitivity

36. Non specific definition of the health outcome • (D) : disease specifically related to exposure. • (d) : disease not related to exposure

37. E0 E1 E2 Prevalence 50% 35% 15% Incidence 150 214.3 250 RR ref 1.43 1.67 Errors in the exposure classification 20% of non exposed (E0) are categorised E1 and 10% of non-exposedare categorised E2.

38. E0 E1 Prevalence 50% 50% Incidence 150 225 RR Ref 1.5 Inaccuracy in the exposure categories

39. Heterogeneity of the population • Non specific definition of health outcome • Errors in exposure classification • Inaccuracy in exposure categories ** RR : true Relative Risk E0 E1 Prevalence 50% 50% Incidence 150 225 RR Ref 1.5 RR : estimated Relative Risk

40. methods to improve epidemiological study where there are low risks • Improve data quality • confounders, diagnosis • Improve statistical power • meta analysis, large studies, pool data • Take careful account of • critical periods of exposure • individual history of exposure • behaviour, space-time activities …

41. improving assessment of exposure: biomarkers of exposure and outcome Biomonitoring assessment of human exposure to chemicals by measuring the chemicals or their metabolites in human specimens (blood, urine‏, hair,…)  biomarkers of exposure and outcome

42. Ecologic studies Unit of observation is group, not individual

43. Ecological studies: objectives  To generateor to test etiologic hypotheses • To evaluate the impact of intervention programs or policies 43

44. Ecological studies: methods • Aggregated data • Statistical unit = « group » (time/space)‏ • Group exposure • Mean exposure, environmental proxy • Group effect • Frequency of disease in the statistical unit • Research of an association between: • Variations of exposure levels • Variation of health indicators 44

45. Limits of geographical studies • Classification bias agregated data  insufficient quality of exposure and disease indicators  errors of classifications (generally non differential) • Surveillance bias if ascertainment of disease or exposure or both differs from one place to another (can be differential) • « Ecological fallacy » 45

46. Ecological Fallacy Incidence rate population A       population B       population C         Level of exposure 46

47. Ecological Fallacy Incidence rate Level of exposure

48.  The Ecological Fallacy is the inability to generalize information gathered at the group level to specific individuals.

49. Time series • A type of ecological study • Looks at the (short-term) temporal association between health events and pollution • Less subject to confounding than many study designs • Time-varying confounders: temperature, humidity, influenza, day of the week, public holidays

50. Time series mortality and mean temperature in Paris1999-2002 versus 2003 50