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1 17 th EPIET Epidemiology Course Menorca, September / October 2011 Environmental Epidemiology (Introduction) Helen Maguire HPA London region with acknowledgement.

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Presentation on theme: "1 17 th EPIET Epidemiology Course Menorca, September / October 2011 Environmental Epidemiology (Introduction) Helen Maguire HPA London region with acknowledgement."— Presentation transcript:

1 1 17 th EPIET Epidemiology Course Menorca, 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 To provide a basic knowledge about Challenges and issues relating to environmental epidemiology Concept of low risk but large impact Methods of investigation Objectives 2

3 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 What is the environment ? 3

4 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 … High risks of adverse health outcome resulting from exposure 4

5 December London 5

6 6

7 Minamata 7

8 8

9 December Bhopal 9

10 10

11 Tchernobyl 11

12 Thyroid cancer in children 12

13 Paris 13

14 Katrina 14


16 Buncefield Explosion Plume stretched for 70 miles across southern England


18 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 Nature of risks in general environment 18

19 ED The 2 most FAQ in environmental health What is the environments 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? space time

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

23 Some challenges in environmental epidemiology EDED ? 23

24 Characteristics of exposure in environmental epidemiology ED -Multiple pollutants (RF) -Multiple routes of exposure -1 RFn D -Low levels of exposure -Long duration of exposure -Changes over time 24

25 Characteristics of health outcomes in environmental epidemiology ED -Multifactorial diseases : n RF1 D -Rare disease -Long latent periods 25

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 EDED 28

29 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, High risks 29

30 Urban air pollution and short-term respiratory diseases –RR = Magnetic fields and children leukaemia –RR = 1.3 … Low risks 30

31 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 Small relative risks do not mean small health impacts 31

32 example calculation of AR and AR% Phosphene exposure incidence genetic mutation exposed0.71 unexposed0.14 RR0.71/0.14 =5.1 attributable risk =0.57 AR%0.57/0.71*100=80%

33 attributable risk for smoking and lung cancer death (Doll and Hill 1956) exposure lung cancer death/100,000 heavy smokers166 non smokers7 RR166/7=23.7 attributable risk166-7=159 AR%159/166*100=95.7%

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

35 Heterogeneity in the populations sensitivity to the exposure % 50% * (S) : normal sensitivity (s) : low sensitivity 35

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

37 Errors in the exposure classification 20% of non exposed (E0) are categorised E1 and 10% of non-exposed are categorised E2. E0E1E2 Prevalence50%35%15% Incidence RRref

38 Inaccuracy in the exposure categories E0E1 Prevalence50% Incidence RRRef1.5 38

39 Heterogeneity of the population Non specific definition of health outcome Errors in exposure classification Inaccuracy in exposure categories E0E1 Prevalence50% Incidence RRRef1.5 ** RR : true Relative Risk 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 … 40

41 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 improving assessment of exposure: biomarkers of exposure and outcome 41

42 Ecologic studies Unit of observation is group, not individual

43 Ecological studies: objectives To generate or 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 population B population C population A Level of exposure Incidence rate 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 Paris versus


52 Conclusion 52 Critical aspects and challenges in environmental epidemiology Difficulties in exposure measurements, outcomes assessments Low risk can have large / important public health impact Question of causality is crucial Epidemiology is one of the tools Risk assessment, Cluster investigation, …

53 H. Morgenstern, Uses of ecologic analysis in epidemiologic research. American Journal of Public Health, Vol. 72, Issue , Talbott E. An Introduction to Environmental Epidemiology CRC Press, 1995 Bertollini R. Environmental epidemiology. Exposure and disease CRC Press, 1996 Aldrich T.E. Environmental epidemiology forward chemosphere 41 (2000) Morgenstern H. Principles of study design in environmental epidemiology EHP 101 (suppl 4) (1993) Hatch M. Measurement issues in environmental epidemiology EHP 101 (suppl 4) (1993) Hemon D. Recherche épidémiologique sur lenvironnement et la santé : quelques aspects méthodologiques Rev Epidém. et Santé Publ. 43 (1995) References 53

54 Thankyou ps …I look forward to meeting you all properly during the next 2 weeks 54

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