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17th EPIET Epidemiology CourseMenorca, September / October 2011

Environmental Epidemiology(Introduction)Helen Maguire HPA London region with acknowledgement of previous work of Amandine COCHETFrench institute for public health surveillance Environmental health department and colleagues at HPA CRCE London

To provide a basic knowledge about

►Challenges and issues relating to environmental epidemiology

►Concept of low risk but large impact

►Methods of investigation

Objectives

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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 ?

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► 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 disordersetc ...

► General environment …

High risks of adverse health outcome resulting from exposure

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December 1952 - London

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December 1952 - London

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1932-1968 - Minamata

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1932-1968 - Minamata

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December 1984 - Bhopal

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December 1984 - Bhopal

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1986 - Tchernobyl

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Thyroid cancer in children

0

20

40

60

80

100

120

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86

19

87

19

88

19

89

19

90

19

91

19

92

19

93

19

94

Years

Inci

den

ce R

ate

per

mil

lio

n

Belarus

Ukraine

Briansk

Gomel

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2003 - Paris

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2005 - Katrina

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Buncefield Explosion

• Plume stretched • for 70 miles • across southern

England

► 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

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E D

The 2 most FAQ in environmental health

• 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?

?

Epidemiologicalstudies

Observational(non-intervention)

Data fromindividuals

Data from groups

Descriptive Analytic

Ecological study

Descriptive Analytic

Cross sectional study Cohort studyCase control

study

Data from groupsData fromindividuals

Experimental(intervention)

Community trialClinical trial,

individual fieldtrial

does this space time

dsitribution = a cluster?

space

       

1 2 3 4 5 6

time

..sometimes there is no doubt about a common exposure

Some challenges in environmental epidemiology

E D?

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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

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Characteristics of health outcomes in environmental epidemiology

E D

- Multifactorial diseases : n RF 1 D- Rare disease- Long latent periods

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Buncefiled oil depot explosion and fire East of England 2005

attendance at A&E after the fire

Fig 1: Distribution of attendances in Hemel Hempstead and Watford A&E between 11/12/05 and 14/12/05, by date and time. (N=244)

0

5

10

15

20

25

30

35

40

45

4-6

6-8

8-10

10-1

212

-14

14-1

616

-18

18-2

020

-22

22-2

4 0-2

2-4

4-6

6-8

8-10

10-1

212

-14

14-1

616

-18

18-2

020

-22

22-2

4 0-2

2-4

4-6

6-8

8-10

10-1

212

-14

14-1

616

-18

18-2

020

-22

22-2

4 0-2

2-4

4-6

6-8

8-10

10-1

212

-14

14-1

616

-18

18-2

020

-22

22-2

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38697 38698 38699 38700

Date & Time

No.

Oil depot worker

Public

Em. Services

Time of explosion

… presenting complaints

Fig 2: Main presenting complaints as percentage for each group

0

10

20

30

40

50

60

70

80

90

Injuries Respiratory Anxiety Headache vomiting Cardiac

Presenting complaints

Pro

port

ion

of c

ompl

aint

s

Members of the public % of 40

Oil depot workers % of 17

Emergency workers % of 187

Characteristics of environmental risks

E D

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► 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

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► Urban air pollution and short-term respiratory diseases– RR = 1.1 - 1.5

► Magnetic fields and children leukaemia– RR = 1.3

► …

Low risks

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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

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example calculation of AR and AR%Phospheneexposure incidence genetic mutation

exposed 0.71

unexposed 0.14

RR 0.71/0.14 = 5.1

attributable risk 0.71-0.14= 0.57

AR% 0.57/0.71*100= 80%

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

exposure lung cancer death/100,000

heavy smokers 166

non smokers 7

RR 166/7= 23.7

attributable risk 166-7= 159

AR% 159/166*100= 95.7%

Further challenges: misclassification Theoretical

baseline situation E0 E1 E2

Prevalence 80% 15% 5%

Incidence* 100 300 500

RR** ref 3.0 5.0

E0 = non exposed, E1=low exposure, E2=high exposure* Incidence : x /100.000, ** RR : true Relative Risk

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Heterogeneity in the population’s

sensitivity to the exposure E0 E1 E2

Prevalence 80% 15% 5%

Incidence (S) 100 300 500

Incidence (s) 100 200 300

Incidence (mean) 100 250 400

RR ref 2.5 4.0

50%%

50%%

* (S) : “normal” sensitivity (s) : low sensitivity35

Non specific definition of the health outcome

E0 E1 E2

Prevalence 80% 15% 5%

Incidence (D) 100 250 400

Incidence (d) 50 50 50

150 300 450

RR ref 2.0 3.0

•(D) : disease specifically related to exposure.•(d) : disease not related to exposure 36

Errors in the exposure classification

20% of non exposed (E0) are categorised E1 and 10% of non-exposedare categorised E2.

E0 E1 E2

Prevalence 50% 35% 15%

Incidence 150 214.3 250

RR ref 1.43 1.67

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Inaccuracy in the exposure categories

E0 E1

Prevalence 50% 50%

Incidence 150 225

RR Ref 1.5

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• Heterogeneity of the population

• Non specific definition of health outcome

• Errors in exposure classification

• Inaccuracy in exposure categories

E0 E1

Prevalence 50% 50%

Incidence 150 225

RR Ref 1.5

E0 E1 E2

Prevalence 80% 15% 5%

Incidence* 100 300 500

RR** ref 3.0 5.0

** RR : true Relative Risk

RR : estimated Relative Risk

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 …

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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

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Ecologic studiesEcologic studies

Unit of observation is group, not individual

Ecological studies: objectives

To generate or to test etiologic hypotheses

To evaluate the impact of intervention programs or policies

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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 indicators44

Limits of geographical studies

• Classification biasagregated data insufficient quality of exposure and disease indicators errors of classifications (generally non differential)

• Surveillance biasif ascertainment of disease or exposure or both differs from one place to another(can be differential)

• « Ecological fallacy »

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Ecological Fallacy

population B

population C

population A

Level of exposure

Incidence rate

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Ecological Fallacy

Incidence rate

Level of exposure

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

Time seriesTime 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

Time series mortality and mean temperature in

Paris

1999-2002 versus 2003

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Epidemiologicalstudies

Observational(non-intervention)

Data fromindividuals

Data from groups

Descriptive Analytic

Ecological study

Descriptive Analytic

Cross sectional study Cohort studyCase control

study

Data from groupsData fromindividuals

Experimental(intervention)

Community trialClinical trial,

individual fieldtrial

Conclusion

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• 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, …

H. Morgenstern, Uses of ecologic analysis in epidemiologic research. American Journal of Public Health, Vol. 72, Issue 12 1336-1344, 1982.

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 forwardchemosphere 41 (2000) 59-67

Morgenstern H. Principles of study design in environmental epidemiology EHP 101 (suppl 4) (1993) 23-38

Hatch M. Measurement issues in environmental epidemiologyEHP 101 (suppl 4) (1993) 49-57

Hemon D. Recherche épidémiologique sur l’environnement et la santé : quelques aspects méthodologiquesRev Epidém. et Santé Publ. 43 (1995) 395-411

References

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Thankyou

ps …I look forward to meeting you all

properly during the next 2 weeks

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