Occ IntroductiontoOccupationalEpidemiologyfortheIH

7/28/2019 Occ IntroductiontoOccupationalEpidemiologyfortheIH

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Introduction to Occupational

Epidemiology for the IndustrialHygienist

Based on a Professional Development Coursewritten by Dr. Chris Rennix, Dr. Robin Leonard,

and Mr. Phill Hunt


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AIHA Occupational EpidemiologyCommittee

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Learning ObjectivesObjectives: Upon completion, the participant will be able to:

Describe the basic roles played by industrial hygienists inoccupational epidemiology

Identify basic epidemiologic terms and apply them to typical

worksite examples during general discussions Select the appropriate disease model based on latency, body

burden, and human physiology

Calculate basic ratios and rates used in epidemiologic studies

Describe basic epidemiologic principles in terms related toindustrial hygiene exposure assessments during generaldiscussions


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Introduction orAre we sampling for health or

compliance? Current view - How is occupational epidemiologydefined?

History - Where did occupational epidemiologyoriginate?

Players - Who does what to whom?

Disease - Does the disease process dictate howand who we sample?


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Current View of Epidemiology

Public perception Current legal precedents

Media perception Medical perception

IH perception

Epidemiologist perception


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History

History of Epidemiology Cholera

Lyme disease

History of Occupational Epidemiology

Lung cancer

Bladder cancer

Hearing loss


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Players

The corporation The worker

The physician The IH

The epidemiologist

The lawyers


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Disease Models

Exposure Induction

Latency Single hit model

Multistage model

Time-windows of exposure

Promotion


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References

Checkowayand Pearce. Research Methodsin Occupational Epidemiology. OxfordUniversity Press, 1989

Rothman. Epidemiology: an introduction.Oxford University Press, 2002.

Ahlbomand Norell. Introduction to Modern

Epidemiology. Epidemiology ResourcesInc, 1990.


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Definitions

Exposure - Presence of a substance in an areawhere a person works

Induction - Time from first exposure to diseaseinitiation

Latency - The time from disease initiation to therecognition of effects

Why are these concepts important to the IH and theepidemiologist?


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Single Hit vsMultistageDisease Models

R

ISK

Time

Exposure

Unexposed worker


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Single Hit vsMultistageDisease Models II

R

ISK

Time

Exposure

Unexposed or lessexposed worker


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Single Hit vsMultistageDisease Models III

R

ISK

Time

Exposure to A

Unexposed to Aand/or B

Exposure to B


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Time WindowsDisease Model

Time/Age

Menarche 1st Birth Perimenopause Menopause

Assuming constantexposure to Chemical

A

Birth of 1st

child before25 yrs old

Birth of 1st

child after 30yrs old

Nonparous


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Occupational Epidemiology StudyTypes and Calculations


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Describe health status of apopulation Explain the etiology of disease (identify risk

factors, modes of transmission)

Predict the occurrence of disease

Evaluate impact of an intervention

Prevent new occurrence, eradicate existingdisease

Objectives of Epidemiologists


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Definitions Types of Studies

Cross-sectional

Cohort

Case-Control

Case-Cohort

Measures of disease frequency

Measures of risk

Measures of exposure


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Incidence

number of new cases of a disease within a definedpopulation, over a specified period of time

Prevalence all cases of a disease within a definedpopulation, over

a specified period of time

Mortality estimate of the proportion of apopulationthat dies

during a specified period

Measures of Disease Frequency


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Measuring disease frequency Count number of cases (numerator)

Count number at risk (denominator)

Lung Cancer in Males

10/320 = .03 6/180 = .03 1/250 = .004

Prevalence (all cases, single point in time)


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The Importance of Denominators

Rates, Ratios, Proportions all require definition ofa whole-- whole group, whole plant, wholepopulation

Cohort definition is critical, because that is howwe establish a rate

Industry studies examined very carefully for

inclusion, exclusion criteria


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Experimental

Assignment of exposure under investigator

control (clinical trials)Non-Experimental

DescriptiveCollecting, sorting, analyzing data can elucidate

important patterns

AnalyticCross-sectional

Longitudinal

Types of Studies


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How old is the plant? Continuous operation?

What kinds, and how much, chemicals or other toxics areused, produced, shipped?

How do we describe the jobs of a group of people in ananalyzable way?

Identifyjob titles, departments, and specific tasksIdentifyhomogeneous exposure groupsUseIH monitoring data to categorize

Where do we get this information?

HR Department; EH&S; Industrial Hygiene

Descriptive EpidemiologyDescribes

What, for example?


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Data on disease and exposure available foreach individual

Longitudinal

Cohort

Prospective

Retrospective

Case-Control

Case-Cohort Cross-Sectional

Analytic Studies


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Individuals enter the study on the basis ofexposure and non-exposure.

Prospective: disease has not occurred at the

time exposed and non-exposed groups aredefined.

Retrospective: disease has occurred at the time

exposure groups are defined.

Cohort Studies


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Cohort studies Prospective Design data collection

to take advantage ofparticipantsavailability

Less bias with

ascertainment ofdisease

Better able to track

changes in exposure

Retrospective Less detail is generally

available onparticipantscharacteristics orexposures.

Comparisons are madeto a general populationor to a cohort selectedto closely resemble thestudy group.

Exposures of the pastare being evaluated.


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Comparinghealth of different groupsCohort Studies

Cohort: any designated group of persons who arefollowed or traced over a period of time

Individuals enter a cohort study on the basis of

exposure and non-exposure. Prospective: disease has not occurred at the time

exposed and non-exposed groups are defined.

Retrospective: disease has occurred at the timeexposure groups are defined.


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Less detail is generally available on participantscharacteristics or exposures.

Comparisons are made to a general population or

to a cohort selected to closely resemble the studygroup.

Exposures of the past are being evaluated.

Retrospective Cohort Studies


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Now you understand

Descriptive epidemiology: the profile ofthe population of interest

Cross-sectional epidemiology: one point in

time; health status and risk factor known atthe level of the individuals

Prevalence : all cases divided by the totalpopulation at one point in time


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?

?

Case-Control (Case-Cohort) Study

??

Exposure Disease

Investigator atbeginning of study

? =To be determined

P

A

Prospective CohortExposure Disease

?

?

P

A

Retrospective CohortExposureDisease

PA

P = present A = absent(Basis of group selection at beginning of study)

=


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AIHA Occupational EpidemiologyCommittee 29

EX POSURE

YES NO

No. initial ly at risk 4000 16,000Deaths 30 60

Person-years at risk 7970 31,940

Risk Ratio = 30/4000 7.5 per 1000

= = 2.000060/16,000 3.75 per 1000

Rate Ratio = 30/7970 pyrs 3.76 per 1000 pyrs

= = 2.0038

60/31,940 pyrs 1.88 per 1000 pyrs

Disease Odds Ratio = 30/(4000-30) 0.00756

= = 2.007660/(16,000-60) 0.00376

Hypothetical Data from a Cohort of 20,000 persons followed up for two years

(from Cancer Epidemiology: Principles and Methods, by Isabel dos Santos Silva, WHO,1999)

Measuresof RelativeRisk


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Case-Control Studies

Investigator looks backward from diseaseto exposure

Identification is via disease

Evaluates a number of exposures in relationto one disease


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Odds RatioOdds Ratio

a+b+c+db + da + c

c + ddcNoDisease

a + bbaDisease

UnexposedExposed


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Nested Case-Control Studies

Used to focus on findings from a cohortstudy.

Directed toward identifying specific causal

risk factors.

Findings can be extrapolated to cohort from

which the cases and controls came. Risks expressed as odds ratios.


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Case-Cohort Studies

All cases from the full cohort are collected asstudy cases

A random sample of the full cohort is thesource of the comparison group It is possible that cases may be selected as controls,

in which case they are included in the referencesubcohortuntil their deaths (mortality studies) ordate of diagnosis (morbidity studies).

Takes advantage of the statistical power ofcohort studies and the focused use of specificexposure data of the case-control approach.


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Bias, Confounders, Effect Modifiers,

Risk Co-factors Healthy Worker Effect

Bias

Selection

Recall

Informational

Confoundermust be associated with both theexposure of interest and the outcome

Certain enzyme polymorphisms cause rapid

metabolism of toxicants

Both cigarette smoking and working top-side on acoke oven cause lung cancer


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Epidemiologic Concept of Causality

Strength of association: How strong is the association between the

exposure and disease?

Usually expressed as relative risk or an oddsratio

The farther the risk from the number one, the

stronger the association


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Epidemiologic Causality

Consistency: Is the association observed by differentresearchers in different conditions,circumstances, places,or times?

Specificity: Is the cause usually found when the disease is

present?

Does the disease usually result when the causeis present?


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Epidemiologic Causality Relationship in time:

Does the exposure (or causal factor) precedethe disease or outcome?

Temporalitythe exposuremustprecede theoutcome

Biological gradient:

Does more exposure (higher amounts per unit

time or longer duration of time exposed) lead tomore severe disease or increased incidence ofdisease?


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Biological plausibility: Is the observed association consistent with

biological ideas about the disease process?

Coherence of the evidence: Does the entire set of observations fit together?


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Experiment: Does removal of the exposure result in a change

in disease frequency?

How does treatment affect different groups in arandomized trial?

Reasoning by analogy: Are there similar known patterns of cause and

effect found in other areas of epidemiology?


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Stepwise Approach to

Epi Study Design


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Review Study Population andsources of exposure

Physical layout of facility, neighborhood Processes generating exposure

Materials used

Jobs. Tasks, activities of of

Workers

Community


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Determine study design

Cross-sectional survey Retrospective cohort

Retrospective case-control

Prospective cohort


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Determine degree ofquantification

Qualitative Ever/never exposed

Semi-quantitative

None, low medium high

Quantitative

Air concentration Force, repetitions


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Determine the measurement tool

Record review Expert judgment

Questionnaires, Interviews

Sampling and analytical methods for directmeasurement


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Informationcollection Conditions of exposures

tasks, product, production information, upsets,accidents, job title, department.

Information on subject

relevant employee information, such as age,years at job, previous jobs within facility, andearlier job history, smoking, and gender

Ethnicity may be an issue but may also be aconfounder


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Design exposure assessmentstrategy

Types of samples Area-task vs personal

Who or where to sample

How many samples How many people or places

How many days

Sampling duration Task or full shift


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Pilot test measurement tool

Are there differences in exposure? Processes left out?

More or fewer measurements?

Interview questions easily understood?


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Summary

Measure what causes or what you suspectcauses the disease

Measure in a way that is relevant to the

disease process Develop a plan

Test it before you spend the big bucks


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Final Discussion Future Issues

Current experience in litigation based on theuse of exposure assessments as evidence

Legal Issues

Liability and professional judgment

Costs

IH/Physician/Epidemiologist interface Management support

Documents

Occ IntroductiontoOccupationalEpidemiologyfortheIH