occ introductiontooccupationalepidemiologyfortheih
TRANSCRIPT
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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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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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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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Epidemiologic Causality
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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Epidemiologic Causality
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