Epidemiological Investigation on OHS Concerns

7/29/2019 Epidemiological Investigation on OHS Concerns

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EPIDEMIOLOGICAL INVESTIGATIONEPIDEMIOLOGICAL INVESTIGATIONOF OCCUPATIONAL HEALTH ANDOF OCCUPATIONAL HEALTH AND

SAFETY CONCERNSSAFETY CONCERNS

by: Gallego, Misena and Rubayatby: Gallego, Misena and Rubayat

OH 206: Workplace SurveysOH 206: Workplace Surveys

Master of Occupational HealthMaster of Occupational Health

College of Public HealthCollege of Public Health

University of the PhilippinesUniversity of the Philippines ManilaManila

Objectives

To understand the purpose and acceptthe importance of occupational

epidemiology in determining causes,measuring risks and establishing

To define Epidemiology and itsapplication to Occupational Health andSafety (OHS)

To discuss Epidemiologic HistoricalPerspectives in relation to OHS

Objectives

To discuss the Stages of OccupationalEpidemiologic Investigation

To discuss the different phases ofoccupational epidemiologicnves ga on

To be able to describe the main typesof study design used in occupationalepidemiology

To be able to illustrate the application

of the above with examples

Objectives

To explain different samplingtechniques to use in the studies

To discuss methods in obtaining datain epidemiological studies

To discuss the basic considerations inthe design of epidemiologicalinvestigations

To discuss various sources ofoccupational epidemiological data

Objectives

To institute control measures base onthe result of the study

To discuss occupational

epidemiological monitoring andsurve ance

To identify the problems inOccupational Epidemiology

To discuss the applications ofOccupational Epidemiology

Summary

Definition

Epidemiology study of the frequency,distribution and determinants of diseasesand other health related conditions in humanpopulations, and the application of this study

to the romotion of health, and to theprevention and control of health problems.

Occupational Epidemiology study of theeffects of workplace exposures on thefrequency and distribution of diseases andinjuries in the population.


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Levels ofApplicationSurveillance

todescribe theoccurrenceofillness and

provide warningsignals of

unrecognized

occupational hazards

enera on an es ng o ypo es s todetermine harm caused byexposure and

quantify its effect

Evaluation ofIntervention Tomeasure changesinthehealth status ofa

populationovertime

Historical Perspective

1700 : Bernardino RamazziniHealth is dependenton identifiable natural external factors.

1775 : Pottreported possible connection betweencancer and occupation

1 : yr on- ar s surm se arsen c umes ascausal agent for scrotal cancers

1874 : Von Volkmannreported skin tumors inparaffin workers

1876 : Bellsuggested shale oil as responsible forcutaneous cancer.

1879 : Harting and Hesse observed lung canceramong Schneeberg miners

1952 : Doll lung cancer among gas workers

1954 : Case and Hosker studied bladder cancer in

Historical Perspective

dye workers

STAGES OFSTAGES OF

OCCUPATIONALOCCUPATIONALEPIDEMIOLOGICEPIDEMIOLOGICINVESTIGATIONINVESTIGATION

PHASES

1. Diagnostic Phase presence of disease isconfirmed

2 Inter-related Avenues of Diagnostic Phase:

a) Intensive follow-up - a detailed, multifaceteds u y o a seem ng y re evan aspec s o adisease even in a population unit.

Example: Outbreak Investigation

PHASES

1. Diagnostic Phase presence of disease isconfirmed

2 Inter-related Avenues of Diagnostic Phase:

b) Surveillance - opposite of intensive follow-up; asease accoun ng process .e. a roa , overa ,organized approach to the collection, collationanalysis, expression and dissemination of dataabout diseases in populations.

Examples: Death certificates, Cancer Registries,Hospital Records, Bureau of Labor Statistics, etc


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PHASES

Exposure Assessment critical step in identifyingworkplace hazards through epidemiological

investigation.

Important factors to consider:

a. Inventory of potentially toxic agents

b. Presence and concentrations

c. Routes of entry

d. Time course of exposure and cumulative duration

e. Engineering and personal controls

f. Host and other considerations

PHASESSummary Worklife Exposure Measures

Exposure measure Formula Units

Cumulative exposure

index (CEI)

(grade x t ime exposed) grade

and time

Mean grade (MG) (grade x time exposed)/total grade

time exposed

Highest grade ever

(HG)

highest grade to which

exposed for days

grade

Time-weighted average

(TWA) grade

(grade x time exposed)/total

time employed

grade

Total time exposed

(TTE)

time exposed time

PHASES

2. Descriptive Phase - describes the population atrisk and the distr ibution of the disease, both intime and space, within these populations; allowsgeneration of a series of initial hypotheses.

3. Investigative Phase involves theimplementation of a series of field studies to testthe initial hypotheses.

PHASES (hypothetical case)Newly diagnosed cases 10

Previously diagnosed living cases 12

Deaths, all causes 5

Deaths, disease of interest 3

Persons in population 100

ears o serve

Incidence 10 persons

Annual incidence rate

Point prevalence (at end of year 5) (10 + 12 - 3) = 19 persons

Period prevalence (five-year period) (10 + 12) = 22 persons

Annual death rate

Annual mortality rate

PHASES

4. Experimental Phase performed undercontrolled conditions to test the hypotheses inmore detail, should the result of phase 3 provepromising.

5. Analytical Phase - the results produced by theabove investigations are analyzed.; oftenenables the epidemiologist to determine whetherany vitalbits of information about the diseaseprocess are missing.

PHASES

Biological markers assess target organexposures, determining susceptibility andestablish early disease. Its uses were:

a. exposure assessment

. sen ang e causa ve ro e o c em caagent/substances in multiple exposures

c. Estimation of burden of exposure

d. Investigation of pathogenic mechanisms

e. Study individual susceptibility

f. Classify exposure/ disease accurately


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PHASES

6. Intervention Phase - appropriate methods forthe control of the disease are examinedeither

under experimental conditions or in the field.Interventions in the disease process are effectedb mani ulatin existin determinants orintroducing new ones.

PHASES

7. Decision-making Phase - a knowledge of theepidemiology of the disease is used to explore

the various options available for its control; ofteninvolves the modeling of the effects. Cost benefitanal sis of the control measures ma be done incombination with other models, in terms ofincreased productivity.

PHASES

8. Monitoring Phase - takes place during theimplementation of the control measures toensure that these measures are being properlyapplied, are having the desired effect on

,developments that are likely to jeopardize thesuccess of the control programs are quicklydetected.

TYPES OF OCCUPATIONALEPIDEMIOLOGICAL STUDIES Case Control Studies

Figure1. Case Control Studies

TYPES OF OCCUPATIONALEPIDEMIOLOGICAL STUDIES Case Control Studies

Figure2. Case of Occupational Cancer in Hardwood industry

TYPES OF OCCUPATIONALEPIDEMIOLOGICAL STUDIES Cross-Sectional Studies - prevalence of a

particular disease or of a set of symptoms orother indication of ill-health is investigated in a

single time-point (or over a relatively narrowperiod of time).

Ex. Chest X-ray survey of quarry workers =

Workers with high exposure to quartz havehigher prevalence of pneumoconiosis than thosewith little or no such exposure


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TYPES OF OCCUPATIONALEPIDEMIOLOGICAL STUDIES Cohort Studies

Figure3. Prospective Cohort


Figure4. Retrospective Cohort


Example:

Time trends in cancer risk and pesticideex osure a lon -term follow-u of Danish,Gardeners (Hansen, E., et.al, 2007)

Findings: There is a substantial pesticideexposure during the late 1940s and 1950s.Among gardeners born in 1915 or later, noexcess cancer risk was found.

SAMPLING TECHNIQUES

Random Sampling - every unit in the populationbeing sampled has exactly the same probabilityof being selected for the sample

Multi-Stage Sampling - involves sampling apopulation in different stages, with the sampleunit being different at each stage

Systematic Sampling - involves sampling a

population systematically i.e. if a 1/n sample isrequired, every nth unit in that population is

sampled. Ex. If a 10%(1/10) sample is required,every 10th unit in the population is sampled.

SAMPLING TECHNIQUES

Purposive Selection - involves the deliberateselection of certain sample units for some reasonor other. The reason may often be that they are

regarded as being "typical" of the populationbeing sampled.

Stratification - involves treating the population tobe sampled as a series of defined sub-populations or strata.

SAMPLING TECHNIQUES

Paired Samples - variations in the samplegroups due to host and managementcharacteristics can sometimes be overcome by

pairing individuals in the different sample groupsaccording to common characteristics (age, sex,location) and then analyzing the paired samples;often greatly increases the precision of the study

Sampling with and without replacement


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SAMPLE SIZES

Sample sizes for estimating disease

prevalence in large populations- To what degree of accuracy do we require the

results?- What sampling method have we used?- What is the size of the smallest subgroup in

the population for which we require accurateanswers?

- What is the actual variability in the populationsurveyed of the variable we wish to measure?

SAMPLE SIZES

Sample sizes needed to detect the presence

of a disease in a population concerns withthe minimum sample size required to find at leastone worker with the disease

Methods of Obtaining Data

Interviews and Questionnaires

Questionnaire Functions:

1. Provides data on individuals which may not beavailable from any other source includingwork lace records or environmentalmeasurements

2. Permits targeted studies of specific workplaceproblems



Questionnaire Functions:

3. Provides information about participantcharacteristics that are necessary for properanal sis and inter retation of ex osure-outcomerelationships, especially possibly confoundingvariables like age and education, and otherlifestyle variables that may affect disease risk likesmoking and diet



Types of Questionnaires:

Mailed Questionnaire

Telephone Questionnaire

- -

Hybrid study design combination of the 3types



Stages of Survey Design

Stage 1 Survey Design and PreliminaryPlanning

Stage 3 Final Survey Design and Planning

Stage 4 Data collection

Stage 5 Data reduction, data file construction,analysis and final report


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Measurement Aspect of Questionnaire Design

Validity

degree to which a questionnairederived

number approaches its true, but possibly unknown,

value.

Reliability measures the likelihood that a given

measurement will yield the same result on repetition,

whether that result is close to the truth or not.



Questionnaires Content, Quality and Length

1. Wording2. Question sequence and structure

.

4. Length

5. Language

6. Clarity and leading questions

7. Questionnaire layout

Basic Considerations in the design ofEpidemiological Investigations

Objectives and Hypothesis

Figure5. Schematic Diagram in the formulation of Objective/Hypothesis (FAO)


Hypothesis

Four Methods involved:

1. Method of Difference if the frequency of adisease is markedly different under two separatecircumstances; cause of disease may be thefactor absent in one circumstance and present inthe other.

2. Agreement if a factor is common to a numberof different circumstances that are associated with

the presence of the disease = may be a cause ofthe disease


Hypothesis

Four Methods involved:

3. Concomitant variation involves the search for

a factor whose frequency or strength varies withthe frequency of the disease

4. Analogy uses the process of deductivereasoning, whereby epidemiological principlesalready established are applied to othersituations.


Hypothesis

Consideration in the Formation of Hypothesis:

1. New hypotheses are commonly formed by

relating observations from several different fields2. The stronger a statistical association, the morelikely it is to suggest a causal hypothesis =Relative risk

3. Observations of change in frequency of diseaseover time have been very productive i.e.,particularly of changes that have occurred overrelatively short period of time.


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Hypothesis

Consideration in the Formation of Hypothesis:4. An isolated or unusual case should receiveparticular attention in the formation of hypothesis

5. Observations that appear to be in conflict or tocreate a paradox are particularly worthy ofconsideration


Hypothesis

How to state a hypothesis:1. The characteristics of the persons to whom thehypothesis applies

2. The cause of being considered usually anenvironmental exposure

3. The expected effect the disease


Hypothesis

How to state a hypothesis:

4. The exposure-response relationship theamount of cause needed to lead to a stated risk ofthe effect

5. The time-response relationship the timeperiod that will elapse between exposure to thecause and the appearance of effect

Sources of OccupationalEpidemiological data

Employee interviews

Employer personnel and production records(these include work records, job descriptions,

,inventories)

Expert judgement


Biomonitoring data

Industrial hygiene records (area, personnel, andcompliance monitoring, and surface wipe

,comprehensive survey reports)


The use of existing data:

Advantages:

cheaper time efficient

able to monitor progress of a disease throughdifferent worker population and able to establishlinkages between disease events

reduced chance of bias


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The use of existing data:

Disadvantages:

data sets are often incomplete

data sources may have been collected forpurposes other than the study objective

Instituting Control Measures

Engineering control

Administrative control includerecommendations and guideline to

PPE control

Note: Ensure that all control measures are wellcommunicated to the workers at a level oftheir understanding

Monitoring and Surveillance

Surveillance continuous observation of diseaseor other safety- and health-related problems ingeneral in a number of different workingpopulations

Monitoring continuous observation of a specificdisease in a particular working population


Surveillance Provide a means of detecting significantdevelopments in existing disease situations Provide a comprehensive and readilyaccess e a a ase on sease, n ury or o erhealth and safety-related problems in workingpopulations for research and planning purposes.


Monitoring If control measures are being employed,provides a means to ascertain whether these

measures are being carried out promptly ande c en y as spec e n e program es gn It provides a means to ascertain whether thecontrol measures being applied are having thedesired and predicted effect on disease incidence~ prompt and comprehensive disease-reportingsystem.


Monitoring It provides a means for a rapid detection ofdevelopments which might jeopardize the control

program, or, in instances where no controlmeasures are e ng mp emen e , w c m gwarrant the introduction of control activities.


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Problems in Occupational Epidemiology

Internal Validity: Selection bias

Self-selection bias Diagnostic bias Bias resultin from refusal to artici ate in astudy

Information bias Differential outcome assessment in prospectivefollow-up (cohort) studies Differential losses in retrospective cohort studies Differential assessment of exposure in case-control studies

Problems in Occupational Epidemiology

Internal Validity: Confounding

Interaction or effect modification

External Validit : can be addressed only after ensuring that internalvalidity is secured.

Applications of OccupationalEpidemiology

Benefit for the workers Benefit for the community at large

Summary

Epidemiological investigation of occupationalhealth and safety concerns is a vital aspect ofclinical epidemiology and occupational hygienesince it rovides essential and ractical informationto be aware of the causes and determinants ofwork-related ill health and injury, which thereby helpin establishing necessary control measures oractions to take to reduce those risks and toevaluate the interventions for the benefit of the

workers and of the community at large.

References

Agius, Raymond. (2006). Occupational Epidemiology. Retrieved December 20,2012, from http://www.agius.com/hew/resource/occepi.htm.

College of Veterinary Medicine, Nursing and Allied Health. (n.d). Epidemiology.USA: Tusekgee University. Retrieved December 30, 2012, fromhttp://www.onemedicine.tuskegee.edu/Epidemiology/chap5_3.htm.

i l i i i ii l i i i i . . .epidemiological approach in investigating disease problems.Veterinary Epidemiology and Economics in Africa. RetrievedDecember 20, 2012, from http://www.fao.org/wairdocs/ILRI/x5436E

/x5436e06.htm.

Hansen, Eva S., et.al. (2007), Time trends in cancer risk and pesticide exposure,a long-term follow-up of Danish gardeners. Scandinavian Journal ofWork, Environment & Health, Vol. 33, No. 6. Denmark: ProquestCentral, pages 465-469.

References

ILO. (n.d). Epidemiology. Encyclopedia of Occupational Health and Safety, 3rd

ed. Retrieved November 24, 2012, from http://www.ilo.org/safework_bookshelf/english?d&nd=170000102&nh=0.

MacMahon, B. and Trichopoulos, D. (1996). Strategies of Epidemiology.

Epidemiology Principles and Methods, 2nd ed. Boston: Little Brown,pages 65-84.

Thomsen, Catherine, MPH, et.al. (2007). Indicators for Occupational Health

Surveillance. CDC: MMWR Recommendations and Reports.Retrieved December 12, 2012, from http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5601a1.htm.

Wikipedia. (n.d). Case control study diagram. Wikipedia: The FreeEncyclopedia. Retrieved December 29, 2012, fromhttp://en.wikipedia.org/wiki/Case-control_study.


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Epidemiological Investigation on OHS Concerns

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