Eohs 5300: Ch2, Environmental Epidemiology

Front 1

How do scientists study the effects of environmental factors-such as man-made and natural substances, and radiation- on human health?

Back 1

Through Environmental epidemiology.

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Environmental epi is:

Back 2

the study of diseases and health conditions in populations that are linked to environmental factors
-exposure (air, water, food, occupational environments)
-association between environmental factors (exposures) and health outcomes.

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Hippocrates (talked about this guy in chapter 1 as well) 460 BC-370 BC)

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Greek physician and "father or western medicine:
wrote book :on airs, waters and places

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Another major historical figure:
Sir Percival Pott (1714-1788)

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-A London surgeon though to be the first individual to describe an environmental cause of cancer.
-chimney sweeps had a high incidence of scrotal cancer due to contract with soot

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Major historical figure: John Snow

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An English Anesthesiologist who linked a cholera outbreak in London to contaminated water from the Thames River in the mid- 1800s.
-disease pattern
-dot map

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Epidemiology's contributions to environmental health

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-concern with populations
-use of observational data
-methodology for study designs
-descriptive and analytic studies

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Concern with populations:

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Environmental epi studies a population in relation to morbidity and mortality
-example: lung cancer mortality is higher in areas with higher concentration of "smokestack" industries?

Hint 7

mortality or mortality rate
morbidity or morbidity rate

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use of observational data

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epidemiology is primarily an observational science that take advantage of naturally occurring situations in order to study the occurrence of disease.

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Methodology for study designs:

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ecological study
cross sectional study
case-control
cohort

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Two classes of epidemiologic studies:
descriptive and analytic

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descriptive- person, place and time variables
analytic- examines causal (etiologic) hypotheses regarding the association between exposures and health conditions

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Ecological study

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the unit of analysis is a population rather than an individual

Hint 11

"an association study between air pollution and lung cancer deaths in different countries"
-"an analysis of the effects of disinfection byproducts on newborn babies, using 109 Massachusetts towns as untis of analysis"

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Cross-sectional study

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A sample of persons from a population is enrolled and their exposures and health outcomes are measured simultaneously

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To assess the prsence (prevalence) of the health outcome at that poin of time without regard to duration.
-Cross sectional study of diabetes
-some with diabetes for many years
-other with diabetes recently diagnosed

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Case-control study

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To associate the disease with a previous exposure(s)
-compare previous exposures between
a group of people with disease (case) vs. a group of people without disease (control)
control group=baseline data

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Cohort study

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Form a cohort and record if each participant is exposed or not exposed and then track them to see if they develop the diease of interest.

Hint 14

prospective or follow-up cohort
-retrospective cohort

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measures of diease frequency:

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prevalence
-point prevalence
-incidence
-incidence rate
-case fatality rate

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Prevalence

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the number of existing cases of a disease, health condition, or deaths in a population at some designated time.

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point prevalence

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all cases of a disease, health condition, or deaths that exist at a particular point in time relative to a specific population from whcih the cases are derived

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incidence

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the occurrence of new disease or mortality whithin a defined period of observation (e.g.; week, month, year or other time period) in a specific population

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CFR-case fatality rate

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provides a measure of the lethality of a disease

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Relative risk

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The ratio of the incidence rate of a disease or health outcome in an exposed group to the incidence rate of the diease or condition in a non-exposed group

Hint 20

a/a+b// c/c+d

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Odds ratio

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A measure of the association for case-control studies
Exposure-odds ratio:
refers to the ratio of odds in favor of exposure among the case (A/C) to the odds in favor of exposure among the non-cases (the controls b/d)

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What is the epidemiologic triangle?

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used for describing the casuality of infectious disease.
-provides a framework for organizing the casuality of other types of environmental problems.

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Host factors

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-personal traits
-behaviors
-genetic predisposition
-immunologic factors
...all influence the chance for disease or its severity

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agents (environmental factors)

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-biological
-physical
-chemical
...necessary for disease to occur

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environment

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-external conditions
-physical or biologic or social
...contribute to the disease process

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Causality

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Certain criteria need to be taken into account in the assessment of a causal association between an agent factor (A) and a disease (B)

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Bradford Hill's criteria of causality

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-strength
-consistency
-specificity
-temporality
-biological gradient
-plausibility
-coherence

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Bias in environmental epi studies

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definition of bias
healthy worker effect
confounding

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defintion of bias

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"systematic deviation of results or inferences from the truth. Processes leading to such deviation. An error in the conception and design of a study -- or in the collection, analysis, interpretation, reporting, publication, or review of data--leading to results or conclusions that are systematically (as opposed to randomly) different from the truth.

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Healthy Worker effect

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refers to the observation that emplyed populations tend to have a lower mortality experience than the general pop.
the healthy worker effect could introduce selection bias into occupational mortality studies

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Confounding

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denotes: "...the distortion of a measure of the effect of an exposure on an outcome due to the association of the xposure with other facotrs that influence the occurrence of the outcome."

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limitations of Epidemiologic studies

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long latency periods
-low incidence and prevalence
-difficulties in exposure assessment
-nonspecific effects