Ch.2 Environmental Epidemiology

Bias

"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." Porta M. A Dictionary of Epidemiology. 5th ed. New York, NY: Oxford University Press; 2008.

Provides a measure of the lethality of a disease.

A London surgeon thought to be the first individual to describe an environmental cause of cancer. Chimney sweeps had high incidence of scrotal cancer due to contact with soot

Host in the "Triangle"

A host is "a person or other living animal, including birds and arthropods, that affords subsistence or lodgment to an infectious agent under natural conditions."

Agent in the "Triangle"

Agent refers to "A factor, such as a microorganism, chemical substance, or form of radiation, whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of a disease."

Major Historical Figure: John Snow

An English anesthesiologist who linked a cholera outbreak in London to contaminated water from the Thames River in the mid-1800s. Snow employed a "natural experiment," a methodology used currently in studies of environmental health problems.

Hill's Criteria of Causality

Biological gradient Plausibility Coherence\Strength Consistency Specificity Temporality

Causality

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

Methodology for Study Designs

Characteristic study designs used frequently in environmental epidemiology: Cross-sectional Ecologic Case-Control Cohort

Epidemiology's Contributions to Environmental Health

Concern with populations Use of observational data Methodology for study designs Descriptive and analytic studies

Confounding

Denotes "... the distortion of a measure of the effect of an exposure on an outcome due to the association of the exposure with other factors that influence the occurrence of the outcome."

Two Classes of Epidemiologic Studies

Descriptive Depiction of the occurrence of disease in populations according to classification by person, place, and time variables. Analytic Examines causal (etiologic) hypotheses regarding the association between exposures and health conditions.

Concern with Populations

Environmental epidemiology studies a population in relation to morbidity and mortality. Example: Is lung cancer mortality higher in areas with higher concentrations of "smokestack" industries?

Use of observational data

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

Study Designs Used in Environmental Epidemiology

Experimental Case Series Cross-Sectional Ecologic Case-Control Cohort

Limitations of Epidemiologic Studies

Long latency periods Low incidence and prevalence Difficulties in exposure assessment Nonspecific effects

Measures of Disease Frequency

Prevalence Point prevalence Incidence Incidence rate Case fatality rate

Case Fatality Rate

Provides a measure of the lethality of a disease.

Point Prevalance

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

Prevalance

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

Healthy Worker Effect

Refers to the observation that employed populations tend to have a lower mortality experience than the general population. The healthy worker effect could introduce selection bias into occupational mortality studies.

Study Endpoints

Self-reported symptom rates Physiologic or clinical examinations Mortality

Incidence

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

Relative Risk (RR)

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

Environmental Epidemiology

The study of diseases and health conditions (occurring in the population) that are linked to environmental factors. These exposures usually are involuntary.

Environment in the "Triangle"

The term environment is defined as the domain in which disease-causing agents may exist, survive, or originate; it consists of "All that which is external to the individual human host."

What is the Epidemiologic Triangle?

Used for describing the causality of infectious diseases Provides a framework for organizing the causality of other types of environmental problems