Chapter 2: Environmental Epidemiology

John Snow

"Father of Epidemiology", studied the London Cholera epidemics of 1848 & 1854, suspected it was from the water, as most cases were found close to the Broad Street pump

Hippocrates

"Founder of Medicine" During the Golden Age in Greece he was a scientist that believed all diseases came from natural causes. He also had high ideals for physicians & an oath was made that is still used today

Sir Percival Pott

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

Agent

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

Case-control study

A study in which subjects who participate are defined on the basis of the presence (cases) or absence (controls) of outcome of interest. Association between exposure and outcome is measured by the odds ratio (OR)

Ecological study

A study in which the units of analysis are populations or groups of people rather than individuals

Cross-sectional study

A study that examines the relationship between diseases (or other health-related characteristics) and other and other variables of interest as they exist in a defined population at one particular time

Cohort study

A type of epidemiologic study where a group of exposed individuals (individuals who have been exposed to the potential risk factor) and a group of non-exposed individuals are followed over time to determine the incidence of disease

Epidemiologic triangle

Agent, host, environment

What's the difference between descriptive epidemiology and analytic epidemiology?

Descriptive epidemiology refers to the depiction of the occurrence of disease in populations with the classification by person, place, and time. On the other hand, analytic epidemiology examines causal hypotheses regarding the association between exposures and health conditions.

Explain the reason why studies of the health effects of smoking among individuals who smoke would not be concern of environmental epidemiology.

Environmental epidemiology is focused in diseases and health conditions towards organisms (especially humans) that are linked to environmental factors. Smoking is much as an internal health risk towards individuals who personally smokes.

List the reasons why epidemiology is important to research studies of environmental health.

Epidemiology is important to the study of environmen- tal health problems because many exposures and health effects associated with the environment occur at the popula- tion level; the epidemiologic methods of natural experi- ments and observational techniques are appropriate; the study designs used in epidemiologic research can be applied directly to the study of environmental health issues; and epidemiology aids in the development of hypothesis and the study of casual relationships.

Analytic epidemiology

Examines causal (etiologic) hypotheses regarding the association between exposures and health conditions

What does early epidemiology share in common with contemporary epidemiology in term of examining the casualty of health problems?

Hippocrates emphasized the role of the environment as an influence on people's health, proposing that environmental and climatic factors such as the weather, seasons, and prevailing winds; the quality of air, water and food; and one's geographic location were influential in causing changes in human health.

Why are cohort studies are an improvement over case-control studies with respect to measurement of exposure data?

If exposure measurement occurs before disease occurrence, cohort studies are much less prone to differential measurement error.

Case series study

Information about patients who share a disease in common is gathered over time

Natural experiments

Naturally occurring events or phenomena having somewhat different conditions that can be compared with almost as much rigor as in experiments where the investigator manipulates the conditions

Case fatality rate

Percentage of population that dies from a specific disease

Describe the importance of the contributions of Sir Percival Pott to environmental health, particularly in the area cancer prevention.

Pott's research helped chimney sweeps to prevent scrotal cancer by using protective clothing, and it also allowed for future research on environmental causes of cancers.

How is ecologic analysis is used to study the health effects of air pollution?

Researchers measures the association between average exposure to air pollution within a census tract and the average mortality in that census tract.

Criteria of Causality

Strength, consistency, specificity, temporality, biological gradient, plausibility, coherence

Incidence rate

The rate at which new events occur in a 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.

Exposure assessment

The study of how much of a substance humans absorb through inhalation, ingestion, or skin absorption.

Bias

The systematic and consistent deviation from objective truth due to either self-interest or dogmatic belief systems.

Latency period

The time interval between initial exposure to a disease-causing agent, and the appearance of the disease or its manifestations in the host

Why are most studies conducted in the field of environmental epidemiology non-experimental?

The use of experimental methodology in environmental epidemiology is difficult to achieve. The majority of research on health outcomes associated with the environment uses observational methods.

Population at risk

Those in the population who are susceptible to a particular disease or condition

What is meant by a cause in environmental epidemiology? Apply Hill's criteria of causality to an example of an association between a specific environmental exposure and health outcome.

*There are four main topics that consider the causes of the environment epidemiology: 1.) Air pollution 2.) Water pollution 3.) Climate change 4.) Chemicals * Hill's 7 Criteria of Casualty: 1.) Strength- (e.g. large increase in scrotal cancer among chimney sweeps) 2.) Consistency- (e.g. relationship between smoking and lung cancer) 3.) Specificity- (e.g. limited to specific workers and to particular sites and types of disease) 4.) Temporality- (e.g. if we assert that air pollution causes lung cancer, we first must exclude persons who have lung cancer from our study; then follow those who are exposed to air pollution to determine whether lung cancer develops.) 5.) Biological Gradient- (e.g. the linear association between the number of cigarettes smoked and the lung cancer death rate) 6.) Plausibility- (e.g. the association between exposure to tars and oils and the development of scrotal cancer is plausible in view of current knowledge about carcinogenesis.) 7.) Coherence- (e.g. cigarette smoking and lung cancer come from the rise in the number of lung cancer deaths associated with an increase in smoking, as well as lung cancer mortality differences between men and women)

Polychlorinated biphenyls (PCBs)

A group of industrial compounds used to manufacture plastics and insulate electrical transformers, and responsible for many environmental problems

Intervention study

An investigation involving intentional change in some aspect of the status of the subjects

Host

An organism on which a parasite lives

Why is epidemiology sometimes called "population medicine?"

Because it has a unique characteristics of epidemiology that makes it study the entire population.

Why are cross-sectional studies are defined as prevalence studies?

Because they assess the prevalence of exposures and health outcomes at a point in time.

Epidemiology

Branch of medical science concerned with the incidence, distribution, and control of diseases that affect large numbers of people.

Explain the work of John Snow using the methodology of the natural experiment.

John Snow used the methodology of the natural experiment to investigate the cholera outbreak. He provided expert witness testimony on behalf of industry with respect to environmental exposure to potential disease agents.

Descriptive epidemiology

The aspect of epidemiology concerned with organizing and summarizing health-related data according to time, place, and person

Confounding

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

Odds Ratios (OR)

The measure of association between exposure and outcome used in case-control studies

Prevalence

The number or proportion of cases of a particular disease or condition present in a population at a given time

Incidence

The number or rate of new cases of a particular condition during a specific time

Point prevalence

The percentage of people in a given population who have a given disorder at any particular point in time