Population-level

The study of the amount and distribution of disease within a population.

Tools: surveillance, vital statistics

Data are often collected on an ongoing basis

Conducted mainly by federal, state, and local health agencies

The study of determinants of disease or reasons for relatively high or low frequency in specific groups.

Tools: focused investigations

Data collected to test a hypothesis

Conducted by health agencies and academic researchers

# of new cases of a disease

# at risk of developing the disease

during a specified time period

# of cases present

# in the population

at a specified time

A population that cannot accept new members and for whihc members cannot become non-members

Defined population in which all members are biologically capable of developing the disease (susceptible to disease with a non-zero risk of developing the disease, not a high-risk of developing the disease).

Whether a person is at risk for the disease may change over time, with short vs. long-term differences in risk status

Already has the disease

Not biologically capable of getting the disease (a woman is not at risk for getting prostate cancer)

has acquired immunity

susceptible / at risk --> diseased --> susceptible / at-risk

vs.

susceptible / at-risk --> diseased

or

susceptible / at-risk --> diseased --> immune

Course of a disease from onset to resolution (Last, 1995)

Course of progression if no medical intervention is taken and disease is allowed to run its full course (Timmreck, 1998).

Proposed models to organize our thinking about multiple causes of disease:

The Epidemiological Triangle

The Wheel Model

Web of Causation

Chinese Boxes

Implies that the agent, host and environment must each be analyzed to understand patterns of disease

Environment, agent, and host at the corners of triangle

Time is in the center

Example: Legionnaire's Disease

Environment: aqueous reservoir

Agent: legionellae bacilli

Host: susceptible host (age, smoking, diabetes, lung disease)

Time!

Implies multiple etiologic factors

Recognition of genetic susceptibility

The genetic core is surrounded by the social environment, biologic environment, and physical environment.

Example: HIV Infection

Genetic core: genetic variants in CCR5 and other genes

Social Environment: Culture of IV Drug Use

Biologic Environment: HIV Strain

Physical Environment: Contaminated Needles

Effects develop as a result of chains of causation.

Each link is the result of a complex geneaology of antecedents.

Example: Breast Cancer

Set of boxes graduated in size so that each fits into the next larger one. Integrates factors at many levels of organization: micro-level, individual-level, and macro-level causes.

Example: Obesity

Micro-level causes: genetic differences in leptin, leptin receptors, satiety, tolerance for high intensity exercise.

Individual-level causes: eating and energy expenditure choices.

Macro-level causes: obesogenic environment with plentiful inexpensive, fat and caloric dense foods and physical exertion engineered out of our daily lives.

1. Define the outbreak and validate its existence

2. examine the distribution of cases by time and place

3. look for combinations/interactions of relevant variables

4. develop hypotheses

5. test hypotheses

6. recommend control measures

7. compile findings

8. disseminate findings for future learning

are there more cases of a known disease than would normally be expected?

pandemic

epidemic

pandemic