Epidemiology 3617

What is Epidemiology?

Study of occurrence and distribution of health-related states
Application of knowledge to control health problems

Surveillance

• Ongoing collection and interpretation of data
• Data is used to
—Assess/monitor population health states
—Investigate, diagnose, and address health problems
• Evaluate the effectiveness of interventions
• CDC does this for U.S.

Levels of Disease

• Endemic
—Baseline, expected presence of disease
• Epidemic
—Presence of disease above the expected level
• Pandemic
—Epidemic that has spread to a larger scale

Investigation

• Systematic inquiry after a disease is detected through surveillance
• Outbreak investigations
—Infectious diseases traced back to the source

Analytic Studies

• Include valid comparison group
• Often conducted with surveillance/investigations

Evaluation

• Determine effectiveness of an intervention
• Formative
—Conducted during planning and implementation
• Summative
—Conducted on well-established programs
—Measures overall outcomes

Linkages

• Interprofessional team approach
• Various geographical locations often involved
• Maintenance of these _______ is essential
--Promotes collaboration and outcome improvement

Policy Development

• Findings from investigations can be used to influence policy
• Epidemiologists often called upon to assist in policy development

Epidemiological Models (1 of 2)

• Epidemiologic triangle

• Agent (cause of disease)
• Host (carrier of disease)
• Environment

Epidemiological Models (2 of 2)

• Natural History of Disease
• Shows expected disease progression without intervention
Stage of Susceptibility, Subclinical, Clinical, Recovery | Disability | Death

Observational studies

Case reports – Detailed single case

Cross-sectional – Data at single point in time (snapshot)

Case-control – Compare past exposure

Cohort – Follow groups over time

Experimental studies

Randomized controlled trial (RCT) Quasi-experimental

Incidence

• Number of new cases during specific time period
• Only those at risk are included in denominator
Example: Only those with a uterus are counted in _______ of uterine cancer

Prevalence

• Number of people who have a disease at a specific point in time
• Counts all new and existing cases

Crude mortality rate

Number of people who died from all causes during a certain time period
Divided by total population

Cause-specific mortality rate

Number of deaths from a specific cause
Divided by total population

Sensitivity

• Ability of test to detect “true positive”
• Indicates people who have the disease

Specificity

• Ability of test to detect “true negative”
• Indicates people that do not have the disease

Appendix 1: Stages of Disease

• Exposure occurs between susceptibility and subclinical.
• Pathologic changes occur in subclinical.
• Onset of symptoms occurs between subclinical and clinical.
• Usual time of diagnosis occurs toward the beginning of clinical