Introduction to epidemiology and demography

Introduction to the Fundamentals of Epidemiology

Basic Epidemiology

What is Epidemiology?

Epidemiology
Epidemiology is the study of the determinants, distribution, and frequency of disease Who gets disease and why Epidemiologists study sick and well people to determine the crucial difference between those who get disease and those who are spared

Important Issues that Epidemiology can Address

Disease
Mortality
Hospitalization
Disability
Quality of Life
Health Status
It’s not just disease!


Epidemiology
Epidemiology weighs and balances Epidemiology contrasts and compares Epidemiologists use RATES events/population at risk

What is Epidemiology?

Some describe it as the study of epidemics What is an epidemic? An epidemic occurs when there are significantly more cases of the same disease than past experience would have predicted.

Uses of Epidemiology

To study the cause (or etiology) of disease(s), or conditions, disorders, disabilities, etc. determine the primary agent responsible or ascertain causative factors determine the characteristics of the agent or causative factors define the mode of transmission determine contributing factors identify and determine geographic patterns

Uses of Epidemiology

To determine, describe, and report on the natural course of disease, disability, injury, and death. To aid in the planning and development of health services and programs To provide administrative and planning data

Example: Use of Epidemiology

In the United States, the National Center for Health Statistics is a data source for information on health and disease http://www.cdc.gov/nchs Globally, the World Health Organization is a data source for information on health and disease http://www.who.int

Leading Causes of Death, USA, 2000

(number of deaths)
1. Heart Disease
2.
Neoplasms
3.
Cerebrovascular Disease
4. Chronic Pulmonary Disease
5. Accidents/Injuries
6. Diabetes mellitus
7. Influenza and pneumonia
8. Alzheimer’s Disease 9. Nephritis, nephrotic syndrome
10. Septicemia

Leading Causes of Death Worldwide, 2000

(Based on number of global deaths)
1. Ischemic Heart Disease
2.
Cerebrovascular Disease
3.
Lower Respiratory Infections
4. HIV/AIDS
5. COPD
6. Perinatal Conditions
7. Diarrhoeal Diseases
8. Tuberculosis
9. Road Traffic Injuries
10. Lung Cancers
WHR 2001

Purpose of Epidemiology

To provide a basis for developing disease control and prevention measures for groups at risk. This translates into developing measures to prevent or control disease.

Two Broad Types of Epidemiology

Descriptive Epidemiology Examining the distribution of disease in a population, and observing the basic features of its distribution Analytic Epidemiology Testing a hypothesis about the cause of disease by studying how exposures relate to the disease

Three essential characteristics of disease that we look for in descriptive studies are...

Person Place Time

Person

Age, gender, ethnicity Genetic predisposition Concurrent disease Diet, exercise, smoking Risk taking behavior SES, education, occupation

Place

Geographic place presence or agents or vectors climate geology population density economic development nutritional practices medical practices

Time

Calendar Time Time since an event Physiologic cycles Age (time since birth) Seasonality Temporal trends



Three essential characteristics that are examined to study the cause(s) for disease in analytic epidemiology are...
Host Agent Environment

Host

Environment
Agent
Epidemiologic Homeostasis

The Epidemiologic Triangle

Host Factors Personal traits behaviors genetic predisposition immunologic factors
Agent
Host
Environment
Influence the chance for disease or its severity

The Epidemiologic Triangle

Agents Biological Physical Chemical
Agent
Host
Environment
Necessary for disease to occur

The Epidemiologic Triangle

Environment External conditions Physical or biologic or social
Agent
Host
Environment
Contribute to the disease process

Epidemics arise when host, agent, and environmental factors are not in balance

Due to new agent Due to change in existing agent (infectivity, pathogenicity, virulence) Due to change in number of susceptibles in the population Due to environmental changes that affect transmission of the agent or growth of the agent

Epidemiologic Activities

…are often framed under the mantle of descriptive and analytic epidemiologyDescriptive epidemiology – person, place & timeDemographic distributionGeographic distributionSeasonal patterns etc.Frequency of disease patternsUseful for:Allocating resourcesPlanning programsHypotheses development

Controlled Trials of Community Interventions

The Demographic Transition

Demographic/ Epidemiologic Transition Framework