EPI 2110, Fall 2004Principles of Epidemiology

Instructor: Kevin E. Kip, Ph.D.Assistant Professor, Epidemiology and

Medicine, Graduate School of PublicHealth, Epidemiology Crabtree Hall,

kipk@edc.pitt.edu

Upon completion of this course, the student will:

1. Understand the history and role of epidemiology as the basic science for Public Health.

2. Develop a population-based perspective of disease and other health-related events.

3. Recognize ethical and professional issues in the conduct of epidemiologic research.

4. Calculate and interpret epidemiologic measures of disease occurrence.

COURSE OBJECTIVESCOURSE OBJECTIVES

5. Calculate and interpret measures of effect used to compare the risk of disease between populations and subgroups.

6. Understand features, strengths, and limitations of descriptive, observational, experimental, and genetic epidemiologic studies.

7. Distinguish between association and causation, including knowledge of criteria to evaluate causal associations.

8. Understand roles of chance, bias, and confounding in the evaluation of epidemiologic research.

COURSE OBJECTIVES (cont.)COURSE OBJECTIVES (cont.)

9. Understand the concept of effect measure modification.

10. Understand the dynamics on infectious disease transmission and methodology used to investigate an epidemic outbreak.

11. Understand the role of screening and public health surveillance in applied epidemiology.

12. Recognize the impact of racial, ethnic, and cultural variability in epidemiologic research.

COURSE OBJECTIVES (cont.)COURSE OBJECTIVES (cont.)

Unit 1:

Introduction to Epidemiology

Unit 1 Learning Objectives:

1. Distinguish between the concepts of

disease and health.

2. Define and understand the uses of

epidemiology.

3. Distinguish between public health,

epidemiology, and clinical medicine.

4. Recognize major historical contributions in

epidemiology.

5. Understand the inter-disciplinary nature of

epidemiology.

Unit 1 Learning Objectives (cont.):6. Understand the “epidemiologic transition” of

causes of mortality from developing to developed countries.

7. Understand practical, ethical, and professional issues in conducting epidemiologic research.

8. Recognize the role of Institutional Review Boards in overseeing the conduct of epidemiologic research.

9. Understand the natural history of disease progression.

10.Distinguish between primary, secondary, and tertiary levels of disease prevention.

Assigned Readings:

Textbook (Gordis):Chapter 1 -- IntroductionChapter 20 – Ethical and Professional

Issues in EpidemiologyChapter 5, pages 95-96 (Natural history of disease

World Health Report 2003, Chapter 1: Global health, today’s challenges, pages 1-22.

DEFINITIONS OF DISEASEDEFINITIONS OF DISEASE

• MULTIPLE DEFINITIONS (E.G.):

• An abnormal condition of an organism or part, especially as a consequence of infection, inherent weakness or environment stress, that impairs physiological functioning. (1973)

DEFINITIONS OF DISEASEDEFINITIONS OF DISEASE

• Literally, DIS-EASE, the opposite of ease, when something is wrong with a bodily function.

• The words “disease”, “illness” and “sickness” are loosely interchangeable, but are better regarded as not wholly synonymous.

DEFINITIONS OF DISEASEDEFINITIONS OF DISEASE

• Thus, M.W. Susser has suggested that they be used as follows:

- Disease is a physiological/psychological dysfunction.

- Illness is a subjective state of the person who feels aware of not being well.

- Sickness is a state of social dysfunction, i.e., a role that the individual assumes when ill. (1995)

PRACTICAL DEFINITION OF PRACTICAL DEFINITION OF DISEASE AND EXPOSUREDISEASE AND EXPOSURE

Disease:Disease: broad array of health conditions that we seek to understand and ultimately modify, including physiologic states, mental health, and the entire spectrum of human diseases (synonym: outcome variable).

Exposure:Exposure: a catch-all term for agents, interventions, conditions, policies, and anything that might affect health (synonym: predictor/explanatory variable).

DEFINITIONS OF HEALTHDEFINITIONS OF HEALTH

• WHO: A state of complete physical,

mental, and social well-being and not

merely the absence of disease or

infirmity. (1948)

DEFINITIONS OF HEALTHDEFINITIONS OF HEALTH (cont’d) (cont’d)

• The word “health” is derived from the old English “HAL” meaning hale, whole, sound in wind and limb.

• The state of an organism functioning normally without disease or abnormality. (1973)

Discussion Question 1Discussion Question 1

When we think of studying “disease”,

is “disease” a stable concept?

Discussion Question 1Discussion Question 1

Probably not, because:

1. Cultural values can influence definitions

and perceptions of disease (especially

psychiatric disorders).

2. Improvements in diagnostic

instrumentation can lead to earlier

detection of asymptomatic disease.

3. Clinical thresholds for disease

classification change over time.

EPIDEMIOLOGYEPIDEMIOLOGY

Greek: EPI - Upon

DEMOS - People

LOGOS - Study of, Body of

Knowledge

DEFINITIONS OF EPIDEMIOLOGYDEFINITIONS OF EPIDEMIOLOGY

• The study of the distribution and determinants of disease frequency in human populations. (1970)

• The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems. (1988)

DEFINITIONS OF EPIDEMIOLOGYDEFINITIONS OF EPIDEMIOLOGY

The underlying premise of epidemiology is that disease not occur at random, but rather in patterns that reflect the operation of underlying factors.

DEFINITIONS OF PUBLIC HEALTHDEFINITIONS OF PUBLIC HEALTH

• The science and art of :

1) preventing disease

2) prolonging life and

3) promoting health and efficiency

through organized community effort.

(1920)

DEFINITIONS OF PUBLIC HEALTH (cont’d)DEFINITIONS OF PUBLIC HEALTH (cont’d)

• To fulfill society’s interest in assuring conditions in which people can be healthy.

• The field of health science concerned with safeguarding and improving the physical, mental and social well-being of the community as a whole. (1992)

THE CONTENT OF PUBLIC HEALTH PRACTICETHE CONTENT OF PUBLIC HEALTH PRACTICE

• Focus on primary prevention.

• Community protection through monitoring and surveillance for infectious and toxic agents.

• Response to unanticipated natural and human-generated disasters.

• Health promotion through programs to notify and educate the community about risks and protective measures.

• Target hard-to-reach populations with clinical services.

Why is epidemiology the basic science of Why is epidemiology the basic science of public health?public health?

PUBLIC HEALTH WORKS BY:• Defining a health problem• Identifying risk factors associated with the

problem• Developing and testing community-level

interventions to control or prevent the causes of the problem

• Implementing interventions to improve the health of the population; and

• Monitoring those interventions to assess their effectiveness

EPIDEMIOLOGY HAS THE METHODOLOGY TO:

• Determine the extent of disease in the community

• Study the natural history and prognosis of disease

• Identify associations and potential etiology (causes) of a disease and risk factors for disease

• Evaluate new preventive and therapeutic measures and new modes of health care delivery

EPIDEMIOLOGY HAS THE METHODOLOGY TO:

• Provide a foundation for developing public policy and regulatory decisions relating to environmental problems.

• In short, the primary goal of epidemiology is to measuremeasure relationships between “exposures” and health outcomes – these may provide a basis for public health initiatives and policies.

THE RELATIONSHIP BETWEEN EPIDEMIOLOGY + CLINICAL PRACTICE

Clinical Practice Uses Population Data:

• Diagnoses are defined and determined from large groups of patients.

• Prognosis is based on experience of large groups of patients with the same disease, stage of disease, and treatments.

• Selection of therapy is based on the results of large treatment studies, such as clinical trials.

Discussion Question 2Discussion Question 2

Why do we study the epidemiology

of diseases in large populations,

such as the community, rather than

focusing on treatment settings?

Discussion Question 2Discussion Question 2

Because:

1. Early development of disease can be assessed more readily in the community.

2. Many individuals with disease do not seek treatment.

3. Many individuals with disease do not have access to or the resources to receive treatment.

Discussion Question 2Discussion Question 2

Because:

4. The co-occurrence of multiple diseases, and ascertainment of familial risks, is better accomplished through an epidemiological framework.

5. Threshold levels between sub-clinical and clinical disease are better determined from individuals not in treatment settings.