Introduction to Epidemiology

Introduction to Epidemiology

• Epidemiology is derived from Greek words, with "epi" meaning upon, "demos" meaning people, and "logos" meaning thought; thus, it is the study of what happens to people.

Definition of Epidemiology

• Epidemiology is the science of disease occurrence, according to Anderson (1930).
• Epidemiology is the study of the distribution and determinants of disease prevalence in man, according to Mac Mahon et al (1970).
• Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems (Dictionary of Epidemiology, Last 1988).
• Epidemiology is the science of applied, practice-oriented research, intended to advance the general knowledge base for community and clinical medicine (Miettinen OS, 2007).
• Study includes surveillance, observation, hypothesis testing, analytic research, and experiments.
• Distribution refers to analysis of times, persons, places, and classes of people affected.
• Determinants include factors that influence health: biological, chemical, physical, social, cultural, economic, genetic, and behavioral.
• Health-related states and events refer to diseases, causes of death, behaviors such as use of tobacco, positive health states, reactions to preventive regimes, and provision and use of health services.
• Specified populations include those with identifiable characteristics, such as occupational groups.
• Application to prevention and control is aligned with the aims of public health: to promote, protect, and restore health.

Key Concepts in Epidemiology

• Distribution is concerned with the pattern and frequency of health events in a population
• Pattern refers to the occurrence of health-related events by time, place, and person characteristics.
• Frequency refers to the measurement of frequency of health-related events (disease, disability, or death) and summarizing this information in the form of rates and ratios.
• Descriptive Epidemiology describes patterns & frequency
• Determinants are factors that influence the occurrence of health-related events, which epidemiological methods are used to search for.
• Analytic Epidemiology searches for causes & other factors

Health-Related States and Events

• Include communicable diseases, non-communicable diseases, injuries, birth defects, maternal-child health, occupational & environmental health, and behaviors related to health (exercise, seat-belt use, etc.).

Three Inter-Related Components

• Frequency, distribution, and determinants are derived.
• Quantifying disease existence or occurrence is the first step and a prerequisite to investigating patterns.
• Distribution involves descriptive epidemiology (person, place, and time) and forms the basis for hypotheses about causal and preventive factors.
• Determinants are derived from the other two components and allow for testing hypotheses.

Aims and Scopes of Epidemiology

• Epidemiology aims to describe patterns of health and disease within populations, interpret these differences, apply results to public health practice, and evaluate the effect of health-related interventions.
• Ultimate aims of epidemiology include eliminating or reducing community health problems and promoting the health and well-being of society as a whole.
• Scopes include the causation and natural history of disease, health status of the population, and evaluation of interventions.

Historical Background

• The roots of epidemiology trace back to Hippocrates around 463 BC, marking the origin of the field.
• Growth occurred from 1600-1905.
• The field has been in development since 1915 to the present day.
• Hippocrates planted the seed; he described the distribution of diseases by season, age, climate, and personal behavior.
• William Farr, "Father of Vital Statistics," collected and analyzed Britain's morbidity & mortality statistics and examined the effects of marital status, occupation etc. on morbidity & mortality statistics.
• John Snow, "Father of Modern Epidemiology," identified modes of transmission including incubation times, cause & effect and made clinical observations of cholera.
• Doll & Hill (1947) studied the effect of smoking among a cohort of English doctors, with a well-designed epidemiological study that demonstrated the cause (smoking) and effect (lung cancer).

Scope of Epidemiology

• It widens and changes over time.
• Originally a study of epidemics, it then became a study of infectious diseases, later extended to non-infectious diseases, and is now a discipline that is beyond the study of diseases.

Importance of Epidemiology

• Clinical medicine requires knowledge of epidemiology for making diagnoses, treatment plans, and prognoses.
• Epidemiology is the cornerstone of public health, contributing to the eradication and control of communicable diseases, as well as the prevention of non-communicable diseases.
• Achievements include the control of infectious diseases like smallpox and childhood infections through mass immunization, and effective screening for breast and cervical cancer.

Differences

Applications of Epidemiology in Public Health

• Preventing disease and promoting health.
• Community health assessment (Community Diagnosis) and priority setting.
• Improving diagnosis, treatment, and prognosis of clinical diseases.
• Evaluating health interventions and programs.

Epidemiological Approach

• Asking questions to get answers: these are related to health events and health action.
• Making Comparisons of a study group to a contrast group is the basic approach in epidemiology to draw inferences.

Asking Questions

• Related to health events:
  • What is the event, what is the magnitude, where did it happen, when did it happen, who are affected, and why did it happen?
• Related to health action:
  • What can be done to reduce the problem, how can it be prevented in the future, what action should be taken by the community, what resources are required, how are activities to be organized, and what difficulties may arise?

The Epidemiologic Approach Explained

• Counts cases or health events, and describes them in terms of time, place, and person.
• Divides the number of cases by an appropriate denominator to calculate rates.
• Compares these rates over time or for different groups of people.