Introduction to Epidemiology: Concepts and Scope

Introduction to Epidemiology

• The presentation is about epidemiology, concepts, uses and scopes
• It is presented by Dr. Saúl Gallardo Aguilar, from the Department of Microbiology, San Salvador, January 2025
• The core objectives are:
  • Defining basic concepts of epidemiology
  • Discussing functions of epidemiology
  • Enumerate the usages, scopes, and objectives of epidemiology

Definition of Epidemiology

• The word epidemiology comes from the greek words:
  • "EPI": Means "over" or "about"
  • "DEMOS": Stands for "town" or "population"
  • "LOGOS": Is "study" or "treatise"
• Epidemiology refers to the study of events that occur above populations

Essence of Epidemiology

• Epidemiology is the part of medicine that studies:
  • Distribution
  • Frequency
  • Determinants
  • Relations
  • Predictions
  • Control of factors related to health
  • Diseases in specific human populations

Factors Studied in Epidemiology

• Epidemiology studies the health of human groups in relation to their environment
• Factors considered are:
  • Lifestyle (promiscuity, drugs, stress, labour risk and mismanagement)
  • Human biology (heredity, aging and congenital malformations)
  • Health system organization (promotion, prevention and rehabilitation)
  • Environment (physical, cultural, social, educational and labour)

Historical Perspective

• Hippocrates is considered the precursor of epidemiology.
• He has always been interested in relationship between diseases and the environment.

Functions of Epidemiology

• Epidemiology identifies health problems in a community
• Epidemiology describes the natural history of diseases
• Epidemiology discovers factors that increase the risk of contracting a disease or its etiology
• Epidemiology clarifies possible mechanisms for transmitting diseases
• Epidemiology predicts behavioral trends associated with a disease
• Epidemiology identifies whether an illness or health problem is preventable and/or controllable
• Epidemiology identifies the most appropriate intervention strategy
• Epidemiology tests effectiveness of intervention strategies

Epidemiology Applications

• Epidemiology knows the magnitude of interventions benefits, when applied, on the disease in the population
• It evaluates intervention programs
• Modern and evidence based medicine is based on the method of epidemiology

Epidemiology Goals

• Anciently, epidemiology usage was limited to study infectious diseases
• Currently, in addition to studying infectious diseases behavior, it studies all population groups health
• Epidemiological factors present in the health-disease process are essential to consider

Epidemiological Triangle

• The Epidemiological Triangle consists of:
  • Environment (physical, social, and economic conditions)
  • Agent (bacteria, virus, parasite, toxins, etc.)
  • Host/Subject (Animal/Human being)
• Changing any of these components will change the existing balance
• Change can either increase or decrease the frequency of the disease
• They can be called causal/determinant factors of the disease.

Epidemiology Branches

• Epidemiology has different sub-branches that study diseases

Descriptive Epidemiology

• Descriptive Epidemiology describes the:
  • Epidemiological phenomenon in time
  • Place
  • Person
• It quantifies the frequency and distribution of the phenomenon through measures of:
  • Incidence
  • Prevalence
  • Mortality

Analytical Epidemiology

• Through observation or experimentation, Analytical Epidemiology establishes possible causal relationships.
• This is done between factors to which people and populations are exposed.
• Those factors are associated to the diseases they present

Experimental Epidemiology

• Busca, mediante el control de las condiciones del grupo a estudiar, sacar conclusiones más complejas que con la mera observación no son deducibles. Se ocupa de realizar estudios en animales de laboratorio y estudios experimentales con poblaciones humanas .

Ecoepidemiology

• Ecoepidemiology uses ecological tools.
• It integrally studies how environmental factors interact with:
  • People
  • Populations in surrounding environments
• How this interaction can influence the evolution of diseases.

Environment Considerations

• Environment involves more than living spaces.
• It covers all:
  • Living beings
  • Objects
  • Water, soil, and air interactions
  • Intangible elements of culture.

Environment Influence

• The environment is the surroundings that affects and conditions life’s circumstances.
• It encompasses natural, social and cultural values in specific time.
• This exists in a location that influences human and future generation´s life

Contributions to Epidemiology

• Analyzing the role of causal agents, host, and environmental factors in disease natural history is essential.
• Describing the frequency/distribution of diseases based on:
  • Age
  • Ethnicity
  • Gender
  • Occupation
  • Incidence in time and space is helpful for community's diagnostics.
• It helps for estimate:
  • Morbidity
  • Mortality risks

Knowledge and Studies in Epidemiology

• Contributing to knowledge of disease processes causes, by observing:
  • Amplitude
  • Clinical behavior of syndromes.
• Studying immediate health problems such has:
  • New diseases.
  • Management problems
• Evaluating efficiency on:
  • Control
  • Eradication programs

Usages and Aplications in Epidemiology

• One can infer many uses and action areas, from the scope and purposes of Epidemiology, such as:
  • Establishing a health situation diagnosis in a community or region.
  • Evaluating the effect of therapeutic measures.
  • Studying disease´s causes
  • Completing the clinical picture of the disease.
  • Evaluating health services.

Glossary of Terms

• A glossary is a compilation of definitions/explanations regarding a topic, in alphabetical order.
• Terms in epidemiology are:
  • Outbreak
  • Case
  • Endemic
  • Epidemic
  • Risk Factor
  • Incidence
  • Lethality
  • Morbidity
  • Mortality
  • Pandemic
  • Population
  • Prevalence
  • Risk.
  • Susceptible
  • Rate

Outbreak

• A localized epidemic.
• A localized increase in:
  • Disease incidence
  • Town
  • Confined institution

Case

• In epidemiology, it refers to a person from de population or a study group.
• This possess a particular disease, sanitary disturbance, or a process under investigation.

Endemic

• Continuous presence of a disease or infectious agent in a determined geographic area.
• It can denote the usual prevalence of a particular disease in that area.

Epidemic

• Manifestation of cases of an illness (or outbreak).
• Happens in in a community or region.
• Frequency exceeds normal expected.

Risk Factor

• It is the behavior, environmental exposition, or characteristics that associates process related to health.
• A key action is to avoid its apparition

Incidence

• It is the number of new cases that appear in a given time.
• Considered within a population that is known

Lethality

• Number of deaths that occurs in an affected group by certain damage

Morbidity

• Any change in the state of physical or mental health.
• It can be expressed in terms of sick people

Mortality

• It is the deaths that occurred in the population (healthy/sick) at some time and place

Pandemic

• Pandemic is a global epidemic that crosses international boundaries.
• Pandemic affects a large number of people

Population

• All inhabitants of a country or area.
• A group considered together.
• In a sampling, it will refer to all units from those that can be extracted a sample.
• These units can be institutions, registries or events

Prevalence

• Number of cases in a determined population
• Number of cases will be specific in the time frame

Risk

• Risk is a probability to happen from an fact.
• Includes probability when an individual gets sick, dies and a period time

Susceptible

• In epidemiology, it refers to animals or people.
• Someone without resistance again pathogen or virus, and not protected

Rate

• Rate means how often the event happens within a population or a period of time.

Epidemiology in Summary

• Epidemiology is a public health branch.
• Epidemiology aims to describe and explain the dynamics of population's health (frequency)
• Also, it aims to identify the elements that shape the health.
• Elements are called determinants
• With this knowledge, it´s a goal to intervene in the course of their natural development.

Presentation by Dr. Saúl Gallardo Aguilar defining basic concepts of epidemiology. It discusses the functions, usages, scopes, and objectives within specific human populations. Epidemiology studies the distribution, frequency, determinants, and control of factors related to health and diseases.