Basic Concepts in Epidemiology

• Epidemiology - study of the distribution and determinants of health-related states and events in specified populations, and the application of this study to the prevention and control of health problem.
• Epidemiology - study upon people

  • Epi - upon
  • Demos - people
  • Logos - study
• Study - includes surveillance, observation, hypothesis testing, analytic research and experiments
• Distribution - refers to analysis of times, persons, places and classes of people affected
• Determinants - includes 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 - the aims of public health - to promote, protect, and restore health.
• Aim of epidemiology:

  • To eliminate or reduce the health problems of community.
  • To promote the health and well-being of society as a whole.
• The seven uses of epidemiology:

  • Study of history of the health of populations
  • Diagnose the health of the community
  • Examine the working of health services
  • Estimate individual risks and chances
  • Identify syndromes
  • Complete the clinical picture
  • Search for causes
• Branches of Epidemiology:

  • Descriptive
  • Analytic
• Descriptive - distribution of health-related states and GENERATE hypothesis.
• Analytic - determinants of health-related states and TEST hypothesis.
• Epidemiologic Approach:

  • Count - cases or health events
  • Divide - the number of cases by an appropriate denominator
  • Compare - rates over time of for different groups of people
• Epidemiologic approach:

  A) Ask Questions

  B) Examine Existing Facts

  C) Test Hypotheses

  D) Conclude: Generate New Facts

  
• Descriptive Epidemiology variables:

  • Time
  • Person
  • Place
• Person variable

  A) Race/Ethnicity

  B) Literacy

  C) Civil Status

  D) Socioeconomic status

  E) Occupation

  
• TIME Variable:

  • Point Epidemics
  • Seasonal Trends
  • Secular Trends
• Point Epidemics - sharp increase in disease frequency within hours, days or weeks due to almost simultaneous exposure to a single source
• Seasonal Trends - cyclical fluctuations in the frequency of disease over a given time period like in influenza and measles.
• Secular Trends - gradual changes in the frequency of disease over long periods of time possibly due to demographic changes, changes in the natural history of disease, and practices of data collection.
• PLACE Variable:

  A) International Comparison

  B) Within country

  C) Localized

  
• Stages of Disease:

  A) Stage of Susceptibility

  B) Pathologic Changes

  C) Stage of Subclinical Disease

  D) Usual Time of Diagnosis

  E) Stage of Clinical Disease

  
• Epidemiologic Triangle:

  • Agent
  • Host
  • Environment
  • Time
• Agent - infectious (microbes) vs non-infectious (risk factors)
• Microbes:

  • Bacteria
  • Viruses
• Risk factors:

  • Smoking
  • High Blood Pressure
  • Exposure to chemicals/radiation
• Factors considered in Agent:

  • Primary agent responsible
  • Characteristics of agent of causative factors
  • Mode of transmission
  • Contributing factors
  • Geographic patterns
• Host - organisms (humans, animals) exposed to and harbor a disease.
• Factors affecting susceptibility to disease:

  • Age, gender
  • Race/ethnicity
  • Occupation
  • Immune status
  • Behaviors
• Environment - external to the host, external surroundings and conditions.
• Characteristics that may cause disease:

  • Weather
  • Population density
  • Geography
  • Season of the year
  • Genetic effects/Family history
• Time - duration when a person is sick, before death or recovery.
• Incubation period - time from infection to symptom development

  • infectious disease
• Latency period - time from exposure to symptom development and ineffectiveness

  • chronic disease
• Early Hypotheses by Epidemiologists on Natural History and Prevention Methods for Disease:

  A) Lyme Disease

  B) 1976

  C) Avoid using long-lasting tampons

  D) Acquired Immunodeficiency Syndrome (AIDS)

  E) 1996

  F) Prions

  G) Staphyloccocal toxin

  H) Severe acute respiratory syndrome

  I) 2003

  J) SARS-COV 2, inhalation

  
• Vectors - a person, animal, or microorganism that carries and transmits the infectious pathogen
• BEINGS Model - a mnemonic device for the major categories of risk factors for disease, some of which are easier to change or eliminate than others
• Biologic and behavioral factors - the risks for particular diseases can be influenced by gender, age, weight, bone density, lifestyle and other factors
• Environmental factors - epidemiologists describe the patterns of the disease based on external surroundings