Epidemiology, Biostatistics, and Preventive Medicine Notes

PREVENTIVE MEDICINE PRMED 6212 (MD 6)

  • Dr. Ronald Robertson MD, MMED-FM, MPPA
  • Week 1: Introduction to Epidemiology, Biostatistics, and Preventive Medicine

Course Description

  • Focus: Preventive medicine and community health, including risk factors for major causes of death and disability, and behavioral techniques.
  • Evaluation: Four coursework evaluations (10% each) and a final assessment (60%).
  • Duration: 16 weeks.

Course Outline

  • Week 1: Introduction to Epidemiology, Biostatistics, and Preventive Medicine.
  • Week 2: Epidemiology and the current trend towards disease prevention.
  • Week 3: Principles of health promotion-based nutritional counseling and components of a weight management plan for chronic disease prevention.
  • Week 4: Primary and secondary prevention methods for alcohol and substance abuse, and recognition of at-risk patients.
  • Week 5: Skills to counsel patients on smoking cessation and tobacco use prevention.
  • Week 6: Risk factors for and prevention methods regarding sexually transmitted diseases, including HIV/AIDS, and methods of preventing unwanted pregnancies.
  • Week 7: Epidemiology of mental illness (depression, acute and chronic stress, suicidality) including risk factors, secondary prevention, and efficacy of treatment.
  • Week 8: Child and adult immunization schedules, including locations and contraindications for administration.
  • Week 9: Epidemiology and prevention of injury and violence, including motor vehicle crashes, firearms, poisoning, suffocation, falls, fires, and drowning. Role of the primary care provider in occupational health and safety.
  • Week 10: Environmental factors influencing public health and risk reduction strategies. Role of the local health department in preventing and treating environmental health problems. Impact of global environmental public health concerns.
  • Week 11: Elements and intervals involved in health screening of individuals in child, adolescent, adult, and older adult groups.
  • Week 12: Health concerns and prevention of health problems in agricultural and rural settings.
  • Week 13: Community service-learning activity to enhance appreciation of community health, including the effects of health disparities, access to health care, and the impact of the social environment on health and behavior.
  • Week 14: Revision.
  • Week 15 & 16: Final Examination.

What is Epidemiology?

  • Origin: Greek words: Epi (on or upon), Demos (people), Logos (the study of).
  • Meaning: The study of what befalls a population.

Definition of Epidemiology

  • 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.

Interpretation of Definition

  • Study: Scientific, systematic, data-driven.
  • Distribution: Frequency, pattern.
  • Determinants: Causes, risk factors.
  • Health-related states and events: Not just diseases.
  • Specified populations: Patient is community, individuals viewed collectively.
  • Application: Since epidemiology is a discipline within public health, applying the study to the control of health problems.

Uses of Epidemiology

  • Assessment of the community’s health.
  • Making individual decisions.
  • Completing the clinical picture.
  • Identifying causes of disease.

Assessment of the Community’s Health

  • Identify and analyze data sources by person, place, and time.
  • Questions to consider:
    • What are the actual and potential health problems in the community?
    • Where are they occurring?
    • Which populations are at increased risk?
    • Which problems have declined over time?
    • Which ones are increasing or have the potential to increase?
    • How do these patterns relate to the level and distribution of public health services available?

Making Individual Decisions

  • Knowledge of cause and effect determines behavior.
  • Individuals may be influenced by epidemiologists’ assessment of risk when making decisions (e.g., quitting smoking, using a condom).

Completing the Clinical Picture

  • Epidemiologists rely on health-care providers and laboratorians to establish proper diagnoses of individual patients during disease outbreaks.

Identifying Causes of Disease

  • Epidemiologic research aims to identify causal factors that influence one’s risk of disease, to inform appropriate public health action.

Core Epidemiological Functions

  • Public health surveillance.
  • Field investigation.
  • Analytic studies.
  • Evaluation.
  • Linkages.
  • Policy development.

Public Health Surveillance

  • Ongoing, systematic collection, analysis, interpretation, and dissemination of health data to guide public health decision making and action.

Field Investigation

  • Coordinated efforts to characterize the extent of an epidemic and identify its cause.

Analytic Studies

  • Descriptive approach: Study of disease incidence and distribution by time, place, and person.
  • Includes calculation of rates and identification of high-risk populations.
  • Used to generate hypotheses for testing with analytic studies.

Evaluation

  • Process of determining the relevance, effectiveness, efficiency, and impact of activities with respect to established goals.

Linkages

  • Epidemiologist participates as a member or leader of a multidisciplinary team (e.g., laboratorians, sanitarians, infection control personnel, nurses, computer information specialists).

Policy Development

  • Epidemiologists provide input, testimony, and recommendations regarding disease control strategies, reportable disease regulations, and health-care policy.

Types of Epidemiology

  • Descriptive
  • Analytic
  • Experimental

Descriptive Epidemiology

  • 5 W’s: What (health issue), Who (person), Where (place), When (time), Why/How (causes, risk factors, modes of transmission).
1. Descriptive Epidemiology
  • Describes disease occurrence in terms of person, place, and time:
    • Person: Age, sex, occupation, socioeconomic group, etc.
    • Place: Geographic variation in prevalence and incidence (local, regional, national, international).
    • Time: Seasonal variations and changes over time.
Person (Descriptive Epidemiology)
  • Pertinent characteristics: Age, sex, occupation, personal habits, socioeconomic status, immunization history, underlying disease, other relevant data.
Place (Descriptive Epidemiology)
  • Considers three different sites:
    • Where the individual was when disease occurred.
    • Where the individual was when infected from the source.
    • Where the source became infected with the etiologic agent.
  • Example: Food poisoning outbreak.
Time (Descriptive Epidemiology)
  • Four time trends:
    • Secular trend: Disease occurrence over a prolonged period (years).
    • Periodic trend: Temporary modification in the secular trend, indicating a change in the disease agent's antigenic characteristics.
    • Seasonal trend: Seasonal changes in disease occurrence due to environmental conditions.
    • Epidemic occurrence: Sudden increase in occurrence due to prevalent factors that support transmission.

2. Analytic Epidemiology

  • Analyzes disease determinants for possible causal relations.
  • Methods:
    • Case-control (or case-comparison) method
    • Cohort method
    • Cross-sectional study
The Case-Control Method
  • Starts with the effect (disease) and retrospectively investigates the cause.
  • Case group: Individuals with the disease.
  • Comparison group: Similar individuals without the disease.
  • Compare groups to determine differences that explain disease occurrence.
  • Example: Investigating factors influencing meningococcal meningitis.
Cohort Method
  • Prospectively studies two populations:
    • One with contact with the suspected causal factor.
    • One without contact.
  • Observe to determine the effect of the factor.
  • Example: Observing two groups, one with blood transfusions and one without, to determine the occurrence of hepatitis B.
Cross-Sectional Study
  • Surveys a population over a limited period to determine the relationship between a disease and variables present at the same time.

3. Experimental Epidemiology

  • Develops a hypothesis and constructs an experimental model in which selected factors are manipulated.
  • Effect of manipulation confirms or disproves the hypothesis.
  • Example: Evaluating the effect of a new drug on a disease.

Epidemiological Approach

  • Organized approach to problem solving:
    1. Confirming the existence of an epidemic and verifying the diagnosis.
    2. Developing a case definition and collating data on cases.
    3. Analyzing data by time, place, and person.
    4. Developing a hypothesis.
    5. Conducting further studies if necessary.
    6. Developing and implementing control and prevention measures.
    7. Preparing and distributing a public report.
    8. Evaluating control and preventive measures.

Epidemiologic Triad or Triangle

  • Consists of:
    • External agent.
    • Susceptible host.
    • Environment that brings the host and agent together.

Epidemiological Triad of TB

  • Host: Poor nutrition, concurrent disease, low immunity.
  • Agent: TB organism.
  • Environment: Crowding, poor ventilation, bad sanitation.

Chain of Infection

  • Six links:
    • Infectious agent (pathogen)
    • Reservoir (normal location of the pathogen)
    • Portal of exit from the reservoir
    • Mode of transmission
    • Portal of entry into a host
    • Susceptible host

Infectious Agents

  • Include bacteria, viruses, fungi, and parasites.
  • Virulence depends on number, potency, ability to enter and survive in the body, and host susceptibility.

Important Terms

  • Pathogenicity: An agent’s ability to cause disease; characterized by virulence and invasiveness.
  • Virulence: Severity of infection, expressed by morbidity (incidence of disease) and mortality (death rate).
  • Invasiveness: An organism's ability to invade tissue.
  • Infecting dose: The number of organisms necessary to cause disease.
  • Specificity: How many hosts can be infected by the agent (broad or narrow range).
  • Reservoir: Site where the organism resides, metabolizes, and multiplies.
  • Source: Site from which the organism is transmitted to a susceptible host.

Reservoir

  • Any person, animal, arthropod, plant, soil, or substance in which an infectious agent normally lives and multiplies.

Portals of Exit

  • Means by which a pathogen exits from a reservoir.
  • For humans: Blood, respiratory secretions, gastrointestinal or urinary tracts.

Portals of Entry

  • Infectious agents enter the body through:
    • Mucous membranes.
    • Non-intact skin.
    • Respiratory, gastrointestinal, or genitourinary tracts.

Susceptible Host

  • Someone at risk of infection.

Disease Occurrence

  • Sporadic: Occurs infrequently and irregularly.

Endemic

  • Constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area.
  • Hyperendemic: Persistent, high levels of disease occurrence.

Epidemic

  • Sudden increase in the number of cases of a disease above what is normally expected in that population in that area.

Outbreak

  • Same definition as epidemic, but often used for a more limited geographic area.

Cluster

  • Aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even if the expected number may not be known.

Pandemic

  • An epidemic that has spread over several countries or continents, usually affecting a large number of people.