Untitled Quiz

Introduction to Epidemiology

• Course offered by Our Lady of Fatima University's College of Medical Laboratory Science, Biostatistics and Epidemiology department.

Epidemiology - Defined

• Study of the distribution and determinants of health-related states among specific populations and the application of that study to control health problems.

Epidemiology Purposes in Public Health Practice

• Discover the agent, host, and environmental factors affecting health.
• Determine the relative importance of illness, disability, and death causes.
• Identify population segments at greatest risk from specific health issues.
• Evaluate health programs and services' effectiveness in improving population health.

Solving Health Problems

• Step 1: Data collection
• Step 2: Assessment
• Step 3: Hypothesis testing
• Step 4: Action
• Parallel steps: Surveillance; determine time, place, and person (Step 1); Inference (Step 2); Determine how and why (Step 3); Intervention (Step 4).

Disease Causation

Theories of Disease Causation

• Ancient Theories: Disease attributed to evil spirits, recovery to good spirits, and punishment. The control measures included sacrifices and casting out demons.

• Filth Theory: Associated disease with the physical environment, especially poor sanitation and filth, and factors like seasons, climate, temperature, and overcrowding. Diseases were also attributed to poisonous substances and gases from the earth.

• Germ or Bacteriological Theory: Koch confirmed Pasteur's claims that germs cause disease; this theory introduced concepts like isolation and quarantine. Measures to control the cause, such as disinfection, fumigation, and cleanliness, were also developed.

Henle-Koch's Postulates (1877, 1882)

• Four postulates used to establish a causal relationship between a specific microorganism and a particular disease:
  • presence of the disease agent in every case of the disease
  • absence of the disease agent in other diseases.
  • Agent must replicate in experimental animals.
  • The agent must be recoverable from experimental animals.

Concept of Multiple Causation

• Disease results from the interaction of several ecological factors within a dynamic system, encompassing the agent, host, and the environment.

Web of Causation for the Major Cardiovascular Diseases

Web of Causation for Myocardial Infarction

Epidemiologic Lever

• Agent and host are at opposite ends of a lever, with the environment at the fulcrum. Disease results from an imbalance between the disease agent and man; the nature and extent of the imbalance depend on characteristics of both host and agent.

The Epidemiologic Triangle

• Triangular model with agent, host, and environment at the corners, visually representing the interaction of these three factors in disease causation.

Environmental Factors of Disease

• External to the host and where the agent exists, survives, or originates. It can be physical, climatological, biological, or socioeconomic.

Reservoir

• Living or nonliving entities in which an infectious agent resides and multiplies, ensuring survival until possible transmission to a susceptible host.
  • physical environment
  • animals or insects
  • human beings (main reservoirs)

Human Reservoirs

• Cases: infection and disease are both present; Carriers: infection without disease.

Animal reservoirs

• Zoonotic Diseases are infectious diseases of animals that can cause disease when transmitted to humans.
  • Rabies
  • Plague

The Agent Factor of Disease

• Agent is any living or nonliving element, substance, or force that can initiate or perpetuate a disease process.

Types of Agents

• Non-living
• Living

Non-Living Agents

• Physical and mechanical agents: extremes of temperature, light, electricity, physical trauma
• Chemical agents: exogenous poisons, endogenous toxic products of metabolism.
• Nutrients: deficiency (anemia from iron deficiency) or excess (obesity from overeating) agents

Living Agents; types

• Bacteria: TB, shigellosis
• Viruses: AIDS, hepatitis
• Fungi: candidiasis, athlete's foot
• Protozoans: amoebiasis, giardiasis
• Helminthes: schistosomiasis, ascariasis

Characteristics of Agents of Diseases

• Inherent Characteristics
• Characteristics Directly Related to Man
• Characteristics Related to Environment

Infectivity

• Ability of an agent to invade and multiply in a host.

Pathogenicity

• Ability of an agent to cause clinically apparent illness; dependent on factors like dosage, presence/absence of capsule, toxigenicity, and the host's condition.

Virulence

• Severity of the reaction produced; measured in terms of fatality.

Immunogenicity

• Ability of an infection to produce specific immunity as in Measles.

Characteristics in Relation to the Environment

• Reservoir of Infection
• Sources of Infection
• Modes of Transmission

Modes of Transmission

• Mechanisms by which an infectious agent moves from reservoir to susceptible human host
  • Contact Transmission
  • Vehicle Transmission
  • Vector Transmission

Contact Transmission

• Direct contact (no intermediary between infected and uninfected, touching, kissing, sexual interactions, Hepatitis A, Staphylococcal infections, sexually transmitted diseases)
• Indirect contact (use of intermediates like tissues, handkerchiefs, towels, bedding, contaminated needles—HIV and hepatitis B)
• Droplet transmission (transfer of respiratory illnesses like influenza and whooping cough, transfer via sneezing, coughing, and laughing).

Vehicle Transmission

• Pathogens spread via contaminated vehicles (e.g., air, food, water, blood, bodily fluids, drugs, intravenous fluids).

Vector Transmission

• Pathogens transmitted via carriers (animals like arthropods like fleas, ticks, flies, lice, mosquitoes).
  • Mechanical vectors transmit pathogens passively on their body parts.
  • Biological vectors transmit pathogens inside their body.

The Host

• Stages in the chain of events, going from inapparent infection to a clinical case of the disease, range of disease severity (inapparent to severe)
• Resistance of the host (immunity level) determines illness severity.
• Infection outcomes (complete recovery, permanent disability/disfigurement, death, chronicity).

Characteristics of the Host

• Non-specific defense mechanisms (skin, mucosal surfaces, tears, saliva, acid pH of gastric juice, phagocytes and macrophages, age, nutrition status, genetic factors)

Other Concepts Related to Causation

• Necessary Versus Sufficient Cause

Types of Causal Relationships

• Necessary and sufficient
• Necessary but not sufficient
• Sufficient but not necessary
• Neither sufficient nor necessary

Herd Immunity

• Resistance of a group to invading infectious agents, based on the immunity of a substantial portion of its members.

Natural History of the Disease

• Two Phases: Pre-pathogenesis (before human involvement; agent, host, environment interactions leading to exposure) and pathogenesis (success invasion and establishment of the agent in the host, through different disease stages from incubation to resolution).
  • Exposure: contact with agent
  • Stage of Susceptibility: pre-exposure stage; individual vulnerable or at risk
  • Pre-pathogenesis: interactions of agent, host, and environment before human involvement
  • Adaptation: the body's response to the agent.
  • Stage of Presymptomatic Disease (Subclinical): pathogenic factors in the body causing changes, but no signs yet.
  • Stages of Subclinical Disease (incubation and latency): asymptomatic stages before disease presentation.
  • Stage of Clinical Disease: the onset of signs/symptoms.
  • Stage of Disability: the outcome is recovery, disability, or death.
• Timelines and stages: Exposure, pathological changes, onset of symptoms, clinical diagnosis, recovery stages (disability or death).

Who is at Risk?

Adaptation

• Failure: If adaptation fails, pathogenesis occurs.
• Response: Body's immediate response, primarily the immune system.

Levels of Prevention

Classifications of Diseases

• Method of grouping diseases based on specific characteristics.
• Ensures universal diagnosis criteria.
• Dependent on current disease knowledge.
• Classifications: Clinical (signs/symptoms) and Etiologic (presumed cause).

Sources of Epidemiologic Data

• Determinants: Socioeconomic and demographic factors, and environmental and behavioral risk factors.
• Inputs: Policy, financing, human resources, organization, and management of the health system.
• Outputs: Information, service availability, and quality of the health system.
• Outcomes: Service coverage; utilization.
• Health Status: Mortality, morbidity/disability, well-being
• Data considerations: Research objectives, data quality, and sensitivity issues.
• Types of Data: Primary (collected firsthand) and secondary (derived from other sources).
• Data Sources:
  • Primary: Queries (interviews, questionnaires, FGD), Observations (direct, with tools)
  • Secondary: Computerized bibliographic databases, surveillance data (census, registries, hospital records, insurance records).

Data Quality and Utility

• Data Characteristics
• Data Availability
• Accessibility for researchers
• Completeness & representativeness
• Value & limitations

Data Privacy and Confidentiality

• Privacy vs. Confidentiality
• Republic Act 10173 (Data Privacy Act of 2012)
• Executive Order No. 2 s. 2016

Sensitive Personal Information

Data Sharing and Linkage

• Sharing: Voluntary release of information
  • Advantages
  • Issues (loss of control, privacy)
• Linkage: Joining data from multiple sources
  • Interoperability requirements

Thank You!