Epidemiology: Disease Distribution, Models & Uses for B.Sc Nursing (5th Sem)

Learn about disease distribution, frequency, epidemiological models, and the aims of epidemiology in this essential guide for 5th-semester B.Sc Nursing students.

Distribution and Frequency of Diseases –

Epidemiology is the study of how diseases spread, their causes, and how to control them in human populations. Different experts have defined it in various ways:

Three Main Components of Epidemiology:

1. Disease Frequency:
   • Measures how often a disease occurs (prevalence, incidence, death rates).
   • Helps find disease causes and develop prevention strategies.
   • Uses statistics to analyze health-related data (e.g., blood pressure, cholesterol levels).
2. Disease Distribution:
   • Studies how diseases spread in different groups based on time, place, and people.
   • Helps in forming disease prevention strategies.
   • This is known as descriptive epidemiology.
3. Disease Determinants:
   • Identifies the causes and risk factors of diseases.
   • Uses research to develop health policies and interventions.
   • This is called analytic epidemiology.

Importance of Epidemiology:

• Helps in disease prevention and control.
• Identifies risk factors for chronic diseases like cancer and heart disease.
• Guides public health policies and healthcare improvements.

Aims and Uses of Epidemiology –

Aims of Epidemiology:

According to the International Epidemiological Association, epidemiology has three main aims:

1. Describe the distribution and magnitude of health and disease in populations.
2. Identify the causes (etiological factors) of diseases.
3. Provide data for planning, implementing, and evaluating disease prevention, control, and treatment programs.

The ultimate goal of epidemiology is to:

• Reduce or eliminate health problems.
• Improve public health and well-being.

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Uses of Epidemiology:

Epidemiology is useful for studying diseases, health conditions, and healthcare services.

According to Thrushfield (1995), epidemiology helps in:

1. Finding the cause of diseases with known origins (e.g., laboratory tests, clinical procedures).
2. Investigating and controlling unknown diseases (e.g., Edward Jenner’s discovery of the smallpox vaccine).
3. Understanding disease ecology and natural history (e.g., studying infectious and non-infectious diseases in different environments).
4. Planning and monitoring disease control programs (e.g., using data for public health surveillance).

According to Morris, epidemiology is used to:

1. Study disease trends (how diseases increase or decrease over time).
2. Diagnose community health problems (measuring disease impact using morbidity and mortality rates).
3. Plan and evaluate health programs (checking if disease prevention efforts are effective).
4. Assess individual risk (determining chances of developing diseases).
5. Identify syndromes (grouping symptoms to define diseases).
6. Understand the natural history of diseases (how diseases progress from infection to recovery or complications).
7. Find causes and risk factors (e.g., linking rubella to congenital birth defects).

Epidemiological Models of Disease Causation

Concept of Disease Causation

• Disease is the opposite of health, causing disharmony and abnormal body function.
• It can range from mild biochemical disturbances to severe conditions leading to death.
• Disease can be caused by multiple factors, including biological, environmental, and social influences.
• Definitions:
  • Webster: A condition where health is impaired, affecting vital functions.
  • Oxford: Disruption in normal body function.
  • Ecological View: A maladjustment of humans to their environment.
  • Sociological View: A social phenomenon shaped by culture and society.
• Disease can vary in onset, severity, and outcome (recovery, disability, or death).

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Theories and Models of Disease Causation

1. Early Theories

• Supernatural Theory: Diseases were believed to be divine punishment.
• Miasmatic Theory: Diseases were caused by “bad air” or mists.
• Environmental Theory: Hippocrates suggested that harmful substances in the environment cause disease.
• Theory of Contagion & Humors: Disease spread through contact or body fluid imbalances (Tridosha concept in Ayurveda).

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2. Germ Theory (19th–20th Century)

• Louis Pasteur & Robert Koch discovered microorganisms as causes of disease.
• Each disease was linked to a specific microorganism (e.g., Cholera – Vibrio cholerae).
• Later, it was found that not everyone exposed to germs got sick, indicating other factors play a role.

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3. Epidemiological Triad Model

• Disease results from an interaction between three factors:
  1. Agent: The cause (bacteria, virus, chemical, etc.).
  2. Host: The individual who can get the disease.
  3. Environment: External factors that influence exposure and spread.
• Example: Tuberculosis only affects people with low immunity or poor living conditions.

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4. Multifactorial Causation Theory

• Many diseases (e.g., heart disease, diabetes, mental illness) result from multiple causes.
• Example: Coronary Heart Disease
  • Causes: Smoking, high cholesterol diet, stress, lack of exercise, genetic factors.
  • Prevention: Healthy diet, exercise, stress management.

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5. Web of Causation Model

• Developed by Mac Mahon & Pugh
• Diseases are caused by multiple interacting factors rather than a single cause.
• Example: Cardiovascular Diseases
  • Factors: Overeating → Obesity → High cholesterol → Artery damage → Heart disease.
• Used for complex diseases like cancer, heart disease, and diabetes.

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Transmission:

Disease Transmission

Disease transmission refers to how infectious diseases spread from a source to a susceptible host. There are three key links in this process:

1. Reservoir (Source of Infection) – Where the disease-causing agent lives and multiplies.
2. Modes of Transmission – How the infectious agent moves from the source to a new host.
3. Susceptible Host – A person or animal that can get infected.

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1. Reservoirs of Infection

A reservoir is where an infectious agent lives, grows, and multiplies before infecting a new host.

Types of Reservoirs:

• Human Reservoir: Most communicable diseases spread from humans.
  • Cases: People who have the disease.
    • Clinical Cases: Show symptoms (mild, moderate, severe).
    • Subclinical Cases: Have the infection but no symptoms, still contagious.
  • Carriers: Infected people who do not show symptoms but spread the disease.
    • Incubatory Carrier: Spreads disease before symptoms appear (e.g., measles).
    • Convalescent Carrier: Spreads disease while recovering (e.g., typhoid fever).
    • Chronic Carrier: Spreads disease for a long time (e.g., hepatitis B).
• Animal Reservoir: Some diseases spread from animals to humans (zoonoses), e.g., rabies, influenza.
• Non-living Reservoirs:
  • Soil: Can harbor bacteria like tetanus and anthrax.
  • Water/Food: Can carry diseases like cholera and typhoid fever.

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COURSES

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BSC NURSING