Prevention in Public Health

Explain the concept of prevention as a core principle for public health.
Distinguish primordial, primary, secondary, and tertiary disease prevention.
Explain the science of screening and provide examples of how screening is applied.
Discuss the principles of disease prevention and health promotion in public health interventions, locally, nationally, and globally.

Two core principles of public health:
- Prevention (this chapter)
- Health equity (see Chapter 4, "At the Heart of Public Health: Social Determinants of Health and Health Equity")
Focus of public health:
- Creating the healthiest possible populations by promoting conditions conducive to health.
- Differentiation from clinical medicine, which focuses on disease and disability progression.
- Public health emphasizes the health of the population rather than just individual health.
Objectives of the chapter:
- Discuss principles of primordial, primary, secondary, and tertiary disease prevention.
- Introduce the concept of screening, including appropriate circumstances for application.
- Apply prevention notions across different populations with local, national, and global examples.

Historical definition of public health (Charles-Edward A. Winslow, 1920):
- "The science and art of preventing disease, prolonging life, and promoting physical health and efficiency through organized community efforts for the sanitation of the environment, control of community infections, education of the individual in personal hygiene, organization of medical and nursing service for early diagnosis and preventive treatment of disease, and development of social machinery for ensuring a standard of living adequate for health maintenance."
- This definition places prevention at the core of public health, remaining relevant over time.
Importance of disease prevention:
- Cornerstone of public health with historical achievements including vaccination and communicable disease control.
- Cost-effectiveness: prevention leads to avertable illness, reducing healthcare costs, improving productivity, and enhancing quality of life.

Historical life expectancy data:
- Global life expectancy gains over 25,000 years increased from mid-30s by 1900 to 30 years increase in the 20th century for high-income countries due to preventing infant and early life mortality.
- Dramatic life expectancy rises attributed to:
  - Accelerating economic growth
  - Effective control of infectious diseases
  - Improved sanitation

Definition of prevention:
- Actions that ward off disease occurrence.
- Ideal interventions may aim for disease eradication (e.g., smallpox, poliomyelitis).
- When disease cannot be entirely prevented, strategies aim to buffer impact.
Levels of prevention:
- Prevention science categorized as "primary," "secondary," and "tertiary." Alternately termed "universal," "selective," and "indicated" prevention.
- Each categorization aids in understanding prevention strategies at different stages of disease impact.

Definition: Actions that prevent illness or injury before they occur.
- Core strategies:
- Immunizing against infectious diseases.
- Ensuring safe water supplies and sanitation.
- Improving nutritional status.
- Reducing hazardous exposures.
- Eliminating health-compromising behaviors.
Primordial prevention:
- Precedes primary prevention; aims to prevent expression of risk factors completely.
- Example: Preventing hypertension by maintaining normal blood pressure from childhood.
Impact of effective primordial and primary prevention (Hypothetical scenario - Primaria):
- A society exemplifying robust health through education, nutrition, and behavioral practices.
- Limited occurrence of chronic diseases, smoking, and substance use.
- Not a reality, but illustrates optimal health potential.

Definition: Actions that focus on minimizing disease impact during early stages.
- Emphasizes the detection and treatment of subclinical diseases.
Role of screening in secondary prevention:
- World Health Organization (WHO) definition of screening:
- "Presumptive identification of unrecognized disease in apparently healthy populations via tests, examinations, or procedures."
- Early detection improves intervention opportunities to control disease.
- Examples of screening tests:
- Pap smear for cervical cancer
- PSA measurements for prostate cancer
- Colonoscopy for colon cancer
- Mammography for breast cancer
- Cholesterol measurements for cardiovascular disease
Key performance measures for screening tests:
- Sensitivity: Ability to correctly identify disease presence (percentage scoring positive).
- Specificity: Ability to correctly identify absence of disease (percentage scoring negative).
- False positive fraction: Percentage of healthy individuals incorrectly identified as positive.
- False negative fraction: Percentage of diseased individuals incorrectly identified as negative.
Example of screening test performance considerations:
- Sensitivity of 80%, specificity of 90%, false positive fraction of 10%, false negative fraction of 20%.
- Context is crucial for evaluation—understanding implications of both false positives and false negatives can inform the acceptability of a screening test.

Definition: Actions aimed at reducing the impact of existing injuries or diseases diagnosed in an individual.
- Focus on managing disease effects post-diagnosis to improve functionality and quality of life.
Examples of tertiary prevention strategies:
- Cardiac rehabilitation programs post-heart attack.
- Interventions for weight loss in type 2 diabetes patients.

Universal preventive interventions: General population education with no specific risks identified.
Selective preventive interventions: Targeted subgroups showing biological, psychological, or social risks (e.g. youth exposed to Adverse Childhood Experiences (ACEs)).
Indicated preventive interventions: High-risk individuals with observable signs or symptoms (monitoring, skills training).

Clinical medicine: Restores health post-illness focus; individual patient care and management.
Public health: Population-centered approach emphasizing disease prevention rather than treatment.
Current challenges:
- Imbalance in funding between clinical medicine and public health.
- Success in treatment overshadowing the necessary investment in preventative measures.