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Community Medicine — Core Topics

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1. Natural History of Disease

Stages (Leavell & Clark Model):

Iceberg Phenomenon

Spectrum of Disease

• Inapparent infection → Mild illness → Moderate illness → Severe disease → Death

Key Concepts:

• Pathological onset: moment disease process begins
• Clinical horizon: threshold at which symptoms become detectable
• Incubation period (infectious) / Latency period (chronic): time from exposure to onset
• Pre-patent period: time from infection to detectability of organism

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2. Steps of Chlorination (Water Treatment)

Steps:

• Turbid water is allowed to settle or treated with alum (coagulant) to remove suspended particles
• Turbidity must be reduced before chlorination for effectiveness

• Water is passed through slow sand filters or rapid sand filters
• Removes remaining particulate matter, some bacteria, and protozoa

• Optimal chlorination occurs at pH 7.0–7.5
• Alkaline water reduces chlorine efficacy

• Methods of chlorination:
  • Breakpoint chlorination: chlorine is added until the "breakpoint" — after all oxidizable matter is satisfied and free residual chlorine appears
  • Superchlorination: adding chlorine in excess of the breakpoint; requires subsequent dechlorination
  • Double chlorination: chlorine added before and after filtration
  • Chloramination: chlorine + ammonia → chloramines (more stable, less taste/odor)

• Water must remain in contact with chlorine for ≥30 minutes before distribution
• Ensures adequate disinfection

• Free residual chlorine of 0.2–0.5 mg/L at the consumer's tap ensures safety
• Tested using orthotoluidine reagent (OT test) or DPD method

• Sodium thiosulfate or activated carbon removes excess chlorine taste/odor

Factors Affecting Chlorination Efficacy:

• Turbidity (↑ turbidity → ↓ efficacy)
• pH (neutral best)
• Temperature (↑ temperature → faster action)
• Contact time
• Organic matter content
• Chlorine demand of the water

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3. Levels of Prevention

Primary Prevention

Secondary Prevention

Tertiary Prevention

Primordial Prevention (4th level — added later)

• e.g., National policies against smoking, junk food marketing to children, urban planning

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4. Primary Health Care (PHC) — Principles and Elements

Core Principles (FAUCET):

• First contact care
• Accessibility and availability
• Universal coverage
• Community participation
• Equity
• Technology appropriateness; intersectoral coordination

8 Essential Elements (Mnemonic: CAME HOME):

1. Current health status education and disease prevention/control
2. Adequate food supply and nutrition
3. Maternal and child health, including family planning
4. Essential drugs provision
5. Health education
6. Oral health (sometimes listed)
7. Mental health
8. Endemic disease control; treatment of common diseases; immunization; safe water/sanitation

Full List (WHO, Alma-Ata):

1. Education about health problems and methods of prevention/control
2. Promotion of food supply and proper nutrition
3. Adequate supply of safe water and basic sanitation
4. Maternal and child health care, including family planning
5. Immunization against major infectious diseases
6. Prevention and control of locally endemic diseases
7. Appropriate treatment of common diseases and injuries
8. Provision of essential drugs

Pillars (Post-Alma-Ata, WHO 2018 — Astana Declaration):

• Universal health coverage
• Health security
• Multi-sectoral policy and action
• Empowered people and communities

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5. Methods of Health Communication

Classification by Channel:

By Direction:

• One-way: Posters, radio, TV — message flows from sender to audience
• Two-way: Counseling, discussion — feedback is possible

SMCR Model (Berlo):

• Each component has attributes affecting communication effectiveness (e.g., credibility of source, clarity of message)

Barriers to Health Communication:

• Language and literacy
• Cultural beliefs
• Physical barriers (hearing/sight impairment)
• Information overload
• Lack of trust

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6. Overcrowding — Criteria

Standard Criteria:

WHO / Indian Standards:

• Minimum floor area: 9.3 m² (100 sq ft) for living room; 4.5 m² for bedroom
• Minimum ceiling height: 2.75 m (9 feet)
• Persons per room: ≤ 2 for adults; children < 10 years count as ½

Health Effects of Overcrowding:

• Airborne infections: TB, measles, influenza, COVID-19
• Skin and scalp infections: scabies, ringworm
• Diarrheal diseases (poor sanitation)
• Mental health: anxiety, aggression, poor sleep
• Domestic violence

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7. Doctor–Patient Relationship

Models of Doctor–Patient Relationship:

1. Szasz and Hollender Model (Classic, 1956):

2. Other Models:

Key Principles:

• Confidentiality: information shared stays private
• Trust: foundation of the relationship
• Informed consent: patient must consent to treatment
• Empathy and communication: essential for compliance and outcomes
• Continuity of care: long-term relationship improves outcomes

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8. Types of Occupational Health Hazards

1. Physical Hazards

2. Chemical Hazards

3. Biological Hazards

4. Ergonomic Hazards

• Poor posture, repetitive motion → musculoskeletal disorders (MSDs)
• Carpal tunnel syndrome (keyboard workers)
• Low back pain (heavy lifting, truck drivers)

5. Psychosocial Hazards

• Job stress, burnout, shift work, workplace bullying
• Associated with depression, anxiety, cardiovascular disease

6. Mechanical Hazards

• Machinery injuries, cuts, falls, entanglement

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9. Family — Definition and Types

Definition:

Types of Family:

By Structure / Composition:

By Authority / Power Structure:

By Residence:

By Descent:

By Marriage Type:

Functions of Family:

1. Biological (reproduction, care of members)
2. Socialization (teaching norms, values)
3. Economic (resource sharing)
4. Psychological (emotional support, security)
5. Health care (primary caregiving unit)

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