Environment and Health - Community Medicine

1. Introduction

2. Classification of Environment

A. Internal Environment

B. External (Macro) Environment

• Micro-environment (domestic/personal environment): The individual's lifestyle, eating habits, smoking, drinking, drug use, etc.
• Physical environment: Non-living things and physical factors (air, water, soil, housing, climate, heat, light, noise, radiation).
• Biological environment: All living organisms surrounding man - viruses, bacteria, insects, rodents, animals and plants.
• Psychosocial environment: Cultural values, customs, habits, beliefs, attitudes, morals, family structure, social relationships, and economic conditions.

3. Components of External Environment

A. Physical Environment

• Air pollution
• Water pollution
• Noise pollution
• Urbanization
• Radiation hazards
• Electromagnetic exposure from telecommunications and broadcasting

B. Biological Environment

• Viruses and microbial agents
• Insects (vectors), rodents, animals, and plants

C. Psychosocial Environment

• Cultural values, customs, habits, beliefs, attitudes
• Family structure and community networks
• Social and economic support systems
• Organization of health and welfare services

4. Environment as a Determinant of Health

"It is an established fact that environment has a direct impact on the physical, mental and social well-being of those living in it."

• Park's Textbook of Preventive and Social Medicine

• Housing and water supply
• Psychosocial stress and family structure
• Social and economic support systems
• Organization of health and social welfare services

5. Air Pollution

Definition

Major Air Pollutants

Particulate Matter - Key Facts

• PM10: particles < 10 µm; penetrate to thoracic region
• PM2.5: particles < 2.5 µm; deposit in smaller airways and alveoli - more dangerous
• WHO AQG (2005): PM2.5 annual mean = 10 µg/m³; 24-hour mean = 25 µg/m³
• PM10 annual mean = 20 µg/m³; 24-hour mean = 50 µg/m³
• No safe threshold for PM has been identified

Health Effects of Air Pollution

• Borne mainly by the respiratory system
• Acute bronchitis
• In extreme pollution events - death by suffocation (e.g., London Smog Disaster, 1952)

• Chronic bronchitis
• Lung cancer
• Bronchial asthma
• Emphysema
• Respiratory allergies
• Cardiovascular diseases
• Neurological effects (from lead)

• Acid rain
• Climate change
• Ecosystem damage

"Mortality in cities with high pollution levels exceeds that in relatively cleaner cities by 15-20%." - Park's Textbook

Indoor Air Pollution

• Combustion of solid fuels (wood, coal, dung) on open fires or traditional stoves
• Tobacco smoke
• Building materials (asbestos, formaldehyde)
• Radon from soil
• Biological contaminants (mold, dust mites)

• Acute lower respiratory infections in young children
• Chronic Obstructive Pulmonary Disease (COPD) in adults
• Lung cancer

6. Water and Health

Water-Related Diseases Classified by Mode

Chemical Contamination of Water

• Fluoride at 1 mg/L: Protective against dental caries
• Excess fluoride: Dental fluorosis (mottled enamel), skeletal fluorosis
• Nitrates: Cause methaemoglobinaemia in infants (cyanosis)
• Hard water (Ca/Mg): Appears to have a beneficial effect against cardiovascular diseases
• Heavy metals (lead, arsenic, mercury): Neurotoxic, carcinogenic at high levels

Water Pollution Law - India

• Central and State Water Boards with wide powers to control pollution
• Legal deterrents against water contamination

7. Housing and Health

1. Respiratory infections: Tuberculosis, common cold, influenza, diphtheria, bronchitis, measles, whooping cough
2. Skin infections: Scabies, ringworm, impetigo, leprosy
3. Rat infestation: Plague
4. Arthropods: Houseflies, mosquitoes, fleas, bugs (vectors of disease)
5. Accidents: A substantial proportion of domestic accidents are due to environmental defects in the home
6. High morbidity and mortality: Observed where housing conditions are sub-standard
7. Psychosocial effects: Sense of isolation, neurosis, and behaviour disorders - particularly in high-rise dwellers and densely populated urban areas

Overcrowding

• Rapid spread of respiratory infections (TB, influenza, diphtheria)
• High morbidity and mortality
• Psychosocial harms: irritability, frustration, lack of sleep, anxiety, violence, mental disorders

8. Environmental Sanitation

Excreta Disposal

1. Soil pollution
2. Water pollution
3. Contamination of food
4. Propagation of flies

• Resulting diseases: typhoid, paratyphoid fevers, cholera, dysentery, hepatitis, helminthiasis

Solid Waste Management

• Rodent and insect breeding
• Soil and water pollution
• Aesthetic deterioration of the community

Noise Pollution

• Hearing impairment (especially industrial workers)
• Sleep disturbance
• Cardiovascular stress
• Psychological effects (annoyance, anxiety)

Radiation Hazards

• Ionizing radiation (X-rays, nuclear): Cancers, genetic mutations
• Non-ionizing radiation (UV, microwave): Skin cancer, cataracts, thermal effects

9. Socioeconomic Environment and Health

1. Economic status: Per capita GNP determines purchasing power, standard of living, and disease patterns. Paradoxically, affluence contributes to coronary heart disease, diabetes, and obesity.
2. Education: Especially female education - closely linked to infant/child mortality reduction. Kerala (India) demonstrates that education compensates poverty's health effects.
3. Nutrition: Closely tied to environment - food production, contamination, and distribution are all environmentally determined.
4. Employment/Occupation: Occupational environment introduces specific health hazards (chemicals, dust, ergonomic stress).

10. Occupational Environment

• Dust: Pneumoconiosis (silicosis, coal worker's pneumoconiosis)
• Chemicals: Pesticide poisoning, heavy metal toxicity
• Noise: Noise-induced hearing loss
• Heat: Heat stroke, heat exhaustion
• Radiation: Radiation sickness, cancers

11. Control and Prevention Strategies

Air Quality

• Legislative controls (Clean Air Acts)
• Motor vehicle emission standards
• Industrial emission controls
• WHO Air Quality Guidelines
• Promotion of clean cooking fuels

Water Safety

• Water treatment (filtration, chlorination, UV)
• Source protection
• Legal frameworks (Water Pollution Act 1974)

Housing Improvement

• Building codes and standards
• Urban planning and slum improvement
• Provision of basic amenities (ventilation, sanitation)

Environmental Health Legislation (India)

• Environment Protection Act, 1986
• Air (Prevention and Control of Pollution) Act, 1981
• Water (Prevention and Control of Pollution) Act, 1974
• Solid Waste Management Rules
• Noise Pollution Control Rules

12. Summary: Key Concepts

Causes of All Types of Pollution and Their Disposal/Management - Community Medicine

OVERVIEW

1. Air Pollution
2. Water Pollution
3. Soil Pollution (Excreta/Refuse)
4. Noise Pollution
5. Radiation Pollution

1. AIR POLLUTION

Definition

Types of Air Pollutants

Causes / Sources of Air Pollution

Health Effects

• Immediate/Acute: Acute bronchitis, respiratory irritation; in extreme cases - death by suffocation (London Smog Disaster, 1952)
• Delayed/Chronic: Chronic bronchitis, lung cancer, bronchial asthma, emphysema, respiratory allergies
• SO₂ causes coughing, mucus secretion, aggravates asthma and COPD
• Lead causes impaired neuropsychological development in children (IQ loss, poor school performance, behavioural difficulties)
• NOₓ causes bronchiolitis obliterans, impaired lung defences
• PM2.5 increases cardiovascular and respiratory disease risk
• Epidemiological studies show sudden increases in air pollution are associated with immediate increases in morbidity and mortality

• Destruction of plant and animal life
• Corrosion of metals, damage to buildings
• Reduced visibility in towns
• Acid rain causing deforestation (SO₂ + water = H₂SO₄)

Prevention and Control of Air Pollution (WHO Recommended)

1. Containment - Prevent escape of toxic substances into ambient air through enclosure, ventilation, and air-cleaning "arresters"
2. Replacement - Replace polluting technology with cleaner alternatives (electricity, solar power, natural gas, central heating instead of coal; unleaded petrol)
3. Dilution - Valid within the self-cleaning capacity of the environment. Establish green belts between industrial and residential areas
4. Legislation - Air (Prevention and Control of Pollution) Act, 1981 (India); WHO Air Quality Guidelines
5. Vehicle emission standards - Catalytic converters, PUC certificates
6. Use of clean fuels - LPG, CNG for domestic cooking and transport
7. Air purification - HEPA filters, UV irradiation (operation theatres, infectious disease wards), chemical mists (triethylene glycol vapours)

2. WATER POLLUTION

Definition

Causes / Sources of Water Pollution

• Dissolved gases (CO₂, H₂S, N₂ from rainfall)
• Dissolved minerals (calcium, magnesium, sodium salts from soil)
• Suspended impurities (clay, silt, sand, mud)
• Microscopic organisms (derived from atmosphere, catchment area, soil)

Water-Related Diseases

• Viral: Hepatitis A, Hepatitis E, poliomyelitis, rotavirus diarrhoea
• Bacterial: Typhoid, paratyphoid fever, bacillary dysentery, E. coli diarrhoea, cholera
• Protozoal: Amoebiasis, giardiasis
• Helminthic: Roundworm, threadworm, hydatid disease
• Leptospiral: Weil's disease

• Shigellosis, trachoma, conjunctivitis, scabies, ascariasis

• Schistosomiasis, Guinea worm (dracunculiasis)

• Malaria, filariasis, arboviral diseases, onchocerciasis, African trypanosomiasis

• High fluoride = dental/skeletal fluorosis
• High nitrates = methaemoglobinaemia in infants (cyanosis)
• Hard water = protective against cardiovascular diseases

Management / Control of Water Pollution

1. Legislation: Water (Prevention and Control of Pollution) Act, 1974 - Central and State Water Boards with enforcement powers
2. Treatment of water supply (large scale):
   • Sedimentation (plain and with coagulants - alum)
   • Filtration (slow sand filters, rapid sand filters)
   • Disinfection - Chlorination (most practical), UV irradiation, ozonation, boiling
3. Treatment of water (small scale):
   • Boiling, chlorination with bleaching powder, solar disinfection
4. Source protection: Safe well construction, sanitary surveying, sealing of well tops
5. Sewage treatment before discharge into water bodies (primary, secondary, tertiary treatment)
6. Industrial effluent treatment before release
7. Surveillance at every point in distribution system

3. SOIL POLLUTION AND EXCRETA DISPOSAL

Public Health Importance of Excreta

1. Soil pollution
2. Water pollution
3. Contamination of foods
4. Propagation of flies

4. SOLID WASTE POLLUTION

Definition

Sources of Refuse

Health Hazards of Improper Solid Waste Disposal

• Decomposition favours fly breeding (disease vectors)
• Attracts rodents and vermin (plague, leptospirosis)
• Pathogens conveyed to food through flies and dust
• Water and soil pollution from drainage/leachate
• Unsightly appearance, nuisance from bad odours
• Correlation between improper disposal and incidence of vector-borne diseases

Methods of Solid Waste Disposal

• Trench method - level ground; 2-3 m deep, 4-12 m wide trench
• Ramp method - sloping terrain
• Area method - filling land depressions, quarries, clay pits; each layer sealed with 30 cm mud cover

• Bangalore method (NEERI method): Organic refuse is placed in trenches 2-3 m wide, 1 m deep; covered with earth; decomposed in 4-8 weeks to form compost.
• Mechanical composting: Industrial scale - refuse pulverized, mixed with sewage sludge/nightsoil in rotating machines. Controlled carbon-nitrogen ratio, temperature, moisture, pH, and aeration. Complete in 4-6 weeks. Used in Netherlands, Germany, Switzerland, Israel.

5. EXCRETA DISPOSAL METHODS

In Unsewered Areas

1. Excreta does not contaminate ground or surface water
2. Excreta does not pollute soil
3. Not accessible to flies, rodents, animals
4. Does not create nuisance from odour or unsightly appearance

In Sewered Areas

• Sewage treatment plants (primary → secondary → tertiary)
• Discharge of treated effluent to water bodies

6. NOISE POLLUTION

Definition

Sources / Causes of Noise Pollution

• Automobiles, factories, industries, aircraft
• Railway junctions, traffic roundabouts, bus terminuses, airports
• Pressure horns, loudspeakers during festivities (especially at night)
• Domestic sources: radios, transistors, televisions
• Industrial machinery and equipment

Properties of Noise

• Loudness/Intensity: Measured in decibels (dB)
  • Normal conversation = 60-65 dB
  • Whispering = 20-30 dB
  • Heavy street traffic = 60-80 dB
  • Boiler factories = ~120 dB
  • Safe daily exposure limit = 85 dB
• Frequency: Measured in Hertz (Hz)

Acceptable Noise Levels (dBA)

Health Effects of Noise

1. Auditory effects: Noise-induced hearing loss (NIHL) - most common occupational disease; tinnitus
2. Non-auditory physiological effects: Hypertension, cardiovascular stress, altered hormonal responses
3. Psychological effects: Irritability, annoyance, anxiety, frustration, mental disorders
4. Sleep disturbance and reduced work efficiency
5. Communication interference causing accidents

Control of Noise Pollution

1. Source control: Engineering controls - mufflers, enclosures, quieter machinery design
2. Transmission control: Sound barriers, green belts, distance from sources
3. Receptor protection: Personal Protective Equipment (PPE) - ear muffs, ear plugs (for occupational exposure)
4. Legislation: Noise Pollution (Regulation and Control) Rules, 2000 (India); WHO guidelines
5. Urban planning: Zoning - separation of industrial, commercial, and residential areas
6. Traffic management: Speed limits, banning pressure horns in hospital/school zones

7. RADIATION POLLUTION

Causes / Sources

Health Effects

• Ionizing: Radiation sickness, cancers (leukaemia, thyroid cancer), genetic mutations, teratogenesis
• UV: Skin cancer, cataracts
• Microwave/electromagnetic: Thermal effects on tissues (still being evaluated)

Control

• Radiation protection standards (distance, shielding, time limits)
• Radiation Protection Act
• International Commission on Radiological Protection (ICRP) guidelines
• Proper disposal of radioactive medical waste

SUMMARY TABLE: All Pollution Types at a Glance

Dynamics of Disease Transmission - Community Medicine

1. Introduction and Concept

1. The Reservoir / Source of infection
2. The Mode of Transmission
3. The Susceptible Host

2. The Epidemiological Triad (Agent - Host - Environment)

• Agent - the cause of disease
• Host - the organism harbouring the disease
• Environment - the external surroundings that allow disease transmission
• Time - incubation periods, duration of illness, epidemic threshold

• The onset of disease (single case to epidemic)
• The distribution of disease in the community

3. Natural History of Disease

Phase 1 - Prepathogenesis Phase

• The period preliminary to the onset of disease in man
• The disease agent has NOT yet entered man
• Factors favouring interaction between agent and host are already existing in the environment
• Also called "man in the midst of disease" or "man exposed to the risk of disease"
• We are all potentially in the prepathogenesis phase of many diseases at any given time

Phase 2 - Pathogenesis Phase

• Begins with the entry of the disease agent into the susceptible human host
• The disease agent multiplies and induces tissue and physiological changes
• Disease progresses through early pathogenesis → advanced disease → outcomes (recovery, disability, death, or carrier state)

4. Reservoir and Source of Infection

Key Definitions

• Source of infection: "The person, animal, object or substance from which an infectious agent passes or is disseminated to the host."
• Reservoir: "Any person, animal, arthropod, plant, soil or substance (or combination of these) in which an infectious agent lives and multiplies, on which it depends primarily for survival, and where it reproduces itself in such a manner that it can be transmitted to a susceptible host."

Note: Source and reservoir are NOT always synonymous.

• Hookworm: reservoir = man; source = soil contaminated with infective larvae
• Tetanus: reservoir = source = soil
• Typhoid: reservoir = case or carrier; source = faeces, urine, contaminated food/water

Homologous vs Heterologous Reservoir

• Homologous reservoir: Same species is victim (e.g., man is reservoir for Vibrio cholerae)
• Heterologous reservoir: Infection derived from a different species (e.g., animals infected with Salmonella)

Types of Reservoirs

5. Human Reservoir - Cases and Carriers

A. Cases

• Epidemiologically, mild ambulant cases are more important sources than severe cases because they continue to spread infection while moving about

• Disease agent multiplies but causes NO signs or symptoms
• Agent is still eliminated from the body via stools, vomiting, secretions
• These persons contribute more to transmission than symptomatic patients because they are unrecognized
• Play a dominant role in maintaining chain of infection (endemicity) in the community
• Detectable only by laboratory tests (culture, antibody response, skin sensitivity tests)
• Examples: rubella, mumps, polio, hepatitis A & B, influenza, diphtheria

• Host does not shed the infectious agent (lies dormant without symptoms)
• Example: herpes simplex (reactivates under stress), ancylostomiasis

• Primary case: First case introduced into the population unit
• Index case: First case to come to the investigator's attention (not always the primary case)
• Secondary cases: Develop from contact with the primary case
• Suspect case: Has signs and symptoms but not yet definitively diagnosed

B. Carriers

6. Modes of Transmission

A. DIRECT TRANSMISSION

• Skin-to-skin, mucosa-to-mucosa, or mucosa-to-skin transfer
• Includes: touching, kissing, sexual intercourse, or continued close contact
• Ensures a larger dose of infection and reduces survival time outside host
• Diseases: STDs, AIDS, leprosy, leptospirosis, skin and eye infections

• Direct projection of droplets of saliva and nasopharyngeal secretions during coughing, sneezing, speaking, or spitting
• Droplets impinge directly on conjunctiva, oro-respiratory mucosa, or skin of a close contact
• Particles ≥10 µm are filtered by the nose
• Particles ≤5 µm penetrate deeply and reach the alveoli
• Droplet spread limited to 30-60 cm between source and host
• Increased risk in close proximity, overcrowding, and poor ventilation
• Diseases: Common cold, diphtheria, whooping cough, tuberculosis, COVID-19, meningococcal meningitis, respiratory infections, eruptive fevers

• Direct exposure of susceptible tissue to the disease agent in soil, compost, or decaying vegetable matter
• Example: Hookworm (skin penetration by infective larvae in soil); tetanus (wound contamination)

• Direct introduction of agent through skin breaks
• Examples: Animal bites (rabies), needlestick injuries (HIV, hepatitis B)

• Agent passes from infected mother to foetus through the placenta
• Examples: Rubella, syphilis, HIV, CMV, toxoplasmosis (TORCH infections)

B. INDIRECT TRANSMISSION

• Characteristics of the agent
• Nature of the inanimate object
• Environmental factors (temperature, humidity)
• If the agent acquires drug resistance, it further facilitates spread

1. Vehicle-Borne Transmission

• Multiply in the vehicle (e.g., S. aureus in food)
• Be passively carried in the vehicle (e.g., hepatitis A virus in water)

• (a) If contamination is heavy → explosive outbreak (e.g., cholera, hepatitis A epidemics)
• (b) Initial cases confined to those exposed to the contaminated vehicle
• (c) When secondary cases occur, primary case may be obscured
• (d) Distance travelled by infectious agent may be great
• (e) Not always possible to isolate the agent in the incriminated vehicle
• (f) When vehicle is controlled or withdrawn → epidemic subsides
• (g) Common source of infection is often traceable

2. Vector-Borne Transmission

• Parasites, bacteria, rickettsia, viruses (arboviruses), spirochaetes

• Transovarial transmission: Infectious agent transmitted vertically from infected female vector to her progeny (e.g., dengue in Aedes mosquito)
• Transstadial transmission: Agent transmitted from one stage of life cycle to another (e.g., nymph to adult)

1. Host feeding preferences
2. Infectivity (ability to transmit the agent)
3. Susceptibility (ability to become infected)
4. Survival rate of vectors in the environment
5. Domesticity (degree of association with man)
6. Suitable environmental factors (temperature, humidity, rainfall)

3. Airborne Transmission

• Tiny particles (1-10 microns) representing the dried residue of droplets
• Formed by evaporation of droplets coughed/sneezed into the air OR generated by atomizing devices (aerosols)
• Can remain airborne for long periods, disseminated by air currents
• Particles 1-5 µm are drawn into alveoli and may be retained there
• Diseases: Tuberculosis, influenza, chickenpox, measles, Q fever, COVID-19, many respiratory infections

• Larger droplets settle on floors, carpets, furniture, clothing, bedding
• Become part of dust; infectious agents may remain viable for varying periods
• Diseases: Tuberculosis, Q fever (Coxiella burnetii), smallpox (historically)

4. Fomite-Borne Transmission

5. Unclean Hands and Fingers

• Diseases: Typhoid, dysentery, cholera, hepatitis A, polio

7. The Susceptible Host

• Obligate host: Only host for the agent (e.g., man in measles and typhoid)
• Primary/definitive host: Host in which parasite attains maturity or passes its sexual stage
• Secondary/intermediate host: Host in which parasite is in larval or asexual state
• Transport host (paratenic host): Organism in which parasite remains alive but does not undergo development

Host Susceptibility Factors

1. Immunity (specific antibodies, cellular immunity)
2. Nutritional status (malnutrition increases susceptibility)
3. Age (children and elderly are more vulnerable)
4. Genetic makeup
5. Level and duration of exposure
6. Overall fitness and co-existing diseases

Immunity in Disease Dynamics

• Acquired following: (a) clinical infection (e.g., chickenpox, rubella), (b) subclinical/inapparent infection (e.g., polio, diphtheria), (c) immunization (killed vaccine, live attenuated vaccine, toxoid)

• Primary response: First exposure → IgM appears first (days 3-10), peaks, then declines; IgG appears slightly later (peaks 7-10 days), then gradually falls over weeks/months
• Secondary (anamnestic) response: Re-exposure → rapid, large IgG response (memory cells activated)

8. Key Epidemiological Concepts in Disease Dynamics

Incubation Period

Serial Interval

Generation Time

• Time of maximum communicability may precede or follow the incubation period
• Example: In mumps, communicability peaks ~48 hours before swelling of salivary glands

Communicable Period

• Some diseases are MORE communicable during the incubation period than during actual illness
• Early diagnosis and treatment can reduce communicability

Secondary Attack Rate (SAR)

SAR = (Number of exposed persons developing disease within incubation period range / Total number of exposed/susceptible contacts) × 100

• Primary case is excluded from both numerator and denominator
• High SAR = highly communicable disease; low SAR = less communicable

9. Herd Immunity

• Large numbers of susceptibles are aggregated
• There is a regular supply of new susceptibles (births, immigrants) lowering herd immunity

10. Types of Epidemics (Dynamics at Population Level)

A. Common-Source Epidemics

• Exposure is brief and essentially simultaneous
• All cases develop within one incubation period
• Epidemic curve: rises and falls rapidly with NO secondary waves, explosive clustering
• Example: Food poisoning outbreak at a banquet
• Key feature: Median incubation period = time for 50% of cases to occur after exposure

• Exposure is prolonged or repeated
• Epidemic curve shows a plateau rather than a sharp peak
• Example: Contaminated water supply over several weeks

B. Propagated Epidemics

• Usually of infectious origin, resulting from person-to-person transmission
• Epidemic shows a gradual rise and tails off over a longer period
• Each wave of cases infects the next group of susceptibles
• Transmission also via arthropod vectors or animal reservoirs
• Speed of spread depends on:
  • Herd immunity
  • Opportunities for contact
  • Secondary attack rate

C. Slow (Modern) Epidemics

• Non-infectious diseases that spread slowly over decades
• Examples: Cardiovascular disease epidemic, obesity epidemic, tobacco-related cancers
• Detected by time-trend analysis, not by traditional epidemic curve

11. Temporal Patterns of Disease Occurrence

Secular (Long-Term) Trend

Periodic (Cyclic) Fluctuations

Seasonal Trend

• Many communicable diseases show seasonal variation
• Measles, varicella, cerebro-spinal meningitis, respiratory infections peak in spring/winter
• Bacterial gastrointestinal infections peak in summer (flies multiply, food spoilage faster)
• Vector-borne diseases (malaria, dengue) peak in monsoon/post-monsoon (mosquito breeding)
• Example: Dengue/DHF in India peaks in September-November (coinciding with late summer and rain)

12. Summary - Chain of Disease Dynamics

RESERVOIR/SOURCE
(Human case/carrier, animal, soil, water)
        ↓
EXIT MECHANISM
(Respiratory secretions, faeces, urine, blood, skin)
        ↓
MODE OF TRANSMISSION
Direct: Contact, Droplets, Soil, Inoculation, Transplacental
Indirect: Vehicle, Vector, Airborne, Fomites, Fingers
        ↓
PORTAL OF ENTRY
(Respiratory tract, GI tract, skin, mucosa, conjunctiva)
        ↓
SUSCEPTIBLE HOST
(Influenced by: immunity, nutrition, age, genetics, exposure dose)
        ↓
DISEASE (or subclinical infection, carrier state, immunity)

13. Key Definitions Summary Table