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Man and Medicine - Chapter 1, Park's Textbook of Preventive & Social Medicine

OVERVIEW (Exam intro quote)

"Those who fail to read history are destined to suffer the repetition of its mistakes."

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I. MEDICINE IN ANTIQUITY

1. Primitive Medicine

• Disease was attributed to supernatural forces (wrath of gods, evil spirits, black magic)
• "Medicine was conceived in sympathy and born out of necessity"
• First doctor = first man; First nurse = first woman
• Treatment: incantations, exorcisms, herbal remedies
• Medicine man, priest, herbalist, magician were early practitioners

2. Indian Medicine (Ayurveda)

• Golden age: 800 B.C. - 600 A.D.
• Two greatest physicians: Charaka (medicine/internal) and Susruta (surgery)
• Tridosha theory of disease: Vata (wind), Pitta (gall/bile), Kapha (mucus) - disease = imbalance of three humors
• Susruta's Samhita describes over 700 medicinal plants, 57 preparations from animal sources, 64 from minerals
• Rhinoplasty - first performed by Indian surgeons (British learned from them during East India Company era)
• Surgery declined during Buddhist times due to doctrine of Ahimsa (non-violence)
• Laws of Manu = code of personal hygiene
• Mohenjo-daro & Harappa: advanced knowledge of sanitation, water supply, engineering
• Declined during Mughal period due to lack of State support
• Indian medicine played in Asia the same role as Greek medicine in the West
• Unani-Tibb: introduced by Muslim rulers around 10th century A.D. (origin: ancient Greek medicine); flourished in Delhi, Aligarh, Lucknow, Hyderabad
• Homoeopathy: propounded by Samuel Hahnemann (1755-1843) of Germany; came to India between 1810-1839; based on "similia similibus curantur" - like treats like

3. Chinese Medicine

• Based on Taoism - balance between Yin (dark/cold/wet/passive) and Yang (bright/hot/dry/active)
• Disease = imbalance between Yin and Yang
• Huang Ti (Yellow Emperor) - first medical classic "Nei Ching" (~2600 B.C.)
• Acupuncture and moxibustion used for treatment
• Pien Ch'iao (500 B.C.) - first clinical physician of China, described pulse diagnosis

4. Egyptian Medicine

• Imhotep (~2980 B.C.) - Egyptian god of medicine; known as "Prince of Peace" - first physician known by name
• Ebers Papyrus (1500 B.C.) - oldest medical document; described 700 drugs
• Disease was attributed to supernatural forces; temple medicine practiced
• Egypt gave the world the first specialist physicians (one physician for one disease)

5. Mesopotamian (Babylonian) Medicine

• Code of Hammurabi (1700 B.C.) - world's first medical legislation; laid down fees and penalties for surgeons
• If surgeon operated and patient died, surgeon's hands were cut off
• Disease was punishment by gods; treatment by priests/magicians
• Ashipu (exorcist) and Asu (physician) - two types of healers

6. Greek Medicine (460-136 B.C.)

• Greeks rejected supernatural theory; viewed disease as a natural process
• Aesculapius (1200 B.C.) - early leader; bore two daughters:
  • Hygiea - goddess of health (preventive medicine)
  • Panacea - goddess of medicine/cure (curative medicine)
  • This created the dichotomy between curative and preventive medicine
  • Famous quote: "Hygiea is fashionable among intellectuals, but Panacea gets the cash"
• Aesculapius's staff (entwined by a serpent) = symbol of medicine
• Hippocrates (460-370 B.C.) - "Father of Medicine"; born on island of Cos
  • Challenged magic; applied clinical methods
  • "Corpus Hippocraticum" - 72 volumes; first scientific clinical case histories
  • Famous saying: "Life is short, the art long, opportunity fleeting, experience treacherous and judgement difficult"
  • Hippocratic Oath - keystone of medical ethics
  • First true epidemiologist - distinguished epidemic from endemic disease
  • Book "Airs, Water and Places" - treatise on social medicine and hygiene
  • Stressed relation between man and his environment
• Theory of four humors: phlegm, yellow bile, blood, black bile (corresponding to cold, hot, warm, dry)
• Galen (131-210 A.D.) - greatest physician after Hippocrates; described anatomy; dominated medicine for 1400 years

7. Roman Medicine

• Romans gave the world its first organized public health system
• Constructed aqueducts, sewers, public baths, sanitary latrines
• Army hygiene, quarantine of leprosy
• Vitruvius - Roman architect who described relationship between environment and disease

8. Middle Ages (500-1500 A.D.)

• Medicine regressed; dominated by theology and church
• Period also called "Dark Ages" for medicine
• Arabic medicine flourished: Avicenna (Ibn Sina, 980-1037 A.D.) - "Canon of Medicine" - most famous medical textbook of medieval times; described 760 drugs; quarantine for TB
• Ibn Khatima - first to suggest that disease was caused by minute organisms (precursor of germ theory)

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II. DAWN OF SCIENTIFIC MEDICINE

1. Revival of Medicine (Renaissance, 1500-1700 A.D.)

• Vesalius (1514-1564) - "Father of Modern Anatomy"; corrected errors of Galen; published "De Humani Corporis Fabrica"
• Harvey (1578-1657) - described circulation of blood; founded modern physiology
• Fracastorius (1483-1553) - proposed "contagion theory" (epidemic disease spread by contact with infected persons or objects); concept of "seminaria" (seeds of disease) - forerunner of germ theory

2. Sanitary Awakening (1800s)

• John Graunt (1620-1674) - father of vital statistics; first to analyze death statistics in London
• William Farr (1807-1883) - developed vital statistics in England
• Edwin Chadwick (1800-1890) - father of modern public health in England; Sanitary Movement began; "Chadwick's Report" on conditions of labouring population (1842)
• First Public Health Act: England, 1848
• Lemuel Shattuck (1793-1859) - father of public health in USA; "Shattuck Report" (1850)
• John Snow (1813-1858) - "Father of Field Epidemiology"; Broad Street pump handle removal (cholera epidemiology, London 1854) - before germ theory was known

3. Rise of Public Health

• Villerme - French physician; first to relate health to poverty
• Virchow - proposed that medicine is a social science; "Typhus is a social disease"

4. Germ Theory of Disease

• Louis Pasteur (1822-1895) - father of bacteriology; germ theory; vaccines for anthrax, rabies; pasteurization
• Robert Koch (1843-1910) - isolated specific causative agents; Koch's postulates; discovered tubercle bacillus (1882), cholera vibrio (1883)
• Germ theory era led to specific preventive measures: quarantine, water purification, immunization, disinfection

5. Birth of Preventive Medicine (Late 19th century)

• Pasteur's anti-rabies treatment (1883)
• Cholera vaccine (1892)
• Diphtheria antitoxin (1894)
• Anti-typhoid vaccine (1898)
• Bruce (1896) - African sleeping sickness transmitted by tsetse fly
• Ross (1898) - malaria transmitted by Anopheles mosquito
• Walter Reed (1900) - yellow fever transmitted by Aedes mosquito

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III. MODERN MEDICINE

A. Curative Medicine

• Primary objective: removal of disease from the patient (not from the mass)
• Allopathic medicine: "treatment of disease by a drug which produces a reaction that neutralizes the disease-producing process"
• Sulphonamides (1935, Domagk) - first major breakthrough in drug therapy
• Penicillin (1929, Fleming; clinical use 1940, Florey & Chain) - revolution in infection treatment
• Limitations: costly, not reaching social periphery, treats individual not community

B. Preventive Medicine

• Primary objective: prevention of disease in the population
• Employs epidemiological methods; focused on population
• Operates at three levels: primary, secondary, tertiary prevention
• Differs from curative medicine in: focus on groups (not individuals), uses epidemiology, mostly employs non-clinical interventions

C. Social Medicine

• Coined by Jules Guerin (1848)
• Virchow - major proponent; "Medicine is a social science and politics nothing but medicine on a large scale"
• Considers social, economic, cultural factors in health and disease
• Focus on health of communities and disadvantaged groups
• Uses social science methods in addition to medical sciences

D. Community Medicine

• Modern term replacing "social medicine"
• Defined as: "medical specialty concerned with preventing disease and promoting health in communities rather than in individuals"
• Also called "population medicine"
• Combines preventive medicine + social medicine + public health

E. Family Medicine

• Concerns with care of individuals in the context of family

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IV. EVOLUTION OF PUBLIC HEALTH (Phases - HIGH YIELD for exams)

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V. HEALTH FOR ALL AND PRIMARY HEALTH CARE

Health for All (HFA)

• 30th World Health Assembly (May 1977): Main social target = Health for All by 2000 A.D.
• HFA = health brought within reach of everyone in a given community
• Calls for equity, community participation, and intersectoral approach

Alma-Ata Declaration (1978)

• Joint WHO-UNICEF conference at Alma-Ata, USSR (now Kazakhstan), September 6-12, 1978
• Governments of 134 countries participated
• Defined Primary Health Care (PHC)
• PHC = "essential health care based on practical, scientifically sound, socially acceptable methods and technology made universally accessible to individuals and families... at a cost that the community and country can afford"
• 8 components of PHC (mnemonic: MATHEMATICS):
  1. Maternal and child health (MCH) & family planning
  2. Adequate nutrition / food supply
  3. Treatment of common diseases and injuries
  4. Health education
  5. Essential drugs
  6. Mental health
  7. Anti-malaria / control of endemic diseases
  8. Traditional medicine (use of appropriate technology)
  9. Immunization (against major diseases)
  10. Clean water supply and sanitation
  • (Note: standard lists use 8 components)

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VI. CONCEPTS OF HEALTH (VERY HIGH YIELD)

Definitions of Health

• WHO definition (1948): "Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity"
• Critique of WHO definition: Utopian, not measurable, static, does not include spiritual/vocational dimensions

Concepts (Chronological evolution)

1. Biomedical concept - health = absence of disease; body = machine; germ theory basis; criticized for ignoring social/psychological factors
2. Ecological concept - Dubos: health = dynamic equilibrium between man and environment; disease = maladjustment to environment
3. Psychosocial concept - health influenced by social, psychological, cultural, economic, political factors; health is both biological and social phenomenon
4. Holistic concept - multidimensional; integrates all previous concepts; individual is a complex system; health = positive quality of life

Dimensions of Health

1. Physical - anatomical integrity, ability to perform tasks
2. Mental - ability to think clearly, make sound judgements
3. Social - ability to interact with others; quality of interpersonal ties
4. Spiritual - purpose and meaning in life; ethics and integrity
5. Emotional - "feeling" (differs from mental = "knowing/cognition")
6. Vocational - work adapted to human capacities; source of self-esteem

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VII. SPECTRUM OF HEALTH AND DISEASE

• Health and disease are not static states; they exist on a continuum
• Spectrum of disease includes: healthy -> sub-clinical disease -> clinical disease -> disability -> death
• Iceberg phenomenon: the visible tip = clinical cases; submerged portion = undiagnosed/subclinical cases

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VIII. KEY EXAM POINTS (High Yield Summary)

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IX. IMPORTANT QUOTES (frequently asked in exams)

• "Medicine is a social science and politics is nothing but medicine on a large scale." - Virchow
• "Life is short, the art long, opportunity fleeting, experience treacherous and judgement difficult." - Hippocrates
• "Where there is love for mankind, there is love for the art of healing." - Hippocrates
• "Hygiea is fashionable among intellectuals but Panacea gets the cash." - (re: preventive vs curative)
• "Those who fail to read history are destined to suffer the repetition of its mistakes." - (opening quote of Park's Ch.1)
• "The first doctor was the first man, and the first woman, the first nurse."

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Concept of Health and Disease - Community Medicine (Park's)

Opening Quote: "Health is NOT mainly an issue of doctors, social services and hospitals. It is an issue of social justice."

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I. CONCEPT OF HEALTH

Background

• Health is perceived differently by biomedical scientists, social scientists, health administrators, ecologists, etc. - creating confusion
• Oldest definition: health = "absence of disease"
• In some cultures: health = harmony = "being at peace with self, community, god and cosmos"
• Ancient Indians and Greeks: health = equilibrium of "humors"
• Modern medicine criticized for preoccupation with disease and neglect of health study
• Health has evolved from an individual concern to a worldwide social goal

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II. WHO DEFINITION OF HEALTH

"Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity."

• WHO, 1948 (Preamble to Constitution)

Criticism of WHO definition:

1. Utopian - "complete" well-being is unachievable
2. Not measurable - no yardstick to measure "complete well-being"
3. Static - does not account for changing health status
4. Negative phrasing - "not merely absence..."
5. Does not include spiritual, vocational, emotional dimensions
6. Difficult to operationalize

Positive points:

• First time mental and social dimensions included
• Set a new standard and direction for health services
• Led to Health for All movement

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III. CHANGING CONCEPTS OF HEALTH (HIGH YIELD)

1. Biomedical Concept

• Health = absence of disease
• Based on germ theory of disease (turn of 20th century)
• Body = machine; disease = breakdown of machine; doctor's job = repair machine
• Criticism: minimized role of environmental, social, psychological, cultural factors; failed to explain chronic diseases, malnutrition, accidents, mental illness, pollution, population explosion

2. Ecological Concept

• Health = dynamic equilibrium between man and his environment
• Disease = maladjustment of human organism to environment
• Dubos defined health: "Health implies the relative absence of pain and discomfort and a continuous adaptation and adjustment to the environment to ensure optimal function"
• Raises two issues: imperfect man and imperfect environment
• Improvement in human adaptation = longer life expectancy

3. Psychosocial Concept

• Health influenced by social, psychological, cultural, economic and political factors
• Health is both a biological and social phenomenon
• Social sciences revealed health is not only a biomedical phenomenon

4. Holistic Concept (Current/Modern)

• Multidimensional - integrates biomedical, ecological, psychosocial concepts
• Whole is greater than sum of parts
• Individual is a complex system with biological, psychological, social, spiritual dimensions
• Health = positive quality of life
• Encompasses the total man in his total environment

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IV. OPERATIONAL DEFINITION OF HEALTH

• "The ability of an individual to perform his normal role functions in society"
• Focuses on functional capacity
• Used in surveys and health assessments

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V. NEW PHILOSOPHY OF HEALTH

1. Health is a fundamental human right
2. Health is a worldwide social goal
3. Health is essential to quality of life
4. Health is intersectoral - depends on agriculture, industry, education, housing, communication, not just medicine
5. Equity - elimination of health disparities
6. Community participation is essential
7. Primary health care is the key strategy

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VI. DIMENSIONS OF HEALTH (HIGH YIELD)

Key point: Many dimensions are "non-medical" - symbolizing that sectors beyond health must contribute to health attainment.

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VII. POSITIVE HEALTH

• More than absence of disease; implies "perfect functioning" of body and mind
• Biologically: every cell and organ functioning at optimum capacity
• Psychologically: sense of perfect well-being and mastery over environment
• Socially: optimal participation in social system
• Dubos critique: "Perfect positive health cannot become a reality because man will never be so perfectly adapted to his environment that his life will not involve struggles, failures and sufferings"
• Positive health = a mirage (ideal but unachievable in absolute terms)
• Better framed as: ability of individual to modify himself continually in the face of changing conditions of life

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VIII. HEALTH AS A RELATIVE CONCEPT

• Health is NOT an absolute state
• Newborn weight: India ~2.8 kg; developed countries ~3.5 kg - yet both considered healthy
• Height/weight standards vary by country and socioeconomic group
• Many "normal" people have heart murmurs, enlarged tonsils, X-ray chest shadows
• Health standards vary among cultures, social classes, age groups
• Health in any society should be defined in terms of prevailing ecological conditions

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IX. DETERMINANTS OF HEALTH

1. Biological Determinants

• Genetic make-up - unique, cannot be altered after conception
• Chromosomal anomalies, errors of metabolism, mental retardation, some diabetes types = genetic origin
• Medical genetics offers hope through genetic screening and gene therapy
• Genetic health = absence from genetic constitution of genes corresponding to serious defects + presence of normal karyotype

2. Behavioural and Socio-cultural Conditions (Lifestyle)

• Lifestyle = the totality of reactions and responses of an individual to their social, cultural and material environment
• "Mode of living" - daily habits of diet, exercise, smoking, alcohol, sexual behaviour
• WHO (1986): lifestyle responsible for ~50% of all mortality
• Lalonde report (Canada, 1974) identified lifestyle as a major determinant

3. Environment

• Physical environment: air, water, soil, housing, climate
• Social environment: family, community, peer groups, norms, values
• Environment is the most important determinant of health in developing countries

4. Socio-economic Conditions

• Income level, education, occupation, social class
• Virchow: "Typhus is a social disease"
• Villerme: first to relate health to poverty
• Poverty trap: poverty → ill health → poverty

5. Health Services

• Availability, accessibility, utilization and quality of health services
• Preventive, curative, rehabilitative services

Lalonde's "Health Field Concept" (Canada, 1974) - HIGH YIELD

1. Human biology (genetics, ageing)
2. Environment (physical, social)
3. Lifestyle (habits, behaviour)
4. Health care organization (services, manpower)

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X. CONCEPT OF DISEASE

Definition

Iceberg Phenomenon of Disease - HIGH YIELD

• Visible tip = clinical cases (diagnosed and treated)
• Submerged portion = undiagnosed/subclinical/latent/carrier cases
• For every clinical case seen, many more exist in the community undetected
• Importance: true burden of disease is much higher than apparent
• Examples: TB, diabetes, hypertension, STIs

Spectrum of Disease - HIGH YIELD

• Graphic representation of variations in manifestations of a disease
• Ranges from sub-clinical infection → mild disease → severe disease → death
• Like a spectrum of light (colours vary from end to end)
• All diseases have a spectrum:
  • Polio: 1000 infections → ~900 subclinical → ~90 non-paralytic → ~9 paralytic → ~1 death (90:9:1 ratio approximately)
  • Tuberculosis: infection → latent TB → active pulmonary TB → miliary TB
• Clinical physician sees only the severe end of the spectrum

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XI. NATURAL HISTORY OF DISEASE - VERY HIGH YIELD

Definition

Two Phases:

Phase 1: Pre-pathogenesis Phase

• Disease process has NOT yet started in man
• Interaction occurring in the environment between:
  • Agent (cause of disease)
  • Host (susceptible individual)
  • Environment (external factors)
• Equivalent to: before the stimulus enters the host

Phase 2: Pathogenesis Phase

• Disease process starts within the host
• Sub-stages:
  1. Early pathogenesis - stimulus enters host; no symptoms yet
  2. Discernible early lesions - tissue changes occur; still subclinical; detectable by screening tests
  3. Advanced disease - clinical signs and symptoms apparent
  4. Outcomes: recovery, disability, death

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XII. LEVELS OF PREVENTION - VERY HIGH YIELD (Leavell & Clark)

Primordial Prevention

• Prevent risk factors from emerging in the first place
• Population-level intervention - directed at entire population
• E.g., preventing obesity epidemic, tobacco use from starting in youth
• Operates in the pre-pathogenesis phase
• Concept introduced by Strasser (1978)

Primary Prevention

• Action taken prior to onset of disease
• Operates in pre-pathogenesis phase
• Two approaches:
  1. Health promotion (non-specific measures)
  2. Specific protection (specific measures, e.g., immunization)
• Goals: prevent disease, prolong life, promote positive health

Health Promotion activities:

• Health education
• Good nutrition
• Attention to personality development
• Provision of adequate housing
• Recreational facilities
• Genetic counselling
• Periodic health examination

Specific Protection activities:

• Immunization
• Use of specific nutrients (iodine, fluoride)
• Protection from occupational hazards
• Protection from accidents
• Use of specific chemoprophylaxis (anti-malarials)

Secondary Prevention

• Action taken to halt progression of early disease (presymptomatic stage)
• Operates at early pathogenesis phase
• Measures: early diagnosis and prompt treatment
• Tools: screening, case finding, periodic health examinations
• Goal: prevent complications, reduce severity, cut duration of illness

Tertiary Prevention

• Operates at advanced disease and disability stages
• Measures:
  1. Disability limitation - prevent further disability
  2. Rehabilitation - restore to useful life despite residual disability
• Types of rehabilitation: medical, social, vocational, psychological

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XIII. MODES OF PREVENTION BY LEVEL

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XIV. INDICATORS OF HEALTH - HIGH YIELD

1. Mortality indicators - CDR, IMR, MMR, Life expectancy
2. Morbidity indicators - Incidence rate, Prevalence rate
3. Disability rates
4. Nutritional status indicators - Anthropometric measurements
5. Health care delivery indicators - Doctor:population ratio, hospital beds
6. Utilization rates - ANC coverage, immunization coverage
7. Demographic indicators - Population growth rate, fertility rate
8. Socioeconomic indicators - Per capita income, literacy, unemployment
9. Health policy indicators - Political commitment, equity
10. Indicators of quality of life - PQLI, HDI
11. Social indicators
12. Other indicators

Most sensitive / commonly asked indicators:

• IMR (Infant Mortality Rate) = most sensitive indicator of health status of a community and socioeconomic conditions; also sensitive indicator of availability, utilization and effectiveness of health care
• Life expectancy at birth = best positive indicator of health; global health indicator
• MMR (Maternal Mortality Rate) = indicator of status of women and quality of obstetric care
• Under-5 mortality rate = indicator of child health and overall socioeconomic development

"Health for All" - WHO Monitoring Indicators (4 categories):

1. Health policy indicators - political commitment, resource allocation, equity, community involvement
2. Social and economic indicators - GNP/GDP, income distribution, adult literacy, housing
3. Indicators for provision of health care - availability, accessibility, utilization, quality
4. Health status indicators - LBW%, IMR, child mortality, life expectancy, MMR, morbidity, disability

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XV. RESPONSIBILITY FOR HEALTH

1. Individual Responsibility - Self Care

• Defined as: "health activities, including promotion, maintenance, treatment care and health related decision making, carried out by individuals and families"
• Activities: diet, sleep, exercise, weight management, alcohol/smoking avoidance, personal hygiene, immunization acceptance, early reporting when sick, family planning
• Shift to chronic disease pattern makes self care a logical necessity

2. Community Responsibility

• Emphasis shifted from health care FOR the people to health care BY the people
• Three ways community participates:
  1. Provide facilities, manpower, logistic support, funds
  2. Active involvement in planning, management, evaluation
  3. Joining and using health services (especially preventive measures)
• Examples: Village Health Guides (1977, India), ASHA under National Health Mission

3. State Responsibility

• Health is a constitutional obligation in most countries
• Article 47 of Indian Constitution: State shall raise level of nutrition, standard of living and improve public health
• State provides health infrastructure, legislation, funding

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XVI. LEVELS OF HEALTH CARE

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XVII. HIGH YIELD EXAM SUMMARY TABLE

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XVIII. IMPORTANT QUOTES (for exams)

• "Health is NOT mainly an issue of doctors, social services and hospitals. It is an issue of social justice."
• "Health is a fundamental human right and a worldwide social goal." - Alma-Ata, 1978
• Dubos: "The concept of perfect positive health cannot become a reality because man will never be so perfectly adapted to his environment that his life will not involve struggles, failures and sufferings."
• "Positive health will always remain a mirage."
• "Something for all, but more for those in need - in proportion to the need." - WHO (Risk approach)
• "Medicine is a social science..." - Virchow

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Principles of Epidemiology & Epidemiological Methods

Community Medicine - Park's Textbook (Exam-Oriented Notes)

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I. DEFINITION OF EPIDEMIOLOGY

Historical Definitions:

1. "That branch of medical science which treats epidemics" - Parkin, 1873
2. "The science of the mass phenomena of infectious diseases" - Frost, 1927
3. "The study of disease, any disease, as a mass phenomenon" - Greenwood, 1934
4. "The study of the distribution and determinants of disease frequency in man" - MacMahon, 1960 (most quoted)

Modern/Current Definition (Park's, most comprehensive):

"The study of the occurrence and distribution of health related events, states, and processes in specified populations, including the study of the determinants influencing such processes, and the application of this knowledge to control relevant health problems."

• Study = surveillance, observation, screening, hypothesis testing, experiments, prediction
• Distribution = analysis by Time, Place, Person
• Determinants = geophysical, biological, behavioural, social, cultural, economic, political factors
• Application = to promote, protect, and restore health

Milestones:

• W.H. Frost = first professor of epidemiology in USA (1927)
• Major Greenwood = first professor of epidemiology and medical statistics, University of London

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II. USES OF EPIDEMIOLOGY (Morris - 7 Uses) - HIGH YIELD

1. Historical study - rise and fall of disease in population; time trends
2. Community diagnosis - identify and quantify health problems (mortality, morbidity rates); forms basis for health planning
3. Working of health services - evaluating effectiveness and efficiency of health services
4. Individual risks and chances - probability that an individual will develop a certain disease; "risk" in epidemiology
5. Identification of syndromes - description and classification of clinical syndromes, determination of natural history
6. Completion of the clinical picture - full spectrum of disease (clinical + subclinical), natural history
7. Search for causes - aetiological research; identification of risk factors

Mnemonic: H-C-W-I-I-C-S or remember "7 uses by Morris"

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III. CONCEPT OF CAUSATION

Pre-Pasteur Theories:

• Supernatural theory, Theory of humors, Contagion theory, Miasmatic theory, Spontaneous generation theory

Germ Theory (Koch-Pasteur era):

• One-to-one relationship: Disease agent → Man → Disease
• Limitations: not every exposed person develops disease; cannot explain chronic/multifactorial diseases

Koch's Postulates:

1. Organism must be present in every case of the disease
2. It must be isolated from the diseased host and grown in pure culture
3. Disease must be reproduced when pure culture is introduced into a healthy susceptible host
4. Organism must be re-isolated from the experimentally diseased host

Epidemiological Triad (Agent-Host-Environment):

• Three interactive factors determine disease occurrence
• Agent: biological, chemical, physical, nutritional, social causes
• Host: intrinsic factors (age, sex, genetics, immunity)
• Environment: physical, biological, psychosocial
• Disease occurs when there is imbalance between these three

Multifactorial Causation:

• Concept first proposed by Pettenkofer of Munich (1819-1901)
• Revived and developed by epidemiologists
• Most diseases have MULTIPLE causes - genetic, social, economic, environmental, psychological
• Gave rise to concept of "risk factors"

Web of Causation:

• Proposed by MacMahon
• Considers ALL predisposing factors and their complex interrelationships
• Visualizes multiple possible interventions
• Example: Web of causation for myocardial infarction
• Key principle: Removal of just ONE important link may be sufficient to control disease

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IV. AGENT, HOST, ENVIRONMENT FACTORS - HIGH YIELD

Agent Factors:

1. Biological agents: bacteria, viruses, fungi, protozoa, helminths, rickettsia
2. Nutrient agents: excess or deficiency (e.g., protein deficiency, vitamin D excess)
3. Physical agents: heat, cold, radiation, noise, trauma
4. Chemical agents: poisons, allergens, drugs, industrial chemicals
5. Mechanical agents: chronic friction, compression
6. Absence/insufficiency/excess of a necessary factor
7. Social agents: poverty, stress, occupational hazards

Host Factors (Intrinsic):

• Age, Sex, Genetic constitution
• Immunity (specific and non-specific)
• Nutritional status, Physiological state
• Personality, habits, lifestyle

Environmental Factors (Extrinsic):

a. Physical environment

• Geography, climate, soil, water, air quality
• Urbanization, radiation, noise, housing

b. Biological environment

• Living things: microbes, insects, rodents, animals, plants
• These act as agents, reservoirs, intermediate hosts, vectors
• Constant adjustment and readjustment (ecological balance)

c. Psychosocial environment

• Cultural values, customs, habits, beliefs, attitudes, religion, education, lifestyle
• Community life, social and political organization
• Psychosocial factors can cause psychosomatic disorders: duodenal ulcer, bronchial asthma, hypertension, CHD, mental disorders

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V. RISK FACTORS

Characteristics of a Risk Factor:

1. Associated with increased probability of disease
2. Precedes the disease
3. Not sufficient in itself to cause disease (only increases probability)

Types:

• Modifiable: smoking, diet, hypertension, obesity, sedentary lifestyle
• Non-modifiable: age, sex, genetic constitution, family history

Risk Factor vs Cause:

• Risk factor = increases probability; need not be necessary or sufficient
• Cause = produces the disease (necessary, sufficient, or both)

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VI. CRITERIA FOR CAUSATION (Hill's Criteria) - VERY HIGH YIELD

1. Strength of association - stronger the association (high relative risk), more likely causal; e.g., smoking-lung cancer: RR = 9-10
2. Consistency - association observed repeatedly in different populations, places, times, by different researchers
3. Specificity - one cause - one effect; a factor leads to a specific disease
4. Temporality - exposure (cause) must PRECEDE the outcome (effect); MOST essential criterion
5. Biological gradient (Dose-response) - as dose increases, disease frequency increases; e.g., more cigarettes smoked = higher lung cancer risk
6. Plausibility - biologically plausible mechanism
7. Coherence - association does not conflict with known natural history and biology of the disease
8. Experiment - disease reduced when exposure removed (intervention evidence)
9. Analogy - similar factors causing similar diseases (analogous situations)

Mnemonic: SCSTT BPCEA (Strength, Consistency, Specificity, Temporality, dose-response, Biological plausibility, Coherence, Experiment, Analogy)

Most essential criterion = Temporality (cause must precede effect)

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VII. BASIC MEASUREMENTS IN EPIDEMIOLOGY - VERY HIGH YIELD

Key Terms:

• Numerator: number of times event has occurred
• Denominator: population at risk or total events
• Population at risk: those capable of having or acquiring the disease
• Mid-year population: population on 1st July (used as denominator for annual rates)
• Person-years: combination of persons × time (used in cohort studies)

Rate vs Ratio vs Proportion:

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VIII. MEASURES OF DISEASE FREQUENCY

A. Incidence

• Measures rate of occurrence of new events
• Dynamic measure (time-dependent)
• Best for acute diseases
• Used to study aetiology

Attack Rate (Incidence proportion):

• Used in epidemic investigations
• Food-specific attack rate: determines which food caused outbreak

Secondary Attack Rate (SAR):

• Measures transmission in households or closed populations
• Indicator of communicability of the disease

B. Prevalence

• Measures existing cases (old + new)
• Static measure
• Best for chronic diseases
• Used for health planning (resource allocation)

Relationship: P = I × D

Prevalence = Incidence × Mean duration of disease

• High prevalence relative to incidence → long duration (e.g., TB, diabetes)
• Low prevalence relative to incidence → short duration (acute, rapidly fatal or rapidly recovering)
• Effective treatment that prolongs life without cure → increases prevalence

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IX. MORTALITY MEASURES - HIGH YIELD

Standardization of Rates:

• Direct standardization: apply age-specific rates of study population to a standard population
• Indirect standardization: apply standard rates to study population → calculate SMR (Standardized Mortality Ratio)
• SMR = (Observed deaths / Expected deaths) × 100
  • SMR >100 = excess mortality; SMR <100 = deficit mortality

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X. DESCRIPTIVE EPIDEMIOLOGY - HIGH YIELD

"Describes the distribution of disease in terms of Person, Place, Time"

Person (Who?):

• Age - most important host factor; strongly related to disease
  • Bimodality: two peaks in age-incidence curve (e.g., Hodgkin's disease, leukaemia, breast cancer)
• Sex - sex-specific rates; some diseases more common in women (diabetes, hypothyroidism, obesity); others in men (lung cancer, CHD)
• Ethnicity/race - genetic and socio-cultural factors
• Occupation - occupational exposures, lifestyle
• Socioeconomic status - income, education, poverty
• Marital status, religion, diet, habits, migration

Place (Where?):

• International differences, national differences, urban-rural differences
• Spot maps, area maps
• Point clusters, area clusters

Time (When?):

1. Secular (long-term) trends - changes over years/decades (e.g., decline of TB, rise of CHD)
2. Cyclic/Periodic fluctuations - regular patterns:
   • Seasonal variation: peak in certain seasons (e.g., cholera in summer, respiratory infections in winter)
   • Annual cycles
3. Short-term fluctuations (Epidemics):
   • Common source: single contaminated source; explosive onset; all cases within one incubation period
   • Propagated: person-to-person spread; gradual rise and fall; multiple incubation periods
4. Irregular/Random variation

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XI. EPIDEMIC INVESTIGATIONS - HIGH YIELD

Types of Epidemics:

A. Common Source Epidemics

1. Point source (single exposure):
   • Epidemic curve: rises and falls rapidly, no secondary waves
   • All cases within ONE incubation period
   • Explosive onset
   • Example: food poisoning at a party
2. Continuous/repeated exposure:
   • Exposure ongoing from same source
   • Epidemic extended or irregular; exceeds one incubation period
   • Example: contaminated water supply, Legionnaire's disease (Philadelphia, 1976)

B. Propagated (Progressive Source) Epidemics

• Person-to-person transmission
• Gradual rise, tails off over longer period
• Multiple incubation periods visible on epidemic curve
• Continues until susceptibles depleted or exposure stops
• Speed depends on herd immunity, contact opportunities
• Examples: hepatitis A, polio, influenza

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XII. ANALYTICAL EPIDEMIOLOGY - VERY HIGH YIELD

Types of Study Designs:

EPIDEMIOLOGICAL STUDIES
├── Observational
│   ├── Descriptive (person, place, time)
│   ├── Analytical
│   │   ├── Case-Control (Retrospective)
│   │   └── Cohort (Prospective)
│   └── Cross-sectional (Prevalence survey)
└── Experimental (Interventional)
    ├── Clinical trials
    ├── Field trials
    └── Community trials

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XIII. CASE-CONTROL STUDY - HIGH YIELD

Odds Ratio (OR):

• OR >1 = positive association (risk factor)
• OR <1 = protective factor
• OR = 1 = no association

Selection of Cases:

• Incident cases (newly diagnosed) preferred over prevalent cases
• Diagnostic criteria must be specified before study
• Sources: hospitals or general population

Selection of Controls:

• Must be free from the study disease
• Must be similar to cases except for absence of disease
• Sources: hospital controls, neighbourhood controls, relatives, general population

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XIV. COHORT STUDY - HIGH YIELD

Types:

1. Prospective cohort - groups identified in present; followed into future
2. Retrospective cohort (historical) - groups identified from records in the past; outcome assessed in present
3. Ambidirectional - combination

Relative Risk (RR):

• RR >1 = positive association
• RR = 1 = no association
• RR <1 = protective

Attributable Risk (AR):

Comparison groups in cohort studies:

1. Internal comparisons - different exposure levels within same cohort
2. External comparisons - exposed vs. separate unexposed cohort
3. Comparison with general population - exposed vs. general population rates

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XV. CROSS-SECTIONAL STUDY (Prevalence Survey)

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XVI. EXPERIMENTAL EPIDEMIOLOGY (Interventional Studies) - HIGH YIELD

Key difference from observational:

• Investigator directly controls the conditions; deliberately applies/withdraws intervention
• Always prospective

Types:

1. Clinical trials - evaluate therapeutic agents (drugs, procedures) in patients
2. Preventive trials - evaluate preventive measures (vaccines, chemoprophylaxis) in healthy persons
3. Risk factor trials - intervene to modify risk factors (e.g., reduce cholesterol, stop smoking)
4. Community trials - intervention applied to entire communities

Randomized Controlled Trial (RCT) - Gold Standard:

• Participants randomly assigned to treatment and control groups
• Randomization ensures comparability
• Blinding: Single-blind (subject unaware), Double-blind (both subject and observer unaware), Triple-blind (subject, observer, analyst unaware)
• Measures: Efficacy (under ideal conditions) vs. Effectiveness (under real-world conditions)

Phases of Clinical Trials:

• Phase I: Safety testing; small group; dose finding
• Phase II: Efficacy testing; small group; short duration
• Phase III: Large-scale RCT; compared with standard treatment or placebo; most important
• Phase IV: Post-marketing surveillance; long-term safety and efficacy

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XVII. MEASURES OF ASSOCIATION - SUMMARY

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XVIII. BIAS IN EPIDEMIOLOGY - HIGH YIELD

Types:

1. Selection bias - systematic difference in selection of study and comparison groups
   • Berkson's bias (hospital admission bias): hospitalized patients not representative
   • Neyman bias (prevalence-incidence bias): prevalent cases ≠ incident cases (survivors only)
2. Information (Observation) bias - systematic error in measuring exposure or outcome
   • Recall bias: cases remember exposure better than controls (common in case-control studies)
   • Observer bias: systematic error by observer
   • Hawthorne effect: subjects change behaviour when they know they are being observed
3. Confounding bias - third variable is associated with both exposure and outcome; distorts true relationship

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XIX. SURVEILLANCE IN EPIDEMIOLOGY

Monitoring vs Surveillance:

Surveillance Definition (Park's):

Sentinel Surveillance:

• Identifies missing cases not captured by routine notification
• Uses a network of selected health care providers (sentinels) to report specific diseases
• Supplements notified cases; particularly used for influenza, HIV, STIs

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XX. CONCEPTS OF CONTROL, ELIMINATION AND ERADICATION

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XXI. HIGH YIELD EXAM SUMMARY TABLE

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