• SPM (Social/Preventive Medicine) - I'll refer to Park's Textbook of Preventive and Social Medicine and include diagrams wherever relevant.
• FMT (Forensic Medicine & Toxicology) - I'll refer to Narayan Reddy's The Essentials of Forensic Medicine and Toxicology.

• Long note (20 marks) - Detailed, structured answer covering all aspects: definition, classification, epidemiology, pathology, clinical features, diagnosis, treatment, prevention, and control. With diagrams where relevant.
• Short note (8 marks) - Concise, focused answer hitting the key points only, well-organized under brief headings.

EPIDEMIOLOGY OF HYPERTENSION

1. INTRODUCTION

2. DEFINITION

3. CLASSIFICATION (WHO/JNC)

When systolic and diastolic fall in different categories, the higher category is selected.

4. CLASSIFICATION BY TYPE

• Essential (Primary) Hypertension - Cause unknown; accounts for 90% of all cases.
• Secondary Hypertension - Due to identifiable causes (accounts for ~10%):
  • Chronic glomerulonephritis / chronic pyelonephritis
  • Tumours of the adrenal glands (phaeochromocytoma, Conn's syndrome)
  • Congenital narrowing of the aorta (coarctation)
  • Toxaemias of pregnancy
  • Oral contraceptive pills (commonest cause of secondary HT today - due to oestrogen component)

5. MAGNITUDE OF THE PROBLEM (Prevalence)

• Global prevalence estimated at 1.13 billion in 2015.
• Overall prevalence in adults: 30-40% worldwide.
• Age-standardized prevalence: 24% in men, 20% in women.
• Prevalence > 60% in persons aged over 60 years.
• Number of hypertensives estimated to increase by 15-20% by 2025 as populations age and adopt sedentary lifestyles.
• Elevated blood pressure is a leading cause of premature death worldwide.

6. THE "RULE OF HALVES" (Iceberg Phenomenon)

• Only ½ of hypertensives in the community were aware of the condition
• Of those aware, only ½ were being treated
• Of those treated, only ½ were adequately controlled

7. INCIDENCE

• Variability of consecutive readings in individuals
• Ambiguity of what constitutes "normal" BP
• Insidious nature of the condition

8. "TRACKING" OF BLOOD PRESSURE

9. RISK FACTORS

A. Non-Modifiable Risk Factors

B. Modifiable Risk Factors

10. PREVENTION OF HYPERTENSION (WHO Recommendations)

1. Primary Prevention

• Salt reduction to < 5 g/day
• Moderate fat intake
• Avoid excess alcohol
• Weight reduction (BMI < 25)
• Regular physical activity
• Behavioural changes (stress reduction, yoga, meditation)
• Health education and self-care (self BP monitoring with log-books)

2. Secondary Prevention

• Screening for hypertension
• Adequate anti-hypertensive treatment
• Regular follow-up and adequate control

11. ORGAN DAMAGE

• Markedly high pressures may exist without organ damage
• Organ damage may occur with only moderate BP elevation

DIABETES MELLITUS

1. DEFINITION

• Insulin secretion
• Insulin action
• Or both

2. COMPLICATIONS

• Retinopathy
• Nephropathy
• Neuropathy

• Heart disease, peripheral arterial disease, cerebrovascular disease
• Obesity, cataracts, erectile dysfunction
• Non-alcoholic fatty liver disease
• Infections - particularly tuberculosis

3. CLASSIFICATION (WHO 2019)

• Essential (Type 2) accounts for the majority of all cases.
• India has 77 million diabetics (second only to China); prevalence 11.8% (2019 survey).

4. EPIDEMIOLOGICAL DETERMINANTS / RISK FACTORS

A. AGENT

• Pancreatic disorders (inflammatory, neoplastic, cystic fibrosis)
• Defective insulin synthesis (abnormal, biologically less active molecule)
• Beta-cell destruction (viral, chemical agents)
• Decreased insulin sensitivity (decreased adipocyte/monocyte insulin receptors)
• Genetic defects (mutation of insulin gene)
• Autoimmunity

B. HOST FACTORS (Non-Modifiable)

C. ENVIRONMENTAL / LIFESTYLE RISK FACTORS (Modifiable)

5. DIAGNOSTIC CRITERIA (WHO 2019)

Diagnosis should be confirmed on a second occasion in the absence of symptoms. In the presence of classic symptoms (polyuria, polydipsia, unexplained weight loss), a single test is sufficient.

Impaired Glucose Tolerance (IGT) / Pre-diabetes:

• Fasting: 6.1-6.9 mmol/L (110-125 mg/dL)
• 2-hour post-load: 7.8-11.0 mmol/L (140-199 mg/dL)
• HbA1c: 5.7-6.4%

6. GLYCAEMIC INDEX (GI)

"Glycaemic index of a food is defined by the area under the two-hour blood glucose response curve (AUC) following ingestion of a fixed portion of test carbohydrate (usually 50 g), as a proportion (%) of the AUC of the standard (either glucose or white bread)."

Classification of Foods by GI:

• Management of diabetes - low GI foods prevent glucose spikes
• Control of obesity - low GI foods provide satiety and prevent overeating

7. LIFESTYLE MODIFICATIONS FOR PREVENTION

a. Primary Prevention - Population Strategy:

• Maintain normal body weight
• Healthy nutritional habits - adequate protein, high dietary fibre, avoidance of sweet foods
• Regular physical exercise
• Avoid excess alcohol
• Avoid diabetogenic drugs (OCP, corticosteroids)

b. Evidence-Based Interventions:

• Tables only when Park's textbook itself has a table (classification tables, diagnostic criteria tables, etc.) - I'll reproduce those as-is.
• For everything else - risk factors, descriptions, mechanisms, lists - I'll write in flowing text with bullet points or numbered lists, not tables.
• Tables only for genuine comparisons where side-by-side format is truly needed.

GLYCAEMIC INDEX

Definition

Concept

• A reduced peak blood glucose level
• A prolonged rate of absorption

Classification (Park's Table)

Clinical Utility

1. Management of diabetes - Low GI foods prevent sharp post-meal glucose spikes, aiding better glycaemic control. Patients are advised to prefer low GI foods to maintain stable blood sugar levels.
2. Control of obesity - Low GI foods provide greater satiety, slow gastric emptying, and reduce overall caloric intake, thereby helping in weight management.

Relationship with Dietary Fibre

• Glycaemic index - British/international spelling (used by WHO, Park's textbook, and most medical literature)
• Glycemic index - American spelling

• All three curves start at the same fasting baseline (~90 mg/dL) at time 0, after ingestion of 50 g of test carbohydrate.
• The area under the curve (AUC) over 2 hours is measured for each food.
• This AUC is then expressed as a percentage of the AUC of the standard (glucose or white bread) - and that percentage IS the glycaemic index.

• High GI food - sharp, tall spike - large AUC - rapid glucose rise and rapid fall (risk of rebound hypoglycaemia)
• Low GI food - gentle, broad, flat curve - small AUC - slow sustained release, better for diabetics and weight control
• GI = (AUC of test food / AUC of standard) × 100

PREVENTION OF ORAL CANCER AND CERVICAL CANCER

PART 1 - PREVENTION OF ORAL CANCER

Background

Key Epidemiological Features Relevant to Prevention

• Tobacco (chewing and smoking) is the single most important causative factor.
• Alcohol has a synergistic effect with tobacco.
• The natural history shows a precancerous stage (leukoplakia, erythroplakia) that can be detected up to 15 years before invasive carcinoma develops - offering a critical window for intervention.
• High-risk groups: tobacco/betel quid chewers, bidi smokers, those who sleep with tobacco quid in the mouth (risk 36 times higher than non-chewers).

a. Primary Prevention

• Tobacco elimination - If tobacco habits are eliminated from the community, a great reduction in oral cancer incidence can be achieved. This is the single most effective measure.
• Public education and motivation - Intensive IEC (Information, Education, Communication) activities for lifestyle change.
• Legislative measures - Banning or restricting the sale of tobacco products.
• Alcohol reduction - Limiting alcohol consumption, especially in tobacco users.

b. Secondary Prevention

• Oral cancers are easily accessible for inspection, enabling early detection.
• Leukoplakia (precancerous lesion) can be cured by cessation of tobacco use alone.
• If detected at the precancerous stage, lesions can be treated or reversed before progression to invasive carcinoma.
• Main treatment modalities: surgery and radiotherapy.
• Primary health care workers (village health guides, multi-purpose workers) are in a strategic position to detect oral cancers during home visits - they serve as a vital link in developing countries.
• In developing countries, over 50% of oral cancers are detected only at an advanced stage - making community-level detection efforts critical.

PART 2 - PREVENTION OF CERVICAL CANCER

Background

Natural History (Basis for Prevention)

• Carcinoma in situ persists for an average of more than 8 years before becoming invasive.
• The entire preinvasive stage may last 15-20 years or longer.
• This prolonged preinvasive phase makes screening-based secondary prevention extremely effective.
• Causative agent: Human Papilloma Virus (HPV) - sexually transmitted; found in more than 95% of cases; necessary but not sufficient cause.

a. Primary Prevention

• Until causative factors are more clearly understood, full primary prevention is limited.
• Measures with potential impact include:
  • Improved personal hygiene and genital hygiene (especially in lower socio-economic groups).
  • Birth control and reduction of early marriage, early coitus, and repeated childbearing.
  • Monogamous sexual behaviour and avoidance of multiple sexual partners.
  • HPV vaccination (current evidence strongly supports this as the most effective primary prevention measure).
  • Avoiding prolonged use of high-oestrogen oral contraceptive pills.

b. Secondary Prevention (Screening)

• Pap smear (Cervical smear): All women should have a Pap test at the beginning of sexual activity, then every 3 years thereafter. Organized population-based Pap smear programmes have markedly reduced incidence and mortality in developed countries.
• VIA (Visual Inspection with Acetic acid): Application of 5% acetic acid to the cervix; a well-defined opaque acetowhite lesion close to the squamo-columnar junction is a positive result. This is cost-effective, easy to perform, and easy to train health workers in - particularly suitable for India.
  • Also: VIAM (VIA with magnification) and VILI (Visual Inspection with Lugol's Iodine).
• Single-visit approach: After a positive VIA, the woman is managed in the same visit at a district hospital - colposcopy, biopsy, and treatment (reduces loss to follow-up).
• IEC activities to sensitize the community about significance of the disease and importance of screening.

Prognosis with Early Detection:

• 5-year survival rate for carcinoma in situ - virtually 100%
• For local invasive disease - 79%
• For regional invasive disease - 45%
• Once symptoms develop, it is difficult to cure and fatal if untreated - reinforcing the value of screening.

DIAGRAM 1 - Multiple Causation of Road Traffic Accidents

DIAGRAM 2 - Haddon's Matrix (Host-Agent-Environment Model for RTA)

Other Important Points / Quick Notes on RTA (Park's)

• ~1.25 million deaths per year globally from road accidents
• For every death - 20-50 non-fatal injuries and 10-20 serious injuries
• 48% of road deaths are vulnerable users (pedestrians, cyclists, motorcyclists)
• >90% of RTA deaths occur in low and middle income countries
• Males under 25 are 3 times more likely to be killed than young females
• Traffic accidents killed 1,77,423 persons in India in 2015

• Speed - pedestrian survival < 50% at impact ≥ 45 km/h
• Drink-driving - risk increases significantly above BAC of 0.04 g/dl
• Motorcycle helmet use - reduces death risk by 40%, severe injury by 70%
• Seat belt use - reduces front-seat fatality by 40-50%
• Distracted driving (mobile phones)
• Driver fatigue
• Non-use of child restraints

DIAGRAM 1 - Natural History & Pathogenesis of RHD

• RF is NOT a communicable disease but results FROM a communicable disease (streptococcal pharyngitis)
• The toxic-immunological hypothesis explains the link - cross-reactive antibodies against streptococcal antigens damage cardiac tissue
• Each recurrent attack causes progressive valve damage
• Mitral stenosis is the most common valvular lesion
• Death typically occurs by age 35 or even earlier
• Insufficiency from acute rheumatic valve disease resolves in 60-80% of patients who adhere to antibiotic prophylaxis

DIAGRAM 2 - Modified Jones Criteria (WHO 2002-2003)

• Primary episode of RF = 2 Major OR 1 Major + 2 Minor + evidence of preceding strep infection
• Recurrent RF with established RHD = 2 Minor alone + strep evidence is sufficient
• Rheumatic chorea / insidious onset carditis = no other criteria required

• J - Joint (Polyarthritis) - most common, 90% of cases
• O - (c)Orditis - Carditis
• N - Nodules (subcutaneous)
• E - Erythema marginatum
• S - Sydenham's chorea

DIAGRAM 1 - Immunopathogenesis (Molecular Mimicry)

DIAGRAM 2 - Valve Lesions in Chronic RHD

• Mitral valve alone - 70% cases (most common)
• Mitral + Aortic - 25% cases
• Aortic alone - 5% cases
• Tricuspid/Pulmonary - rare
• Mitral stenosis is the hallmark of RHD
• Pathology = commissural fusion + leaflet thickening + chordal shortening + calcification

DIAGRAM 3 - Three Levels of Prevention

• Secondary prevention with Benzathine Benzyl Penicillin (1.2 million units IM every 3-4 weeks) is the cornerstone of RHD control in developing countries
• Duration depends on whether carditis/residual valve disease is present - can be lifelong in those with residual valve lesions
• RHD is one of the most readily preventable chronic diseases (Park's) - yet kills by age 35 if untreated

• All content strictly from Park's Textbook of Preventive and Social Medicine only
• Diagrams that exist in Park's will be pulled directly from the textbook
• If Park's has no diagram for a topic, I'll generate one based only on what Park's text describes - no outside sources
• No mixing with other references

SPM SHORT NOTES - 8 MARKS EACH

(Park's Textbook of Preventive and Social Medicine)

Q1. INDICATORS OF HEALTH

Definition

• Health indicator - measures a specific aspect of health
• Health index - an amalgamation of several health indicators

Characteristics of an Ideal Indicator (Park's)

• Valid - measures what it is supposed to measure
• Reliable and objective - same answer regardless of who measures
• Sensitive - responds to changes in the situation
• Specific - reflects only changes in the situation concerned
• Feasible - data collection is practically possible
• Relevant - contributes to understanding the phenomenon

Classification of Health Indicators (Park's)

1. Mortality indicators - Crude death rate, Life expectancy, Infant mortality rate (IMR), Under-5 mortality rate, Maternal mortality rate
2. Morbidity indicators - Incidence, Prevalence, notification rates
3. Disability rates - Event-type and person-type disability indicators
4. Nutritional status indicators
5. Health care delivery indicators
6. Utilization rates
7. Indicators of social and mental health
8. Environmental indicators
9. Socio-economic indicators
10. Health policy indicators
11. Indicators of quality of life
12. Other indicators (e.g., HALE, QALY, DALYs)

Key Single Best Indicators

• Best overall health indicator - Life expectancy at birth
• Best indicator of health of children / socioeconomic development - Infant Mortality Rate (IMR)
• Best sensitive indicator - IMR

Q2. ICEBERG PHENOMENON OF DISEASE

Definition

Park's Diagram (Fig. 10):

Components of the Iceberg

• Symptomatic / clinical disease
• What the physician sees

• Presymptomatic disease
• Inapparent / subclinical infections
• Undiagnosed cases
• Carriers

Examples (Park's)

Significance

• The hidden part constitutes an important undiagnosed reservoir of infection or disease in the community
• Its detection and control is a challenge to modern preventive medicine
• One major deterrent in chronic disease study is the absence of methods to detect the subclinical state - the bottom of the iceberg
• Explains why community-based screening is essential

Q3a. EPIDEMIOLOGICAL TRIAD

Background

The Triad

The Three Components

• Biological agents (bacteria, viruses, parasites, fungi)
• Chemical agents (dietary factors, tobacco, solvents, poisons)
• Physical agents (radiation, heat)
• Nutritional deficiencies

• Level of immunity
• Genetic makeup
• Age, sex, nutritional status
• Level of exposure

• Biological environment
• Social, cultural and physical aspects
• Conditions in which the pathogen lives

• Incubation periods
• Duration of illness
• Life expectancy of host/pathogen

Significance

Q3b. ADVANCED TRIANGLES OF EPIDEMIOLOGY

Traditional Triangle (Fig. 5)

Limitations of the Traditional Model

Advanced (Adapted) Model of the Triangle (Fig. 6)

Key Differences from Traditional Model

• "Agent" is replaced by "Causative factors" - implying multiple aetiological factors
• "Host" is replaced by "Groups or populations and their characteristics"
• "Environment" now includes behaviour, culture, physiological factors, and ecological elements
• Time remains at the centre

Q4. SPECTRUM OF DISEASE (Spectrum of Health)

Definition

The Spectrum

Gradient of Infection

Example

Relationship with Iceberg

FATAL ←————————————————→ SUBCLINICAL
  ↑                              ↑
(Tip of iceberg)        (Bottom of iceberg)

Significance

• The sequence of events can be interrupted by early diagnosis, treatment or preventive measures
• It allows inclusion of all cases - both subclinical and clinical - in study of disease
• Helps understand why the same organism produces different severity in different people

Q5. WEB OF CAUSATION

Origin

Concept

Important Principle

• The relative importance of individual factors is expressed in terms of "relative risk"
• In a multifactorial event, individual factors are not all of equal weight

Advantages of this Model

• More suitable for non-communicable / chronic diseases
• Helps identify multiple points of intervention
• Acknowledges that disease cannot always be explained by a single agent
• Useful in studying diseases like CHD, cancer, diabetes, hypertension

Difference from Epidemiological Triad

Q6. ROLE OF JOHN SNOW IN PUBLIC HEALTH

Background

The Cholera Epidemic of 1854 (Golden Square, London)

• Cases clustered around the Broad Street water pump
• People living near other water pumps had fewer deaths
• The boundary line on the map shows equal distances between the Broad Street pump and other pumps - and cases fell predominantly within the Broad Street pump boundary

Findings and Action

• Hypothesize that cholera was a water-borne disease, long before the birth of bacteriology (the cholera bacillus was not discovered until 1883 by Koch)
• Identify the Broad Street water pump as the source of infection
• Remove the handle of the Broad Street pump - and the epidemic was controlled. This is the classic example of disease control by removing one link in the chain of causation

Contributions to Public Health

• Pioneered the use of spot maps / place distribution in epidemiology
• Demonstrated the descriptive epidemiology method (person, place, time)
• Proved that disease can be controlled without knowing the causative organism - by epidemiological reasoning alone
• His work established the foundation for epidemiological investigation of outbreaks
• His approach is used to this day in field epidemiology and outbreak investigation

Q7. MORBIDITY INDICATORS

Need

Morbidity Rates Used (Park's)

• Incidence rate = Number of new cases in a defined population in a specified time period
• Prevalence rate = Number of existing cases (new + old) in a defined population at a given point in time
• Relationship: Prevalence = Incidence × Mean duration of disease

Other Important Measures

• HALE (Health-Adjusted Life Expectancy) - Life expectancy adjusted for time spent in poor health; equivalent number of years in full health a newborn can expect to live
• QALY (Quality-Adjusted Life Years) - Measures disease burden including both quality and quantity of life lived; used to assess value for money of medical interventions. Each year in perfect health = 1.0; a year in poor health = < 1.0
• DALY (Disability-Adjusted Life Years) - Years of healthy life lost due to disease or disability

Significance

• Identify the true burden of disease (including subclinical cases)
• Plan and allocate health resources
• Monitor programme effectiveness
• Compare health status across populations and time

Q8. CHAIN OF TRANSMISSION OF DISEASE

The Three Links (Park's Fig. 16)

LINK 1: SOURCE / RESERVOIR OF INFECTION

• Cases (clinical cases - severe, mild, inapparent)
• Carriers - Healthy carrier, incubatory carrier, convalescent carrier, chronic carrier

• e.g., Rabies (dogs/foxes), Brucellosis (cattle), Plague (rats), Leptospirosis (rats)

LINK 2: MODES OF TRANSMISSION

• Direct contact (STDs, scabies)
• Droplet spread (influenza, measles)
• Contact with soil (hookworm, tetanus)
• Transplacental (rubella, syphilis, HIV)

• Vehicle-borne (contaminated food, water, milk, blood)
• Vector-borne:
  • Mechanical (flies transmitting typhoid)
  • Biological (malaria parasite in mosquito)
    • Propagative (plague in rat flea - multiplies, no change in form)
    • Cyclo-propagative (malaria in Anopheles - changes form and number)
    • Cyclo-developmental (microfilaria in mosquito - develops, no multiplication)
• Airborne - Droplet nuclei (TB, measles, chickenpox), dust
• Fomites - Inanimate objects (towels, utensils, surgical instruments)

LINK 3: SUSCEPTIBLE HOST

• Immunity (specific and non-specific)
• Genetic makeup
• Nutritional status
• Age and sex
• Concurrent disease

Significance

Q9. INTERNATIONAL CLASSIFICATION OF DISEASES (ICD)

Background

Definition / Purpose

• The foundation for identification of health trends and statistics globally
• The international standard for reporting diseases and health conditions
• A diagnostic classification standard for all clinical and research purposes
• Defines the universe of diseases, disorders, injuries and related health conditions in a comprehensive, hierarchical fashion

Functions of ICD

• Easy storage, retrieval and analysis of health information for evidence-based decision-making
• Sharing and comparing health information between hospitals, regions, settings and countries
• Data comparison in the same location across different time periods

ICD-10

• Came into effect on 1st January 1993 (10th revision)
• Used widely across the world for coding diseases, causes of death and health conditions

ICD-11 (Current - 21st Century Update)

• Designed for use with digital health applications
• Accessible online or downloadable free of charge in multiple languages
• Comprises over 55,000 entities and 120,000 clinical terms
• Can code millions of terms with thousands of new categories

• New chapter on sexual health (gender incongruence reclassified - not a mental health condition)
• New chapter on traditional medicine
• Stroke now classified as a neurological disorder (not circulatory system) - a landmark change
• HIV recognized as a chronic condition with updated therapy codes
• Allergy coded under diseases of the immune system
• Better reporting of antimicrobial resistance
• Enhanced mental health descriptions for simpler diagnosis

Significance

• National mortality statistics
• Hospital morbidity data
• Epidemiological surveillance
• Health resource allocation and planning

SPM SHORT NOTES - 8 MARKS (EXPANDED)

(Park's Textbook of Preventive and Social Medicine)

Q1. INDICATORS OF HEALTH

Definition

• Health indicator - measures a specific aspect of health
• Health index - an amalgamation of several health indicators

Characteristics of an Ideal Indicator

• Valid - measures what it is supposed to measure
• Reliable and objective - same answer regardless of who measures
• Sensitive - responds to changes in the situation
• Specific - reflects only changes in the situation concerned
• Feasible - data collection is practically possible
• Relevant - contributes to understanding the phenomenon

Why a Profile of Indicators is Needed

Classification of Health Indicators (Park's - 12 Categories)

• (a) Crude death rate - number of deaths per 1000 population per year; useful for comparison but affected by age-sex composition
• (b) Life expectancy at birth - average number of years lived if current age-specific mortality rates persist; best overall health indicator
• (c) Age-specific death rates - deaths in a specific age group per 1000 of the same age group
• (d) Infant Mortality Rate (IMR) - deaths under 1 year per 1000 live births; most universally accepted, sensitive indicator of availability, utilization and effectiveness of health care; sensitive indicator of the whole population's health status and socioeconomic conditions
• (e) Child death rate - deaths at ages 1-4 years per 1000 children in that group; may be 25 times higher in least developed vs developed countries
• (f) Under-5 proportionate mortality rate - proportion of total deaths in under-5 age group; may exceed 60 per 1000 live births in communities with poor hygiene
• (g) Adult mortality rate - probability of dying between 15 and 60 years per 1000 population
• (h) Maternal mortality rate - accounts for greatest proportion of deaths among women of reproductive age in developing world
• (i) Disease-specific mortality rate - e.g., CHD causes 25-30% of deaths in western countries
• (j) Proportional mortality rate - proportion of all deaths attributed to a specific disease; indicates magnitude of preventable mortality
• (k) Case fatality rate - measures risk of dying from a particular disease

• Event-type: days of restricted activity, bed disability days, work/school-loss days
• Person-type: limitation of mobility and activity (ADL)
• HALE (Health-Adjusted Life Expectancy) - years in full health a newborn can expect
• QALY (Quality-Adjusted Life Years) - quality + quantity of life; 1 year perfect health = 1.0 QALY
• DALY (Disability-Adjusted Life Years) = YLL (Years of Life Lost) + YLD (Years Lived with Disability); 1 DALY = 1 year of healthy life lost
• DFLE (Disability-Free Life Expectancy) - average years expected to be lived free of disability

WHO "Health for All" Indicators (4 Categories - Park's Table 2)

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

Q2. ICEBERG PHENOMENON OF DISEASE

Concept

Park's Diagram (Fig. 10):

Components

• Symptomatic/clinical disease
• What the physician sees and what appears in statistics

• Presymptomatic disease - disease present but not yet manifest
• Inapparent/subclinical infections - agent multiplies but no signs/symptoms; detected only by lab tests
• Undiagnosed cases - diseased but never sought care
• Carriers - harbour the agent without apparent disease

Subclinical Infection - Key Points (Park's)

• Subclinical cases are also called inapparent, covert, missed or abortive cases
• The disease agent multiplies and is eliminated into the environment just like clinical cases
• Persons who are sick "unbeknown to themselves and others" - contribute MORE to transmission than symptomatic patients and do not appear in any statistics
• Subclinical infection occurs in most infectious diseases - e.g., rubella, mumps, polio, hepatitis A and B, Japanese encephalitis, influenza, diphtheria
• Subclinical infections are responsible for the natural immunity shown by adults to many microbes
• Latent infection (e.g., herpes simplex, Brill-Zinser disease) - distinct from subclinical; host does not shed the agent which lies dormant

Examples of Iceberg Diseases (Park's)

• Hypertension, diabetes, anaemia, malnutrition, mental illness - unknown morbidity far exceeds known morbidity
• Polio - for every paralytic case, there are hundreds of subclinical cases
• Hypertension - "Rule of Halves" - only ½ are aware, ½ of those treated, ½ adequately controlled

Significance

• Hidden part = important undiagnosed reservoir of infection/disease
• Its detection is a challenge to modern preventive medicine
• Explains why community screening is essential
• Absence of methods to detect subclinical state is a major deterrent in chronic disease study

Q3a. EPIDEMIOLOGICAL TRIAD

Background

Park's Diagram (Fig. 4):

The Three Components

• Biological - bacteria, viruses, parasites, fungi, molds
• Chemical - dietary chemicals, tobacco smoke, solvents, radiation, heat, poison
• Physical - radiation, heat, mechanical forces
• Nutritional deficiencies - protein, vitamins, minerals
• One or several agents may contribute to an illness

• Level of immunity (specific and non-specific)
• Genetic makeup - some pathogens thrive only in limited temperature range
• Level of exposure, state of health, overall fitness
• Age, sex, nutritional status
• Behaviour and lifestyle

• Biological - insects, animals, microorganisms in the environment
• Social, cultural, and physical aspects
• Environment can be within a host (internal) or external in the community
• Surroundings in which the pathogen lives and their effect on it

• Incubation periods
• Life expectancy of host or pathogen
• Duration of illness
• Threshold of an epidemic in a population
• Severity of illness in relation to how long a person is infected

Disease occurs when:

• The agent is virulent/numerous enough
• The host is susceptible
• The environment favours transmission

Application

• Breaking the agent leg: antibiotics, vaccination
• Breaking the host leg: improving nutrition, immunization
• Breaking the environment leg: sanitation, vector control

Q3b. ADVANCED TRIANGLES OF EPIDEMIOLOGY

1. Traditional Triangle of Epidemiology (Fig. 5)

Why an Advanced Model was Needed

2. Advanced (Adapted) Model of the Triangle (Fig. 6)

Key Differences from Traditional Model

What the Advanced Model Covers

• All facets of the communicable disease model
• Causes of today's non-communicable diseases, disabilities, injuries, deaths
• Behaviour and lifestyle factors
• Chronic disease interactions
• Ecological elements

Q4. SPECTRUM OF DISEASE (Spectrum of Health)

Definition

The Spectrum (from one end to the other)

Subclinical → Mild → Moderate → Severe → Fatal
(Inapparent)   infection        illness    death

"Gradient of Infection"

Examples

• Leprosy - excellent example of spectral concept: ranges from tuberculoid (high immunity end) to lepromatous (low immunity end)
• Polio - vast majority are subclinical; very few develop paralysis
• Rabies - one of the few exceptions where the spectrum is almost invariably fatal once symptomatic
• Almost every disease has a spectrum: tuberculosis, hepatitis, meningococcal infection, etc.

Relationship with Iceberg

Significance

• Allows inclusion of all cases - both subclinical and clinical - in disease study
• The sequence can be interrupted by early diagnosis, treatment or preventive measures introduced at a particular point
• Helps explain why the same organism causes different severity in different individuals
• Forms the basis for understanding herd immunity - if many people have subclinical disease, they develop immunity which protects the community

Q5. WEB OF CAUSATION

Origin

Concept

• Heredity
• Diet high in saturated fat
• Obesity
• Physical inactivity
• Hypertension
• Hyperlipidaemia
• Smoking
• Stress
• Diabetes
• Age, sex

Important Principle

Why the Web Model is Superior for Chronic Diseases

• Acknowledges multiple causation - no single agent explanation
• Shows multiple intervention points
• Reflects the biological complexity of modern diseases
• Helps quantify the contribution of each factor (via relative risk)
• Useful in planning multi-pronged prevention strategies

Q6. ROLE OF JOHN SNOW IN PUBLIC HEALTH

Background

The Cholera Epidemic of 1854 (Broad Street, Golden Square - London)

Method - Spot Map (Place Distribution)

• Deaths clustered around the Broad Street water pump
• A boundary line showing equal distances between the Broad Street pump and other pumps
• Fatal cases fell predominantly within the Broad Street pump zone
• People nearest to other pumps had fewer deaths
• The workhouse nearby (with its own water supply) had very few deaths despite being in the epidemic zone

Key Analysis - Person, Place, Time

• Place - spot mapping; cases concentrated around Broad Street pump
• Person - those using the Broad Street pump were affected; those with other water sources were spared
• Time - epidemic curve showed a sharp rise and fall

Action Taken

Significance of Snow's Work

1. Demonstrated that cholera is waterborne, long before Koch discovered Vibrio cholerae (1883) - purely by epidemiological reasoning
2. Pioneered the use of spot maps to study place distribution of disease
3. Established the method of descriptive epidemiology - person, place, time
4. Proved that disease can be controlled without knowing the causative agent - one of epidemiology's most important lessons
5. His approach is the foundation of field epidemiology and outbreak investigation used worldwide to this day
6. His work inspired Maxcy's rodent reservoir hypothesis for typhus (1920s using spot map by place of employment), and epidemiological evidence for AIDS as an infectious disease (case clustering by sexual contact and blood product use)

Q7. MORBIDITY INDICATORS

Why Morbidity Indicators are Needed

Morbidity Rates Used (Park's)

• Incidence rate = new cases in defined population in specified time ÷ population at risk × 1000
• Prevalence rate = all existing cases (new + old) at a point in time ÷ total population × 1000
• Relationship: Prevalence ≈ Incidence × Mean duration of disease
• Incidence measures risk; prevalence measures burden

Composite Morbidity-Disability Measures (Park's)

• HALE (Health-Adjusted Life Expectancy) - life expectancy adjusted for time spent in poor health; equivalent number of years in full health a newborn can expect based on current ill-health and mortality rates
• QALY (Quality-Adjusted Life Years) - measures disease burden including both quality and quantity of life; used in assessing value-for-money of medical interventions
  • 1 year in perfect health = 1.0 QALY
  • 1 year in poor health = < 1.0 QALY
  • Death = 0.0
• DALY (Disability-Adjusted Life Years) = YLL + YLD
  • Originally developed by Harvard University for World Bank (1990); adopted by WHO in 2000
  • YLL (Years of Life Lost) = deaths at each age × expected remaining life years (by global standard)
  • YLD (Years Lived with Disability) = incident cases × average duration × severity weight (0 = perfect health, 1 = dead)
  • 1 DALY = 1 year of healthy life lost
  • Japanese life expectancy used as standard (longest in world)
  • Reveals hidden burden - e.g., 5 out of 10 leading causes of disability (1990 WHO report) were psychiatric conditions; yet psychiatric conditions cause only 1.4% of deaths
• DFLE (Disability-Free Life Expectancy) - average years expected free of disability

Q8. CHAIN OF TRANSMISSION OF DISEASE

The Three Links (Park's Fig. 16)

LINK 1: SOURCE / RESERVOIR

• Hookworm: reservoir = man; source = contaminated soil
• Typhoid: reservoir = case/carrier; source = faeces, urine, contaminated food/water

• Clinical cases (mild, moderate, severe, fatal) - epidemiologically, mild/ambulant cases are more important sources because they spread infection widely, unlike severe cases confined to bed
• Subclinical cases - equally important; contribute MORE to transmission than symptomatic patients; do not appear in statistics; responsible for maintaining endemicity
• Primary case - first case introduced into a population
• Index case - first case to come to the attention of the investigator (may not be the primary case)
• Secondary cases - develop from contact with primary case

• Healthy carrier - never shows illness; most dangerous as unsuspected
• Incubatory carrier - in the incubation period, already infectious
• Convalescent carrier - recovering patient still shedding organism (e.g., typhoid)
• Chronic carrier - persistent shedding for months/years (e.g., typhoid Mary, HBsAg carrier)
• Carriers play a dominant role in maintaining endemicity

• Rabies (dogs, foxes, bats)
• Plague (rats)
• Brucellosis (cattle, goats)
• Leptospirosis (rats)
• Homologous reservoir - same species (e.g., man for vibrio cholerae)
• Heterologous reservoir - other species (e.g., animals/birds with salmonella)

LINK 2: MODES OF TRANSMISSION

• Direct contact - STIs, scabies, ringworm
• Droplet spread - within ~1 metre; influenza, measles, whooping cough
• Contact with soil - hookworm, tetanus
• Transplacental (vertical) - rubella, syphilis, HIV, toxoplasmosis

• Vehicle-borne - contaminated food, water, milk, blood, instruments, fomites
• Airborne:
  • Droplet nuclei - tiny particles (<5 microns) that remain suspended in air for long periods; can travel long distances; TB, measles, chickenpox
  • Dust - dried secretions on dust particles
• Vector-borne:
  • Mechanical transmission - agent carried on feet/proboscis of insect; NO multiplication in vector; e.g., flies transmitting typhoid
  • Biological transmission - agent undergoes development/multiplication in vector; requires extrinsic incubation period:
    • Propagative - multiplies only, no change in form; e.g., plague bacilli in rat flea
    • Cyclo-propagative - changes in form AND number; e.g., malaria parasite in Anopheles mosquito
    • Cyclo-developmental - develops only, no multiplication; e.g., microfilaria in mosquito
  • Transovarial transmission - agent transmitted from infected female to her progeny (vertical in vector)
  • Transstadial transmission - agent passes from one stage of life cycle to next (e.g., nymph to adult)

• Man-arthropod-man: malaria
• Man-snail-man: schistosomiasis
• Mammal-arthropod-man: plague
• Bird-arthropod-man: encephalitis
• Man-cyclops-fish-man: fish tapeworm
• Man-snail-crab-man: paragonimiasis

LINK 3: SUSCEPTIBLE HOST

• Immunity - specific (antibodies, cell-mediated) and non-specific (skin, mucous membranes, phagocytes)
• Genetic makeup - HLA associations (e.g., HLA-B8 in RF)
• Nutritional status - malnutrition increases susceptibility
• Age and sex - e.g., extremes of age more vulnerable
• Concurrent disease - immunocompromised states
• Behaviour - personal hygiene, sexual behaviour, occupation

Breaking the Chain

• Treating the source (reservoir) with antibiotics
• Interrupting transmission by sanitation, vector control, condom use
• Protecting the host by vaccination, chemoprophylaxis

Q9. INTERNATIONAL CLASSIFICATION OF DISEASES (ICD)

Background

Definition

• Foundation for identification of health trends and statistics globally
• International standard for reporting diseases and health conditions
• Diagnostic classification standard for all clinical and research purposes
• Defines the universe of diseases, disorders, injuries and related conditions in a comprehensive, hierarchical fashion

Functions of ICD

• Easy storage, retrieval and analysis of health information for evidence-based decision-making
• Sharing and comparing health information between hospitals, regions, settings and countries
• Data comparison in the same location across different time periods
• Basis for national mortality statistics, hospital morbidity data, resource allocation, research

ICD-11 (Adopted by World Health Assembly 2019; effective 1st January 2022)

• Designed for use with digital health applications
• Accessible online or downloadable free of charge in multiple languages
• Comprises over 55,000 entities and 120,000 clinical terms
• Can code millions of terms with thousands of new categories

1. Certain infectious and parasitic diseases
2. Neoplasms
3. Diseases of blood and blood forming organs
4. Disorders of the immune system (allergy now coded here)
5. Endocrine, nutritional and metabolic diseases
6. Mental, behavioural or neurodevelopmental disorders
7. Sleep-wake disorders (new chapter)
8. Diseases of the visual system
9. Diseases of the nervous system (stroke now here - landmark change)
10. Diseases of the ear and mastoid process
11. Diseases of the circulatory system
12. Diseases of the respiratory system
13. Diseases of the digestive system
14. Diseases of the skin
15. Diseases of musculoskeletal system and connective tissue
16. Diseases of the genitourinary system
17. Conditions related to sexual health (new chapter - gender incongruence here)
18. Pregnancy, childbirth and puerperium
19. Conditions in perinatal/neonatal period
20. Developmental anomalies
21. Symptoms/signs not elsewhere classified
22. Injury, poisoning or consequences of external causes
23. External causes of morbidity and mortality
24. Factors influencing health status/contact with health services
25. Codes for special purposes
26. Supplementary chapter - Traditional Medicine Conditions (new) V. Supplementary section for functioning assessment X. Extension codes

• Stroke reclassified as neurological disorder (not circulatory) - "long overdue"
• Gender incongruence moved to sexual health chapter - not a mental health condition; reduces stigma
• HIV recognized as a chronic condition with updated therapy codes
• Allergy under diseases of the immune system
• ADHD - symptoms no longer required within a fixed age range for diagnosis
• Better coding for antimicrobial resistance (aligned with Global AMR Surveillance System)
• Enhanced mental health descriptions for simpler diagnosis
• New traditional medicine chapter

Linkages with other Classifications (ICD-11)

• ICD-O (Oncology)
• ICD-10 (External Causes of Injury)
• ICF (International Classification of Functioning, Disability and Health)
• ICPC (International Classification of Primary Care)
• SNOMED-CT, OrphaNet

ICF (International Classification of Functioning, Disability and Health)

• Framework for organizing information on functioning and disability (WHO 2001)
• Conceptualizes functioning as a "dynamic interaction between a person's health condition, environmental factors and personal factors"
• Integrates medical model and social model of disability as a bio-psycho-social synthesis
• Provides standard language for definition and measurement of disability