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PSM / Community Medicine - Exam Preparation Guide (NEET PG / INI-CET / MBBS Prof)

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1. Concept of Health & Disease (HIGH YIELD)

Definitions to know:

• WHO definition of health - "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity"
• Operational definition: absence of objective disease + absence of subjective illness
• Dimensions of health: Physical, Mental, Social, Spiritual, Emotional, Vocational

Levels of Prevention (must-know framework):

Disease Causation Models:

• Germ theory: one agent → one disease (historically important but limited)
• Epidemiological Triad: Agent + Host + Environment + Time - the classic triangle
• Web of causation (MacMahon): multiple interacting causes - used for NCDs
• Wheel model, Iceberg phenomenon (visible disease vs. subclinical cases)

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2. Epidemiology (Highest Weightage)

Study Designs - Quick Comparison:

Epidemic Investigation Steps (Park's classic sequence):

1. Verify diagnosis
2. Confirm epidemic
3. Define cases - descriptive epidemiology (person, place, time)
4. Formulate hypothesis
5. Test hypothesis (analytic epidemiology)
6. Draw conclusions, recommend control measures
7. Write report

Types of Epidemics:

• Common source - single source, explosive onset (e.g., food poisoning)
• Propagated - person-to-person, gradual rise (e.g., measles)
• Mixed - starts as common source, then propagated

Key Epidemiological Measures:

• Attack rate = (cases / population at risk) x 100
• Secondary attack rate (SAR) = new cases in household / susceptible contacts x 100
• Case Fatality Rate (CFR) = deaths / cases x 100
• Incidence = new cases / population at risk / time
• Prevalence = existing cases / total population at a point in time
• Prevalence = Incidence x Duration (for stable endemic disease)

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3. Biostatistics (High Weightage - especially INI-CET)

Central Tendency & Dispersion:

• Mean, Median, Mode - know when each is preferred
• Normal distribution: Mean = Median = Mode
• Positively skewed: Mean > Median > Mode
• Standard Deviation (SD): 1 SD = 68.2%, 2 SD = 95.4%, 3 SD = 99.7%

Statistical Tests (commonly asked):

Screening Tests:

• Sensitivity = TP / (TP + FN) - ability to detect true positives; best for ruling OUT disease (SnNout)
• Specificity = TN / (TN + FP) - ability to correctly identify negatives; best for ruling IN disease (SpPin)
• PPV = TP / (TP + FP) - increases with higher prevalence
• NPV = TN / (TN + FN) - increases with lower prevalence
• ROC curve: plots sensitivity vs. (1-specificity); area under curve = overall test accuracy

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4. Vaccines & Cold Chain

Immunization Schedule (India UIP) - key facts:

• Birth: BCG, OPV-0, Hep B-1
• 6, 10, 14 weeks: DPT, OPV, IPV, Hep B, Hib, Rotavirus, PCV
• 9 months: Measles-Rubella (MR-1), Vitamin A-1
• 16-24 months: DPT booster, OPV booster, MR-2, Vitamin A-2
• 5 years: DPT booster 2

Cold Chain:

• Vaccines most sensitive to heat: BCG, measles, OPV (first to destroy)
• OPV and measles: store at -15°C to -25°C (freezer)
• Most others: +2°C to +8°C (refrigerator)
• Cold chain equipment: ILR (Ice-Lined Refrigerator), Walk-in cooler, Walk-in freezer
• Freeze indicator (FI-11) placed in cold box - if triangle is blue, freeze has occurred

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5. Demography & Health Indicators

Key Demographic Rates:

• CBR (Crude Birth Rate): live births / mid-year population x 1000
• TFR (Total Fertility Rate): current India ~2.0
• IMR (Infant Mortality Rate): current India ~28/1000 (NFHS-5)
• MMR (Maternal Mortality Ratio): deaths per 100,000 live births; India ~97 (SRS 2018-20)
• Life Expectancy at birth (India): ~70.19 years

Composite Indices:

• HDI (Human Development Index): income + health + education
• PQLI (Physical Quality of Life Index): infant mortality + literacy + life expectancy at age 1 - max score 100
• DALY: Disability-Adjusted Life Year = YLL + YLD
• QALY: Quality-Adjusted Life Year - used in health economics

Demographic Transition (4 stages):

1. High birth + high death rate (no growth)
2. High birth + falling death (rapid growth)
3. Falling birth + low death (moderate growth)
4. Low birth + low death (stable) - India currently between stage 2 and 3

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6. Nutrition

Protein-Energy Malnutrition (PEM):

• Kwashiorkor: protein deficiency, edema, moon face, dermatosis, fatty liver - adequate calories but poor protein
• Marasmus: total calorie deficiency, severe wasting, old man face - no edema
• Marasmic Kwashiorkor: combined

Grading of PEM:

• Gomez classification (weight for age): Grade I = 75-90%, Grade II = 60-75%, Grade III = <60% of expected
• IAP grades: Grade I = 71-80%, Grade II = 61-70%, Grade III = 51-60%, Grade IV = <50%

Nutritional Deficiencies:

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7. Environment & Occupational Health

Water Quality:

• WHO coliform standard: 0 coliforms/100 mL (treated water)
• MPN (Most Probable Number) - coliform test index
• Chlorine demand: amount of chlorine absorbed by water before free residual appears
• Residual chlorine in supply: 0.2 mg/L (minimum); 0.5 mg/L in cholera areas

Occupational Diseases (commonly asked):

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8. National Health Programs (Very High Yield)

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9. Health Planning & Management

Health Committees (India) - chronological order:

1. Bhore Committee (1946) - foundation of Indian public health system
2. Mudaliar Committee (1962)
3. Chadha Committee (1963)
4. Mukherjee Committee (1965)
5. Shrivastav Committee (1975) - community health workers (CHWs)
6. Bajaj Committee (1986)

Primary Health Care (Alma Ata Declaration, 1978):

• "Health for All by 2000 AD"
• 8 elements: Education, Nutrition, Water & sanitation, MCH (including FP), Immunization, Endemic disease control, Essential drugs, Treatment of common diseases
• Mnemonic: E-NEW-MET

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10. Biomedical Waste (BMW)

Categories & Disposal:

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Quick Revision Mnemonics

• ICEBERG phenomenon: visible cases (clinical) float above, but most cases are subclinical below the surface
• Levels of Prevention = Primordial, 1°, 2°, 3° - "Prevent Perfectly, Stop Spreading, Support Survival"
• DALY = YLL + YLD (Years of Life Lost + Years Lived with Disability)
• PQLI components: IMR + Life expectancy at age 1 + Literacy rate

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Exam Weightage Summary

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