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ANSWERS FROM PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE

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CHAPTER 1 - CONCEPTS (Short Notes)

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Q: Primordial Prevention is more appropriately used in Non-communicable Diseases

• In NCDs like hypertension, diabetes, coronary heart disease - risk factors (e.g., high-fat diet, sedentary lifestyle, smoking, obesity) are deeply embedded in societal and cultural patterns
• Primordial prevention aims at preventing these risk factor patterns from ever emerging in society - e.g., through health policy, food labeling, built environments that encourage physical activity
• For communicable diseases, the focus is more on primary, secondary, and tertiary prevention - the causative agents are known and the response is direct
• For NCDs, by the time risk factors appear in individuals, societal patterns are already established - hence primordial prevention addresses the root cause BEFORE risk factors take root

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Q: Life expectancy is one of the best indicators of a country's level of development

1. It integrates all causes of mortality across all age groups into a single number
2. It reflects the overall health status, nutrition, sanitation, and medical care available in a country
3. It correlates strongly with GDP, literacy, and human development index (HDI)
4. Unlike crude death rate, it is not affected by age structure of the population
5. It allows comparisons between countries with different demographic profiles
6. Higher life expectancy = better maternal health, child survival, adult health, and healthcare access
7. It is easily understood by policymakers and the public

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Q: DALY (Disability-Adjusted Life Year)

• YLL (Years of Life Lost) = due to premature death
• YLD (Years Lived with Disability) = number of years lived with disability weighted for severity

• 1 DALY = 1 lost year of healthy life
• Combines mortality and morbidity into one metric
• Allows comparison of disease burdens across different diseases and countries
• Used for health priority setting and resource allocation
• Example: A disease causing early death has high YLL; a chronic disabling disease has high YLD

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Q: Disability Rates

1. Point prevalence of disability = Number with disability at a point in time / Total population × 1000
2. Period prevalence = over a specified period
3. Incidence rate of disability = New cases of disability / Population at risk
4. Case fatality rate vs disability rate - they measure different outcomes

• Impairment - loss/abnormality of structure or function
• Disability - restriction/lack of ability to perform normal activity
• Handicap - social disadvantage resulting from impairment/disability

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Q: Isolation and Quarantine are NOT synonymous

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Q: Health is Multi-dimensional - Justify

1. Physical dimension - Body structure, function, fitness, absence of disease
2. Mental/Psychological dimension - Emotional stability, self-confidence, decision-making, coping with stress
3. Social dimension - Ability to interact with others, maintain relationships, fulfill social roles
4. Spiritual dimension - Values, beliefs, meaning and purpose
5. Emotional dimension - Ability to express and manage emotions
6. Vocational dimension - Ability to work and contribute productively
7. Environmental dimension - Interaction with and adaptation to surroundings

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Q: A Family Plays an Important Role in Health and Disease - Justify

• Genetic factors transmitted through family (hereditary diseases)
• Family dietary habits influence nutrition and NCDs
• Smoking, alcohol use patterns spread within families
• Socioeconomic status of family determines access to healthcare

• Family provides emotional support during illness
• Family members are primary caregivers
• Compliance with treatment depends on family support
• Home sanitation and hygiene are family responsibilities

• Communicable diseases spread within families (TB, COVID, food poisoning)
• Family size affects risk (larger = more transmission)
• Family is the smallest epidemiological unit for contact tracing

• Health behaviors learned within family (hand washing, diet)
• Maternal and child health managed at family level
• Family planning practiced at family level

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CHAPTER 2 - PRINCIPLES OF EPIDEMIOLOGY

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SECTION A: EPIDEMIC INVESTIGATION

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Q1: Define "Epidemic" [2 Marks]

• The number of cases indicating the presence of an epidemic will vary according to the agent, size and type of the population exposed, previous experience or lack of exposure to the disease
• The excess over the expected (endemic) occurrence must be statistically significant (>2 standard errors above endemic level)
• An epidemic may affect a small or large number of persons - even 2 cases of smallpox constitutes an epidemic because it is normally absent

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Q2: Steps in Investigation of an Epidemic [6 Marks] - Gastroenteritis after community feast

• Clinically examine a sample of patients presenting with acute gastroenteritis
• Collect stool samples, blood cultures, food samples for laboratory confirmation
• Confirm the causative agent (Salmonella, Staphylococcus, Vibrio, etc.)
• Do not wait for lab results to proceed with investigation

• Compare current number of cases with past occurrence (same time, previous years)
• Epidemic exists when observed frequency significantly exceeds expected frequency
• In a common-source outbreak like this (community feast), the existence is usually obvious

• Obtain a map of the area
• Conduct a census: house-to-house visit to count population exposed
• Identify all persons who attended the community feast
• Divide into segments for systematic search

• Conduct medical survey - identify all cases including those who did not seek care
• Prepare and administer an epidemiological case sheet collecting: name, age, sex, foods eaten at the feast, time of onset, symptoms, duration
• Calculate attack rates for each food item consumed
• Food-specific attack rates help identify the vehicle food
• Search for secondary cases (household contacts)

• Time: Construct an epidemic curve (date/time of onset vs. number of cases). A sharp, single-peaked curve with short incubation = point-source/common-source epidemic
• Place: Prepare a spot map of case distribution; cluster around feast location confirms common source
• Person: Analyze by age, sex, food items eaten; calculate food-specific attack rates

• Based on analysis: identify probable causative food, time of contamination, source of pathogen
• Hypothesis: "The food item X served at the feast was the vehicle of infection"

• Use a case-control study or cohort study among feast attendees
• Calculate Relative Risk (cohort) or Odds Ratio (case-control) for each food item
• The food with the highest attack rate among those who ate it (vs. those who didn't) = likely vehicle
• Statistical testing (chi-square) to confirm significance

• Identify the causative agent, vehicle food, and source of contamination
• Determine where the chain broke down (food handler, storage, preparation)

• Document all findings, methodology, and conclusions
• Submit to health authorities

• Continue surveillance till twice the incubation period after the last case
• Monitor for recurrence

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Q3: Immediate Control Measures During Investigation [2 Marks]

1. Treatment of cases - Oral/IV rehydration therapy for dehydration from gastroenteritis; hospitalize severe cases
2. Notification - Report to District Health Officer / CMO
3. Remove or recall suspected food - Identify and destroy contaminated food remaining from the feast
4. Closure of suspected source - Prevent further access to contaminated food/water
5. Safe water supply - Ensure clean drinking water (chlorination if needed)
6. Sanitation measures - Proper disposal of excreta and vomitus
7. Food handler screening - Examine food handlers for illness
8. Health education - Inform community about safe food and water practices
9. Chemoprophylaxis if indicated (e.g., contacts of cholera case)

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Q: Define Outbreak. How does Outbreak differ from Epidemic? [Burdwan MC]

• WHO uses "outbreak" to avoid public panic while referring to a limited epidemic
• In practice, the terms are used interchangeably in field epidemiology
• Both require investigation and control measures

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Q: Define "Attack Rate" and calculate it [Village population 1500, 45 cases]

AR = (Number of new cases among exposed population / Total exposed population) × 100

• Total village population (population at risk) = 1,500
• Cases admitted with acute watery diarrhoea = 45
• Attack Rate = 45/1500 × 100 = 3%

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SECTION B: EPIDEMIOLOGICAL STUDY DESIGNS

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Q: Define Epidemiology. Classify Epidemiological Studies. [MCK / Jagannath Gupta]

EPIDEMIOLOGICAL STUDIES
├── OBSERVATIONAL (No intervention)
│   ├── DESCRIPTIVE
│   │   ├── Case reports / Case series
│   │   └── Ecological (Correlational) studies
│   └── ANALYTICAL
│       ├── Cross-sectional (Prevalence) study
│       ├── Case-Control (Retrospective) study
│       └── Cohort (Prospective/Retrospective) study
└── EXPERIMENTAL (Intervention)
    ├── Randomized Controlled Trial (RCT)
    ├── Field Trial
    ├── Community Trial
    └── Quasi-experimental

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Q: Cohort Study - Steps, Advantages, Disadvantages, Bias [MCK / JNM Kalyani / ESI Joka]

1. Define the study population (cohort) - Select exposed and unexposed groups from a disease-free population
2. Define exposure - Clearly define what constitutes exposure (e.g., smoking, radiation)
3. Baseline data collection - Collect demographic, clinical, and exposure data from all participants
4. Follow up - Follow both exposed and unexposed groups over time (prospective = forward; retrospective = existing records)
5. Outcome measurement - Ascertain disease development in both groups
6. Data analysis - Calculate Incidence in exposed (Ie) and Incidence in unexposed (Io)
7. Compute Relative Risk (RR) = Ie / Io
8. Compute Attributable Risk (AR) = Ie - Io
9. Interpret results - RR >1 indicates positive association

1. Establishes temporal relationship - exposure precedes disease (causal inference)
2. Allows calculation of true incidence rates and RR
3. Multiple outcomes from a single exposure can be studied
4. Minimizes selection and recall bias
5. Good for studying rare exposures
6. No ethical concern about withholding treatment

1. Expensive and time-consuming (especially prospective)
2. Impractical for rare diseases (need huge sample sizes)
3. Loss to follow-up can introduce bias
4. Exposure status may change over time
5. Not feasible for long latency diseases (e.g., cancer)

1. Selection bias - Non-random selection of exposed/unexposed groups
2. Attrition bias - Differential loss to follow-up between groups
3. Information bias - Errors in measuring exposure or outcome
4. Confounding - Third variable associated with both exposure and outcome
5. Surveillance bias (Neyman bias) - Exposed group monitored more intensively

• When exposure is rare
• When studying multiple outcomes of one exposure
• When incidence rate calculation is required
• When temporal sequence needs to be established

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Q: Case-Control Study - Design, Steps, Advantages, Disadvantages, Bias [PC Sen / MJN]

1. Define cases - Persons aged 35-65 diagnosed with osteoarthritis of knee (confirmed by X-ray, clinical criteria)
2. Define controls - Persons aged 35-65 without osteoarthritis from the same community/hospital
3. Match controls - Match for age, sex, socioeconomic status to control confounding
4. Ratio - 1:1 or 1:2 (case:control ratio)
5. Exposure assessment - Measure BMI, weight, history of obesity in both groups
6. Data collection - Interview, records review, anthropometric measurements
7. Analysis - Calculate Odds Ratio (OR) = (a×d)/(b×c)
8. Interpretation - OR >1 = obesity associated with osteoarthritis

1. Relatively quick and inexpensive
2. Ideal for rare diseases
3. Can study multiple exposures for one outcome
4. No ethical issue of exposing subjects
5. Smaller sample size needed

1. Cannot calculate true incidence or RR (only OR)
2. Susceptible to recall bias (cases remember past exposure better)
3. Selection bias in choosing controls
4. Temporal relationship not always clear
5. Not suitable for rare exposures

1. Recall bias - Cases recall past exposure differently from controls
2. Selection bias - Non-representative selection of cases or controls
3. Interviewer bias - Interviewers probe cases more thoroughly than controls
4. Berkson's bias - Hospital-based controls may not represent general population
5. Neyman bias - Prevalent cases may differ from incident cases

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Q: Cross-Sectional Study - Steps [Barasat GMC - prevalence of obesity, 3 months]

1. Define study population - Medical students of the institution
2. Sampling - Use random sampling (stratified by year of study); calculate sample size using prevalence formula: n = Z²pq/d²
3. Data collection tool - Structured questionnaire + anthropometric measurements (height, weight, BMI)
4. Define obesity - BMI ≥ 25 (Asian cutoff) or BMI ≥ 30 (WHO standard)
5. Field work - Administer questionnaire, measure all students
6. Data entry and analysis - Calculate prevalence = Number with BMI ≥25/Total studied × 100
7. Statistical analysis - Chi-square for associations; logistic regression for risk factors
8. Report writing - Present findings with confidence intervals

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Q: Cohort Study for Radiation Effects Among Nuclear Plant Workers Over 5 Years [JNM Kalyani]

1. Define cohort: workers in the nuclear plant (exposed) and administrative staff/matched non-exposed workers (unexposed)
2. Baseline assessment: full medical examination, baseline CBC, liver/kidney function, radiation dose records
3. Exposure measurement: dosimetry badges for radiation quantification
4. Follow-up: 5-yearly health assessments; record all diseases/cancers
5. Outcome ascertainment: cancer registry, hospital records, death certificates
6. Analysis: Calculate incidence rates, RR, attributable risk for various outcomes

1. Expensive, long duration
2. Loss to follow-up (workers may quit/transfer)
3. Dose assessment may be difficult
4. Confounding from other occupational exposures
5. Latency period may exceed 5 years for some cancers

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Q: Study Design for Association between Screen Time and Mental Disorders in Adolescence [Sagore Dutta]

• Screen time (exposure) in early childhood; mental disorders (outcome) in adolescence
• Need temporal sequence: exposure precedes outcome
• Retrospective cohort: use existing records/parent surveys for early childhood screen time; current mental health assessment for adolescents

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Q: Nested Case-Control Study [MJN Coochbehar]

• Cases arise from within the established cohort
• Controls are selected from the same cohort (risk-set sampling)
• Biological samples collected at baseline can be tested retrospectively
• Combines efficiency of case-control with temporal validity of cohort
• Less expensive than full cohort analysis
• Reduces recall bias as data collected prospectively

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Q: Relative Risk (RR) - Definition, Calculation [Diamond Harbour GMC&H]

RR = Incidence in exposed (Ie) / Incidence in unexposed (Io)

• Incidence in exposed = 120/800 = 0.15 (15%)
• Incidence in unexposed = 30/1200 = 0.025 (2.5%)
• RR = 0.15 / 0.025 = 6

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Q: RR and AR are NOT synonymous [Midnapore / JNM Kalyani]

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Q: Incidence is Preferred Over Prevalence in Studying Disease Causation [JNM Kalyani]

1. Incidence captures new events - reflects actual risk of developing disease
2. Establishes temporal sequence: exposure → new disease onset
3. Prevalence is affected by disease duration and survival - a disease causing rapid death has low prevalence despite high incidence
4. For cohort and analytical studies, incidence allows calculation of RR and AR
5. Prevalence includes long-standing cases whose risk factors may have changed
6. Incidence is unaffected by cure or death of existing cases

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Q: Randomization is the Heart of Clinical Trial [Barasat GMC / Gouri Devi]

1. Eliminates selection bias - ensures both groups are comparable at baseline
2. Controls for known AND unknown confounders simultaneously (unique to RCT)
3. Makes statistical inference valid
4. Ensures comparability of groups for all baseline characteristics
5. Foundation of internal validity of RCT
6. Allows intention-to-treat analysis

• Randomization controls allocation bias
• Blinding controls performance and detection bias
• Both serve different purposes

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Q: Randomization and Blinding are NOT used for the Same Purpose [Deben Mahata]

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Q: Bias and Confounding are NOT synonymous [CNMC]

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Q: Sentinel Surveillance is Useful for Early Outbreak Detection [MCK]

1. Targeted monitoring at strategically placed sites (PHCs, hospitals, airports)
2. Data collected regularly and quickly - early warning system
3. Cost-effective - doesn't require reporting from all facilities
4. Sentinel sites report consistently - trend analysis possible
5. Can detect emergence of new pathogens or drug resistance early
6. Used for influenza (sentinel flu surveillance), HIV (sentinel sero-surveillance)
7. Timely data allows rapid public health response

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Q: Cohort Study is Gold Standard for Temporal Association but Inappropriate for Rare Diseases [Sagore Dutta]

• Exposure measured BEFORE disease onset - clear temporal relationship
• True incidence can be calculated
• RR can be directly calculated
• Example: Framingham Study - established smoking as risk factor for CHD

• If disease is rare, enormous sample sizes needed (e.g., to find 100 cases of aplastic anaemia, may need 100,000+ participants)
• Follow-up over many years is expensive
• Loss to follow-up becomes major problem
• Case-control study is more efficient for rare diseases - start with cases who already have the disease

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Q: Monitoring and Surveillance are NOT synonymous [Jhargram]

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SECTION C: IMMUNIZATION

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Q: National Immunization Schedule (UIP) - Age, Dose, Route, Site [KPCMCH]

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Q: OPV is Administered at Birth Despite Subsequent Doses Being Scheduled [Tamralipto]

1. Maternal antibody interference - Maternal antibodies in gut can neutralize subsequent OPV doses; birth dose establishes gut immunity before maternal antibodies interfere
2. Priming the gut - The neonatal gut is immunologically naïve at birth - OPV-0 establishes mucosal immunity (secretory IgA) in the gut early
3. Herd immunity - Early vaccination reduces fecal-oral transmission
4. Polio eradication strategy - Every opportunity used for immunization
5. Missed opportunity prevention - Baby may not return; birth dose ensures at least one dose
6. Sabin strains - Live attenuated virus replicates in gut providing local immunity
7. Cocooning strategy - Protects the infant from early exposure

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Q: Hepatitis B Vaccine Given Within 24 Hours of Birth [SANAKA / PC Sen]

1. Perinatal transmission - A major route of HBV transmission in India is from HBsAg-positive mothers to neonates during delivery
2. Window of effectiveness - Vaccine given within 24 hours provides >90% protection against perinatal transmission; effectiveness drops sharply if delayed
3. MTCT prevention - Vertical transmission occurs through exposure to maternal blood/secretions during delivery - early vaccine interrupts this
4. Chronicity in infants - 90% of perinatally infected infants become chronic HBV carriers (vs 5% in adults) - prevention is critical
5. HBsAg-positive mothers - Should also receive HBIg simultaneously for passive-active immunization
6. Global strategy - WHO recommends birth dose within 24 hours as part of HBV elimination strategy

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Q: AEFI - Classification with Examples [Malda / JMN]

1. Vaccine product-related reaction - caused by inherent properties of vaccine
   • Example: BCG lymphadenitis, febrile seizure after DPT
2. Vaccine quality defect-related reaction - due to defect in manufacturing
   • Example: Contaminated vaccine causing sepsis
3. Immunization error-related reaction - due to error in preparation, handling, or administration
   • Example: Wrong site, wrong dose, non-sterile injection causing abscess
4. Immunization anxiety-related reaction - from anxiety about immunization
   • Example: Vasovagal syncope, hyperventilation
5. Coincidental events - occur after immunization but not caused by it
   • Example: Fever from concurrent infection coinciding with immunization date

• Level 1 - Most certain (meets all criteria)
• Level 2 - Probable
• Level 3 - Possible

• Serious = Hospitalization, life-threatening, death, persistent disability (medical/regulatory category)
• Severe = Intense/distressing symptoms (clinical grade) - may or may not be serious

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Q: AEFI in 9-month-old after MR Vaccine - Diagnosis, Investigation, Prevention [JMN]

• Onset within 30 minutes of vaccination
• Systemic manifestations: breathing difficulty (bronchospasm), generalized rash (urticaria), unconsciousness (hypotension/shock)
• MR vaccine contains gelatin and neomycin - known allergens

1. Immediate medical management (epinephrine 0.01 mg/kg IM)
2. Fill AEFI reporting form and notify district immunization officer within 24 hours
3. Preserve the vaccine vial (same batch) from the session site
4. Collect details: vaccine name, batch number, expiry date, VVM status, cold chain temperature records
5. Review injection technique - correct site, dose, route
6. Review session site practices
7. AEFI investigation committee review (Causality Assessment)

1. Screen children for known allergies before vaccination
2. Keep anaphylaxis kit (epinephrine, antihistamine, oxygen) at every session site
3. Observe all vaccinated children for 30 minutes post-vaccination
4. Train health workers in recognition and management of anaphylaxis
5. Ensure cold chain maintenance
6. Functioning hub-cutter must be present (for needle disposal)

1. Local reactions - pain, swelling, redness at site
2. Systemic reactions - fever, malaise, myalgia
3. Anaphylaxis/Anaphylactoid reactions
4. Neurological reactions - febrile seizures, encephalopathy
5. BCG-specific: local ulcer, regional lymphadenitis, disseminated BCG

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Q: HPV Vaccination - Started to Prevent Second Most Common Cancer in Women [PC Sen / CNMC / Midnapore]

• Cervical cancer is the 2nd most common cancer among Indian women (after breast cancer)
• ~99.7% of cervical cancers are caused by high-risk HPV types
• HPV 16 and 18 account for ~70% of cervical cancers
• HPV 6 and 11 cause 90% of genital warts

1. Cervarix (Bivalent) - HPV 16, 18
2. Gardasil (Quadrivalent) - HPV 6, 11, 16, 18
3. Gardasil 9 (Nonavalent) - covers 9 HPV types

• Above 15 years: 3 doses (0, 1-2, 6 months)

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Q: Drop-out and Left-out in Immunization [Jhargram / RGMCH]

• Underserved/remote areas
• Migratory population
• Social/cultural barriers
• Lack of awareness

• Side effects after first dose
• Distance to facility
• Long waiting time
• Poor communication about next visit date

1. Microplanning to identify left-out areas
2. Outreach sessions in remote areas
3. Tracking system - mother-child protection card
4. Home visits by ASHA workers
5. SMS/phone reminders
6. Village health and nutrition days (VHND)
7. Intensified Mission Indradhanush for catching up

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Q: Cold Chain System in UIP [Malda]

1. National level: Vaccine stores
2. State level: State vaccine stores (-20°C for OPV)
3. District level: District vaccine store (ILR + Deep freezer)
4. PHC level: Ice-lined refrigerator (ILR) +2°C to +8°C
5. Session site: Vaccine carrier with ice packs (4-6 hours)

• ILR (Ice-Lined Refrigerator) - maintains +2°C to +8°C even during power failure (for 8-12 hours)
• Deep Freezer - for OPV (-15 to -25°C)
• Vaccine carrier - insulated box with ice packs for outreach
• Cold boxes - for transport
• VVM (Vaccine Vial Monitor) - attached to vials to detect heat exposure

• Never freeze inactivated vaccines (Pentavalent, IPV, Td) - causes flocculation and reduced efficacy
• OPV must be stored frozen; can be stored at +2°C to +8°C for limited time
• Functioning hub-cutter must be present at every session site

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Q: Open Vial Policy [ICARE]

1. Vaccine has not expired
2. VVM has not reached the discard point
3. Vaccine was stored at +2°C to +8°C
4. Vaccine was not contaminated

• BCG (must be discarded within 2-4 hours of reconstitution)
• Measles/MR vaccine (must be discarded within 4 hours of reconstitution)
• Any lyophilized (freeze-dried) vaccine after reconstitution

• Reduces vaccine wastage
• Encourages more sessions (without fear of wasting partly used vials)
• Increases immunization coverage

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Q: Purpose of Vaccination is Not Only Individual Protection but also to Reduce Disease Load in Community [ESI Joka]

1. Herd immunity - When a sufficient proportion of the population is immunized, the pathogen cannot spread - even unvaccinated persons are indirectly protected
2. Herd immunity threshold (HIT): Depends on basic reproduction number (R0)
   • Measles (R0 = 12-18): HIT = ~95%
   • Polio (R0 = 5-7): HIT = ~80-85%
3. Protection of vulnerable groups - immunocompromised, infants, elderly who cannot be vaccinated
4. Interruption of transmission - breaks chain of infection in community
5. Eradication potential - sufficient herd immunity + surveillance = elimination/eradication (e.g., smallpox eradication)

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Q: Polio Eradication - Current Strategies [KPCMCH]

1. Routine immunization - OPV + fIPV in UIP schedule
2. Pulse Immunization (NIDs) - National Immunization Days - mass OPV campaign targeting 0-5 years twice a year
3. Sub-National Immunization Days (SNIDs) - targeted high-risk areas
4. Mop-up operations - around confirmed cases
5. Acute Flaccid Paralysis (AFP) surveillance - case detection (target: ≥2/100,000 children <15 years)
6. Environmental surveillance - poliovirus in sewage
7. Switch from tOPV to bOPV (2016) - bivalent OPV (types 1 and 3 only; type 2 removed as circulating VDPV2 risk)
8. fIPV introduction - fractional IPV intradermal to maintain type 2 immunity after tOPV withdrawal
9. Intensified Mission Indradhanush - for unvaccinated children

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SECTION D: SCREENING FOR DISEASE

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Q: Define Screening. Difference Between Screening and Case Finding. False Positive vs False Negative for Fatal Disease [Bankura]

• A false negative means a diseased person is told they are healthy - they miss treatment opportunity, disease progresses, may die
• A false positive means a healthy person is told they may have disease - causes anxiety, further testing (inconvenient but not fatal)

• High sensitivity = Low false negative rate
• Useful for screening fatal/serious diseases

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Q: Iceberg Phenomenon in Screening [Part of longer question visible in last image]

• Visible part (tip): Clinical cases - diagnosed, symptomatic
• Submerged part (below waterline): Subclinical cases, latent infections, carriers, undiagnosed cases

• Screening aims to detect the submerged part of the iceberg
• Early detection at subclinical stage enables treatment before complications
• The submerged part is the reservoir of infection (communicable diseases) or early-stage disease (NCDs)

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Q: Population Attributable Risk [KPC Medical College]

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Q: Standard Error [Midnapore]

• SE decreases as sample size increases (larger sample = more precise estimate)
• SE is used to calculate confidence intervals: 95% CI = Mean ± 1.96 × SE
• SE ≠ Standard Deviation (SD measures variability within sample; SE measures variability of sample means)
• Smaller SE = more reliable estimate
• Used in hypothesis testing and significance testing

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Q: Source and Reservoir of Disease are NOT the Same [PC Sen]

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Q: The "5 F's" in Transmission of Fecal-Oral Diseases [PC Sen]

1. Fingers - contaminated hands spreading fecal organisms to mouth
2. Flies - mechanical transmission of fecal organisms by flies
3. Food - contaminated food (especially uncooked or improperly handled)
4. Fluid (Water) - contaminated drinking water
5. Fomites - contaminated objects (utensils, surfaces)

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Q: Epidemiologically, Carrier is More Important than Cases [Jagannath Gupta]

1. Larger numbers - For every clinical case, there may be many more carriers (iceberg analogy)
2. Undetected - Carriers don't present to healthcare, not isolated, not treated
3. Mobile - Carriers continue their normal activities, contacting many people
4. Prolonged - Chronic carriers shed the agent for long periods (typhoid carrier - years)
5. Continued transmission - When clinical cases are isolated and treated, carriers continue to spread the disease
6. Hard to detect and control - Mass screening needed; ethical issues in isolation

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Q: Influenza Vaccine Must be Taken Yearly [NBMC]

1. Antigenic drift - Influenza virus undergoes continuous minor mutations in hemagglutinin (H) and neuraminidase (N) antigens each year - last year's vaccine may not match new circulating strains
2. Waning immunity - Antibody levels from previous year's vaccine decline over 6-12 months
3. Annual reformulation - WHO Global Influenza Surveillance Network identifies circulating strains each year and recommends composition for next year's vaccine
4. Seasonal variation - Different strains circulate in different seasons
5. High-risk groups - Elderly, pregnant women, healthcare workers, immunocompromised need annual protection

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Summary Table - Key Distinctions Asked Repeatedly

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All answers derived from: Park's Textbook of Preventive and Social Medicine (accessed via library database, ISBN 9789382219163).Your credits are exhausted. You can purchase a top-up or subscribe to a plan to continue using Orris. If you're already subscribed, your daily credits will reset tomorrow.