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Chapter 2 - Complete WBUHS Answers

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PART A: OUTBREAK INVESTIGATION

Q1. Define "Epidemic" [2 Marks - Tamralipto GMC]

• Greek origin: Epi (upon) + demos (people)
• Epidemicity is relative to usual frequency in same area, same season
• Even a single case of a disease long absent from a population may require full epidemic investigation

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Q2. Epidemic vs Outbreak [1+1 Marks - Burdwan MC / IQ City]

85 cases in 3 days after a feast = OUTBREAK (also a point-source epidemic - single exposure event)

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Q3. Steps of Outbreak/Epidemic Investigation [6-8 Marks - Tamralipto, Burdwan, IQ City, Midnapore, Barasat GMC]

• Time: Draw epidemic curve - histogram of cases by time of onset
  • Single peak (bell-shaped) = point-source; progressive peaks = propagated
• Place: Spot map - cases cluster at feast location
• Person: Age, sex, specific food items consumed

• Compare attack rates among those who ate specific foods vs. those who did not
• Calculate Relative Risk (RR) for each food item
• Food with highest RR + statistical significance = likely vehicle

Why retrospective cohort (not case-control)? The exposed population (feast attendees) is well-defined and enumerable.

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Q4. Define "Attack Rate" and Calculate [4 Marks - Barasat GMC]

AR = (Number of persons developing disease / Number exposed to risk) × 100

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Q5. Epidemic Curve - Draw and Interpret [3 Marks - IQ City]

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Q6. Immediate Control Measures During Investigation [2-5 Marks]

1. ORT / IV fluids for dehydrated cases; antibiotics where indicated (Ciprofloxacin for Vibrio/Salmonella)
2. Remove suspected contaminated food from circulation; stop consumption of feast food
3. Safe water: chlorination; distribute ORS; advise boiling water
4. Sanitation: proper disposal of excreta/vomitus; disinfect contaminated areas
5. Notify District Health Officer/CMO; activate disease surveillance
6. Deploy medical team; set up treatment camp in the village
7. Screen and remove symptomatic food handlers from duty

• Safe piped water supply or deep tube wells
• Sanitary latrines (Swachh Bharat Mission)
• Solid waste management and drainage improvement
• Health education on personal hygiene, hand-washing, food safety
• Regulation of food vendors at community gatherings
• Regular water quality testing

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Q7. Hepatitis A Outbreak - Block X [2+5+3 Marks - College of Medicine & Sagore Dutta]

1. Verify: LFT (↑bilirubin, ↑ALT), serology (anti-HAV IgM)
2. Confirm epidemic, define cases, count and list
3. Epidemic curve + spot map of cases vs. food stalls visited
4. Hypothesis: specific food stall/contaminated water is vehicle
5. Analytical study: Case-control study comparing food stall exposure between cases and matched healthy controls who attended the fair
6. Inspect food stalls: water source, hand-washing facilities, food handler health
7. Laboratory: stool/water samples, food handler serology

• Supportive treatment (rest, IV fluids; avoid hepatotoxins)
• Closure and sanitization of implicated stalls
• Safe water for all vendors; mandatory hand-washing
• Health education to parents, children, vendors
• Active surveillance; post-exposure immunoglobulin for close contacts

• Hepatitis A vaccination in the district
• Licensing, regular inspection, and hygiene certification for food vendors at public gatherings
• Compulsory hand-washing stations at fairs
• Water quality monitoring
• Food safety in school health curriculum

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PART B: EPIDEMIOLOGICAL STUDY DESIGNS

Q8. Define Epidemiology & Classify Studies [2+3 - MCK/Jagannath Gupta]

"Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the prevention and control of health problems."

EPIDEMIOLOGICAL STUDIES
├── OBSERVATIONAL
│   ├── DESCRIPTIVE: Case report, Cross-sectional, Ecological
│   └── ANALYTICAL: Case-Control, Cohort
└── EXPERIMENTAL
    ├── RCT (Randomized Controlled Trial)
    ├── Field Trial
    └── Community Trial

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Q9. Cross-Sectional Study - Prevalence of Obesity Among Medical Students [2+13=15, Barasat GMC]

1. Define study population (all medical students by year)
2. Calculate sample size: n = Z²pq/d² (p ≈ 30%, d = 5%, Z = 1.96 → n ≈ 323)
3. Sampling: Stratified Random Sampling (stratify by year of study, random within each stratum)
4. Prepare questionnaire: demographics, diet, physical activity, screen time
5. Define obesity: BMI ≥ 25 kg/m² (Asian cut-off); measure height (stadiometer) and weight (calibrated scale)
6. Calculate BMI = Weight (kg) / Height (m)²
7. Data entry and analysis (Epi Info/SPSS):
   • Overall prevalence; prevalence by sex and year
   • Chi-square for associations with risk factors
8. Write report with recommendations

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Q10. Cohort Study [Steps, Advantages, Disadvantages, Bias] - JNM Kalyani, MCK, RGKMC, Deben Mahata, COM Sagore Dutta, ESI Joka

1. Selection of cohorts:
   • Exposed cohort: Radiation workers / Obese individuals (BMI ≥ 25) - free of outcome disease at start
   • Unexposed cohort: Non-exposed workers / Non-obese - matched for age, sex, smoking
2. Baseline data collection: Exposure measurement (dosimetry/BMI), baseline health check-ups, investigations
3. Follow-up over defined period (5 years/15 years): periodic examinations; monitor for outcome (cancer/hypertension)
4. Outcome assessment: Standardized diagnostic criteria; blinded assessment
5. Analysis:
   • Incidence rate in exposed and unexposed groups
   • RR = Incidence in exposed / Incidence in unexposed
   • AR = Incidence in exposed - Incidence in unexposed

• Obese: 200/2000 = 10% incidence
• Non-obese: 100/4000 = 2.5% incidence
• RR = 10/2.5 = 4.0 → Obese individuals have 4× the risk of hypertension

1. Establishes temporal relationship (cause precedes effect)
2. Directly measures incidence rates
3. Can study multiple outcomes of one exposure
4. Less susceptible to recall and selection bias
5. Gold standard for causation (after RCT)
6. RR calculated directly

1. Time-consuming and expensive
2. Large sample size needed
3. Inappropriate for rare diseases - need enormous cohort to detect cases; case-control preferred
4. Attrition/loss to follow-up major problem
5. Healthy worker effect may bias occupational studies
6. Changes in diagnostic criteria over follow-up period

• Selection bias: Healthy worker effect
• Attrition bias: Differential loss to follow-up
• Information bias: Changes in diagnostic criteria, observer bias
• Confounding: Age, smoking, diet

"Cohort study is gold standard for temporal association but inappropriate for rare diseases" - because it would need an impractically large cohort and prolonged follow-up to accumulate enough cases of a rare disease.

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Q11. Case-Control Study [Design, Advantages, Disadvantages, Bias] - PC Sen, ESI Joka, MJN Coochbehar, NRS

1. Define cases: OA knee (clinical + radiological: K-L grade ≥ 2), age 35-65 years, from orthopaedic OPD
2. Define controls: Same age range, no OA knee; matched for age (±5 years) and sex; from same hospital (other OPD) or community
3. Obtain exposure data: BMI measurement + recall of past weight; standardized questionnaire (blinded interviewer) on occupation, physical activity, diet, joint injuries
4. Calculate Odds Ratio (OR):

1. Control confounding: Matching, stratification, multivariate logistic regression

1. Quick and inexpensive
2. Suitable for rare diseases
3. Studies multiple risk factors simultaneously
4. Small sample size needed
5. No attrition problems (no follow-up)
6. Ethical - no intervention
7. Good for diseases with long latency period

1. Susceptible to recall/memory bias
2. Susceptible to selection bias
3. Cannot calculate incidence or RR directly (only OR approximates RR for rare diseases)
4. Cannot study rare exposures
5. Temporality may be uncertain
6. Berkesonian bias in hospital-based studies
7. Cannot study multiple outcomes of a single exposure

1. Recall (Memory) Bias - Cases recall past exposure more vividly than controls (differential misclassification)
2. Selection Bias - Cases and controls not representative of general population
3. Berkesonian Bias - Differential hospital admission rates for cases vs. controls with different diseases
4. Interviewer Bias - Awareness of case/control status influences depth of questioning; controlled by double-blinding
5. Confounding Bias - Third variable (age, sex, occupation) distorts observed association

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Q12. Cohort Study for OCP and Breast Cancer / Rare Fatal Disease [ESI Joka, Bankura Sammilani]

• Best design: Case-Control Study - most practical for rare diseases; efficient use of resources
• Steps: identify all available cases of the disease nationally; recruit matched controls; obtain exposure history retrospectively

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Q13. RCT - Two Drugs for Hypertension / Randomization and Blinding [IQ City, Deben Mahata, Barasat GMC]

1. Frame research question: Is Drug A superior to Drug B in reducing BP?
2. Define eligibility criteria (inclusion/exclusion)
3. Calculate sample size (expected BP difference, alpha = 0.05, power = 80%)
4. Recruit, obtain informed consent
5. Randomization: Computer-generated random numbers → allocate to Drug A or B
6. Double-blinding: Identical tablets; neither participant nor investigator knows assignment
7. Administer drugs for 6 months; monitor compliance and adverse events
8. Outcome assessment: BP at 6 months by blinded assessor
9. Analysis: Intention-to-treat; t-test/ANOVA for mean BP difference

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Q14. Relative Risk - Calculation [Diamond Harbour GMC&H]

• Exposed with silicosis: 120/800 = 15%
• Unexposed with silicosis: 30/1200 = 2.5%
• RR = 15/2.5 = 6.0
• Interpretation: Exposed workers have 6× the risk of developing silicosis - strong causal association

• RR: Ratio - measures strength of association (useful for etiology, causation)
• AR (Attributable Risk): Difference - Incidence(exposed) - Incidence(unexposed) = 15% - 2.5% = 12.5% - measures excess risk due to exposure (useful for public health impact, prevention)

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Q15. Bias and Confounding - Not Synonymous [CNMC]

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Q16. Epidemic Curve Types / Time Trends [RGKMC]

1. Point-source: Single common exposure → single bell-shaped peak; ends within one incubation period
2. Propagated: Person-to-person spread → progressive multiple peaks, each = one generation time
3. Mixed: Point-source followed by person-to-person spread

• Secular: Decades-long changes (decline of smallpox, rise of NCD)
• Cyclical/Periodic: Regular fluctuations every few years (influenza, cholera pandemics)
• Seasonal: Regular annual variation (monsoon cholera, winter measles)
• Short-term fluctuations: Sudden point epidemics

• Completeness and changes in reporting system
• Changes in case definition or diagnostic criteria
• Population demographic changes
• Artefactual changes (better surveillance detecting more cases)

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PART C: IMMUNIZATION

Q17. National Immunization Schedule for Infant [KPCMCH]

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Q18. AEFI - Classification, Serious vs Severe [Malda, JMN, IPGMER]

1. Vaccine Product-Related Reaction: Inherent properties of vaccine. Example: VAPP (oral poliovirus), BCG adenitis
2. Vaccine Quality Defect-Related Reaction: Manufacturer defect in a batch. Example: Higher reaction rates from a specific lot
3. Immunization Error-Related Reaction: Improper handling or administration. Examples: Abscess (non-sterile technique), toxic shock (contaminated multi-dose vial), wrong route (BCG subcutaneously)
4. Immunization Anxiety-Related Reaction: Psychological. Example: Vasovagal syncope, hyperventilation, fainting
5. Coincidental Event: Would occur regardless of vaccination. Example: Fever from concurrent viral infection

• Serious: Administrative/regulatory classification - any event resulting in death, hospitalization, life-threatening illness, or permanent disability
• Severe: Intensity grade (Grade 3/4 on clinical severity scale)
• A reaction can be serious but not severe (e.g., hospitalization for mild rash) or severe but not serious (e.g., intense pain at injection site not requiring hospitalization)

• Diagnosis: Anaphylaxis (onset within 30 min, dyspnoea, rash, unconsciousness) - most serious vaccine product-related reaction
• Immediately: Adrenaline (epinephrine) 1:1000 IM (0.01 mg/kg, max 0.5 mg) into anterolateral thigh; oxygen; IV access; antihistamine (chlorphenamine); IV corticosteroids; refer to district hospital
• Investigate: AEFI committee notification; review cold chain; check vaccine lot number; investigate other children from same session

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Q19. Drop-out and Left-out Children [Jhargram, RGMC]

• Outreach sessions (mobile immunization teams)
• Due list preparation and default tracking by ASHA/ANM
• Village Health, Nutrition and Sanitation Days (VHND)
• Mission Indradhanush - targets left-outs and drop-outs
• Microplanning to identify unreached settlements
• IEC activities through ASHA and anganwadi workers
• Open Vial Policy (see below)

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Q20. HPV Vaccination [CNMC, Midnapore, Santiniketan, Burdwan, PC Sen]

• Cervical cancer is the 2nd most common cancer in women in India (hence: "HPV vaccination to prevent second most common cancer")
• HPV types 16 and 18 cause ~70% of cervical cancers
• Vaccines available: Cervarix (bivalent), Gardasil (quadrivalent), Gardasil-9 (nonavalent)
• India's Cervavac (indigenously developed quadrivalent) introduced in NIS 2023
• Target: Girls aged 9-14 years (before sexual debut); 2 doses 6 months apart; IM deltoid

• Direct individual immunity (individual protection)
• Herd immunity - high coverage reduces community HPV circulation, protecting even unvaccinated individuals
• Reduces overall community cancer burden
• Applies to all vaccines: the dual purpose is individual immunity AND community disease load reduction

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Q21. Serious Additional Points

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