Sensitivity vs. Specificity

Core Definitions

The 2×2 Table

                   Disease +        Disease −
Test Positive   | True Positive  | False Positive |
Test Negative   | False Negative | True Negative  |

• Sensitivity = TP ÷ (TP + FN) → reads down the Disease+ column
• Specificity = TN ÷ (TN + FP) → reads down the Disease− column

Practical Mnemonics

• SnNout: High Snsitivity → a Negative result rules out disease (few false negatives)
• SpPin: High Specificity → a Positive result rules in disease (few false positives)

The Sensitivity-Specificity Trade-off

When to Prioritize Each

Key Takeaway

• Sensitivity is about catching all the sick — high sensitivity = few missed cases.
• Specificity is about correctly clearing the healthy — high specificity = few false alarms.
• No single test is perfect at both; the clinical context determines which matters more.

Post-Exposure Prophylaxis (PEP) for Needle Stick Injury

Immediate First Aid (All Cases)

1. Do NOT suck the wound
2. Wash thoroughly with soap and water for several minutes
3. Allow wound to bleed freely (do not squeeze)
4. Apply antiseptic (povidone-iodine or 70% alcohol)
5. Report to occupational health/emergency department immediately
6. Document time, nature of exposure, source patient details

HIV PEP

Treat as a medical emergency — PEP must be started within 72 hours (ideally within 1–2 hours). Efficacy drops significantly with delay and is ineffective after 72 hours. (Harrison's, p. 5977)

Risk Assessment

Preferred PEP Regimen

• Duration: 28 days (full course must be completed)
• Consider drug resistance in source patient when selecting regimen
• Pregnancy/breastfeeding: consult specialist — avoid efavirenz in first trimester

Follow-Up Testing (HIV)

Hepatitis B PEP

• HBIG dose: 0.06 mL/kg IM (ideally within 24 hours, up to 7 days)
• Risk of transmission per needle stick from HBsAg+ source: 6–30% (much higher than HIV)

Hepatitis C PEP

No effective PEP exists for Hepatitis C. (Harrison's, p. 9430)

• Immunoglobulin (IG) is not recommended — shown to be ineffective
• No vaccine available
• Risk per needle stick from HCV+ source: ~1.8%

Management:

1. Baseline HCV antibody + ALT
2. Follow-up at 4–6 weeks (HCV RNA), 3 months, and 6 months
3. If HCV RNA becomes positive (acute HCV): refer for early antiviral treatment with direct-acting antivirals (DAAs) — very high cure rate (~95%+)

Summary Table

Special Considerations

• Source patient testing: Rapid HIV, HBsAg, HCV Ab should be obtained from the source (with consent) to guide decisions
• Unknown source: Treat based on risk assessment of the environment (e.g., needle from HIV ward = higher risk)
• Pregnancy: Avoid certain antiretrovirals; specialist consultation required
• Complete the 28-day HIV PEP course — partial courses offer incomplete protection

Answer for Q2(a)

1. Physical hazard
   • Long duty hours (8 to 10 hours daily in OT), prolonged standing, and inadequate rest causing fatigue and musculoskeletal strain.
2. Biological hazard
   • Needlestick injury while suturing, creating risk of blood-borne infections such as HIV, HBV, and HCV.
3. Psychological hazard
   • High stress and emotional exhaustion (burnout features), shown by irritability, poor concentration, and fear after the exposure incident.

Q2(b) What ergonomic advice would you give Dr. Aditya to manage his musculoskeletal issues in the OT? (2 Marks)

1. Maintain neutral posture in OT
   • Keep neck and back straight, shoulders relaxed, elbows close to body, and avoid prolonged trunk bending/twisting during procedures.
   • Use adjustable OT table/stool and proper operating height to reduce strain on lower back and upper limbs.
2. Micro-breaks and stretching
   • Take short breaks (1 to 2 minutes every 30 to 45 minutes when feasible) for neck, shoulder, wrist, and back stretching.
   • Alternate static posture and shift weight between legs; use anti-fatigue footwear/mats if available.
3. Work organization
   • Rotate tasks when possible, avoid excessively long continuous operating hours, and ensure adequate recovery sleep to reduce cumulative musculoskeletal stress.

Q2(c) Outline the immediate Post-Exposure Prophylaxis (PEP) protocol he must follow for the needle-stick injury. (2 Marks)

1. Immediate first aid
   • Wash the injured site immediately with soap and running water.
   • Do not squeeze/scrub the wound and do not use harsh chemicals.
2. Report and risk assessment
   • Report immediately to hospital infection control/occupational health.
   • Document exposure details (type of needle, depth of injury, visible blood, source patient status).
3. Baseline investigations
   • Test source patient (with consent) for HIV, HBsAg, anti-HCV.
   • Baseline tests for exposed HCW: HIV, HBsAg/anti-HBs, anti-HCV, liver/renal profile as per protocol.
4. Start PEP promptly
   • HIV PEP: start as early as possible (preferably within 2 hours, not later than 72 hours), continue for 28 days if indicated.
   • HBV prophylaxis: HBV vaccine booster ± HBIG depending on vaccination/antibody status.
   • HCV: no effective PEP; do serial follow-up testing and early treatment if infection develops.
5. Follow-up
   • Clinical review for drug side effects, adherence counseling, and repeat serology as per institutional schedule.

Q5(a) Identify the socio-cultural and economic barriers preventing Mr. Ramlal from seeking care. (2 Marks)

1. Stigma and fear of social labeling due to suspected TB.
2. Fear of loss of family reputation (concern about daughter’s marriage prospects).
3. Fear of community gossip and discrimination (“if neighbors find out”).

1. Daily-wage dependency leading to fear of wage loss if he attends tests/treatment.
2. Perceived/real cost of investigations and repeated visits.
3. Opportunity cost of time away from work and possible travel expenses.

Q5(b) How should the physician communicate to address stigma while ensuring confidentiality? (2 Marks)

1. Empathetic, non-judgmental communication:
   • Acknowledge his fears: “I understand your concern about family and work.”
   • Avoid blame and normalize TB as a treatable disease.
2. Assure strict confidentiality:
   • Explain that his reports and diagnosis are private and shared only with authorized health staff.
   • Conduct counseling in a private setting.
3. Provide clear reassurance:
   • Early testing prevents complications and protects family.
   • Government TB services are free in public programs, reducing financial burden.
4. Shared decision-making:
   • Offer practical options (same-day sample, convenient timing) so he can continue work.

Q5(c) Demonstrate counseling using the “GATHER” approach. (3 Marks)

• Welcome respectfully, ensure privacy, build rapport.

• Explore symptoms, beliefs, fears, family concerns, work constraints, and understanding of TB.

• Explain in simple language:
  • TB is curable.
  • Sputum test and chest X-ray are needed for confirmation.
  • Diagnosis and treatment are available free under national TB program.
  • Confidentiality will be maintained.

• Help him choose feasible options:
  • Early-morning sputum sample timing
  • Nearest testing center
  • Minimize wage loss by scheduling around work
  • Involve trusted family member only with his consent.

• Explain next steps clearly:
  • Where/when to give sputum
  • When report will come
  • If positive, treatment duration, adherence, follow-up, cough etiquette, nutrition.

• Fix follow-up date, provide contact for doubts, and refer to TB health worker/counselor for continued support and treatment linkage.