A 32-year-old healthcare worker from Delhi sustains a needlestick injury with blood from a patient of unknown HIV status. The source patient's rapid HIV test is negative. Which investigation should be performed on the healthcare worker at baseline to establish a reference point for post-exposure prophylaxis (PEP) monitoring?

## Baseline Investigation for Occupational Exposure and PEP Monitoring **Key Point:** Fourth-generation antigen-antibody ELISA at baseline (before starting PEP) and at defined intervals (6 weeks, 3 months, 6 months) is the standard investigation protocol for monitoring healthcare workers after occupational HIV exposure, as per NACO PEP guidelines. ### Why Fourth-Generation ELISA for PEP Monitoring? **High-Yield:** The fourth-generation test is chosen because: - Establishes baseline seronegative status before PEP initiation - Detects both antibodies and p24 antigen, reducing window period - Monitors for seroconversion during and after PEP - Cost-effective and widely available in India - Recommended by NACO, CDC, and WHO for occupational exposure follow-up ### PEP Monitoring Protocol (NACO Guidelines) | Time Point | Investigation | Purpose | |------------|---------------|---------| | Baseline (Day 0) | Fourth-gen Ag-Ab ELISA | Establish seronegative status | | 6 weeks | Fourth-gen Ag-Ab ELISA | Early seroconversion detection | | 3 months | Fourth-gen Ag-Ab ELISA | Confirm seroconversion if positive | | 6 months | Fourth-gen Ag-Ab ELISA | Final follow-up | **Clinical Pearl:** Even if the source patient is HIV-negative, baseline testing of the exposed healthcare worker is mandatory to: 1. Prove pre-exposure seronegative status (medico-legal documentation) 2. Establish reference for detecting any seroconversion 3. Differentiate occupational acquisition from pre-existing infection **Mnemonic:** **PEP Follow-up = 4th Gen at 0, 6w, 3m, 6m** → Four-generation test at four time points. ### Occupational Exposure Management Algorithm ```mermaid flowchart TD A[Needlestick/Occupational Exposure]:::urgent --> B[Assess source patient HIV status]:::decision B -->|Positive or Unknown| C[Start PEP within 2 hours]:::action B -->|Negative| D[Baseline 4th-gen ELISA on exposed worker]:::action C --> E[Baseline 4th-gen ELISA on exposed worker]:::action D --> F[PEP monitoring at 6w, 3m, 6m]:::action E --> F F --> G{Seroconversion?}:::decision G -->|Yes| H[Confirm with repeat test + RNA PCR]:::action G -->|No at 6 months| I[Occupational exposure resolved]:::outcome H --> J[Initiate ART]:::action ``` **Warning:** Do NOT use CD4 count at baseline — it is not indicated in seronegative individuals and does not help with PEP monitoring. CD4 count is only relevant after HIV diagnosis is confirmed. [cite:Park 26e Ch 8; NACO PEP Guidelines 2017]