Which of the following best describes the CD4+ T-cell count threshold below which a person with HIV is classified as having AIDS in the absence of an AIDS-defining illness?

Explanation

## AIDS Case Definition by CD4+ Count **Key Point:** According to the CDC and WHO case definitions, a CD4+ T-cell count <200 cells/μL in a person with HIV constitutes an AIDS diagnosis, regardless of the presence of clinical symptoms or opportunistic infections. **High-Yield:** This CD4+ threshold of 200 cells/μL is the immunological criterion for AIDS classification and is critical for determining when to initiate prophylaxis for opportunistic infections (OI) and for staging disease severity. ### CD4+ Count-Based Risk Stratification | CD4+ Count | Clinical Stage | OI Prophylaxis | Key Complications | |---|---|---|---| | >500 cells/μL | Early | None (if CD4 >200) | Minimal OI risk | | 200–499 cells/μL | Intermediate | PCP prophylaxis (if <200) | Increased OI risk | | <200 cells/μL | Advanced AIDS | PCP, MAC, CMV prophylaxis | High OI mortality | | <50 cells/μL | Severe AIDS | Intensive prophylaxis | CMV, cryptococcal disease, toxoplasmosis | **Mnemonic:** **"200 is the AIDS threshold"** — This single number is essential for clinical decision-making in HIV management. ### Clinical Implications 1. **Opportunistic Infection Risk:** CD4 <200 cells/μL increases risk of Pneumocystis jirovecii pneumonia (PCP), toxoplasmosis, and cryptococcal meningitis 2. **Prophylaxis Initiation:** TMP-SMX prophylaxis is indicated when CD4 <200 cells/μL 3. **ART Urgency:** Patients with CD4 <200 cells/μL require urgent ART initiation 4. **Immune Reconstitution:** With effective ART, CD4 recovery typically occurs at ~50 cells/μL per month **Clinical Pearl:** In India, the National AIDS Control Organization (NACO) guidelines recommend ART initiation for all PLHIV regardless of CD4 count, but CD4 <200 cells/μL remains the threshold for AIDS classification and OI prophylaxis decisions.