USMLE Guide: HIV/AIDS

Introduction

This guide aims to provide a comprehensive overview of HIV/AIDS, a significant topic frequently tested on the United States Medical Licensing Examination (USMLE). It will cover the basics of HIV/AIDS, including epidemiology, pathophysiology, clinical presentation, diagnosis, treatment, and prevention.

Table of Contents

1. Epidemiology
2. Pathophysiology
3. Clinical Presentation
4. Diagnosis
5. Treatment
6. Prevention

Epidemiology

• Human Immunodeficiency Virus (HIV) is a retrovirus that causes Acquired Immunodeficiency Syndrome (AIDS).
• Worldwide, an estimated 38 million people are living with HIV/AIDS as of 2019.
• Sub-Saharan Africa is the most affected region, accounting for approximately 67% of all people living with HIV/AIDS globally.
• Transmission occurs mainly through sexual contact, blood exposure, and perinatal transmission.

Pathophysiology

• HIV primarily targets CD4+ T lymphocytes, macrophages, and dendritic cells, leading to their destruction.
• It enters the host cell via CD4 receptor and co-receptors (CCR5 or CXCR4) using viral envelope proteins (gp120 and gp41).
• The viral RNA is reverse transcribed into DNA using the viral enzyme reverse transcriptase.
• The viral DNA integrates into the host genome via the viral enzyme integrase, leading to persistent infection.
• HIV replication occurs within the host cell, resulting in the production of new viral particles that can infect other cells.

Clinical Presentation

• Acute HIV infection (Acute Retroviral Syndrome): Fever, lymphadenopathy, rash, myalgia, sore throat, headache, and fatigue, typically 2-4 weeks after exposure.
• Asymptomatic (Chronic) HIV infection: May last for several years without notable symptoms.
• AIDS: Characterized by severe immune suppression and the development of opportunistic infections, malignancies, and HIV-related complications.

Diagnosis

• HIV screening is recommended for all individuals aged 13-64 years as part of routine care.
• Initial screening test: Fourth-generation immunoassay (detects both HIV antigen and antibodies).
• If positive, confirmatory test: HIV-1/HIV-2 differentiation immunoassay or nucleic acid testing (NAT).
• Diagnosis of AIDS: CD4+ T-cell count <200 cells/μL or the presence of specific opportunistic infections/malignancies.

Treatment

• Antiretroviral Therapy (ART) is the cornerstone of HIV management.
• Combination therapy: Typically consists of three or more antiretroviral drugs from two or more classes (e.g., Nucleoside Reverse Transcriptase Inhibitors, Non-Nucleoside Reverse Transcriptase Inhibitors, Protease Inhibitors, Integrase Strand Transfer Inhibitors).
• ART aims to suppress viral replication, preserve immune function, and delay disease progression.
• Adherence to ART is crucial to prevent drug resistance.

Prevention

• Safe sexual practices: Condom use, regular testing, and partner notification.
• Pre-exposure prophylaxis (PrEP): Daily use of antiretroviral medication (e.g., tenofovir/emtricitabine) for individuals at high risk of HIV acquisition.
• Post-exposure prophylaxis (PEP): Administration of antiretroviral medication within 72 hours following high-risk exposure to prevent HIV infection.
• Needle/syringe exchange programs and harm reduction strategies to reduce transmission among people who inject drugs.
• HIV testing and counseling to promote early detection and treatment.

Remember, this guide only provides a brief overview of HIV/AIDS. For a more in-depth understanding, refer to reputable textbooks and resources specifically tailored for the USMLE.