Infectious Diseases: HIV/AIDS and STIs for USMLE
This module focuses on key infectious diseases, specifically HIV/AIDS and Sexually Transmitted Infections (STIs), crucial for success in the USMLE. We will cover their epidemiology, pathogenesis, clinical manifestations, diagnosis, and management, emphasizing the integration of knowledge required for clinical decision-making.
Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS)
HIV is a retrovirus that primarily targets CD4+ T cells, leading to a progressive decline in immune function. AIDS is the most advanced stage of HIV infection, characterized by severe immunosuppression and opportunistic infections.
Reverse transcriptase, integrase, and protease.
Clinical Manifestations of HIV/AIDS
The clinical course of HIV infection is typically divided into several stages, each with distinct manifestations.
| Stage | CD4 Count (cells/µL) | Key Clinical Features |
|---|---|---|
| Acute Retroviral Syndrome | 500 | Flu-like illness (fever, rash, lymphadenopathy, pharyngitis), high viral load |
| Clinical Latency (Asymptomatic) | 200-499 | Often asymptomatic, gradual CD4 decline |
| Symptomatic HIV Infection | 50-199 | Persistent generalized lymphadenopathy, oral candidiasis, herpes zoster, constitutional symptoms |
| AIDS | < 50 | Opportunistic infections (PCP, MAC, CMV, Toxoplasmosis), AIDS-defining cancers (Kaposi's sarcoma, lymphoma), wasting syndrome |
Remember that AIDS is a clinical diagnosis defined by the presence of specific opportunistic infections or cancers, or a CD4 count below 200 cells/µL.
Diagnosis and Management of HIV/AIDS
Diagnosis relies on serological testing and confirmation with nucleic acid tests. Management involves antiretroviral therapy (ART) to suppress viral replication and preserve immune function.
Antiretroviral therapy (ART) is the cornerstone of HIV management. It typically involves a combination of drugs from different classes that target various stages of the HIV life cycle. Common classes include Nucleoside Reverse Transcriptase Inhibitors (NRTIs), Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs), Protease Inhibitors (PIs), Integrase Strand Transfer Inhibitors (INSTIs), and Entry Inhibitors. The goal of ART is to achieve and maintain viral suppression (undetectable viral load), restore immune function (increase CD4 count), prevent opportunistic infections, and reduce transmission.
Text-based content
Library pages focus on text content
Sexually Transmitted Infections (STIs)
STIs are infections transmitted primarily through sexual contact. They represent a significant public health challenge due to their prevalence, potential for serious complications, and role in facilitating HIV transmission.
Common STIs and Their Characteristics
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Each STI has unique epidemiological patterns, clinical presentations, diagnostic methods, and treatment regimens. Understanding these differences is vital for accurate diagnosis and effective management.
Key STIs for USMLE
Focus on the following STIs, paying attention to their characteristic lesions, diagnostic tests, and treatment protocols:
| STI | Causative Agent | Primary Lesion/Symptom | Diagnostic Test | Treatment |
|---|---|---|---|---|
| Chlamydia Trachomatis | Bacteria | Urethritis, cervicitis, discharge; often asymptomatic | Nucleic Acid Amplification Test (NAAT) | Azithromycin or Doxycycline |
| Neisseria Gonorrhoeae | Bacteria | Urethritis, cervicitis, discharge; often asymptomatic | NAAT | Ceftriaxone (often with Azithromycin) |
| Syphilis (Treponema pallidum) | Bacteria | Primary: Chancre; Secondary: Rash, condyloma lata; Tertiary: Neurosyphilis, gummas | RPR/VDRL (screening), FTA-ABS (confirmatory) | Penicillin G |
| Herpes Simplex Virus (HSV) | Virus | Painful vesicles/ulcers | Viral culture, PCR, serology | Acyclovir, Valacyclovir, Famciclovir |
| Human Papillomavirus (HPV) | Virus | Genital warts (condyloma acuminata), cervical dysplasia/cancer | Visual inspection, Pap smear, HPV DNA testing | Podophyllin, cryotherapy, surgical removal; vaccination (Gardasil) |
| Trichomoniasis (Trichomonas vaginalis) | Protozoa | Vaginal discharge (frothy, yellow-green), dysuria, dyspareunia | Microscopy, NAAT | Metronidazole or Tinidazole |
Always consider co-infection with other STIs, especially in patients diagnosed with HIV or syphilis.
Prevention and Public Health Implications
Effective prevention strategies include safe sex practices (condom use), regular screening, partner notification, and vaccination (e.g., HPV, Hepatitis B). Public health efforts focus on education, access to testing and treatment, and reducing stigma.
Nucleic Acid Amplification Test (NAAT).
Learning Resources
Comprehensive information on HIV/AIDS from the Centers for Disease Control and Prevention, covering transmission, prevention, testing, and treatment.
Detailed information on various STIs, including symptoms, prevention, testing, and treatment guidelines from the CDC.
A review of infectious diseases relevant to the USMLE Step 1, often including high-yield facts and clinical correlations.
An in-depth clinical resource providing comprehensive, evidence-based information on HIV infection, suitable for advanced learners.
A clinical guide on evaluating and managing patients presenting with potential STIs, focusing on diagnostic approaches and treatment.
An animated video explaining the pathophysiology of HIV infection, ideal for visual learners.
A concise video covering the clinical presentation, diagnosis, and management of syphilis.
A detailed overview of HIV/AIDS, including epidemiology, pathogenesis, clinical manifestations, and treatment from a medical professional perspective.
A comprehensive portal to information on various STDs, offering detailed articles on each condition.
A broad overview of HIV/AIDS, covering its history, biology, social impact, and global health aspects.