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Overview

  • Human immunodeficiency virus (HIV) is a blood-borne and sexually transmitted infection that leads to acquired immunodeficiency syndrome (AIDS).

  • HIV belongs to the Lentivirus genus of the retroviridae family.

  • An enveloped, single-stranded RNA virus that primarily infects CD4+ T lymphocytes (though it can infect other cell that express CD4, such as macrophages).

  • Viral life cycle

    1. Infection of the host cell via binding to CD4 and fusion of the viral envelope and cell membrane.

    2. The viral RNA is reverse transcribed in DNA and integrated into the host genome.

    3. There is a period of latency, followed by an active viral replication phase.

    4. New viral particles “bud off” of the cell membrane of the infected cell.

    5. This eventually results in cellular destruction and consequently impairment of the host’s immune system.

Clinical Presentation

  • HIV can spread via blood, semen, vaginal fluid, or breast milk.

  • Primary HIV infection can be asymptomatic or present as a viral prodrome occurring 2 to 4 weeks after exposure.

  • Symptoms include fever, reactive cervical lymphadenopathy, pharyngitis, maculopapular rash, orogenital ulcers, and meningoencephalitis.

  • Leukopenia and decreased CD4 count can also occur with associated opportunistic infections.

Diagnosis

  • HIV is diagnosed via anti-HIV antibodies detected in serum. These are persistently present 3 months following exposure.

World Health Organization (WHO) 2007 Clinical Staging System

  • Takes into account the myriad of clinical manifestations associated with HIV infection (Appendices A and B).

  • Useful for establishing baseline, assessing the effect of therapy, monitoring long term follow-up, and prognosticating.

  • Immune status (as measured by CD4 count) is useful in clinical decision making.

  • The likelihood of developing clinical manifestations of immunodeficiency has been shown to correlate with decreasing CD4 count.

  • Normal absolute CD4 count in adults is 500 to 1500 cells per mm3 of blood (normal values require age-adjustment, as children generally have higher CD4 counts than adults). Opportunistic infections and other manifestations of HIV become more likely when CD4 counts drop below 200 cells/mm3.

Center for Disease Control (CDC) Staging System

  • Incorporates both clinical manifestations and CD4 count. It was initially designed for surveillance purposes, though it provides an adequate overview of a patient’s clinical picture (Table 11-1).

  • Classified into one of five stages (0, 1, 2, 3, unknown) as follows:

    • Stage 0—HIV-positive patient, with a previous negative HIV test within 6 months of seroconversion. These patients remain Stage 0 until 6 months after diagnosis.

    • Stage 1—Acute HIV infection. Occurs within 2 to 4 weeks after HIV infection. Symptoms may include flu-like illness.

    • Stage 2—Clinical latency (HIV inactivity or dormancy). Asymptomatic or chronic HIV infection.

    • Stage 3—AIDS. Presence of AIDS-defining condition = Stage 3.

    • Stage unknown—No information available on CD4 count and no information available on AIDS-defining conditions.

Table 11-12014 CDC HIV Age-Specific Infection Stage

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