Chapter 52: The Acquired Immunodeficiency Syndrome

DEFINITION AND HISTORY

• Patients with serologic evidence of infection with the human immunodeficiency virus (HIV) can be diagnosed as having acquired-immunodeficiency syndrome (AIDS) based upon "clinical" or "immunologic" criteria (see Table 52–1).

  — Patients with AIDS diagnosed based on clinical criteria are classified as having "clinical AIDS."

  — Patients with AIDS diagnosed based on a blood CD4 T cell count of less than 200/μL are classified as having "immunological AIDS."

• Patients with HIV are living longer in the era of highly active antiretroviral therapy (HAART).

• United Nations estimated that 30 to 35 million people worldwide were living with HIV infection in 2007, with the majority being infected by heterosexual contact.

ETIOLOGY AND PATHOGENESIS

Human Immunodeficiency Virus 1

• The primary cause of AIDS is infection with HIV-1.

• HIV-1 is a member of the Lentivirinae subfamily of retroviruses.

  — Retroviruses are RNA viruses that induce a chronic cellular infection by converting their RNA genome into a DNA provirus that is integrated into the genome of the infected cell.

• Infection by these lenetviruses is characterized by long periods of clinical latency followed by gradual onset of disease-related symptoms.

Transmission of HIV

• The four main routes of HIV infection are:

  • — Sexual contact with an infected partner.

    • The risk for HIV transmission through sexual contact may be increased in persons with other concurrent sexually transmitted diseases.

  • — Parenteral drug use.

    • Sharing needles and syringes is the main mode of transmission.

  • — Exposure to infected blood or blood products.

    • Ninety percent of those who receive a contaminated unit of blood become infected.

    • Risk of HIV transmission through transfusion of a unit of red blood cells tested negative for antibodies to HIV is approximately 1 in 493,000 transfusions.

  • — Perinatal exposure.

    • HIV-1 may be transmitted in utero, intrapartum (at the time of delivery) or postpartum, through ingestion of HIV-1-infected mother's milk.

    • The risk of infection from mother to infant differs in various parts of the world, ranging from approximately 15 percent in Europe and approximately 40 to 50 percent in Africa.

    • The risk of perinatal transmission is increased from mothers with more advanced HIV disease, higher HIV-1 viral load in the plasma, or a history of cigarette smoking and/or active drug abuse.

    • Antiretroviral agents in pregnancy and delivery, with subsequent administration to the infant for the first 6 weeks of life, has resulted in ...