Human Immunodeficiency Virus Infection



  • HIV is the etiologic agent of AIDS. HIV suppresses CD4+ T cells leading to impaired cell-mediated immunity.
  • HIV-1 is more common worldwide, whereas HIV-2 is mainly prevalent in West Africa.
  • An acute phase with flulike symptoms develops 2 to 4 weeks after acquiring infection, followed by a long asymptomatic period (5 to 15 years in adults, shorter in children), followed, if untreated, by development of nonspecific signs and symptoms (weight loss, adenopathy, hepatosplenomegaly, failure to thrive) and clinical immunodeficiency.
  • AIDS is the advanced stage of untreated HIV when the infected individual will experience progressive immunologic deterioration and eventually become susceptible to opportunistic infections and cancers.


  • As of 2015, there were an estimated 36.7 million people living with HIV worldwide, and as of 2013, 1.3 million in the United States. The highest prevalence of HIV is in Sub-Saharan Africa.
  • In 2015, there were 39,513 new HIV diagnoses in the United States, 120 in those <13 years of age and 8,737 in those between the ages of 13- to 24 years Centers for Disease Control and Prevention (CDC).
  • In 2015, approximately 90% of new diagnoses among 13 to 24-year-old men had male-to-male sex as the primary risk factor.
  • African American individuals made up approximately 55% of new diagnoses in 2015 among those 13 to 24 years old.


  • Sexual contact
    • Unprotected orogenital, vaginal, or anal sex: Anal receptive sex is highest risk.
  • Exposure to infected blood or body fluids
    • Needle sharing (injection drug use)
    • Occupational exposure (i.e., needle stick): Risk of transmission from an HIV-contaminated needle is 1:300.
    • Blood transfusion: All donated blood in the United States is screened for HIV.
    • Mucous membrane exposure to infected blood or fluids
  • Perinatal infection can occur either in utero or during labor and delivery.
    • Risk of an HIV-infected mother (not on treatment) giving birth to an infected infant is ~20% (in the absence of breastfeeding), with increased rate of transmission for women with low CD4 counts or higher viral titers. Vaginal delivery, especially with rupture of membranes >8 hours, appears to increase the risk of infant infection.
    • Risk of perinatal transmission if mother is effectively treated (undetectable viral load) is <2%.
    • Presence of untreated sexually transmitted infections (STIs), chorioamnionitis, and prematurity all increase the risk of mother-to-child transmission of HIV.
  • Breast milk
    • Overall risk of breastfeeding is ~15%.
    • In countries where breastfeeding is the norm, up to 30% of perinatally acquired HIV infections occur through breastfeeding.
    • Breastfeeding is not recommended in the United States.
  • HIV is not believed to be transmitted by the following:
    • Bites
    • Sharing utensils, bathrooms, bathtubs
    • Exposure to urine, feces, vomitus (except where these fluids may be grossly contaminated with blood, and even then transmission is rare, if it happens at all)
    • Casual contact at home, school, or day care center


  • Prevention of mother-to-child transmission: All pregnant women should be offered HIV testing at the first prenatal visit. In areas of high incidence, repeat testing should be done at 36 weeks of gestation. Women not tested before or during labor should undergo expedited HIV testing.
    • Antenatal three-drug antiretroviral therapy (ART) for all HIV-positive pregnant women
    • Delivery via elective cesarean section for selected cases
    • Postnatal ART prophylaxis for infants:
      • 4-week course of zidovudine for low-risk mothers (on ART with suppressed viral load)
      • For high-risk mothers (not on ART or on ART but with elevated viral load) combination ART with two to three drugs is recommended. One regimen consists of zidovudine for 6 weeks, plus nevirapine given in 3 doses (at birth, 48 hours after the first dose, and 96 hours after second dose). Some experts recommend a three-drug regimen with the addition of lamivudine to zidovudine and nevirapine. However, the optimal duration of nevirapine and lamivudine is not known with guidelines stating a range of 2 to 6 weeks.
  • Postexposure prophylaxis
    • ART initiated after possible HIV exposure: unprotected sex or sexual assault, needle sharing, occupational exposure
    • Consists of three-drug ART for 28 days
    • Must be initiated within 72 hours of exposure
  • Preexposure prophylaxis
    • Daily tenofovir/emtricitabine approved by the U.S. Food and Drug Administration (FDA) for patients 18 years and older
    • Recommended for high-risk individuals: men who have sex with men or heterosexual men/women with HIV-positive partners, multiple sexual partners, recent STI, and injection drug users who share injection equipment
  • General measures: condom use, avoidance of needle sharing, no breastfeeding

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