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Human Immunodeficiency Virus: Overview and Risk Factors

Worldwide, more than 40 million people are infected with human immunodeficiency virus (HIV). About 40,000 new infections occur every year in the United States.

HIV infects and destroys cells of the immune system. Over time, people with HIV develop infections and cancers due to their weakened immune systems. These include pneumonia, tuberculosis, dementia, meningitis, liver disease, chronic diarrhea, arthritis, herpes, Kaposi’s sarcoma, lymphoma, and other disorders.

Transmission of HIV occurs through sexual intercourse, intravenous drug use, mother–to–infant infection (during pregnancy or during breast–feeding), blood transfusions, or open wounds.

When someone becomes infected, the initial symptom is a flu–like or mononucleosis–like syndrome (headache, fever, chills, cough, and muscle aches) with a rash that occurs within four to 14 days of infection and lasts less than three weeks. Patients then return to their normal state of health for two to 10 or more years, while the virus slowly grows within the cells of the immune system.

Risk Factors

  • High–risk sexual intercourse: This includes heterosexual and homosexual contact. Nearly 90 percent of cases occur through heterosexual transmission. Condom use reduces, but does not eliminate, the risk.
  • Blood transfusion: Since 1985, screening of blood products has significantly decreased the HIV transmission rate. The risk of transmission due to blood transfusion is now about one in two million.
  • Injection drug use: Drug injection is a particularly important source of the HIV epidemics in Eastern Europe, Asia, and the Middle East.
  • Transmission from mother to child: Children are at risk while in utero, during delivery, and during breast–feeding. However, the combination of antiviral therapy, cesarean delivery, and avoidance of breast–feeding in HIV–positive mothers has reduced the risk significantly.
  • Occupational exposure: Risk of transmission after an accidental needle stick exposure is less than 1 percent.


Human Immunodeficiency Virus: Diagnosis and Treatment >>