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Human Immunodeficiency Virus (HIV): Overview and Risk Factors

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

HIV is a retrovirus that infects and destroys cells containing the CD4+ antigen, particularly CD4+ T–helper cells. The virus enters the body through disrupted mucosal barriers and rapidly infects CD4+ cells, ultimately disabling the immune system. Over time, morbidity and mortality occur due to opportunistic infections and malignancies that result from compromised immunity.

Acquired immunodeficiency syndrome (AIDS) is defined as the presence in an HIV–infected person of a CD4+ helper T cell count of less than 200 cells/mL, or the presence of any AIDS–defining illness, usually an opportunistic infection. Examples include: candidiasis of the esophagus or respiratory tract; cryptosporidiosis with persisting diarrhea; cytomegalovirus (other than of the liver); Herpes simplex virus with a mucocutaneous lesion that persists beyond 1 month; Kaposi’s sarcoma; Mycobacterium avium complex infection; Pneumocystis carinii pneumonia; or toxoplasmosis of the brain. A complete listing is downloadable (PDF) at http://www.aidsinfo.nih.gov/other/cbrochure/english/01_en.pdf.

Transmission of HIV occurs by sexual intercourse, intravenous drug use, perinatal infection, breast–feeding, blood products, and open wound–fluid interchange. Transmissibility rises in direct proportion to the HIV viral load.

Upon seroconversion, the initial presentation is a flu–like or mononucleosis–like syndrome (headache, fever, chills, cough, myalgias, adenopathy) with a rash that occurs within 4 to 14 days of infection and lasts less than 3 weeks. Patients then return to their baseline state of health for 2 to 10 or more years, while the virus replicates within T cells and the CD4+ cell count declines.

As the number of CD4+ T cells declines, patients become more susceptible to infection and neoplasm. Once the CD4+ cells are sufficiently depleted, patients experience multiple opportunistic infections and malignancies that may affect any organ system. These include:

  • Pulmonary: Upper respiratory infections, sinusitis, pneumonia, tuberculosis.
  • Neurologic: Bell’s palsy, dementia, meningitis, cerebritis, spinal cord dysfunction, peripheral neuropathy.
  • Gastrointestinal: Esophagitis, diarrhea, liver disease.
  • Rheumatologic: Arthritis.
  • Dermatologic: Kaposi’s sarcoma, herpetic lesions, molluscum contagiosum, abscess.
  • Hematologic: Lymphoma, thrombocytopenia.

Risk Factors

High–risk sexual intercourse. This includes heterosexual and homosexual contact. Nearly 90% of cases occur through heterosexual transmission. Condom use reduces, but does not eliminate, the risk. Factors associated with increased risk of transmission include male–male sexual intercourse, lack of circumcision (female–to–male transmission),1 and sexual intercourse during menses (female–to–male transmission).

Blood transfusion. Since 1985 the screening of blood products has significantly decreased the HIV transmission rate. The risk of transmission due to blood transfusion is now about 1 in 2 million.

Injection drug use. Drug injection is a particularly important source of the HIV epidemics in Eastern Europe, Asia, and the Middle East.

Perinatal transmission. Children are at risk while in utero, during delivery, and postnatally via breast–feeding. Perinatal transmission rates can be as high as 40%. However, the combination of antiretroviral therapy, elective cesarean delivery, and avoidance of breast–feeding in HIV–positive mothers has reduced perinatal transmission significantly.

Occupational exposure. Risk of transmission after an accidental needle stick exposure is less than 1%.


Human Immunodeficiency Virus (HIV): Diagnosis and Treatment >>