Evidence is overwhelming that Human Immunodeficiency virus (HIV) causes Acquired Immunodeficiency Syndrome (AIDS). HIV infects a number of cell types important to activating and sustaining an effective immune response. Chief among these cells are CD4 T-helper cells. "CD4 T cells play a central role in immune protection. They do so through their capacity to help B cells make antibodies, to induce macrophages to develop enhanced microbicidal activity, to recruit neutrophils, eosinophils, and basophils to sites of infection and inflammation, and, through their production of cytokines and chemokines, to orchestrate the full panoply of immune responses." HIV replication destroys CD4 T-helper cells. Loss of CD4 T-helper cells reduces the body's ability to fight off infection by organisms which are ordinarily kept in check by a healthy immune system.


The CDC states:

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Nearly 25% of people who are infected with HIV don’t know they are infected.

Risk Factors


During the initial phase of HIV infection, viral replication increases dramatically, then declines to a steady state during the chronic asymptomatic phase of HIV illness. Many individuals have only minor symptoms initially. Others develop a flu-like illness within a month or two after exposure to the virus. Early HIV symptoms may be mistaken for another type of viral infection:

HIV infection can be verified by a number of tests.

A diagnosis of AIDS requires: HIV confirmation plus CD4 T cell count < 200 cells per cubic millimeter (200/mL) of blood or HIV confirmation plus an AIDS defining condition.

The CDC identifies the following illnesses as AIDS defining conditions:
  • Bacterial infections, multiple or recurrent
  • Candidiasis of bronchi, trachea, or lungs
  • Candidiasis of esophagus
  • Cervical cancer, invasive
  • Coccidioidomycosis, disseminated or extrapulmonary
  • Cryptococcosis, extrapulmonary
  • Cryptosporidiosis, chronic intestinal (>1 month's duration)
  • Cytomegalovirus disease (other than liver, spleen, or nodes), onset at age >1 month
  • Cytomegalovirus retinitis (with loss of vision)
  • Encephalopathy, HIV related
  • Herpes simplex: chronic ulcers (>1 month's duration) or bronchitis, pneumonitis, or esophagitis (onset at age >1 month)
  • Histoplasmosis, disseminated or extrapulmonary
  • Isosporiasis, chronic intestinal (>1 month's duration)
  • Kaposi sarcoma
  • Lymphoid interstitial pneumonia or pulmonary lymphoid hyperplasia complex
  • Lymphoma, Burkitt (or equivalent term)
  • Lymphoma, immunoblastic (or equivalent term)
  • Lymphoma, primary, of brain
  • Mycobacterium avium complex or Mycobacterium kansasii, disseminated or extrapulmonary
  • Mycobacterium tuberculosis of any site, pulmonary, disseminated, or extrapulmonary
  • Mycobacterium, other species or unidentified species, disseminated or extrapulmonary
  • Pneumocystis jirovecii pneumonia
  • Pneumonia, recurrent
  • Progressive multifocal leukoencephalopathy
  • Salmonella septicemia, recurrent
  • Toxoplasmosis of brain, onset at age >1 month
  • Wasting syndrome attributed to HIV

Symptoms of opportunistic infections common in people with AIDS may include:

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AIDS is diagnosed when an HIV (+) person has a CD4 T cell count of less than or equal to 200/mL or if they develop an AIDS defining illness.