It is established beyond reasonable doubt that AIDS, the acquired immunodeficiency syndrome, is caused by infection with HIV, the human immunodeficiency virus. This conclusion rests on an overwhelming body of evidence gathered since the early 1980s, and it is the basis of the treatments that have transformed HIV from a near-certain death sentence into a manageable condition. The link is one of the most thoroughly documented in modern medicine.
The case that HIV causes AIDS is supported by every line of medical and scientific evidence: the virus is found in essentially all AIDS patients, it specifically destroys the immune cells whose loss defines the disease, its presence predicts who will fall ill, and blocking it with drugs prevents and reverses the illness. The strength and consistency of this evidence place the conclusion among the most secure in medicine.
HIV was identified in 1983 and 1984 as a new virus present in patients with the mysterious immune collapse then appearing around the world. Researchers showed that it infected and killed the very immune cells, called CD4 cells, whose disappearance marks AIDS, and that the level of virus tracked the course of the disease. The decisive confirmation came with antiretroviral drugs: by suppressing the virus, they halt the destruction of the immune system and prevent AIDS, exactly as the causal link predicts.
Despite the evidence, a small movement denied that HIV causes AIDS, claiming the syndrome had other causes. These claims are thoroughly refuted by the science, but they did real harm. When the government of South Africa embraced AIDS denial in the early 2000s and delayed providing antiretroviral drugs, researchers later estimated that hundreds of thousands of lives were lost as a result, a tragic demonstration of the consequences of rejecting well-established medical fact.
Because the cause is understood, HIV can now be controlled. Modern antiretroviral therapy keeps the virus suppressed, allowing people with HIV to live long and healthy lives and preventing them from passing it on. What was once a fatal mystery is now a manageable chronic infection, a direct result of the hard-won and firmly established knowledge that HIV is what causes AIDS.
