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Human immunodeficiency virus infection and acquired immune deficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV).[9][10][11] Following initial infection a person may not notice any symptoms, or may experience a brief period of influenza-like illness.[4] Typically, this is followed by a prolonged period with no symptoms.[5] If the infection progresses, it interferes more with the immune system, increasing the risk of developing common infections such as tuberculosis, as well as other opportunistic infections, and tumors which are otherwise rare in people who have normal immune function.[4] These late symptoms of infection are referred to as acquired immunodeficiency syndrome (AIDS).[5] This stage is often also associated with unintended weight loss.[5]

HIV is spread primarily by unprotected sex (including anal and oral sex), contaminated blood transfusions, hypodermic needles, and from mother to child during pregnancy, delivery, or breastfeeding.[12] Some bodily fluids, such as saliva, sweat and tears, do not transmit the virus.[13] HIV is a member of the group of viruses known as retroviruses.[14] Methods of prevention include safe sex, needle exchange programs, treating those who are infected, pre- and post-exposure prophylaxis, and male circumcision.[4] Disease in a baby can often be prevented by giving both the mother and child antiretroviral medication.[4] There is no cure or vaccine; however, antiretroviral treatment can slow the course of the disease and may lead to a near-normal life expectancy.[5][6] Treatment is recommended as soon as the diagnosis is made.[15] Without treatment, the average survival time after infection is 11 years.[7]

In 2018 about 37.9 million people were living with HIV and it resulted in 770,000 deaths.[8] An estimated 20.6 million of these live in eastern and southern Africa.[16] Between the time that AIDS was identified (in the early 1980s) and 2018, the disease caused an estimated 32 million deaths worldwide.[8] HIV/AIDS is considered a pandemic—a disease outbreak which is present over a large area and is actively spreading.[17] HIV originated in west-central Africa during the late 19th or early 20th century.[18] AIDS was first recognized by the United States Centers for Disease Control and Prevention (CDC) in 1981 and its cause—HIV infection—was identified in the early part of the decade.[19]

HIV/AIDS has had a large impact on society, both as an illness and as a source of discrimination.[20] The disease also has large economic impacts.[20] There are many misconceptions about HIV/AIDS, such as the belief that it can be transmitted by casual non-sexual contact.[21] The disease has become subject to many controversies involving religion, including the Catholic Church's position not to support condom use as prevention.[22] It has attracted international medical and political attention as well as large-scale funding since it was identified in the 1980s.[23]
Acute infection
A diagram of a human torso labelled with the most common symptoms of an acute HIV infection
Main symptoms of acute HIV infection
The initial period following the contraction of HIV is called acute HIV, primary HIV or acute retroviral syndrome.[24][25] Many individuals develop an influenza-like illness or a mononucleosis-like illness 2–4 weeks after exposure while others have no significant symptoms.[26][27] Symptoms occur in 40–90% of cases and most commonly include fever, large tender lymph nodes, throat inflammation, a rash, headache, tiredness, and/or sores of the mouth and genitals.[25][27] The rash, which occurs in 20–50% of cases, presents itself on the trunk and is maculopapular, classically.[28] Some people also develop opportunistic infections at this stage.[25] Gastrointestinal symptoms, such as vomiting or diarrhea may occur.[27] Neurological symptoms of peripheral neuropathy or Guillain–Barré syndrome also occurs.[27] The duration of the symptoms varies, but is usually one or two weeks.[27]

Owing to their nonspecific character, these symptoms are not often recognized as signs of HIV infection. Even cases that do get seen by a family doctor or a hospital are often misdiagnosed as one of the many common infectious diseases with overlapping symptoms. Thus, it is recommended that HIV be considered in people presenting with an unexplained fever who may have risk factors for the infection.[27]

Clinical latency
The initial symptoms are followed by a stage called clinical latency, asymptomatic HIV, or chronic HIV.[1] Without treatment, this second stage of the natural history of HIV infection can last from about three years[29] to over 20 years[30] (on average, about eight years).[31] While typically there are few or no symptoms at first, near the end of this stage many people experience fever, weight loss, gastrointestinal problems and muscle pains.[1] Between 50% and 70% of people also develop persistent generalized lymphadenopathy, characterized by unexplained, non-painful enlargement of more than one group of lymph nodes (other than in the groin) for over three to six months.[24]

Although most HIV-1 infected individuals have a detectable viral load and in the absence of treatment will eventually progress to AIDS, a small proportion (about 5%) retain high levels of CD4+ T cells (T helper cells) without antiretroviral therapy for more than five years.[27][32] These individuals are classified as "HIV controllers" or long-term nonprogressors (LTNP).[32] Another group consists of those who maintain a low or undetectable viral load without anti-retroviral treatment, known as "elite controllers" or "elite suppressors". They represent approximately 1 in 300 infected persons.[33]