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Acquired immune deficiency syndrome


Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the HIV and AIDs article more useful, or one of our other health articles.

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What is acquired autoimmune deficiency syndrome (AIDS)?

AIDS is currently defined as an illness characterised by the development of one or more AIDS-indicating conditions. It is diagnosed in people infected with HIV when they develop certain opportunistic infections or malignancies for the first time. The following list relates to diagnosis in adults. Congenital HIV and Childhood AIDS has its own separate article.

The human immunodeficiency virus (HIV) which causes acquired immune deficiency syndrome (AIDS) has brought about a global epidemic of massive proportions. HIV is a retrovirus and also the term often applied to the infection before the deterioration of the immune system to produce a full-blown picture of AIDS.

How common is AIDS? (Epidemiology)

Worldwide1 2

  • 38.4 million people globally were living with HIV in 2021.

  • 1.5 million people became newly infected with HIV in 2021.

  • 650,000 people died from AIDS-related illnesses in 2021.

  • 28.7 million people were accessing antiretroviral therapy in 2021.

  • 84.2 million people have become infected with HIV since the start of the epidemic.

  • 40.1 million people have died from AIDS-related illnesses since the start of the epidemic.

  • AIDS-related deaths have been reduced by 68% since the peak in 2004 and by 52% since 2010.

  • In 2021, around 650,000 people died from AIDS-related illnesses worldwide, compared to 2.0 million people in 2004 and 1.4 million people in 2010.

  • AIDS-related mortality has declined by 57% among women and girls and by 47% among men and boys since 2010.

  • About 2.8 million children and adolescents are living with HIV, nearly 88% of them in sub-Saharan Africa.

  • Only 54% of infected children and adolescents were on HIV treatment as compared to 85% of pregnant women living with HIV.

  • In 2020, at least 300,000 children were newly infected with HIV, or one child every two minutes. That same year, 120,000 children and adolescents died from AIDS-related causes, or one child every five minutes.

Notable progress has been made to the extent that it could be said that the end of the AIDS epidemic is in sight. In many parts of Africa the prevalence appears to be getting stable. This means that the number of people dying from the disease is roughly equal to the number of new cases. However, whilst new HIV infections have dropped by 38% globally since 2001, 2.1 million people were newly infected in 2013. There are also 22 million people who are not accessing life-saving treatment. Access to AIDS services are still patchy due to such issues as geography, gender and socio-economic factors.3

United Kingdom4

The total number of people newly diagnosed with HIV continued to decrease in 2019 to 4,139 (1,139 females and 3,000 males). This was a 10% fall from 4,580 in 2018 and a fall of 34% from a peak of 6,312 new diagnoses reported in 2014. In 2019, a total of 98,552 people (30,388 females and 68,088 males) were seen for HIV care in the UK.

The number of deaths among people with HIV remained stable with 622 deaths (498 males and 124 females) in 2019. This represents a crude mortality rate of 631 per 100,000 population living with diagnosed HIV infection.

The decline in new HIV diagnoses in recent years is largely driven by a steep fall in diagnoses among gay and bisexual men. New HIV diagnoses among people who probably acquired HIV through heterosexual contact also declined. For injecting drug use, new HIV diagnoses remained stable and low at around 100 per year. Other transmission routes remained rare in the UK.

Of the 61 people diagnosed in 2019 who acquired HIV through vertical transmission, five aged under 15 years were born in the UK.

Late HIV diagnoses (UK surveillance definition of a late HIV diagnosis is a reported CD4 count below 350 cells/mm³ within 91 days of diagnosis):

  • People diagnosed late with HIV are estimated to have been unaware of their infection for at least three to five years, increasing the likelihood of ill health and premature death as well as onward transmission.

  • The overall number of persons diagnosed late decreased from 1,861 in 2015 to 1,279 in 2019; equivalent to 39% and 42% of all new diagnoses respectively.

  • People diagnosed late in 2019 had a mortality rate of 23/1,000 compared to 3/1,000 among those diagnosed promptly.

AIDS-defining conditions in adults

Candidiasis of bronchi, trachea or lungs.

Lymphoma, Burkitt's (or equivalent term).

Candidiasis, oesophageal.

Lymphoma, immunoblastic (or equivalent term).

Cervical carcinoma, invasive.

Lymphoma, primary, of brain.

Coccidioidomycosis, disseminated or extrapulmonary.

Mycobacterium avium complex (MAC) or M. kansasii, disseminated or extrapulmonary.

Cryptococcosis, extrapulmonary.

Mycobacterium tuberculosis, any site (pulmonary or extrapulmonary).

Cryptosporidiosis, chronic intestinal (>1 month's duration).

Mycobacterium, other species or unidentified species, disseminated or extrapulmonary.

Cytomegalovirus (CMV) disease (other than liver, spleen or nodes).

Pneumocystis jirovecii pneumonia.

CMV retinitis (with loss of vision).

Pneumonia, recurrent.

Encephalopathy, HIV-related.

Progressive multifocal leukoencephalopathy.

Herpes simplex: chronic ulcer(s) (>1 month's duration); or bronchitis, pneumonitis or oesophagitis.

Salmonella septicaemia, recurrent.

Histoplasmosis, disseminated or extrapulmonary.

Toxoplasmosis of brain.

Isosporiasis, chronic intestinal (>1 month's duration).

Wasting syndrome due to HIV.

Kaposi's sarcoma.

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AIDS symptoms

When HIV infection is diagnosed in a routine test, as for blood donation, in pregnancy, or after counselling a person with a lifestyle that puts him or her at risk, there is not usually full AIDS but just infection with HIV. When the disease is suspected, HIV counselling must precede testing. There is a characteristic presentation of the infection that is described in the separate article Primary HIV Infection. Once the diagnosis is made, the separate article Managing HIV-positive Individuals in Primary Care becomes relevant. The separate article HIV and Skin Disorders outlines the many dermatological manifestations of the disease.

Complications associated with HIV infection:5

  • Advanced HIV disease or AIDS. A person with HIV is said to have AIDS if they develop certain conditions including:

    • Opportunistic infections such as pneumocystis pneumonia, cytomegalovirus (CMV) retinitis, and cryptococcal meningitis.

    • Certain malignancies such as Kaposi's sarcoma, non-Hodgkin's lymphoma, and carcinoma of the cervix.

    • Wasting and diarrhoea, which may be a result of advanced disease or opportunistic infection.

    • Neurological: neuropathies and neurocognitive dysfunction including HIV-associated dementia may occur as a direct result of HIV infection itself or due to antiretroviral therapy (ART).

    • Mental health problems, including depression, anxiety, and alcohol and substance abuse.

    • Metabolic abnormalities, eg dyslipidaemia and insulin resistance, and cardiovascular disease.

    • Renal disease (acute or chronic).

    • Bone disease: the risk of osteoporosis is about four times higher in people living with HIV.

See also the separate article on Complications of HIV Infection.

Modes of transmission

Awareness of modes of transmission is very important, as the key to tackling this disease lies less in treating it than in preventing its spread. The relative importance of the various means of transmission varies considerably from country to country and even within countries.

The risk of acquiring HIV is:1

  • 35 times higher among people who inject drugs than adults who do not inject drugs.

  • 30 times higher for female sex workers than adult women.

  • 28 times higher among gay men and other men who have sex with men than adult men.

  • 14 times higher for transgender women than adult women.

Mother-to-child transmission

There are separate articles on Congenital HIV and Childhood AIDS and the Management of HIV in Pregnancy.

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Investigations for HIV are described in the separate article Human Immunodeficiency Virus (HIV). Further investigations for AIDS-defining conditions may be indicated. Media interventions can improve the uptake of testing but this might not be sustained.6

AIDS treatment and management

The basis of management is described in the separate article Human Immunodeficiency Virus (HIV). There may be defining conditions such as Pneumocystis jirovecii pneumonia that will need treatment. Antiretroviral therapy (ART) has improved the prognosis enormously in terms of duration of survival but premature death is to be expected.

Treatments with ART have shown considerable progress since the first antiretroviral was approved for use by the FDA in 1987. Impressive improvements in life expectancy and quality of life have ensued. There are, however, still many problems. Although ART is able to suppress the viral load in the plasma, it fails to eradicate it,and once ART is initiated, treatment needs to be continued for life. The side-effects of long-term ART include lipodystrophy, lactic acidosis, insulin resistance, and hyperlipidaemia.

Some people will wish to use herbal remedies and a Cochrane review was able to find a small number of trials, some of which seemed to have adequate methodology.7 There was no significant clinical benefit and objective criteria such as CD4 count were unaffected. Since the review there have been a few studies in the literature suggesting some benefit from herbal remedies but larger trials are needed.8 9

There may be some value in providing prophylactic treatment. A Cochrane review found some benefit in treating latent tuberculosis.10 Another review found only one trial that examined the benefit of prophylactic co-trimoxazole in children. It was from Zambia and the result was positive.11 Prophylactic co-trimoxazole was subsequently endorsed as official WHO policy for exposed infants. However, this guidance has been the subject of controversy and its benefits have been questioned by several subsequent trials.12

The value of prophylaxis against oropharyngeal candidiasis is uncertain, especially in children. There is also insufficient evidence to draw conclusions about the effectiveness of clotrimazole, nystatin, amphotericin B, itraconazole or ketoconazole with regard to oropharyngeal candidiasis prophylaxis for adults.13

Impact of acquired immune deficiency syndrome in Africa

The impact of AIDS in southern Africa has been devastating. Some communities have been very hard hit with many deaths and economic hardship related to loss of the workforce of young adults. However, significant progress has been made. Campaigns to reduce homophobia are encouraging MSM to declare their sexuality and come forward for testing and treatment. Innovative work with sex workers and injectable drug users, antiretroviral treatment of children, condom distribution programmes and mother-to-child transmission prevention services are all beginning to bear fruit. Life expectancy has increased by five years since the height of the epidemic.14


Advances in antiretroviral therapy (ART) have meant that HIV infection is now a manageable chronic disease. People living with HIV who are adherent and clinically responding to ART can expect a normal or near-normal lifespan.

The most important factor in reducing mortality and morbidity in HIV infection is early diagnosis as this allows prompt initiation of ART. Without ART, CD4 count slowly declines, eventually resulting in the development of the constitutional symptoms, opportunistic infections, and malignancies associated with advanced HIV disease (AIDS).

Prevention of AIDS15

The eradication of AIDS is based on prevention rather than cure: this means education and action. Education promotes the use of barrier contraception and advises against risk-taking behaviour - eg, multiple sexual partners or injecting drug use.

The use of mother-to-child transmission prevention strategies is another important strand of AIDS prevention programmes. In South Africa, for example, expansion of the strategy resulted in the mother-to-child transmission rate falling to 3.5%.

Further reading and references

  1. HIV Fact sheet; UNAIDS, 2022
  3. The Gap Report; UNAIDS, 2014
  4. HIV in the United Kingdom; GOV.UK
  5. HIV infection and AIDS; NICE CKS, May 2021 (UK access only)
  6. Vidanapathirana J, Abramson MJ, Forbes A, et al; Mass media interventions for promoting HIV testing.; Cochrane Database Syst Rev. 2005 Jul 20;(3):CD004775.
  7. Liu JP, Manheimer E, Yang M; Herbal medicines for treating HIV infection and AIDS.; Cochrane Database Syst Rev. 2005 Jul 20;(3):CD003937.
  8. Zhao HL, Sun CZ, Jiang WP, et al; Eight-year survival of AIDS patients treated with Chinese herbal medicine. Am J Chin Med. 2014;42(2):261-74. doi: 10.1142/S0192415X14500177.
  9. Liu J; The use of herbal medicines in early drug development for the treatment of HIV infections and AIDS. Expert Opin Investig Drugs. 2007 Sep;16(9):1355-64.
  10. Akolo C, Adetifa I, Shepperd S, et al; Treatment of latent tuberculosis infection in HIV infected persons. Cochrane Database Syst Rev. 2010 Jan 20;(1):CD000171.
  11. Grimwade K, Swingler GH; Cotrimoxazole prophylaxis for opportunistic infections in children with HIV infection.; Cochrane Database Syst Rev. 2006 Jan 25;(1):CD003508.
  12. Dow A, Kayira D, Hudgens M, et al; Effects of cotrimoxazole prophylactic treatment on adverse health outcomes among HIV-exposed, uninfected infants. Pediatr Infect Dis J. 2012 Aug;31(8):842-7. doi: 10.1097/INF.0b013e31825c124a.
  13. Pienaar ED, Young T, Holmes H; Interventions for the prevention and management of oropharyngeal candidiasis associated with HIV infection in adults and children. Cochrane Database Syst Rev. 2010 Nov 10;(11):CD003940. doi: 10.1002/14651858.CD003940.pub3.
  14. HIV & AIDS in South Africa; AVERT, 2020
  15. Understanding the HIV epidemic; Be in the Know

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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