Aids

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For other uses, see AIDS (disambiguation).

Acquired immunodeficiency syndrome (AIDS) Classification & external resources
The Red ribbon is a symbol for solidarity with HIV-positive people and those living with AIDS.
ICD-10	B24.
ICD-9	042
DiseasesDB	5938
MedlinePlus	000594
eMedicine	emerg/253
MeSH	D000163

List of abbreviations used in this article AIDS: Acquired immune deficiency syndrome HIV: Human immunodeficiency virus CD4+: T helper cells CCR5: Chemokine (C-C motif) receptor 5 CDC: Centers for Disease Control and Prevention WHO: World Health Organization PCP: Pneumocystis pneumonia TB: Tuberculosis MTCT: Mother-to-child transmission HAART: Highly active antiretroviral therapy STI/STD: Sexually transmitted infection/disease

Acquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS or Aids) is a collection of symptoms and infections resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV) in humans,The Relationship Between the Human Immunodeficiency Virus and the Acquired Immunodeficiency Syndrome. NIAID. Retrieved on 2008-03-10. and similar viruses in other species (SIV, FIV, etc.). The late stage of the condition leaves individuals susceptible to opportunistic infections and tumors. Although treatments for AIDS and HIV exist to decelerate the virus\'s progression, there is currently no known cure. HIV is transmitted through direct contact of a mucous membrane or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid, and breast milk.Divisions of HIV/AIDS Prevention (2003). HIV and Its Transmission. Centers for Disease Control & Prevention. Retrieved on 2006-05-23.San Francisco AIDS Foundation (2006-04-14). How HIV is spread. Retrieved on 2006-05-23. This transmission can come in the form of anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, or breastfeeding, or other exposure to one of the above bodily fluids.

Most researchers believe that HIV originated in sub-Saharan Africa during the twentieth century.

Gao F, Bailes E, Robertson DL, et al (1999). "Origin of HIV-1 in the Chimpanzee Pan troglodytes troglodytes". Nature 397 (6718): 436–441. doi:10.1038/17130. PMID 9989410.  It is now a pandemic. In 2007, an estimated 33.2 million people lived with the disease worldwide, and it claimed the lives of an estimated 2.1 million people, including 330,000 children. Over three-fourths of these deaths occurred in sub-Saharan Africa, retarding economic growth and destroying human capital. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but routine access to antiretroviral medication is not available in all countries.Palella FJ Jr, Delaney KM, Moorman AC, et al (1998). "Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection. HIV Outpatient Study Investigators". N. Engl. J. Med 338 (13): 853–860. PMID 9516219. 

HIV/AIDS stigma is more severe than that associated with other life-threatening conditions and extends beyond the disease itself to providers and even volunteers involved with the care of people living with HIV.

Contents 1 Symptoms 1.1 Pulmonary infections 1.2 Gastrointestinal infections 1.3 Neurological diseases 1.4 Tumors and malignancies 1.5 Other opportunistic infections 2 Cause 2.1 Alternative hypotheses 2.2 Misconceptions 3 Diagnosis 3.1 WHO disease staging system for HIV infection and disease 3.2 CDC classification system for HIV infection 3.3 HIV test 4 Transmission and prevention 4.1 Sexual contact 4.2 Exposure to infected body fluids 4.3 Mother-to-child transmission (MTCT) 5 Treatment 6 Epidemiology 7 Prognosis 7.1 Economic impact 7.2 Stigma 8 History 9 Notes and references 10 External links

Symptoms

A generalized graph of the relationship between HIV copies (viral load) and CD4 counts over the average course of untreated HIV infection; any particular individual\'s disease course may vary considerably.                      CD4⁺ T Lymphocyte count (cells/mm³)                      HIV RNA copies per mL of plasma

The symptoms of AIDS are primarily the result of conditions that do not normally develop in individuals with healthy immune systems. Most of these conditions are infections caused by bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune system that HIV damages. Opportunistic infections are common in people with AIDS.Holmes CB, Losina E, Walensky RP, Yazdanpanah Y, Freedberg KA (2003). "Review of human immunodeficiency virus type 1-related opportunistic infections in sub-Saharan Africa". Clin. Infect. Dis. 36 (5): 656–662. PMID 12594648.  HIV affects nearly every organ system. People with AIDS also have an increased risk of developing various cancers such as Kaposi\'s sarcoma, cervical cancer and cancers of the immune system known as lymphomas.

Additionally, people with AIDS often have systemic symptoms of infection like fevers, sweats (particularly at night), swollen glands, chills, weakness, and weight loss.Guss DA (1994). "The acquired immune deficiency syndrome: an overview for the emergency physician, Part 1". J. Emerg. Med. 12 (3): 375–384. PMID 8040596. Guss DA (1994). "The acquired immune deficiency syndrome: an overview for the emergency physician, Part 2". J. Emerg. Med. 12 (4): 491–497. PMID 7963396.  After the diagnosis of AIDS is made, the current average survival time with antiretroviral therapy (as of 2005) is estimated to be more than 5 years,Schneider MF, Gange SJ, Williams CM, Anastos K, Greenblatt RM, Kingsley L, Detels R, Munoz A (2005). "Patterns of the hazard of death after AIDS through the evolution of antiretroviral therapy: 1984–2004". AIDS 19 (17): 2009–2018. PMID 16260908.  but because new treatments continue to be developed and because HIV continues to evolve resistance to treatments, estimates of survival time are likely to continue to change. Without antiretroviral therapy, death normally occurs within a year. Most patients die from opportunistic infections or malignancies associated with the progressive failure of the immune system.Lawn SD (2004). "AIDS in Africa: the impact of coinfections on the pathogenesis of HIV-1 infection". J. Infect. Dis. 48 (1): 1–12. PMID 14667787. 

The rate of clinical disease progression varies widely between individuals and has been shown to be affected by many factors such as host susceptibility and immune function health care and co-infections, as well as factors relating to the viral strain.Campbell GR, Watkins JD, Esquieu D, Pasquier E, Loret EP, Spector SA (2005). "The C terminus of HIV-1 Tat modulates the extent of CD178-mediated apoptosis of T cells". J. Biol. Chem. 280 (46): 38376–39382. PMID 16155003. Senkaali D, Muwonge R, Morgan D, Yirrell D, Whitworth J, Kaleebu P (2005). "The relationship between HIV type 1 disease progression and V3 serotype in a rural Ugandan cohort". AIDS Res. Hum. Retroviruses. 20 (9): 932–937. PMID 15585080.  The specific opportunistic infections that AIDS patients develop depend in part on the prevalence of these infections in the geographic area in which the patient lives.

Pulmonary infections

X-ray of Pneumocystis jirovecii caused pneumonia. There is increased white (opacity) in the lower lungs on both sides, characteristic of Pneumocystis pneumonia

Pneumocystis pneumonia (originally known as Pneumocystis carinii pneumonia, and still abbreviated as PCP, which now stands for Pneumocystis pneumonia) is relatively rare in healthy, immunocompetent people, but common among HIV-infected individuals. It is caused by Pneumocystis jirovecii. Before the advent of effective diagnosis, treatment and routine prophylaxis in Western countries, it was a common immediate cause of death. In developing countries, it is still one of the first indications of AIDS in untested individuals, although it does not generally occur unless the CD4 count is less than 200 per µL.Feldman C (2005). "Pneumonia associated with HIV infection". Curr. Opin. Infect. Dis. 18 (2): 165–170. PMID 15735422. 

Tuberculosis (TB) is unique among infections associated with HIV because it is transmissible to immunocompetent people via the respiratory route, is easily treatable once identified, may occur in early-stage HIV disease, and is preventable with drug therapy. However, multidrug resistance is a potentially serious problem. Even though its incidence has declined because of the use of directly observed therapy and other improved practices in Western countries, this is not the case in developing countries where HIV is most prevalent. In early-stage HIV infection (CD4 count >300 cells per µL), TB typically presents as a pulmonary disease. In advanced HIV infection, TB often presents atypically with extrapulmonary (systemic) disease a common feature. Symptoms are usually constitutional and are not localized to one particular site, often affecting bone marrow, bone, urinary and gastrointestinal tracts, liver, regional lymph nodes, and the central nervous system.Decker CF, Lazarus A (2000). "Tuberculosis and HIV infection. How to safely treat both disorders concurrently". Postgrad Med. 108 (2): 57–60, 65–68. PMID 10951746. 

Gastrointestinal infections

Esophagitis is an inflammation of the lining of the lower end of the esophagus (gullet or swallowing tube leading to the stomach). In HIV infected individuals, this is normally due to fungal (candidiasis) or viral (herpes simplex-1 or cytomegalovirus) infections. In rare cases, it could be due to mycobacteria.Zaidi SA, Cervia JS (2002). "Diagnosis and management of infectious esophagitis associated with human immunodeficiency virus infection". J. Int. Assoc. Physicians AIDS Care (Chic Ill) 1 (2): 53–62. PMID 12942677. 

Unexplained chronic diarrhea in HIV infection is due to many possible causes, including common bacterial (Salmonella, Shigella, Listeria, Campylobacter, or Escherichia coli) and parasitic infections; and uncommon opportunistic infections such as cryptosporidiosis, microsporidiosis, Mycobacterium avium complex (MAC) and cytomegalovirus (CMV) colitis. In some cases, diarrhea may be a side effect of several drugs used to treat HIV, or it may simply accompany HIV infection, particularly during primary HIV infection. It may also be a side effect of antibiotics used to treat bacterial causes of diarrhea (common for Clostridium difficile). In the later stages of HIV infection, diarrhea is thought to be a reflection of changes in the way the intestinal tract absorbs nutrients, and may be an important component of HIV-related wasting.Guerrant RL, Hughes JM, Lima NL, Crane J (1990). "Diarrhea in developed and developing countries: magnitude, special settings, and etiologies". Rev. Infect. Dis. 12 (Suppl 1): S41–S50. PMID 2406855. 

Neurological diseases

Toxoplasmosis is a disease caused by the single-celled parasite called Toxoplasma gondii; it usually infects the brain causing toxoplasma encephalitis but it can infect and cause disease in the eyes and lungs.Luft BJ, Chua A (2000). "Central Nervous System Toxoplasmosis in HIV Pathogenesis, Diagnosis, and Therapy". Curr. Infect. Dis. Rep. 2 (4): 358–362. PMID 11095878. 

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease, in which the gradual destruction of the myelin sheath covering the axons of nerve cells impairs the transmission of nerve impulses. It is caused by a virus called JC virus which occurs in 70% of the population in latent form, causing disease only when the immune system has been severely weakened, as is the case for AIDS patients. It progresses rapidly, usually causing death within months of diagnosis.Sadler M, Nelson MR (1997). "Progressive multifocal leukoencephalopathy in HIV". Int. J. STD AIDS 8 (6): 351–357. PMID 9179644.  AIDS dementia complex (ADC) is a metabolic encephalopathy induced by HIV infection and fueled by immune activation of HIV infected brain macrophages and microglia which secrete neurotoxins of both host and viral origin.Gray F, Adle-Biassette H, Chrétien F, Lorin de la Grandmaison G, Force G, Keohane C (2001). "Neuropathology and neurodegeneration in human immunodeficiency virus infection. Pathogenesis of HIV-induced lesions of the brain, correlations with HIV-associated disorders and modifications according to treatments". Clin. Neuropathol. 20 (4): 146–155. PMID 11495003.  Specific neurological impairments are manifested by cognitive, behavioral, and motor abnormalities that occur after years of HIV infection and is associated with low CD4⁺ T cell levels and high plasma viral loads. Prevalence is 10–20% in Western countriesGrant I, Sacktor H, McArthur J (2005). "HIV neurocognitive disorders", in H. E. Gendelman, I. Grant, I. Everall, S. A. Lipton, and S. Swindells. (ed.): The Neurology of AIDS (PDF), 2nd, London, UK: Oxford University Press, 357–373. ISBN 0-19-852610-5.  but only 1–2% of HIV infections in India.Satishchandra P, Nalini A, Gourie-Devi M, et al (2000). "Profile of neurologic disorders associated with HIV/AIDS from Bangalore, South India (1989–1996)". Indian J. Med. Res. 11: 14–23. PMID 10793489. Wadia RS, Pujari SN, Kothari S, Udhar M, Kulkarni S, Bhagat S, Nanivadekar A (2001). "Neurological manifestations of HIV disease". J. Assoc. Physicians India 49: 343–348. PMID 11291974.  This difference is possibly due to the HIV subtype in India.

Cryptococcal meningitis is an infection of the meninx (the membrane covering the brain and spinal cord) by the fungus Cryptococcus neoformans. It can cause fevers, headache, fatigue, nausea, and vomiting. Patients may also develop seizures and confusion; left untreated, it can be lethal.

Tumors and malignancies

Kaposi\'s sarcoma

Patients with HIV infection have substantially increased incidence of several malignant cancers. This is primarily due to co-infection with an oncogenic DNA virus, especially Epstein-Barr virus (EBV), Kaposi\'s sarcoma-associated herpesvirus (KSHV), and human papillomavirus (HPV).Boshoff C, Weiss R (2002). "AIDS-related malignancies". Nat. Rev. Cancer 2 (5): 373–382. PMID 12044013. Yarchoan R, Tosatom G, Littlem RF (2005). "Therapy insight: AIDS-related malignancies — the influence of antiviral therapy on pathogenesis and management". Nat. Clin. Pract. Oncol. 2 (8): 406–415. PMID 16130937. 

Kaposi\'s sarcoma (KS) is the most common tumor in HIV-infected patients. The appearance of this tumor in young homosexual men in 1981 was one of the first signals of the AIDS epidemic. Caused by a gammaherpes virus called Kaposi\'s sarcoma-associated herpes virus (KSHV), it often appears as purplish nodules on the skin, but can affect other organs, especially the mouth, gastrointestinal tract, and lungs.

High-grade B cell lymphomas such as Burkitt\'s lymphoma, Burkitt\'s-like lymphoma, diffuse large B-cell lymphoma (DLBCL), and primary central nervous system lymphoma present more often in HIV-infected patients. These particular cancers often foreshadow a poor prognosis. In some cases these lymphomas are AIDS-defining. Epstein-Barr virus (EBV) or KSHV cause many of these lymphomas.

Cervical cancer in HIV-infected women is considered AIDS-defining. It is caused by human papillomavirus (HPV).Palefsky J (2007). "Human papillomavirus infection in HIV-infected persons". Top HIV Med 15 (4): 130–3. PMID 17720998. 

In addition to the AIDS-defining tumors listed above, HIV-infected patients are at increased risk of certain other tumors, such as Hodgkin\'s disease and anal and rectal carcinomas. However, the incidence of many common tumors, such as breast cancer or colon cancer, does not increase in HIV-infected patients. In areas where HAART is extensively used to treat AIDS, the incidence of many AIDS-related malignancies has decreased, but at the same time malignant cancers overall have become the most common cause of death of HIV-infected patients.Bonnet F, Lewden C, May T, et al (2004). "Malignancy-related causes of death in human immunodeficiency virus-infected patients in the era of highly active antiretroviral therapy". Cancer 101 (2): 317–324. PMID 15241829. 

Other opportunistic infections

AIDS patients often develop opportunistic infections that present with non-specific symptoms, especially low-grade fevers and weight loss. These include infection with Mycobacterium avium-intracellulare and cytomegalovirus (CMV). CMV can cause colitis, as described above, and CMV retinitis can cause blindness. Penicilliosis due to Penicillium marneffei is now the third most common opportunistic infection (after extrapulmonary tuberculosis and cryptococcosis) in HIV-positive individuals within the endemic area of Southeast Asia.Skoulidis F, Morgan MS, MacLeod KM (2004). "Penicillium marneffei: a pathogen on our doorstep?". J. R. Soc. Med. 97 (2): 394–396. PMID 15286196. 

Cause

For more details on this topic, see HIV.

Scanning electron micrograph of HIV-1 budding from cultured lymphocyte.

AIDS is the most severe acceleration of infection with HIV. HIV is a retrovirus that primarily infects vital organs of the human immune system such as CD4⁺ T cells (a subset of T cells), macrophages and dendritic cells. It directly and indirectly destroys CD4⁺ T cells.Alimonti JB, Ball TB, Fowke KR (2003). "Mechanisms of CD4+ T lymphocyte cell death in human immunodeficiency virus infection and AIDS.". J. Gen. Virol. 84 (7): 1649–1661. doi:10.1099/vir.0.19110-0. PMID 12810858.  CD4⁺ T cells are required for the proper functioning of the immune system. When HIV kills CD4⁺ T cells so that there are fewer than 200 CD4⁺ T cells per microliter (µL) of blood, cellular immunity is lost. In some countries, such as the United States, this leads to a diagnosis of AIDS. In other jurisdictions, such as in Canada, AIDS is only diagnosed when a person infected with HIV is diagnosed with one or more of several AIDS-related opportunistic infections or cancers.Public Health Agency of Canada (Note that this source is mistaken in its assertion that the U.S. definition of AIDS requires a CD4 count of <200.)McGovern, Theresa and Smith, Raymond (1998). AIDS, Case Definition of. TheBody.com. Retrieved on 2008-03-10.AEGIS^{[dead link]} Acute HIV infection progresses over time to clinical latent HIV infection and then to early symptomatic HIV infection and later to AIDS, which is identified either on the basis of the amount of CD4⁺ T cells in the blood, and/or the presence of certain infections, as noted above.

In the absence of antiretroviral therapy, the median time of progression from HIV infection to AIDS is nine to ten years, and the median survival time after developing AIDS is only 9.2 months.Morgan D, Mahe C, Mayanja B, Okongo JM, Lubega R, Whitworth JA (2002). "HIV-1 infection in rural Africa: is there a difference in median time to AIDS and survival compared with that in industrialized countries?". AIDS 16 (4): 597–632. PMID 11873003.  However, the rate of clinical disease progression varies widely between individuals, from two weeks up to 20 years. Many factors affect the rate of progression. These include factors that influence the body\'s ability to defend against HIV such as the infected person\'s general immune function.Clerici M, Balotta C, Meroni L, et al (1996). "Type 1 cytokine production and low prevalence of viral isolation correlate with long-term non progression in HIV infection". AIDS Res. Hum. Retroviruses. 12 (11): 1053–1061. PMID 8827221. Morgan D, Mahe C, Mayanja B, Whitworth JA (2002). "Progression to symptomatic disease in people infected with HIV-1 in rural Uganda: prospective cohort study". BMJ 324 (7331): 193–196. doi:10.1136/bmj.324.7331.193. PMID 11809639.  Older people have weaker immune systems, and therefore have a greater risk of rapid disease progression than younger people. Poor access to health care and the existence of coexisting infections such as tuberculosis also may predispose people to faster disease progression.Gendelman HE, Phelps W, Feigenbaum L, et al (1986). "Transactivation of the human immunodeficiency virus long terminal repeat sequences by DNA viruses". Proc. Natl. Acad. Sci. U. S. A. 83 (24): 9759–9763. PMID 2432602. Bentwich Z, Kalinkovich, A, Weisman Z (1995). "Immune activation is a dominant factor in the pathogenesis of African AIDS.". Immunol. Today 16 (4): 187–191. PMID 7734046.  The infected person\'s genetic inheritance plays an important role and some people are resistant to certain strains of HIV. An example of this is people with the homozygous CCR5-Δ32 variation are resistant to infection with certain strains of HIV.Tang J, Kaslow RA (2003). "The impact of host genetics on HIV infection and disease progression in the era of highly active antiretroviral therapy". AIDS 17 (Suppl 4): S51–S60. PMID 15080180.  HIV is genetically variable and exists as different strains, which cause different rates of clinical disease progression.Quiñones-Mateu ME, Mas A, Lain de Lera T, Soriano V, Alcami J, Lederman MM, Domingo E (1998). "LTR and tat variability of HIV-1 isolates from patients with divergent rates of disease progression". Virus Research 57 (1): 11–20. PMID 9833881. Campbell GR, Pasquier E, Watkins J, et al (2004). "The glutamine-rich region of the HIV-1 Tat protein is involved in T-cell apoptosis". J. Biol. Chem. 279 (46): 48197–48204. doi:10.1074/jbc.M406195200. PMID 15331610. Kaleebu P, French N, Mahe C, et al (2002). "Effect of human immunodeficiency virus (HIV) type 1 envelope subtypes A and D on disease progression in a large cohort of HIV-1-positive persons in Uganda". J. Infect. Dis. 185 (9): 1244–1250. PMID 12001041.  The use of highly active antiretroviral therapy prolongs both the median time of progression to AIDS and the median survival time.

Alternative hypotheses

Main article: AIDS reappraisal

A small minority of scientists and activists question the connection between HIV and AIDS,Duesberg PH (1988). "HIV is not the cause of AIDS". Science 241 (4865): 514, 517. doi:10.1126/science.3399880. PMID 3399880.  the existence of HIV itself,Papadopulos-Eleopulos E, Turner VF, Papadimitriou J, et al (2004). "A critique of the Montagnier evidence for the HIV/AIDS hypothesis". Med Hypotheses 63 (4): 597–601. doi:10.1016/j.mehy.2004.03.025. PMID 15325002.  or the validity of current testing and treatment methods. Though these claims have been examined and widely rejected by the scientific community,For evidence of the scientific consensus that HIV is the cause of AIDS, see (for example):

• (2000) "The Durban Declaration". Nature 406 (6791): 15–6. doi:10.1038/35017662. PMID 10894520.  – full text here.
• Cohen J (1994). "The Controversy over HIV and AIDS" (PDF). Science 266 (5191): 1642–1649. 
• Focus on the HIV-AIDS Connection: Resource links. National Institute of Allergy and Infectious Diseases. Retrieved on 2006-09-07.
• O\'Brien SJ, Goedert JJ (1996). "HIV causes AIDS: Koch\'s postulates fulfilled". Curr. Opin. Immunol. 8 (5): 613-8. PMID 8902385. 
• Galéa P, Chermann JC (1998). "HIV as the cause of AIDS and associated diseases". Genetica 104 (2): 133–42. PMID 10220906.  they continue to be promulgated through the InternetSmith TC, Novella SP (2007). "HIV denial in the Internet era". PLoS Med. 4 (8): e256. doi:10.1371/journal.pmed.0040256. PMID 17713982.  and have had a significant political impact, particularly in South Africa, where governmental acceptance of AIDS denialism has been blamed for an ineffective response to that country\'s AIDS epidemic.Watson J (2006). "Scientists, activists sue South Africa\'s AIDS \'denialists\'". Nat. Med. 12 (1): 6. doi:10.1038/nm0106-6a. PMID 16397537. Baleta A (2003). "S Africa\'s AIDS activists accuse government of murder". Lancet 361 (9363): 1105. doi:10.1016/S0140-6736(03)12909-1. PMID 12672319. Cohen J (2000). "South Africa\'s new enemy". Science 288 (5474): 2168-70. doi:10.1126/science.288.5474.2168. PMID 10896606. 

Misconceptions

Main article: HIV and AIDS misconceptions

A number of misconceptions have arisen surrounding HIV/AIDS. Three of the most common are that AIDS can spread through casual contact, that sexual intercourse with a virgin will cure AIDS, and that HIV can infect only homosexual men and drug users. Other misconceptions are that any act of anal intercourse between gay men can lead to AIDS infection, and that open discussion of homosexuality and HIV in schools will lead to increased rates of homosexuality and AIDS.Blechner MJ (1997). Hope and mortality: psychodynamic approaches to AIDS and HIV. Hillsdale, NJ: Analytic Press. ISBN 0-88163-223-6. 

Diagnosis

Since June 5, 1981, many definitions have been developed for epidemiological surveillance such as the Bangui definition and the 1994 expanded World Health Organization AIDS case definition. However, clinical staging of patients was not an intended use for these systems as they are neither sensitive, nor specific. In developing countries, the World Health Organization staging system for HIV infection and disease, using clinical and laboratory data, is used and in developed countries, the Centers for Disease Control (CDC) Classification System is used.

WHO disease staging system for HIV infection and disease

Main article: WHO Disease Staging System for HIV Infection and Disease

In 1990, the World Health Organization (WHO) grouped these infections and conditions together by introducing a staging system for patients infected with HIV-1.World Health Organization (1990). "Interim proposal for a WHO staging system for HIV infection and disease". WHO Wkly Epidem. Rec. 65 (29): 221–228. PMID 1974812.  An update took place in September 2005. Most of these conditions are opportunistic infections that are easily treatable in healthy people.

• Stage I: HIV infection is asymptomatic and not categorized as AIDS
• Stage II: includes minor mucocutaneous manifestations and recurrent upper respiratory tract infections
• Stage III: includes unexplained chronic diarrhea for longer than a month, severe bacterial infections and pulmonary tuberculosis
• Stage IV: includes toxoplasmosis of the brain, candidiasis of the esophagus, trachea, bronchi or lungs and Kaposi\'s sarcoma; these diseases are indicators of AIDS.

CDC classification system for HIV infection

Main article: CDC Classification System for HIV Infection

In the beginning, the Centers for Disease Control and Prevention (CDC) did not have an official name for the disease, often referring to it by way of the diseases that were associated with it, for example, lymphadenopathy, the disease after which the discoverers of HIV originally named the virus.Centers for Disease Control (CDC) (1982). "Persistent, generalized lymphadenopathy among homosexual males.". MMWR Morb Mortal Wkly Rep. 31 (19): 249–251. PMID 6808340. Barré-Sinoussi F, Chermann JC, Rey F, et al (1983). "Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS)". Science 220 (4599): 868–871. doi:10.1126/science.6189183. PMID 6189183.  They also used Kaposi\'s Sarcoma and Opportunistic Infections, the name by which a task force had been set up in 1981.Centers for Disease Control (CDC) (1982). "Opportunistic infections and Kaposi\'s sarcoma among Haitians in the United States". MMWR Morb Mortal Wkly Rep. 31 (26): 353–354; 360–361. PMID 6811853.  In the general press, the term GRID, which stood for Gay-related immune deficiency, had been coined.Altman LK. "New homosexual disorder worries officials", The New York Times, 1982-05-11.  However, after determining that AIDS was not isolated to the homosexual community, the term GRID became misleading and AIDS was introduced at a meeting in July 1982.Kher U. "A Name for the Plague", Time, 1982-07-27. Retrieved on 2008-03-10.  By September 1982 the CDC started using the name AIDS, and properly defined the illness.Centers for Disease Control (CDC) (1982). "Update on acquired immune deficiency syndrome (AIDS)—United States.". MMWR Morb Mortal Wkly Rep. 31 (37): 507–508; 513–514. PMID 6815471.  In 1993, the CDC expanded their definition of AIDS to include all HIV positive people with a CD4⁺ T cell count below 200 per µL of blood or 14% of all lymphocytes.1993 Revised Classification System for HIV Infection and Expanded Surveillance Case Definition for AIDS Among Adolescents and Adults. CDC (1992). Retrieved on 2006-02-09. The majority of new AIDS cases in developed countries use either this definition or the pre-1993 CDC definition. The AIDS diagnosis still stands even if, after treatment, the CD4⁺ T cell count rises to above 200 per µL of blood or other AIDS-defining illnesses are cured.

HIV test

Main article: HIV test

Many people are unaware that they are infected with HIV.

Kumaranayake L, Watts C (2001). "Resource allocation and priority setting of HIV/AIDS interventions: addressing the generalized epidemic in sub-Saharan Africa". J. Int. Dev. 13 (4): 451–466. doi:10.1002/jid.798.  Less than 1% of the sexually active urban population in Africa has been tested, and this proportion is even lower in rural populations. Furthermore, only 0.5% of pregnant women attending urban health facilities are counseled, tested or receive their test results. Again, this proportion is even lower in rural health facilities.

Kumaranayake L, Watts C (2001). "Resource allocation and priority setting of HIV/AIDS interventions: addressing the generalized epidemic in sub-Saharan Africa". J. Int. Dev. 13 (4): 451–466. doi:10.1002/jid.798.  Therefore, donor blood and blood products used in medicine and medical research are screened for HIV. Typical HIV tests, including the HIV enzyme immunoassay and the Western blot assay, detect HIV antibodies in serum, plasma, oral fluid, dried blood spot or urine of patients. However, the window period (the time between initial infection and the development of detectable antibodies against the infection) can vary. This is why it can take 3–6 months to seroconvert and test positive. Commercially available tests to detect other HIV antigens, HIV-RNA, and HIV-DNA in order to detect HIV infection before the development of detectable antibodies are available. For the diagnosis of HIV infection these assays are not specifically approved, but are nonetheless routinely used in developed countries.

Transmission and prevention

Estimated per act risk for acquisition
of HIV by exposure routeSmith DK, Grohskopf LA, Black RJ, et al (2005). "Antiretroviral Postexposure Prophylaxis After Sexual, Injection-Drug Use, or Other Nonoccupational Exposure to HIV in the United States". MMWR 54 (RR02): 1–20. 

Exposure Route	Estimated infections per 10,000 exposures to an infected source
Blood Transfusion	9,000Donegan E, Stuart M, Niland JC, et al (1990). "Infection with human immunodeficiency virus type 1 (HIV-1) among recipients of antibody-positive blood donations". Ann. Intern. Med. 113 (10): 733–739. PMID 2240875.
Childbirth	2,500Coovadia H (2004). "Antiretroviral agents—how best to protect infants from HIV and save their mothers from AIDS". N. Engl. J. Med. 351 (3): 289–292. PMID 15247337.
Needle-sharing injection drug use	67Kaplan EH, Heimer R (1995). "HIV incidence among New Haven needle exchange participants: updated estimates from syringe tracking and testing data". J. Acquir. Immune Defic. Syndr. Hum. Retrovirol. 10 (2): 175–176. PMID 7552482.
Percutaneous needle stick	30Bell DM (1997). "Occupational risk of human immunodeficiency virus infection in healthcare workers: an overview.". Am. J. Med. 102 (5B): 9–15. PMID 9845490.
Receptive anal intercourse*	50European Study Group on Heterosexual Transmission of HIV (1992). "Comparison of female to male and male to female transmission of HIV in 563 stable couples". BMJ. 304 (6830): 809–813. PMID 1392708. Varghese B, Maher JE, Peterman TA, Branson BM,Steketee RW (2002). "Reducing the risk of sexual HIV transmission: quantifying the per-act risk for HIV on the basis of choice of partner, sex act, and condom use". Sex. Transm. Dis. 29 (1): 38–43. PMID 11773877.