AIDS-defining clinical conditions (also known as AIDS-defining illnesses or AIDS-defining diseases) is the list of diseases published by the Centers for Disease Control and Prevention (CDC) that are associated with AIDS and used worldwide as a guideline for AIDS diagnosis. CDC exclusively uses the term AIDS-defining clinical conditions, but the other terms remain in common use.

This list governs the US government's classification of HIV disease. This is to allow the government to handle epidemic statistics and define who receives US government assistance. However, considerable variation exists in the relative risk of death following different AIDS-defining clinical conditions.

Definition

According to the CDC definition, a patient has AIDS if they are infected with HIV and have either:

  • a CD4+ T-cell count below 200 cells/µL
  • a CD4+ T-cell percentage of total lymphocytes of less than 14%
  • or one of the defining illnesses.

A patient presenting one of the above conditions but with laboratory evidence against HIV infection is not normally considered to have AIDS, but an AIDS diagnosis may be given if the patient has had Pneumocystis jirovecii pneumonia, and has not:

Defining illnesses

2008 definition

Are the following:

  1. Candidiasis of bronchi, trachea, or lungs
  2. Candidiasis esophageal
  3. Coccidioidomycosis, disseminated or extrapulmonary
  4. Cryptococcosis, extrapulmonary
  5. Cryptosporidiosis, chronic intestinal for longer than 1 month
  6. Cytomegalovirus disease (other than liver, spleen or lymph nodes)
  7. Cytomegalovirus retinitis (with loss of vision)
  8. Encephalopathy (HIV-related)
  9. Herpes simplex: chronic ulcer(s) (for more than 1 month); or bronchitis, pneumonitis, or esophagitis
  10. Histoplasmosis, disseminated or extrapulmonary
  11. Isosporiasis, chronic intestinal (for more than 1 month)
  12. Kaposi's sarcoma
  13. Lymphoma, Burkitt's
  14. Lymphoma, immunoblastic (or equivalent term)
  15. Lymphoma, primary, of brain
  16. Mycobacterium avium complex or Mycobacterium kansasii, disseminated or extrapulmonary
  17. Mycobacterium, other species, disseminated or extrapulmonary
  18. Mycobacterium tuberculosis, any site (extrapulmonary)
  19. Pneumocystis jirovecii pneumonia (formerly Pneumocystis carinii)
  20. Progressive multifocal leukoencephalopathy
  21. Salmonella sepsis (recurrent)
  22. Toxoplasmosis of the brain
  23. Tuberculosis, disseminated
  24. Wasting syndrome due to HIV

Added in 1993

  1. Cervical cancer (invasive)
  2. Mycobacterium tuberculosis, any site (pulmonary)
  3. Pneumonia (recurrent)

Children < 13 years

Additional conditions are included for children younger than 13:[1]

History

In 1993, the CDC added pulmonary tuberculosis, recurrent pneumonia and invasive cervical cancer[2] to the list of clinical conditions in the AIDS surveillance case definition published in 1987[3] and expanded the AIDS surveillance case definition to include all HIV-infected persons with CD4+ T-lymphocyte counts of fewer than 200 cells/μL or a CD4+ percentage of less than 14. Outside the US, however, diagnosis with a listed opportunistic infection is still required.

It has been suggested that other conditions (such as penicilliosis) should be included in other countries.[4]

Common Defining Conditions

Kaposi's Sarcoma

Kaposi’s Sarcoma (KS) is an extremely common disease that arises in AIDS patients and HIV-infected individuals. The condition is characterized by large purple lesions on the skin and mouth. KS presents itself differently for everyone affected by it, and its symptoms and progression varies from person to person as well.[5] There are four different populations that are at risk for KS, all of which are caused by infection with human herpesvirus 8. In the United States, almost every case of Kaposi’s Sarcoma is indirectly caused by HIV infection. The disease is the most common among male homosexuals, presumably because human herpesvirus 8 exists with the most prevalence within this population. The remaining types of KS are known as Classic (Mediterranean), Endemic (African), and Transplant-related Kaposi’s Sarcoma. Classic KS is common in regions of the Middle East, where herpesvirus 8 is fairly prevalent. KS occurrences in these regions are mainly found in older men, which is thought to be due to the natural decline of the immune system’s strength when we age. Endemic KS presents itself the same way, but is a result of many people in certain regions of Africa being infected with human herpesvirus 8. In contrast to older men being affected in Classical infections, Endemic KS mainly affects young children, as the virus is transferred from mother to child via saliva. The final type of KS, transplant-related, is theoretically capable of manifesting in anyone. Transplant patients must take very strong immunosuppressant drugs to ensure that the body does not reject their new heart, liver, etc. However, a consequence of this is, of course, that their immune system becomes quite weak, and therefore very susceptible to infections. In a similar manner to how HIV contributes to KS, transplant patients are also at high risk for it, especially if the transplant was performed in a country where human herpesvirus 8 is endemic.[6] In recent years, however, incidences of Kaposi’s sarcoma in the United States have dwindled so much that physicians today often fail to consider it as a possibility when making diagnoses.

Toxoplasmosis

In the central nervous system, the most common AIDS-defining condition is toxoplasmosis. Caused by the parasite Toxoplasma gondii, toxoplasmosis in HIV-infected patients mainly presents as encephalitis, or inflammation of the brain, but can take other forms as well, such as inflammation of the retinas or lungs. Toxoplasma, like most parasites, carries out its infection in distinct stages of life. Strangely enough, while many tissues can harbor the parasite, it is only capable of reproducing sexually in cats.[7] Cats are carriers of the oocyst- the infective form of Toxoplasma Gondii. Once these oocysts have entered a human, they can differentiate into their next stage of life, the tachyzoite. These cells can invade our own, rapidly divide by means of binary fission, lose our cells, and travel throughout our bodies. As a result of the immune response that this invasion causes, the tachyzoites become dormant, forming cysts called bradyzoites that are commonly found in the brain and skeletal muscle. In immunocompromised patients, such as those with HIV, the infection becomes much more deadly, as without a consistent or strong enough immune response following bradyzoite formation, tachyzoites can escape from the cysts, facilitating further systemic infection and inflammation.[8] In physiologically typical individuals, the infection will generally be taken care of by the immune system, rarely causing any actual illness. In fact, it is estimated that in some areas of the world, more than sixty percent of people have been exposed to the Toxoplasma parasite in their lifetime. HIV patients, on the other hand, often suffer from intense pain, difficulty seeing and breathing, or partial blindness due to toxoplasmosis as a result of an insufficient immune response.[9]

References

  1. ↑ Schneider E, Whitmore S, Glynn KM, Dominguez K, Mitsch A, McKenna MT (December 2008). "Revised surveillance case definitions for HIV infection among adults, adolescents, and children aged <18 months and for HIV infection and AIDS among children aged 18 months to <13 years--United States, 2008". MMWR Recomm Rep. 57 (RR-10): 1–12. PMID 19052530.
  2. ↑ CDC. 1993 Revised Classification System for HIV Infection and Expanded Surveillance Case Definition for AIDS Among Adolescents and Adults
  3. ↑ Centers for Disease Control (CDC) (August 1987). "Revision of the CDC surveillance case definition for acquired immunodeficiency syndrome. Council of State and Territorial Epidemiologists; AIDS Program, Center for Infectious Diseases". MMWR Morb. Mortal. Wkly. Rep. 36 (Suppl 1): 1S–15S. PMID 3039334.
  4. ↑ Lee N (April 2008). "Penicilliosis: an AIDS-defining disease in Asia". Hong Kong Med J. 14 (2): 88–9. PMID 18382013.
  5. ↑ Pitchenik, A.E., et al. “Clinical Presentation and Natural History of AIDS-Related Kaposi's Sarcoma.” Hematology/Oncology Clinics of North America, Elsevier, 19 June 2005, https://www.sciencedirect.com/science/article/abs/pii/S0889858805703828
  6. ↑ “Kaposi Sarcoma.” Kaposi Sarcoma | Johns Hopkins Medicine, 8 Aug. 2021, https://www.hopkinsmedicine.org/health/conditions-and-diseases/sarcoma/kaposi-sarcoma.
  7. ↑ English ED, Striepen B. The cat is out of the bag: How parasites know their hosts. PLoS Biol. 2019 Sep 5;17(9):e3000446. doi: 10.1371/journal.pbio.3000446. PMID 31487278; PMCID: PMC6748446.
  8. ↑ Ayoade F, Joel Chandranesan AS. HIV-1 Associated Toxoplasmosis. [Updated 2022 Sep 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441877/
  9. ↑ Basavaraju A. Toxoplasmosis in HIV infection: An overview. Trop Parasitol. 2016 Jul-Dec;6(2):129-135. doi: 10.4103/2229-5070.190817. PMID 27722101; PMCID: PMC5048699.
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