What are the AIDS (Acquired Immune Deficiency Syndrome)-defining illnesses?

AIDS-Defining Illnesses

AIDS-defining illnesses are specific conditions that, when present in a person with HIV infection, establish the diagnosis of AIDS, including aggressive non-Hodgkin's lymphoma, Kaposi sarcoma, and invasive cervical cancer, along with 20 other clinical conditions defined by the CDC. 1

Definition and Classification

AIDS is diagnosed in HIV-infected individuals who meet one of the following criteria:

1. CD4+ T-lymphocyte count less than 200 cells/μL
2. CD4+ T-lymphocyte percentage of total lymphocytes less than 14%
3. Presence of one or more AIDS-defining clinical conditions 1

The 23 Clinical Conditions That Define AIDS

Cancers

• Kaposi sarcoma (caused by HHV-8/KSHV) 2
• Aggressive non-Hodgkin's lymphoma (including primary CNS lymphoma)
• Invasive cervical cancer 1

Opportunistic Infections

Fungal Infections

• Pneumocystis jiroveci (formerly carinii) pneumonia (PCP)
• Candidiasis of bronchi, trachea, lungs, or esophagus
• Extrapulmonary cryptococcosis
• Disseminated or extrapulmonary histoplasmosis
• Chronic intestinal cryptosporidiosis
• Disseminated or extrapulmonary coccidioidomycosis

Viral Infections

• Cytomegalovirus disease (other than liver, spleen, or nodes)
• Cytomegalovirus retinitis (with vision loss)
• Chronic herpes simplex ulcers (>1 month duration)
• Progressive multifocal leukoencephalopathy

Bacterial Infections

• Mycobacterium tuberculosis (pulmonary or extrapulmonary)
• Mycobacterium avium complex or Mycobacterium kansasii (disseminated or extrapulmonary)
• Other species of Mycobacterium (disseminated or extrapulmonary)
• Recurrent bacterial pneumonia (≥2 episodes in 12 months)
• Recurrent Salmonella septicemia

Protozoal Infections

• Toxoplasmosis of the brain
• Isosporiasis with diarrhea (>1 month duration)

Other Conditions

• HIV wasting syndrome
• HIV encephalopathy 1

Epidemiology and Incidence

The incidence of AIDS-defining illnesses varies by CD4 count level:

• At CD4 counts >200 cells/μL: Tuberculosis, recurrent bacterial pneumonia, and Kaposi sarcoma may occur
• At CD4 counts 50-200 cells/μL: PCP, esophageal candidiasis, and brain toxoplasmosis become more common
• At CD4 counts <50 cells/μL: Cytomegalovirus disease and Mycobacterium avium complex infection predominate 3

Impact of Antiretroviral Therapy

The introduction of highly active antiretroviral therapy (HAART) has dramatically changed the landscape of AIDS-defining illnesses:

• AIDS-defining cancers have declined significantly (Kaposi sarcoma by up to 90%) 1
• The 5-year survival rate for patients with AIDS-related Kaposi sarcoma improved from 12.1% in the pre-ART era to as high as 88% currently 2
• Non-AIDS-defining cancers now represent an increasing proportion of malignancies in people living with HIV 1

Clinical Pearls

• AIDS-defining illnesses may present atypically in HIV-infected patients, especially with advanced immunosuppression
• Multiple AIDS-defining conditions often coexist in the same patient
• Non-malignant causes of lymphadenopathy should be considered in people living with HIV 1
• The risk of developing opportunistic infections increases progressively as CD4 counts fall below 200 cells/mm³ 4

Prevention

• Early HIV diagnosis and prompt initiation of antiretroviral therapy is the most effective strategy to prevent AIDS-defining illnesses
• Prophylaxis against common opportunistic infections (particularly PCP and toxoplasmosis) is indicated at specific CD4 thresholds
• Regular monitoring of CD4 counts helps identify patients at risk for specific opportunistic infections 1