The 1993 Centers for Disease Control and Prevention (CDC) classification system for HIV-infected adolescents and adults categorises persons on the basis of clinical conditions associated with HIV infection and CD4 cell counts^[1]. The system is based on three ranges of CD4 cell counts and three clinical conditions, and is represented by a matrix of nine mutually exclusive categories.

In practice, this means that a person's stage of HIV disease is described by a sub category consisting of a letter (the clinical category) and a number (the CD4 cell count range). Thus, someone with asymptomatic infection and a CD4 cell count of 400 cells/mm³ would be in category A2, while a person with cervical dysplasia and a CD4 cell count of 80 cells/mm³ would be in category B3.

CD4 cell count categories

The three CD4 cell count categories are:

• Category 1: 500 cells/mm³ or more.

• Category 2: 200 to 499 cells/mm³.

• Category 3: Less than 200 cells/mm³.

Categorisation should be based on the lowest accurate CD4 cell count, not necessarily the most recent one. So someone whose CD4 cell count declined steadily over a period of months until it reached 180 cells/mm³, but then rose to above 200 cells/mm³ again and remained at that level (perhaps as the result of anti-viral treatment), would be placed in category 3, not category 2.

Clinical categories

There are three clinical categories: A, B and C.

Category A

Category A consists of one or more of the conditions listed below in an adolescent or adult (13 years or older) with documented HIV infection. Conditions listed in Categories B and C must not have occurred.

• Asymptomatic HIV infection.

• Persistent generalised lymphadenopathy.

• Acute (primary) HIV infection with accompanying illness (sometimes known as seroconversion illness) or history of acute HIV infection.

Category B

Category B consist of symptomatic conditions in an HIV-infected adolescent or adult that are not included among conditions listed in Category C and that meet one of the following criteria:

• The conditions are attributed to HIV infection or are indicative of a defect in cell-mediated immunity.

• The conditions are considered by physicians to have a clinical course or to require management that is complicated by HIV infection

This category includes all such symptomatic conditions, with the exception of those placed in Category C. Examples of conditions in this category include, but are not limited to:

• Bacillary angiomatosis.

• Candidiasis (thrush) in the mouth or upper throat.

• Candidiasis of the vagina or vulva, which is persistent, frequent, or responds poorly to treatment.

• Cervical abnormalities of moderate or severe extent or cervical cancer.

• Constitutional symptoms such as fever or diarrhoea lasting longer than one month.

• Shingles involving at least two distinct episodes or more than one skin area.

• Idiopathic thrombocytopenia purpura.

• Listeriosis.

• Oral hairy leukoplakia.

• Pelvic inflammatory disease, particularly if complicated by tubo-ovarian abscess.

• Peripheral neuropathy.

For classification purposes, Category B conditions take precedence over those in Category A. For example, someone previously treated for oral or persistent vaginal candidiasis (and who has not developed a Category C disease) but who is now asymptomatic, should be classified in clinical Category B.

Category C

Category C includes the following conditions listed in the AIDS surveillance case definition. For classification purposes, once a Category C condition has occurred, the person will remain in Category C.

• Candida in the oesophagus, trachea, bronchi or lungs.

• Invasive cervical cancer.

• Coccidiodomycosis.

• Cryptococcus outside the lungs.

• Cryptosporidiosis with diarrhoea lasting for more than one month.

• Cytomegalovirus disease outside the liver, spleen or lymph nodes.

• Cytomegalovirus retinitis.

• Herpes simplex virus causing prolonged skin problems or involving the lungs or oesophagus.

• HIV-related encephalopathy.

• Chronic intestinal isosporiasis lasting longer than one month.

• Kaposi's sarcoma.

• Burkitt's, immunoblastic or primary brain lymphoma.

• Widespread Mycobacterium avium intracellulare, M. kansasii or other species.

• Pneumocystis pneumonia (PCP).

• Recurrent bacterial pneumonia.

• Progressive multifocal leukoencephalopathy.

• Recurrent Salmonella septicaemia.

• Toxoplasmosis of the brain.

• HIV wasting syndrome.