CDC classification system

The most widely accepted classification system of HIV infection, initially published by the U.S. Centers for Disease Control and Prevention (CDC) in 1986, is based on certain conditions associated with HIV infection (see Table 1). This classification system was intended for use in conducting public health surveillance and it has been a useful epidemiological tool for many years. In 1993, the CDC classification was revised (CDC 1993b). Since then, the clinical definition of AIDS has been expanded in the USA (not in Europe) to include HIV-infected patients with a CD4+ T-cell count of less than 200 cells/^l or less than 14 % of all lymphocytes, even in the absence of the listed conditions.

Thus, the current CDC classification categorizes persons on the basis of clinical conditions and CD4+ T-lymphocyte counts. There are three clinical categories (A, B, C - see Table 1) and three CD4+ T-lymphocyte categories (1, 2, 3 - see Table 2). For example, a patient with oropharyngeal candidiasis and a CD4+ T-cell count of 250/^l would be classified as B2; someone with asymptomatic infection and a CD4+ T-cell count of 550/^l would be in category A1. Categorization of the CD4+ T-cells should be based on the lowest accurate CD4+ T-cell count ("CD4 nadir") and not on the most recent one.

For children less than 13 years of age, there is a modified and revised classification system for HIV infection (see chapter "Antiretroviral Therapy in Children"). It should also be noted that, besides the CDC classification, the World Health Organization (WHO) has also published a staging system for HIV infection. The WHO classification is an approach for use in resource-limited settings and is widely used in Africa and Asia.

Table 1. Clinical categories of the CDC classification system in HIV-infected persons

Category A

Asymptomatic HIV infection

Acute (primary) HIV infection with accompanying illness or history of acute HIV infection

Persistent generalized lymphadenopathy

Category B

Symptomatic conditions* that are not included among conditions listed in clinical Category C. Examples include, but are not limited to:

Bacillary angiomatosis

Candidiasis, oropharyngeal (thrush)

Candidiasis, vulvovaginal; persistent, frequent, or poorly responsive to therapy

Cervical dysplasia (moderate or se-vere)/cervical carcinoma in situ

Constitutional symptoms, such as fever (38.5° C) or diarrhea lasting longer than 1 month

Hairy leukoplakia, oral

Herpes zoster (shingles), involving at least two distinct episodes or more than one dermatome

Idiopathic thrombocytopenic purpura Listeriosis

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

Peripheral neuropathy

Category C - AIDS-defining illnesses**

Candidiasis of bronchi, trachea, or lungs

Candidiasis, esophageal

Cervical cancer, invasive*

Coccidioidomycosis, disseminated or extra-pulmonary

Cryptococcosis, extrapulmonary

Cryptosporidiosis, chronic intestinal (greater than 1 month's duration)

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

Cytomegalovirus retinitis (with loss of vision)

Encephalopathy, HIV-related

Herpes simplex: chronic ulcer(s) (greater than 1 month's duration); or bronchitis, pneumonitis, or esophagitis

Histoplasmosis, disseminated or extrapulmonary

Isosporiasis, chronic intestinal (greater than 1 month's duration)

Kaposi's sarcoma

Lymphoma, Burkitt's (or equivalent term)

Lymphoma, immunoblastic (or equivalent)

Lymphoma, primary, of brain

Mycobacterium avium complex or M. kansa-sii, disseminated or extrapulmonary

Mycobacterium tuberculosis, any site (pulmonary or extrapulmonary)

Mycobacterium, other species or unidentified species, disseminated or extrapulmo-nary

Pneumocystis pneumonia

Pneumonia, recurrent*

Progressive multifocal leukoencephalopathy

Salmonella septicemia, recurrent

Toxoplasmosis of brain

Wasting syndrome due to HIV

* These conditions must meet at least one of the following criteria: a) the conditions are attributed to HIV infection or are indicative of a defect in cell-mediated immunity; or b) the conditions are considered by physicians to have a clinical course or to require management that is complicated by HIV infection.

** Once a Category C condition has occurred, the person will remain in Category C.

Table 2. The CD4+ T-lymphocyte categories*

Category 1: >500 CD4+ T-cells/|jl Category 2: 200-499 CD4+ T-cells/jl Category 3: <200 CD4+ T-cells/jl *Categorization is based on the lowest accurate CD4+ T-cell count, not the most recent one

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