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Classification System for HIV Infection and Surveillance Case Definition for AIDS in Adolescents and Adults in Hong Kong


AIDS represents the late stage of HIV infection with profound immunosuppression and the occurrence of unusual opportunistic infections and tumours. The first AIDS Surveillance Definition was developed by the US Centers for Disease Control and Prevention (CDC) before HIV was discovered. The definition emphasized on clinical diseases related to a then unknown agent. With advances in knowledge of HIV, the 1987 Surveillance Definition required evidence of HIV infection (or lack of evidence of other causes of immune suppression) and a diagnosis of at least one of the specified diseases that was moderately to highly indicative of cellular immune dysfunction. Twenty-three diseases were listed and labelled as AIDS defining conditions.

In 1993, CDC revised the classification system for HIV infection and AIDS Surveillance Definition for Adolescents and Adults. Both clinical parameters and CD4 counts were used in the new classification system. As for surveillance definition a CD4 level of less than 200/ul had become a criterion for AIDS, and that three other diseases were included as AIDS-defining conditions - recurrent pneumonia, any site of mycobacterium tuberculosis and invasive cervical cancer.

In Hong Kong, the Scientific Committee of the Advisory Council on AIDS recommended adoption of a slightly modified (from CDC 1993) classification system for HIV infection and a clinical approach to AIDS surveillance definition. The local classification system and AIDS surveillance system should however be kept under periodic review and revision made when appropriate, taken into consideration the international and local development in this area, as well as changes in local disease pattern.

Classification for HIV infection in Adolescents & Adults in Hong Kong

CD4+ T-cell categories

Clinical categories

Asymptomatic, acute (primary) HIV or PGL
Symptomatic, not (A) or (C) conditions
(C) #
AIDS-indicator conditions

(1) 500/uL
(2) 200-499/uL


I. CD4+ T-Lymphocyte Categories

The lowest accurate, but not necessarily the most recent, CD4 count should be used for classification.

II. Clinical Categories

Category A

  • Asymptomatic HIV infection
  •  Persistent generalized lymphadenopathy
  • Acute (primary) HIV infection

Category B

Conditions attributed to HIV infection /indicative of defect in cell-mediated immunity or whose clinical course or management is complicated by HIV infection. It includes the conditions listed below which are however not exhaustive :

  • Bacillary angiomatosis
  • Oropharyngeal candidiasis
  • Vulvovaginal candidiasis (persistent, recurrent or refractory)
  • Cervical dysplasia (moderate or severe)/cervical carcinoma in situ
  • Constitutional symptoms
  • Oral hairy leukoplakia
  • Herpes zoster (>1 episode or >1 dermatome)
  • Idiopathic thrombocytopenic purpura
  • Listeriosis
  • Pelvic inflammatory disease
  • Peripheral neuropathy

Category C

  • Candidiasis of bronchi, trachea, or lungs
  • Candidiasis, esophageal
  • Cervical cancer, invasive
  • Coccidioidomycosis, disseminated or extrapulmonary
  • Cryptococcosis, extrapulmonary
  • Cryptosporidiosis, chronic intestinal
  • Cytomegalovirus retinitis
  • Cytomegalovirus disease (other than liver, spleen or nodes)
  • Encephalopathy, HIV-related
  • Herpes simplex, chronic ulcer, bronchitis, pneumonitis or esophagitis
  • Histoplasmosis, disseminated or extrapulmonary
  • Isosporiasis, chronic intestinal
  • Kaposi's sarcoma
  • Lymphoma, Burkitt's
  • Lymphoma, immunoblastic
  • Lymphoma, primary of brain
  • Mycobacterium avium complex or kansasii, disseminated or extrapulmonary
  • Mycobacterium tuberculosis, extrapulmonary or pulmonary/cervical lymph node (only if CD4 #
  • Mycobacterium, other species, disseminated or extrapulmonary
  • Penicilliosis, disseminated #
  • Pneumocystis carinii pneumonia
  • Pneumonia, recurrent
  • Progressive multifocal leukoencephalopathy
  • Salmonella septicemia, recurrent
  • Toxoplasmosis of brain
  • Wasting syndrome due to HIV

#Modification of the CDC 1993 Classification system :- (1) Penicilliosis has been added and (2) pulmonary or cervical lymph node tuberculosis included only if CD4

AIDS Surveillance Definition for Adolescents & Adults in Hong Kong

For surveillance purpose, AIDS is defined only if a patient develops one or more of the conditions listed under category C in the classification system described in section 2.

Reporting of HIV/AIDS

HIV/AIDS is not a statutory notifiable disease in Hong Kong but a voluntary reporting system has been adopted since 1985. Medical and dental practitioners are urged to report HIV infection and AIDS cases to the Department of Health using the form DH 2293. In addition, in order to enhance the detection and understanding of any new or changing diseases arising from HIV infection, practitioners shall also report unusual complications or presentations (which are not known AIDS defining illnesses) occurring in HIV-infected patients.