HIV infection

Key Information

Appropriate Tests


HIV serology, HIV Ab and Ag combination assay, with consent and after counselling.

A positive test should be repeated on a further specimen for confirmation.

A negative test does not exclude infection.

Seroconversion usually occurs within 1 month but may be delayed up to 3 months, even following a high risk exposure.

HIV p24 antigen has only limited sensitivity; HIV-1 RNA (viral load) may be of use during this 'window period'.

Initial assessment

Full blood count; Lymphocyte immunophenotyping (absolute CD4, CD8 counts), Syphilis serology, Hepatitis B serology, Hepatitis C serology, Cytomegalovirus Ab, Toxoplasma Ab, HIV p24 antigen, HIV-1 RNA (viral load).


Full blood count, Lymphocyte immunophenotyping - CD4 and CD8 levels indicate degree of immunosuppression.

HIV-1 RNA provides a measure of viral load and is particularly useful in following the response to therapy.

Beta-2-microglobulin is of limited value HIV drug resistance studies.

Criteria for HIV infection

Either repeatedly positive tests for HIV antibody supported by a positive confirmatory test or direct identification of HIV by virus isolation.

CDC classification (original)


Group I


  • Acute mononucleosis syndrome

See under Lymphocytosis.

Group II


  • Asymptomatic infection


Group III


  • Persistent generalised lymphadenopathy

See Lymphadenopathy.

Group IV


  • AIDS and 'AIDS related complex'

See Category C below and AIDS.

CDC staging system (1993)


Category A


  • Acute seroconversion illness


  • Asymptomatic patients


  • Progressive generalised lymphadenopathy

See Lymphadenopathy.

Category B


Symptomatic HIV disease


  • Bacillary angiomatosis

Cat scratch disease antibodies.

  • Vaginal Candidiasis

Persistent or poorly responsive to therapy. See Candidiasis.

  • Oral Candidiasis

See Candidiasis.

  • Cervical dysplasia

See Cervical lesion.

  • Cervical carcinoma in-situ

See Cervical lesion.

  • Constitutional symptoms


  • Fever >38.5ºC

See Pyrexia of unknown origin.

  • Diarrhoea >1 month


  • Oral hairy leukoplakia


  • Herpes zoster infection

On two occasions or involving more than one dermatome.

See Varicella zoster infection.

  • Immune thrombocytopenia

Full blood count, Platelet Ab. See Thrombocytopenia.

  • Listeriosis


  • Pelvic inflammatory disease


  • Peripheral neuropathy


Category C

See AIDS for listing of AIDS defining illnesses.

AIDS surveillance case definition

Basis for notification of AIDS.

CD4 count <0.2 x 109/L

This criterion is used by the CDC but has not been adopted in Australasia.

Category C patients

Any patient with HIV infection and an AIDS defining illness is included in the Australasian AIDS surveillance case definition.


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