HIV: seroconversion and diagnosis

HIV seroconversion is symptomatic in 60-80% of patients and typically presents as a glandular fever type illness. Increased symptomatic severity is associated with poorer long term prognosis. It typically occurs 3-12 weeks after infection

Features

• sore throat
• lymphadenopathy
• malaise, myalgia, arthralgia
• diarrhoea
• maculopapular rash
• mouth ulcers
• rarely meningoencephalitis

Diagnosis

• HIV antibodies
  • may not be present in early infection, but most people develop antibodies to HIV at 4-6 weeks but 99% do by 3 months
  • usually consists of both a screening ELISA (Enzyme Linked Immuno-Sorbent Assay) test and a confirmatory Western Blot Assay
• p24 antigen
  • a viral core protein that appears early in the blood as the viral RNA levels rise
  • usually positive from about 1 week to 3 - 4 weeks after infection with HIV

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combination tests (HIV p24 antigen and HIV antibody) are now standard for the diagnosis and screening of HIV

• if the combined test is positive it should be repeated to confirm the diagnosis

• some centres may also test the viral load (HIV RNA levels) if HIV is suspected at the same time </aside>

• testing for HIV in asymptomatic patients should be done at 4 weeks after possible exposure

• after an initial negative result when testing for HIV in an asymptomatic patient, offer a repeat test at 12 weeks

The main tests available to test for HIV are:

• HIV antibody
  • enzyme-linked immunosorbent assays (ELISAs) are often used for screening
  • Western blot was previously used as a confirmation test but HIV-1/HIV-2 differentiation assays are now more commonly used
  • most people develop antibodies to HIV at 4-6 weeks but 99% do by 3 months
• HIV antibody and HIV antigen
  • often referred to as 'fourth-generation' tests
  • p24 antigen can be detected as early as 2-3 weeks after exposure
  • the sensitivity of these fourth-generation tests approaches 100% for patients with chronic HIV infection
  • now the first-line test for HIV screening of asymptomatic individuals or patients with signs and symptoms of chronic infection
• HIV RNA (qualitative or quantitative)
  • not routinely used for screening/testing
  • however, may be useful for diagnosis of neonatal HIV infection and screening blood donors