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Epidemiologic data suggest that AIDS is caused by at least 2 types of HIV, HIV-1 and HIV-2. HIV-1 has been isolated from patients with AIDS and asymptomatic infected individuals. The closely related HIV-2 was first isolated from patients in West Africa in 1986, and the first case of AIDS due to HIV-2 in a patient was reported in the United States in 1988. HIV-2 appears to be endemic only in West Africa, but HIV-2 also has been identified in individuals who have lived in West Africa or had sexual relations with individuals from that region. HIV-2 infection is rare in the United States (<100 cases reported to date); most of the reported cases are from the northeastern states and involve persons from West Africa.
Both HIV-1 and HIV-2 are transmitted by sexual contact, sharing contaminated needles, exposure to infected blood or blood products, or from an infected mother to her fetus or infant. During the course of HIV-2 infection, antibodies are formed against the viral proteins p26 and gp34. Immunosuppressed patients may fail to develop these antibodies. At-risk patients with positive results for HIV-1/-2 antigen and antibody combination assays and/or indeterminate or negative results on HIV-1 antibody by Western blot (especially those showing reactivity only with HIV-1 core [p18, p24, or p55] and polymerase [p31, p51, or p66] proteins) should be investigated for the presence of HIV-2 antibodies.
Screening for and detection of HIV-2 antibodies in asymptomatic individuals
Reactive screening test results suggest the presence of HIV-2 antibodies. All repeatedly reactive serum specimens are automatically confirmed by an HIV-2 antibody immunoblot assay with an additional charge. HIV-2 antibody immunoblot results are reported as Positive, Negative, or Indeterminate.
Negative screen results indicate the absence of HIV-2 antibodies. These results should be interpreted with caution in patients who are at high risk or have symptoms or signs of HIV infection.
This test is not offered as a screening or confirmatory test for blood donor specimens.
This test is not offered for maternal/newborn HIV screening for specimens originating in New York.
All results that are reactive by HIV-2 antibody screening test and positive by confirmatory test should be verified by testing second serum specimens. Positive confirmatory HIV-2 antibody test results are required by statute in most states to be reported to the state departments of health for surveillance of communicable diseases.
False-reactive HIV-2 antibody screening test results may occur in patients with HIV-1 infection due to cross-reactivity of HIV-1 antibodies with the viral core and polymerase proteins used in the HIV-2 antibody screening tests.
Patients at risk for HIV-2 infection and suspected to have acute HIV-2 infection may have a) negative HIV-2 antibody screen results, or b) repeatedly reactive HIV-2 antibody screen results but negative or indeterminate confirmatory test results. For such patients, testing for HIV-2 RNA or proviral DNA (FHV2Q / HIV-2 DNA/RNA Qualitative Real-Time PCR) is recommended.
Assay performance characteristics have not been established for the following types of serum specimen:
-Presence of particulate matter
See HIV Serologic Interpretive Guide in Special Instructions for further interpretive information.
1. Constantine N: HIV antibody assays May 2006. In HIV InSite Knowledge Base (online textbook). Available at: http://hivinsite.ucsf.edu/InSite?page=kb-00&doc=kb-02-02-01
2. Branson BM, Handsfield HH, Lampe MA, et al: Centers for Disease Control and Prevention: Revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings. MMWR Morb Mortal Wkly Rep 2006;55(RR14);1-17
3. Hariri S, McKenna MT: Epidemiology of human immunodeficiency virus in the United States. Clin Microbiol Rev 2007;20:478-488
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