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Since the first case reports from Los Angeles in 1981, the HIV epidemic has continued to expand. In the U.S., more than a million people are currently living with HIV/AIDS, and the disease has killed more than 22 million people world-wide. Two recent issues of MMWR review the epidemiology of HIV/AIDS and describe current efforts toward prevention (MMWR 2008, Vol. 55, No. 21 & 24). There are an estimated 250,000 to 300,000 HIV-infected people in the U.S. who are unaware of their infection. As an extension of the Advancing HIV Prevention initiative which began in 2003, the CDC will publish new recommendations for HIV testing of adults, adolescents, and pregnant women by the end of 2008. It is expected that testing on all people between the ages of 13 and 64 will be suggested as part of routine physical examinations, with annual testing recommended for those considered at high risk of infection. HIV can be transmitted during pregnancy, labor & delivery, or breastfeeding. The CDC has recommended that all pregnant women be counseled and encouraged to be tested for HIV infection. Substantial progress has been made in reducing perinatal HIV transmission rates from 25-30% in 1991 to the current < 2% transmission rate. This reduction is attributed to increased HIV screening of pregnant women, use of antiretroviral drugs, and elective cesarean deliveries. Human immunodeficiency virus exists as two distinct viral species, designated HIV-1 and HIV-2. Each species is further subdivided into subgroups, including M, N, & O for HIV-1, and subgroups A-G for HIV-2. The vast majority (99.6%) of HIV infections worldwide are caused by HIV-1, group M. The less prevalent viral types are largely confined to West Africa. The detection of antibody to the HIV-1 virus is the best method of screening for HIV infection. IgM is the first antibody class to appear. Levels peak between 7 and 41 days after infection and disappear by 108 days. Unfortunately, reliable serum tests for HIV-1 IgM antibodies are not available. IgG anti-HIV-1 appears at about 11 days and peaks between 70 and 189 days. There have been reports of delayed antibody response to HIV-1 infection, but most persons produce detectable levels of antibody within 3 months of the infection. HIV-1 antibody tests have been replaced by newer combination tests for HIV-1 and HIV-2. Results are reported as HIV-1/2 antibody. The assay does not distinguish between HIV-1 and HIV-2. Specimens that test reactive to HIV-1/2 antibody are automatically forwarded for confirmatory testing that initially includes a Western blot for antibodies to specific HIV-1 viral proteins. Any specimen that is reactive for HIV-1/2 antibody, but negative or indeterminate by HIV-1 Western blot is subsequently tested specifically for HIV-2. Specimens that are reactive in the initial screening test, but are indeterminate or nonreactive by Western blot may represent the seroconversion phase of disease, or may be due to cross-reacting antibody from a variety of conditions. Causes of false positive EIA results include multiparity, previous blood transfusion, chronic liver disease, renal transplantation and chronic renal failure, autoimmune disorders, influenza vaccination, and receipt of hepatitis B immunoglobulin. Reference value is nonreactive. Specimen requirement is one SST tube of blood. |
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