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Check out new HIV testing approaches Could they impact epidemic in United States?
Approaches allow patients to be diagnosed earlier than ever
What will it take to stem the incidence of HIV in the United States? According to the Centers for Disease Control and Prevention (CDC), about 56,300 people were newly infected with HIV in 2006, the most recent year for which data are available.1 More than half (53%) of these infections occurred in men who have sex with men (MSM). Black/African American men and women also were found to be at risk. Their estimated incidence rates were seven times as high as the incidence rate among whites.
U.S. public health officials have stepped up testing efforts since 2006 when the CDC called for voluntary HIV screening to become a routine part of medical care for all patients ages 13 to 64.2 (To read more about the recommendations, see "New HIV screening guidelines issued How will they impact your practice?" December 2006, p. 133.) While increased testing is an important strategy in the fight against HIV, results for standard HIV tests usually are not positive until several weeks after infection occurs. This gap in detection is problematic, as those with recent HIV infection generally have very high amounts of virus in their body fluids and might be more likely to transmit HIV infection to others.3
Research is looking at new diagnostic tools that will allow patients to be diagnosed earlier than ever. The Food and Drug Administration (FDA) recently approved Abbott's ARCHITECT HIV Ag/Ab Combo assay, which can simultaneously detect HIV antigen and antibodies. Science also is eyeing adding nucleic acid testing (NAT) to rapid testing to boost HIV detection yield. Results of a just-published paper indicate that adding NAT testing to a community-based HIV testing program increased the HIV detection yield by 23%.3
How might such diagnostic tools impact the incidence of HIV in the United States? Early and accurate diagnosis of HIV is critical in controlling the HIV epidemic, says Sheldon Morris, MD, MPH, assistant clinical professor at the University of California, San Diego's (UCSD) Antiviral Research Center. "To those of us in the HIV prevention and testing field there is a need to have a strategy for detection of early HIV infection which could be the ARCHITECT [assay] or a nucleic acid strategy," states Morris, lead author of the current research. "Areas of high prevalence should be using these tests, and there should be an expected reduction in HIV transmission."
Test arrives by year end
The ARCHITECT HIV Ag/Ab Combo assay is the first test approved in the United States that can simultaneously detect HIV antigen (a protein produced by the virus immediately after infection) and antibodies, which are developed days later as the body works to fight off the infection. Abbott's new assay detects the HIV p24 antigen. The test will be available before the end of the year, says Darcy Ross, senior manager for Abbott Diagnostics' Division of Public Affairs.
The early phase of HIV infection (when symptoms begin to emerge) cannot be detected by most routinely used serological HIV tests. Conventional HIV tests detect HIV-specific antibodies in blood or oral fluids that are produced by the immune system during seroconversion or the development of detectable antibodies, which occurs approximately 22-25 days after initial infection. Testing for the antigen reduces the "window period" in which an individual might have been exposed to HIV and might have a reactive test result.
In a study conducted in a high-risk population, the Abbott assay detected nearly two-thirds of early, acute HIV infections.4 In the study, blood samples were collected every six months from men who have sex with men, all who were HIV antibody negative at enrollment. The previous seronegative specimens from patients who subsequently tested HIV antibody positive were tested individually with two HIV RNA assays. Those determined positive by both methods were classified as acute infections. The specimens then were tested with the Abbott assay and two third-generation HIV antibody tests. The Abbott combination assay detected 61.9% (13) of the acute infections. Only 14.3% (3) of the acute samples were identified as positive by one of the third-generation antibody tests. There were a total of 21 acute infections among 217 samples from seronegative individuals.4
The new test will run on Abbott's existing ARCHITECT line of diagnostic testing instruments. It already has been approved for use outside the United States; in Europe, HIV antigen-antibody combination testing is routine in public health settings. In fact, United Kingdom HIV testing guidelines specify the HIV combination test as the first-line test.
The new Abbott assay represents the first in what are known as fourth-generation HIV detection tests, says Peter Leone, MD, professor of medicine at the University of North Carolina at Chapel Hill and medical director of the North Carolina HIV/STD Prevention and Control Branch.
"We think that this test, and there may be other fourth-generation assays that will be available in the next year or so, really has a way of changing the landscape of HIV testing in the U.S., allowing us to close the gap," says Leone.
Can NAT testing work?
How can adding NAT testing to standard tests for HIV identify more patients with HIV infection? To perform the current study, researchers looked at more than 3,000 patients who sought HIV testing in clinics and other testing sites in and near San Diego. Many of the sites serve populations at high risk for HIV infection. The research was designed as a prospective study of the Early Test, a testing program developed by UCSD to identify and stage HIV infection.
Patients first were tested for HIV infection with a rapid saliva test. If test results were positive for HIV, a counselor gave patients their test results, and a blood sample was obtained for standard HIV tests. If the results were negative, a blood sample was obtained for the nucleic acid test. Patients who took the nucleic acid test were told that if the results were positive, they would be contacted by a staff member within two weeks. If patients had not been contacted in two weeks, they were instructed to call a voicemail number or log in to a web site to retrieve their results by using an anonymous personal identification number to protect their privacy.
Of 3,151 persons tested, 79 had newly diagnosed cases of HIV, researchers report. A total of 64 had positive results from the rapid HIV test, and 15 had positive results only by NAT testing. Of all HIV infections, 44% (in 35 persons) were in the acute and early stages. Most participants (56%) and persons with HIV (91%) were men who have sex with men.3
The Early Test program is ongoing, says Morris. The next steps in researchers for UCSD investigators might yield a comparative effectiveness study with fourth generation testing.
Cost analyses are yet to be published for either test, notes Morris. Researchers also will be looking at the "cut-off" for prevalence where test strategies similar to the Early Test remain effective, he states.