Rapid HIV tests hold mirror to unknowingly infected
A quarter of those with HIV don’t know it
Nearly two-thirds of new HIV infections in the United States are transmitted by people who do not know they have the disease.
A growing array of rapid HIV tests is changing this longstanding problem, providing results in as little as 20 minutes that can help prevent transmission and get those unknowingly infected into treatment.
The problem before the development of rapid tests was that many public health and community settings were reluctant to offer a test that was going to have to be sent to a central laboratory for results. In many cases, the patient would be long lost to follow-up by the time the results came back.
"Now you can give the test results during the same visit," says Bernard Branson, MD, medical epidemiologist and associate director for lab diagnostics in the division of HIV/AIDS at the Centers for Disease Control and Prevention (CDC). "It makes it a lot more feasible. It allows us to do testing in more places and do a better job of identifying [cases]."
It is estimated that between 180,000 and 280,000 people in the United States currently are unaware that they are HIV-infected. Oblivious to their HIV, they likely will continue the risk factors that resulted in their own infection and continue the chain of transmission to others.
"We estimate that those people represent about 25% of those infected in the United States and that they are responsible for 60% of the new infections," Branson says.
To attack the problem, the CDC is wielding a variety of new rapid tests — the most recently approved of which doesn’t even need to screen blood. The OraQuick Advance test (OraSure Technologies Inc., Bethlehem, PA) can detect antibodies to both HIV-1 and HIV-2 in saliva or other oral fluids.
"You swab between the lip and the gum," adds Branson. "Potentially, even in places like emergency rooms, this could make it a whole lot more feasible to test. You could even do HIV tests at the time you do vital signs. It takes 20 minutes."
For the time being, however, the CDC is targeting community and public health settings where testing may not be typically done. Such centers will receive the lion’s share of the agency’s recent $2.3 million bulk purchase of OraQuick Advance tests.
"Most of that is going to community-based organizations and other places where drawing blood or even doing a [rapid] finger-stick test is not feasible," he explains.
Four rapid tests now on market
A total of four rapid HIV tests have been approved in the last two years, all of which can yield results in less than two hours, the CDC reports.
It’s important to note though that the rapid tests, like the traditional enzyme immune assay (EIA), are screening tests. Due to the possibility of false positives, a positive HIV test result must be confirmed by the Western blot test.
"Our experience in doing post-marketing surveillance with the OraQuick tests is that the number of false positives has been less than one per 1,000 persons tested," Branson continues. "We at CDC have conducted studies where in aggregate, we have tested 16,000 people — all of whom had parallel EIA testing — and we have not discovered any false negatives."
The CDC’s recommendations for HIV counseling are to tell people at that time of a rapid-test positive result that they have a reactive test and it should be considered a "preliminary positive," he notes. However, they should be advised that the result will not be known for sure until the confirmatory test is done.
"We recommend that people do the confirmatory test immediately," Branson points out. "In settings where they are able to draw blood, that’s preferable to have a blood specimen for a Western blot test.
"In other settings where they are not easily able to draw blood, . . . they can send the oral fluid specimen into a laboratory for Western blot testing," he adds.
The rate of false positive actually was less with a rapid HIV blood test in a study that included the conventional EIA screening test.1
The median time from blood collection to patient notification of result was 66 minutes with the rapid test compared to 28 hours for EIA.
"In the study of about 5,000 pregnant women, who had relatively low [HIV] prevalence, the specificity of the OraQuick [rapid blood] test was 99.6 and the specificity of the EIA was 99.8," says Branson. "The difference was basically four false positives with one vs. 11 false positives with the [EIA]."
In that regard, pregnant women have become a primary target for rapid test intervention, as HIV detection can allow treatment to prevent transmission to newborns.
The timely administration of antiretroviral drugs during pregnancy can reduce the risk of mother-to-child HIV transmission to 1% to 2% and also improve the health of the mother, the CDC emphasizes. Without any intervention, the chance of transmission is approximately 25% in the United States.
CDC urging routine rapid testing
The study by Branson and colleagues was dubbed the Mother-Infant Rapid Intervention At Delivery (MIRIAD). It implemented 24-hour counseling and voluntary rapid HIV testing for women in labor at 16 U.S. hospitals. Again, a rapid HIV-1 antibody test for whole blood was used.
Of the 5,744 women who were offered rapid HIV testing, 4,849 (84%) consented. HIV-1 test results were positive for 34 of the women. Based on the feasibility of rapid testing demonstrated in MIRIAD, the CDC now recommends that pregnant women be informed that HIV testing will be routinely done during labor if their HIV status is unknown unless they decline testing.
Along the same clinical lines, the rapid tests have clear implications for source-patient testing following needlesticks to health care workers. "I think we are seeing that now," Branson explains.
"In fact, that is one of the primary uses of some rapid tests in hospitals. What we are currently investigating is the possibility of using different rapid tests in combination to essentially give you rapid confirmatory results," he notes.
While the rapid tests are becoming a key weapon against HIV both in the public health and clinical setting, they can’t simply be distributed far and wide. The Food and Drug Administration requires training that includes instruction on administering the tests and providing counseling.
The CDC HIV prevention web site cites several problems in the training area, noting that 60% of the community-based organizations that receive grants from CDC plan to offer rapid HIV testing but have little or no training.
By the same token, not all rapid HIV test training provided by manufacturers meets CDC’s training requirements. Individual states may have various training requirements of their own, and the need for new training is relatively constant given the current explosion in diagnostic technology.
To meet the challenge, the CDC conducted 40 training sessions on rapid HIV testing during 2003 and 2004. More than 850 health care workers enrolled in the three-day sessions.
The CDC also is working with other agencies and sharing its rapid HIV test curriculum. While training is required, the tests do not have to be done by a laboratory professional.
"It was a brand new process, so CDC undertook a pretty extensive training program, because in our prevention programs, there were people with no prior laboratory experience," Branson explains.
"To be honest with you, training to do the test is the least difficult part [compared] to training people about blood and body fluid precautions, OSHA requirements, and counseling. That takes quite a bit of effort," he adds.
1. Bulterys M, Jamieson DJ, O’Sullivan MJ, et al. Rapid HIV-1 testing during labor: A multicenter study. JAMA 2004; 292:219-223.