CDC launching new era in testing by giving OK to rapid screening tests
New fingerstick tests will bring access to the streetsIn a move that is likely to have profound and far-reaching consequences, the Centers for Disease Control and Prevention has made an about-face on rapid HIV screening tests.
In the Feb. 27, 1998, issue of Mortality and Morbidity Weekly Report, the CDC will recommend a change in U.S. Public Health Service policy. It will urge that under at least some circumstances, health care providers should be able to disclose provisional results of HIV tests, instead of making patients wait two weeks while a confirmatory test is performed.
The new recommendations are expected to be incorporated into regulations by the U.S. Food and Drug Administration (FDA). When that happens, the effect will be the opening of a vast new market in the United States for rapid HIV screening tests, CDC experts say.
Though dozens of rapid tests are already in widespread use abroad, scant incentive exists for test manufacturers to mount the expensive clinical trials needed for approval in the United States, because the FDA at present prohibits the disclosure of provisional rapid-test results, says Bernard M. Branson, MD, MPH, medical epidemiologist at the National Center for HIV, STD and TB Prevention at the CDC, and chief architect of the new CDC recommendations.
With a new policy in place, many new rapid tests for HIV will be submitted for FDA approval, experts say. Most of the new tests are simple fingerstick tests that incorporate a new technology perfected within the last year, and which — in theory — could be used by anyone, from outreach workers to consumers of home-test kits.
Two new tests are in clinical trials, a third is already available, and another is expected to become available within the next year or so, CDC experts say. (For details, see story, p. 26.)
The anticipated influx of new rapid tests promises to have a dramatic impact in two different ways. First, the new tests will greatly increase access, making it much easier for people to learn their HIV status, says Branson.
"By cutting down on the cost and the technological requirements of rapid tests, and by getting rid of the waiting time, HIV testing doesn’t have to be clinic-based anymore," he says. "Now it can done as street outreach."
Indeed, one reason driving the CDC’s turnaround on rapid tests was researchers’ frustration over the effects of a two-week waiting period. As it stands now, almost 30% of U.S. patients who get HIV testing never come back for their results, says Charles A. Schable, chief of the National Center for Infectious Disease at the CDC. Studies have found that the waiting period is too burdensome for clients who have a hard time taking off from work or finding child care, Branson says.
But when clients in a Dallas study were given the chance to learn their test results right away, they understood the provisional nature of positive results, and they also came back to get confirmation and more counseling, Branson says.
The second arena in which new tests will make an impact relates to accuracy. Studies in Honduras and other sites abroad have shown that using two different rapid tests side by side provides far greater accuracy than using a single rapid test alone, Branson says. Rapid tests could be used in the same fashion in the United States if there were more than one on the market; but without a new policy on the disclosure of results, that would never happen, researchers realized.
Ethical concerns are raised by the prospect of outreach workers offering injecting drug users an on-the-spot HIV test, or home-test consumers being able to perform an instant test on themselves, say Branson and Schable. How will clients decide whether or not they are ready to get on-the-spot information about their HIV status? How will counselors help clients understand a provisionally positive result?
As this issue of AIDS Alert went to press, the new CDC recommendations called for disclosure of provisional results by clinicians only in certain circumstances, says Schable. Tests were to be offered to the following kinds of clients:
• those in high-risk populations (such as those presenting at TB and STD clinics);
• mothers presenting in labor, with no history of prenatal care and with unknown HIV status;
• health care workers who are victims of a needlestick, and possibly other high-risk situations.
Ways to convey provisional positive results were also still being worked out at press time. For example, patients who test positive, but who live in a low-prevalence part of the country and engage in no activities that put them at risk for HIV infection, might be told a positive reaction means they "probably" or "very likely" don’t have HIV. In higher-risk settings, patients might be told that a positive test means they "probably are" infected.
Whether the tests will perform as well in the United States as they have abroad is still unknown, experts add. For one thing, using a single rapid test in a low-prevalence population will give a lower positive predictive value, says Branson.
Suppose, for example, a single rapid test that has 99.4% specificity is administered to 1,000 people, meaning six will test false-positive. That error rate won’t matter much in areas with a high prevalence of HIV,because in all probability the people testing false-positive will have the disease. But if the same test was performed on 1,000 white, affluent suburban housewives — a low-prevalence population — in all likelihood all positive results will be false, and positive predictive values plummet to zero.
Two rapid tests used together abroad seem to overcome that difficulty by ensuring virtually 100% accuracy. However, no one knows for sure if paired tests will perform the same way here as they do abroad. "I have confidence in these tests, but until we have more data, we can’t extrapolate and say for sure how they will work here," says Mark Rayfill, PhD,assistant chief for Interna tional Laboratory Activities of the HIV Retrovirus Disease Branch of the Division for AIDS, STDs, TB and Laboratory Research at the National Center for Infectious Diseases. To get those data, researchers need more rapid tests, Rayfill adds.
But two other roadblocks may keep the tests from reaching the market as fast as researchers would like.
For one thing, Paris-based Sanofi Diagnostics, Pasteur, holds patent rights in the United States to the HIV-2 antigen, which the FDA says new HIV tests must be able to detect to be approved. Thus, it’s possible other companies submitting products for licensure could face a court challenge.
The bigger hurdle, at least for some pharmaceutical firms, is simply cost. Saliva Diagnostics Systems (SDS), a small firm based in Vancouver, WA, has three rapid tests it would like to launch in the United States. But without a backer, that will prove tough, says Paul Slowey, PhD,chief operating officer and vice president of SDS.
"People want these kinds of tests very badly right now," says Slowey. That’s why the new rapid HIV tests will eventually find their way not only into the U.S. market, but into home-test kits as well, Slowey adds. "It’s simple: Consumers want to know."