Die Rapidtests haben leider eine Fehlerquote von bis zu 10%, da sie nur die Antikörper nachweisen und die bilden sich erst im Laufe einiger Wochen.
Das Fatale daran: Gerade in der ersten Zeit nach der Infektion ist der Virus am ansteckendsten...
The New York Times
June 6, 2005
H.I.V. Tests Pose Choice of Breakthroughs
By RICHARD PÉREZ-PEÑA
For almost two decades, H.I.V. tests had two glaring flaws. They did not detect the earliest stage of infection, when people are more likely to spread the virus. And they took days to produce results, and many people never returned to learn whether they were infected.
Now, technology has put public health officials in a quandary: which problem to address. New generations of tests can largely eliminate either the long waiting time for results, or the failure to find early infections. But the choice is pulling H.I.V. specialists in competing directions, in New York City and nationally. Experts on both sides of the debate would like to see both types of tests used, but say that expense and logistics make that impractical.
Some health agencies, including those in New York City and New York State, have embraced quick tests that produce preliminary results in minutes, rather than days. North Carolina and San Francisco have gone another way, adopting tests that catch many early infections with H.I.V., the virus that causes AIDS, that other tests miss.
A group of prominent H.I.V. doctors and researchers in New York City say North Carolina and San Francisco made the right call, and they are urging the city's Department of Health and Mental Hygiene to change directions.
"Nobody is criticizing the city, because they've been very proactive on this," said Dr. Frederick P. Siegal, medical director of the H.I.V. center at St. Vincent's Hospital Manhattan in Greenwich Village. "We just think there's an even better direction we'd like to try, or a combination of directions."
Dr. Fred Valentine, director of the AIDS research center at New York University, who is also pushing the city to switch, said, "In the best of all worlds, you'd test everybody both ways," but that would require pouring much more money into testing.
Since the 1980's, standard testing for H.I.V., the human immunodeficiency virus, has meant drawing a vial of blood and using it to perform two types of laboratory tests. Typically, the subject is asked to return a week later for an answer, and that has been a serious problem.
"Overall, in the United States, in public testing sites, 32 percent of the people who test positive don't come back for their results," said Dr. Bernard M. Branson, of the Divisions of H.I.V./AIDS Prevention at the federal Centers for Disease Control and Prevention.
In 2002, a test became available that can produce initial results in as little as 20 minutes, using just a drop of blood, and last year, federal regulators approved a rapid test that uses an oral swab. People who test positive are still advised to have a conventional blood test for confirmation.
A number of state and local governments have adopted rapid testing, none more enthusiastically than New York City. The city has made rapid tests the standard in its sexually transmitted disease clinics, which will perform about 50,000 of them this year, and it has begun using them in its jails, said Dr. Scott Kellerman, assistant health commissioner for H.I.V. programs.
But rapid testing, like traditional blood tests, cannot detect the first phase of H.I.V. infection. Those tests do not look for the virus itself but rather for antibodies that the immune system makes to fight the infection. It takes time for the body to produce enough antibodies to be detectable.
Dr. Branson and other researchers say the newest, most sensitive tests, like those used by New York City, usually find antibodies within three to four weeks of infection, though some experts caution that an estimate of a month or more might be more realistic. But most government and private labs across the country still use older antibody tests that take longer to detect infection.
In the first weeks after infection, the virus multiplies at an astonishing rate, until the body builds up its defenses. Scientists say that on average, there are 1,000 times as many copies of H.I.V. in the blood during that phase as there are several months later.
"These are the most important people to find, because they have the highest viral load, which means they are most infectious, and these people are recently infected, which means they're an active part of the high-risk sexual network," said Dr. Jeffrey D. Klausner, director of sexually transmitted disease programs for San Francisco.
Some experts say that people in the first few months of infection may account for 40 percent to 50 percent of the new infections in others, but such high estimates are disputed.
A partial solution is to test for the RNA of the virus itself, which can be detected within 10 days of infection. Blood banks have done this for a decade.
The RNA test is expensive, so instead of a test on each blood sample, the samples are combined into pools of 10 to 100. Most pools test negative, meaning that all the samples in the pool are negative. If a pool tests positive, it is broken down into smaller groups and retested until the infected sample is found. Like conventional antibody testing, RNA testing takes several days.
North Carolina adopted this technique in 2003 for all publicly financed testing. San Francisco also made RNA testing standard in its sexually transmitted disease clinic in 2003, but it uses rapid antibody tests in other settings. No other public health agencies in the United States routinely use RNA testing, H.I.V. experts say.
In North Carolina, 4 percent of the infections found by RNA tests are not detected by antibody tests, said Dr. Christopher D. Pilcher, director of the testing program run by the state and the University of North Carolina. In San Francisco, Dr. Klausner said, the figure is 10 percent.
The problem of people not learning their test results is a fairly minor one in North Carolina, Dr. Pilcher said, so the state can afford to use tests that do not produce immediate results. Unlike states like New York, North Carolina does not guarantee anonymity in H.I.V. testing; the state knows the identity of each subject, and it tracks down those who do not return for their results.
Dr. Kellerman said New York City was interested in trying RNA testing in the future. But for now, he said, it probably does not make sense for the city.
The cost of RNA testing in North Carolina has worked out to $3.63 per person tested, Dr. Pilcher said. But in San Francisco, where more tests are needed because there are more H.I.V.-positive results, RNA testing costs around $30 per person, Dr. Klausner said.
New York City would likely fall somewhere in between, with a cost for RNA testing comparable to the cost of rapid antibody testing, about $10 per person.
* Copyright 2005 The New York Times Company
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