The AIDS virus may escape detection for more than a year after a person has been infected, much longer than previously assumed, a new study has suggested.
The study raises serious questions about the dependability of the two blood tests widely used to determine whether a person has been exposed to the deadly acquired immune deficiency syndrome virus.
If subsequent studies verify that the virus can go undetected in the human body for up to a year or more, it may mean that there are some people who are infected but erroneously believe themselves to be virus-free simply because of a negative blood test.
Until now, it has generally been thought that the delay between infection and the production of antibodies, which can be picked up by the blood tests, was about three months.
The new study, reported in the Sept. 12 issue of the British journal, Lancet, was conducted at the National Cancer Institute by a team of scientists from the United States and Finland. The study was done on a group of 25 sexually active homosexual males who tested negative according to the standard tests.
But by using a new type of test that is still in the research stage, the researchers found that nine of the 25 subjects had signs of infection.
"If people think the latency period is very short, they may be wrong," one of the researchers, Genoveffa Franchini, told the Washington Post. "The results surprised us.
"What it means is clear. The period before the development of antibodies is longer than anyone thought. But we still don't know how long people are infected with this disease before it appears on tests,"
U.S. Public Health Service officials Friday cautioned the public not to make premature conclusions about the impact that the new finding may have on the present system of testing.
Dr. Gary Noble, Public Health Service AIDS coordinator, said in a telephone interview that "it is far too early on the basis of a single study involving 25 patients" for anyone who has tested negative to begin worrying that he or she might actually be infected, provided that they have not engaged in high-risk behavior since taking the test.
Noble noted that counselors at testing centers routinely tell people who have high-risk behavior that may expose them to AIDS that they should be retested in six months if the first test was negative.
An American Red Cross official discounted the harmful impact that the finding could have on the risk of the blood supply being contaminated.
Dr. Gerald Sandler, associate vice president for medicine, said that the possibility of blood donors being contaminated by the AIDS virus has grown less and less since the introduction of blood testing methods in 1985.
"Each month in this country it is getting safer to have a blood transfusion in this country," he said.
Currently, it is estimated that only one in 10,000 donors pass on the AIDS virus to a transfusion recipient without detection. Medical authorities calculate that among the 14 million blood donations annually, the virus is passed to about 75 people.
The standard tests used to determine whether an individual has been exposed to the AIDS virus do so by identifying antibodies produced in response to virus.
The investigational test used by the National Cancer Institute researchers reportedly is more accurate because it identifies the presence of certain proteins in the virus itself, not just the virus antibodies. It is one of several experimental tests being developed that may be more accurate than the current ELISA (enzyme-linked immunosorbent assay) or the western blot.