Just a single donor's tissue might slip through each year infected with HIV or hepatitis, but U.S. donations could be made even safer with genetic testing for the viruses, researchers have found. The U.S. Food and Drug Administration is moving toward recommending genetic screening for tissue, said Dr. Jesse L. Goodman, who runs the FDA's unit overseeing safety of the blood and tissue supply. Introduced five years ago, genetic testing is already widely used for blood. ``This is a wonderful advance. We like seeing this applied to blood and tissues. It is making things safer,'' said Goodman. Nearly always at the time of death, about 20,000 donors supply tissue _ such as bone, knee ligaments, heart valves and skin for burns _ to about 1 million patients a year in this country. Very few serious infections are transmitted, but an occasional case makes a stir. In 2002, dozens of transplant patients came down with hepatitis C from an infected donor's tissue distributed in Oregon, and one woman likely died as a result. Tissues from a single donor are used in an average of 50 patients. The researchers from the American Red Cross and Puget Sound Blood Center/Northwest Tissue Center in Seattle examined infection data on tissue from 11,391 donors to five U.S. tissue banks. They published their results in Thursday's New England Journal of Medicine. They estimated the chance of a donor's infection at 1 in 55,000 for HIV, 1 in 34,000 for hepatitis B, and 1 in 42,000 for hepatitis C. That would translate into perhaps one infected donor a year with any of the diseases. With genetic testing, the probabilities could be cut to 1 in 100,000 for hepatitis B, 1 in 173,000 for HIV, 1 in 421,000 for hepatitis C, the researchers calculated. They estimate the cost at $9 million _ or $5 per donated sample. In another study in the same journal issue, other researchers led by the American Red Cross reported that genetic testing of donated blood is already helping prevent transmission of about five HIV and 56 hepatitis C cases each year. Donated tissue undergoes several layers of screening to weed out samples with infectious disease. Hospitals, families, and medical records rule out certain donors. Bacterial cultures are taken from tissues, and viral tests are run on blood taken shortly before or after the donor's death. However, the viral tests, which typically read levels of immunity antibodies, can miss some early infections. Genetic testing _ known as nucleic acid-amplification testing or NAT _ reflects the presence of the virus itself and so detects infections earlier. While the FDA does not legally require NAT testing, blood banks are using it routinely in cooperation with the federal agency. Some tissue banks have started to use it in recent months. ``I think it's going to become the standard of practice, whether it's required or not,'' said biologist Margery Moogk, a board member of the American Association of Tissue Banks. She also directs the Northwest Tissue Center, which joined in the study. It is conceivable that spending the money on other areas of preventive medicine could protect more people, Dr. Goodman suggested in an editorial. Many doctors and administrators are bullish about more screening despite the expense, partly to guard against lawsuits. Some of the researchers in the tissue study acknowledged taking lecture or consulting fees from testing companies or owning equity in them.