But for a small percentage of blood recipients, the transfusion may cause more harm than help.

But hundreds of blood recipients may be silently infected, experts say, and there is no effective treatment for them.

To ensure the health of blood recipients, travelers are deferred from donating until the window where symptoms may appear has passed.

If the disease can be spread through transfusions, it may be more difficult to detect in blood recipients, delaying treatment.

There were delays in screening blood donors and in setting up procedures for notifying blood recipients," he wrote.

As a result, blood recipients "may face a potential risk of transfusion-transmitted infections, such as H.I.V. and hepatitis," the advertisements said.

But the ads, which were placed by the New York Blood Center, may have had the opposite effect, since they caused a flood of calls from frightened blood recipients.

And when reports came in that other blood recipients had been infected, calls for tests of both the blood supply and donors met a powerful resistance that would allow thousands of continuing deaths.

As with other blood transfusion services, the ARCBS has had to strike a balance between protecting blood recipients against infection, and accepting enough donors to maintain an adequate supply of blood.

The inclusion of homo- and bisexual men on the prohibited list has created some controversy, but the FDA and Red Cross cite the need to protect blood recipients from HIV as justification for the continued ban.

This notion is contradicted by a report by the Transfusion Safety Study Group (TSSG), which compared HIV-negative and HIV-positive blood recipients who had been given blood transfusions for similar diseases.

The report in Science said HTLV-1 in donated blood "would contribute to the introduction of the agent into populations of the country where infection is not endemic, and it may present a future health risk to blood recipients and their sexual partners."