On April 19, after the transfusion recipients became infected, doctors tested the donor's blood and stool for salmonella, but did not find it.

Transmission via blood is thought to have occurred in three other transfusion recipients.

Concern is greatest for transfusion recipients being treated with drugs that suppress the immune system because they are more susceptible to such infection.

Between 1980 and 1990, 30,000 Canadian transfusion recipients were infected with hepatitis C from tainted blood.

As a result, tens of thousands of hemophiliacs and transfusion recipients were infected and died.

Federal health officials estimate that 12,000 transfusion recipients may have been infected with the virus before the development of a screening test.

Earlier, the health agency had considered recommending widespread testing of all transfusion recipients.

They also said that the true incidence cannot be known because many transfusion recipients die from an underlying disease before Lyme has time to develop.

Confusion could also result from the common practice of treating transfusion recipients with antibiotics for their underlying condition.

Most transfusion recipients are fairly sick, and half die of other causes within two years anyway.