San Francisco Chronicle (SF); Thursday, July 4, 1991
Kenneth Chang, Chronicle Staff Writer

The figure is based on a three- year study of more than 100,000 donations from Northern California, according to Dr. Michael P. Busch, a researcher at the blood bank.

In today's issue of the New England Journal of Medicine, the researchers report on the first two years of the study, in which they found only one instance of HIV- tainted blood among nearly 72,000 donations.

Since writing the article, the researchers have tested an additional 30,000 blood donations, none of which contained the HIV virus.

"Our screening techniques are very effective," said Dr. Herbert A. Perkins, director of the Irwin Memorial Blood Bank and one of the study's authors. "While the risk is not zero, it is so low that it should not be any cause for concern."

The situation today is a "dramatic reduction in risk" from a decade ago, when as much as 1 percent of the blood supply may have been contaminated with the HIV virus, which causes acquired immune deficiency syndrome, said Busch.

At that time, scientists did not understand the role of the virus in causing AIDS, and the screening tests did not yet exist.

By contrast, contracting AIDS from a blood transfusion is now an "exceedingly rare" occurence, even in areas such as San Francisco that have a large number of people infected with HIV, the researchers report.

'SILENT INFECTIONS'

Blood donations are routinely tested for antibodies that the immune system produces in response to HIV. However, because the antibodies do not appear until two to three months after infection, there has been lingering concern that donations with so-called "silent infections" might be slipping into the nation's blood supply.

After passing the standard screening tests for HIV infection, the blood of the donors was combined into "pools" of 50 samples each, and the researchers tested each pool for HIV by trying to grow cultures of the virus. Many of the pools were also tested with a sophisticated technique called polymerase chain reaction, or PCR, which can amplify one HIV virus by a million-fold to permit easy detection.

Only one pool tested positive with both techniques, the scientists reported, and they assumed that the blood of only one of the 50 donors in the pool had contaminated the sample.

Correcting for possible errors in the tests, they calculated the risk that any one blood donation is contaminated to be 1 in 61,000.

QUANTIFYING THE RISK

The study's principal investigator, Dr. Girish N. Viras, said the study "provides a scientific basis for patients and physicians to quantify the risk for HIV infection in fully screened blood."

About 3.6 million Americans receive blood transfusions each year. Each transfusion averages four units of blood, so that if the data applies nationwide, as many as 200 people will receive HIV-tainted blood each year, Vyas said.

However, that risk pales against other risks of blood transfusions, Vyas said. For example, as many as one person in a hundred who receives a blood transfusion will get hepatitis, he said.

"The risk of getting hepatitis is probably 50 times greater, and the morbidity and mortality associated with hepatitis from a transfusion is at least 10 times greater than AIDS," Vyas said.

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