Abacterium commonly associated with stomach infections is posing new concerns about the safety of the nation's blood supply after being linked to the deaths of seven patients who received transfusions since 1987.

All seven died of complications from shock, which they suffered shortly after being transfused. Five of those deaths occurred in the last two years.

Concern that the bacterium, Yersinia enterocolitica, seems to be spreading in the general population is prompting the nation's blood experts to take steps to protect the 4 million people who receive blood each year in the United States. Yersinia is increasingly responsible for gastrointestinal infections in the general public.

The nation's blood banks, however, object that the proposals could cause them to discard usable blood, leading to shortages and increased costs.

In the most controversial step to date, an advisory panel recommended last month that the Food and Drug Administration reduce from 42 days to 25 days the period that blood may be stored.

The Blood Products Advisory Committee made the non-binding recommendation after learning that each of the seven Yersinia deaths involved blood that had been stored for at least 25 days.

That period is believed to be critical because the bacterium is difficult to detect in its early stages. Later, when the contaminated blood is stored under refrigeration, it grows quickly and produces large amounts of a lethal toxin, which can cause blood recipients to go into severe shock and die.

An earlier recommendation came last spring from the journal Transfusion. Because Yersinia is increasingly responsible for gastrointestinal infections in the general public, the journal editorialized it was "reasonable" to screen out donors who reported recent stomach distress, including diarrhea.

Blood banks, however, said such screening would eliminate too many potential donors and cause shortages.

The FDA plans in the near future to issue a warning to doctors about Yersinia and to ask hospitals and blood banks to report all cases of suspected contamination.

There is no such reporting requirement now, which transfusion experts say has caused the problem to be understated.

Gerald V. Quinnan, acting director of the FDA's Center for Biologics Evaluation and Research, wrote in a recent memorandum, "Until a specific, feasible solution . . . is found, (FDA) is recommending that physicians transfusing blood products carefully weigh the need for transfusion against all risks."

Federal regulators and transfusion experts stress that the Yersinia bacterium is still considered a rare cause of transfusion-related deaths. The risk of dying from a contaminated pint of blood is about one in 2 million.

"Is this a new HIV (human immunodeficiency virus)? No. This is not that at all," said Steven D. Douglas, an advisory panel member and professor of microbiology at the University of Pennsylvania. "Is it a disease that merits major review by the FDA, by the blood bank world, by the people developing testing? Yes. This is not post-AIDS hysteria."

Of the seven confirmed Yersinia deaths, each of the patients experienced an abnormal drop in blood pressure, which caused them to go into shock within minutes after being transfused with the contaminated blood.

One patient suffered "explosive diarrhea" within 10 minutes of receiving blood, according to one unpublished medical report. Another patient's kidneys and liver shut down. All seven died from the effects of irreversible shock.

Because blood is a raw product, there is always a risk of bacterial contamination, transfusion experts said. Indeed, before the introduction of modern systems of collecting and storing blood, bacterial contamination commonly occurred after transfusion.

That is no longer the case. But regulators and transfusion experts are alarmed by the recent cases of Yersinia because it is difficult to detect in its early stages, appears to be increasing in the general public and produces lethal toxins at refrigerated storage temperatures.

Federal regulations call for blood to be stored at 4 degrees Centigrade for up to 42 days. Most disease-causing organisms are unable to grow at that temperature. Yersinia is an exception, growing at low levels that cannot be detected for several weeks. Then it proliferates.

Many blood banks have argued against cutting back the 42-day federal limit on storing blood, saying it would cause shortages and increase costs. The FDA apparently is sufficiently concerned about possible shortages that it may ask the advisory panel to reconsider its vote, agency spokesman Brad Stone said.

Blood centers that buy large amounts of blood from other blood banks would be especially hard hit if the storage limit was reduced, Harold Kaplan of the New York Blood Center told the advisory panel last month. Centers that sell blood usually keep the freshest blood for their regional hospitals and ship "older" blood to the purchasing centers.

Kaplan's blood bank buys more than 200,000 pints of blood from Europe annually and purchases tens of thousands of other pints from American blood centers, so it would be especially at risk.

William C. Sherwood, director of the American Red Cross's blood center serving the Philadelphia region, said blood banks also would be forced to throw away more blood if a shorter shelf life were required.

In 1979, when blood could be stored for only 21 days, Sherwood's blood bank discarded nearly 5 percent of all blood it collected because it was too old, he told the advisory panel. After the storage period was increased to 42 days several years ago, the Philadelphia blood bank was able to reduce the amount of blood it wasted to 1.76 percent of its collections.

In addition, Sherwood estimated that replacing the discarded blood would add $3.35 to the price charged in Philadelphia for a pint of red cells -- currently $62 a pint -- or $1.2 million annually. Nationwide, the additional costs could be as high as $74 million, he estimated.

Several panel members who voted in favor of cutting the shelf life said they were "troubled" by the potential impact. They said they were persuaded, however, by safety concerns about Yersinia and other testimony that blood banks could maintain an adequate supply at 25 days.

After investigating the Yersinia contamination cases, officials at the Centers for Disease Control said their findings "suggest that a re-evaluation of the procedures for donor screening, blood collection and blood storage is appropriate. This is especially important because new methods . . . permit longer storage of (blood) before use."

Blood banks have opposed such screening proposals, saying they would be too general and cause blood shortages.

Kaplan said one industry survey found that screening out donors who had a stomach infection before giving blood could eliminate more than 13 percent of them. Red Cross officials reported similar findings.