Mad Cows: Researchers say that they've found a second person who got mad cow disease from a blood transfusion. Well, he didn't really have mad cow disease. That is, he had no symptoms of it. What he did have was a history of having received blood from a person with known "mad cow" disease, or variant Crueztfeld-Jakob disease. He died of unrelated causes, but in the interest of science had a special autopsy to check for the prions that are associated with mad cow. They found the prions, but that doesn't necessarily mean he would have gotten the disease. The natural history of variant Crueztfeld-Jakob disease has yet to be fully understood. Science is still on the learning curve for this one.

Still, you can't blame them for being cautious with the blood supply. Better safe than sorry. But I wouldn't lie awake worrying if you have had a blood transfusion in the past.