Hi Hoping,
Today, most platelets are from a single donor using pheresis. Pheresis allows whole blood to be drawn from a donor, the cells, plasma, and platelets are separated with everything but the platelets being returned to the donor via an IV in the other arm. Given that your spouse had platelets so many years ago, it is likely that they were pooled platelets with 5-6 donors platelets pooled into a bag (just as Kati stated). If he got more than one "unit" of platelets, that exposes someone to many more donors. Other blood products may have used as well (like fresh frozen plasma) to control bleeding or to reverse the use of anticoagulants (e.g heparin) prior to surgery.
While most blood products are considered "leukoreduced" these days, they were not just a few years ago. Filters were often used to remove WBC's during transfusion IF the doctor requesting the transfusion specified leukoreduced blood. Also, some plasma will be in most blood products. I think I saw Dr. Peterson state that XMRV could be in plasma as well but I would have to research where I read it.
Regardless, trying to prove cause and effect at this point is extremely difficult. One thing to remember though....the Red Cross does keep track of blood donations so if they find out someone has something that could possibly infect someone else, they will notify all blood banks that have products made from that donors blood. This can include plasma, platelets, packed red blood cells, as well as other components. As far as how far back the ARC (American Red Cross) keeps segments from donor units, I'm not sure. That would be the key to finding any XMRV and it would be very unlikely they would find it due to the small sample size, the type of sample, and how long it had been stored.
Sorry for the long story...my brain needs more coffee!
~ JT
