@Rarebear is right, blood and plasma donations are free of infection risk if they follow normal procedures.
I think all the donation centers affiliated with the Red Cross use a whole new (sterile) kit of needle, tubes, bags for each donation. And they swab the puncture are thoroughly with disinfecting solution before they put the needle in. They certainly do every time I have donated. (anyone else a ‘Gallon Club’ card holder?)
And good point too that they can’t test for diseases we don’t know about. My mom found out she had hepatitis-C in the early ‘80s and it probably came from transfusions needed during one of three C-section births in the 50’s.