^^^ Are you referring to the possibility of an organ donation transmitting a disease? Organs are tested up the wazoo, but there have indeed been cases of disease transmission by organ transplant. If family is available, they are asked if the donor has any significant medical history or any risk factors for various diseases. Depending on the need for the organ, sometimes a choice is made to use it despite the possibility or actuality of disease transmission.
If I was dying and needed a heart, and a donor organ was offered to me with the possibility that the donor had hepatitis, for example, I would take it.
Even if a donor is unsuitable to provide solid organs, often items like skin, bone and corneas can still be used. My philosophy is that once I am dead, I want to be stripped for any parts that can be helpful to someone else. I have made sure to let my family know of my wishes in this regard.