Re: are blood transfusions safe?
The blood supply is pretty safe, as far as catching a virus, but not 100% I know someone who got Hepatitis C from a transfusion 3 years ago. This is because blood is tested for the antibodies to viruses, but not for the viruses themselves, so if the donor has the virus but does not produce antibodies for some reason, the virus would not show up in the testing.
For this reason, make sure you really need the blood and that waiting is not an option. Some doctors are very careful to order blood only when you REALLY need it, but some are more lax, and order it before that point.
The chances of a reaction to the blood are small but also possible, so a nurse should be there for awhile at the beginning of the transfusion, taking your temperature every few minutes and so on, until it's clear you're not reacting.