When I first read this I was having a lot of "Day After" problems, headaches ate., so I ignored it, because I couldn't make sense of it.
We (Nurses) use multi- dose vials all the time, though they are disappearing. If you use a different, (clean or new) needle and syringe each time there is no danger.
What he actually did (as reported last night) was change the needles without changing syringes, which is dangerous. If you pull back while injecting you can draw blood into the syringe, contaminating it.
Two things. How could he not know this, especially for many if not most injections, you have to pull back to see if you are in a blood vessel or not.
(some meds MUST NOT be injected into a vessel, some MUST be, either way, you pull back.)
If these were meds given IV during surgery, the injection port is very high on the tubing, and it would be almost impossible for blood or viral infections to be drawn the 2 to 4 feet upward, against liquid flow and gravity, to contaminate the syringe, but you still have diluted the med with the IV fluid.
This is all very odd.
He also has a lot of past charges of malpractice.
WW