Is a used syringe infectious

Answer 1

ALL used syringes and needles should always be considered as "infectious", or more aptly, it is "contaminated".

First, whatever was in the syringe still coats the inside of the syringe. Anything else put in that syringe will pick up trace amounts of the last liquid that was in the syringe.

Second, needles can contaminate the syringe with backflow of a person's blood, rendering both automatically contaminated.

Third, removable needles carry microscopic bits of blood and skin cells, which means it is contaminated. Since each person's skin contains bacteria and yeast, even the same person should never reuse a needle because it will inject skin bacteria and yeast into the tissues or into the vein. So even with a clean barrel of the syringe, the needle will still be "dirty".

These facts are in addition to blood-borne infectious germs and viruses.

Answer 2

A syringe is discarded after use because universal precautions involves treating it as if it was infectious, even if we believe it is not.