HIV can survive in a used needle for up to six weeks, according to NAM Aidsmap. When a discarded needle is reused, blood in the vacuum-sealed barrel of the needle can have live HIV in it and cause infection, according to AIDS Vancouver Island.
While used needles can be dangerous, there have been no reported cases of HIV infection caused by contact with a discarded needed, according to AIDS Vancouver Island. This is because HIV is readily killed when exposed to air, so when there is contact with oxygen in the needle of a syringe, blood in the needle is typically not infectious. Only reusing the needle poses a risk of infection.