- Needles and syringes come into contact with blood. If they are contaminated with blood from an infected person and then reused on another person, blood-borne pathogens can be directly injected into the bloodstream. - Human Immunodeficiency Virus (HIV) is a virus transmitted primarily through blood, semen, vaginal fluids, rectal fluids, and breast milk. Sharing contaminated needles is a high- risk activity for HIV transmission. - Hepatitis B and Hepatitis C viruses are also commonly transmitted through the reuse of needles.