B. An individual who is HIV positive. HIV positive individuals definitely make risky partners. However, it is very difficult to know whether a potential partner is HIV positive. Many HIV positive people show no signs of disease. Even a recent negative result for an HIV test may not be entirely reliable because a recently infected individual would likely test negative.
People share needles for all sorts of reasons like steroids, diabetes, allergies, etc.
Everyone but the first user of the equipment is at risk of being infected with viruses from all those who used it before. The possibility that an intravenous drug user who shares needles might be infected with HIV is very high. The rate of new infection has been successfully controlled in some countries and certain areas in the United States where health officials use measures such as the distribution of clean hypodermic needles, more drug treatment programs, and explicit sex education. It is estimated that as many as 30,000 Americans became HIV-infected from contaminated blood products before all FDA regulations on the testing of blood products were enforced. In addition to the risky partners mentioned above, other risk groups would include recipients of transplants or transfusions.