The answer to the first question is that less than 1% of the US population has HIV so the likelihood that the person before you had HIV
was less than 1 in 100, or, if you believe that persons with piercings are more likely to have HIV
, maybe twice as high- 1 out 50 chance. Then, what is the likelihood of transmission through (worst case) improperly cleaned shared needle - estimates are the probability of infection would be about 1 in 100. Any cleaning, etc would reduce these odds.