Though it’s declined since its discovery in the early 1980s, HIV is still a problem
A 2013 study from the Centers for Disease Control and Prevention (CDC) reported that over 1.1M people have HIV, with nearly 16% unaware of it. (For context, the 2010 Census reported a total of 308M+ US citizens.) The study looked at participants at least 13 years of age.
Unfortunately, we’re not able to see how the number distributes (i.e. are more people in their ’20s and/or ’30s affected than people in their ’40s and/or ’50s?), but that’d be useful to find out.