Huh?

I don't understand this article, which is making headlines. Was there some mass orgy or did someone go around stabbing people with dirty needles?

Midwest high school copes with HIV scare
NORMANDY, Missouri (AP) -- Students at a suburban St. Louis high school headed to the gymnasium for HIV testing this week after an infected person told health officials as many as 50 teenagers might have been exposed to the virus that causes AIDS.
Officials refused to give details on who the person was or how the students at Normandy High School might have been exposed, but the district is consulting with national AIDS organizations as it tries to minimize the fallout and prevent the infection -- and misinformation -- from spreading