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.
Health Department spokesman Craig LeFebvre has said the possibilities on how the students may have been exposed include sexual activity, intravenous drug use, piercings and tattoos.
"There's potential for stigma for all students regardless of whether they're positive or negative," Normandy School District spokesman Doug Hochstedler said Thursday. "The board wants to be sure all children are fully educated."
A teacher in a neighboring district singled out a girl who dates someone at Normandy High and instructed her to get tested, Hochstedler said. A competing school's football team initially balked at playing Normandy's 8-0 team.
Jasmine Lane, a 16-year-old sophomore, said her boyfriend from a neighboring high school broke up with her on learning of the news - after she bought them tickets to homecoming.
"I cried so hard," she said.
Hochstedler said that as far as he knows, no other district has had to handle a similar situation.
Appearing on The Early Show, Dr. Stanton Lawrence, superintendent of the Normandy School District, told co-anchor Harry Smith that the students "amazingly" have been very resilient to word of the health scare.
"The day we sent it out, I was in high school going classroom-to-classroom," Lawrence said. "Our students were engaged just as they routinely are. We provided additional counseling support, but the students reacted very, very well, as did the parents."
Students at the school of 1,300 are being tested voluntarily, and the district is getting advice on the best ways to support kids in crisis.
But some are feeling stigmatized.
Sophomore Tevin Baldwin said that many of his classmates in this working-class city of about 5,000 residents want to transfer out of the district, which encompasses other towns.
"Nobody knows what's going on," he said. The district declined to respond to his assertion.
Marcus Holman, a 14-year-old freshman, said he never imagined HIV would become such a widespread threat at school.
"I'm just trying to pass, get to the next grade, safely," he said.
The St. Louis County Health Department said last week that a positive HIV test raised concern that students at Normandy might have been exposed. The department is not saying whether the infected person was a student or connected with the school, only that the person indicated as many as 50 students may have been exposed.
Hochstedler said the district doesn't know the person's identity, or even whether he or she is a student.
"We do know there was some potential exposure between that person and students," he said. "We don't know the individual or the route of transmission."
Lawrence told Smith that, according to health officials, it is not believed that the carrier knowingly transmitted the virus. He also suggested that, even with what is known about HIV and AIDS and its dangers, students could make mistakes.
"Children are children, and if adults can make questionable decisions, certainly we have to understand that our young people will do this from time to time," he said on The Early Show. "I think what's important is that we respond, as we did, as expeditiously as possible, and let what is best for the kids drive our decision-making."
The district learned Oct. 9 of the potential exposure and within a business day worked out with the Health Department how to release the information and handle testing, he said.
"They took a very proactive stance," he said. "There's no precedent for this."
Students are being tested at six stations in the high school gymnasium, one class at a time. Only representatives from the Health Department are with the students, who are offered educational materials and a chance to ask questions before they are given an opportunity to be tested with a mouth swab, Hochstedler said. They may decline.
They exit through a separate door, and no one in the school would know who did or did not get tested.
"It's entirely up to the student," he said. "There's a lot of stigma associated with this."
The district will never know whether or how many of its students tested positive, he said.
"Once they're tested," he said, "it's an issue between the department and the child and his family."
So far, the district has met twice with parents and begun to ask ministers in the community to stress the importance of responsible behavior, Lawrence said.
Students in grades four through 12 already take classes that discuss the consequences of risky behavior, including HIV, he said.