Parents of some children at an elementary school are afraid that the youngsters may have been exposed to the virus that leads to AIDS after as many as 19 third-graders, including one who is HIV positive, were pricked by the same needle.
It happened on the Taylor Elementary School playground on Wednesday, when one child brought her mother's diabetes testing needle to school and started pricking her classmates.
Some parents said the incident bothered them when they first heard of it, because a substitute teacher allegedly ignored children's complaints that the little girl was stabbing them with the needle. They said their concerns became much more serious after school officials informed them Thursday that one of the children who was stuck with the needle is HIV positive.
The parents don't know how worried to be about the risk to their children, because they do not know when the needle was used on the child who is HIV positive.
"We don't know if that was before or after whose child," said Carmen Ortiz, whose daughter, Carmen Mendoza, attends the school.
Eight-year-old Carmen is like many of her classmates -- she doesn't even know what HIV is, but she can tell by her parents' reaction.
"I don't really know what it is, but I'm scared," she said.
"This is something that's not to be played with," said Mike Gonzalez, another parent of a child at the school. "You've got now little kids that are in danger."
Parents were told to bring their children to St. Christopher's Hospital for blood tests. They were given prescriptions for Retrovir and Epovir, drugs the prescribing doctor said can prevent HIV infection. They are given to health care workers within 24 hours of an accidental needle stick.
As of Thursday evening, the parents of five children said the test results were negative for the potentially deadly virus. The children will be tested twice more.
"I have to keep coming back month to month for three months … agony for me, you know," said parent Magdalia Rios.
In a meeting closed to the media, school and health officials tried to explain how this could have happened, parents said. School officials also had to answer complaints that the teacher initially dismissed the students' complaints about the needle.
Paul Vallas, chief executive officer of the School District of Philadelphia, promised there would be a full investigation.
Most of all, though, parents wanted to know if their child may have been exposed to HIV, but they'll will have to wait at least three weeks before they know the answer.
"We're waiting for some type of answer," parent Michael Gonzales said. "They said, 'Here's a card. In three weeks, make an appointment and we will tell you if your child is OK or not.'"
Meanwhile, health officials are urging parents to give their children the HIV drugs along with Pepcid, because the drugs can be rough on the stomach. Kids taking the drugs are already complaining about the side effects.
"I drank it and when I started walking it makes me dizzy," third-grader George Whitaker said.
School officials said they will help parents cover any medical costs and help provide transportation for the testing that will need to be done in three weeks.
When an accidental exposure to HIV happens -- say to a nurse or an emergency medical technician -- there are standard protocols to follow. Those protocols have been used in this case, and being exposed to HIV doesn't mean contracting the virus, experts said.
Some experts said there's a greater risk of getting hepatitis C from a needle stick than there is of contracting HIV.
"Exposure doesn't mean automatic infection under any circumstance," said Jane Shull of Philadelphia FIGHT, an AIDS service organization that provides primary care, consumer education, advocacy, and research on potential treatments and vaccines.
But Shull said it's vital to give antiviral drugs immediately.
"You do want to do this quickly, before the virus gets a foothold in your body," she said.
The arsenal of medications available to doctors has changed dramatically within the past decade. A whole new class of drugs, the fusion inhibitors, came out two years ago, and many of the drugs that were used previously are being combined to make them easier to take. They need to be taken fewer times a day, and generally have milder side effects.
Shull believes if the drug regimen is followed, this horrible incident eventually will be little more than a distant memory.
"If you're willing to put up with these side effects, then you go from a situation where you really had a risk to something where you're really OK," she said.
ABC News affiliate WPVI in Philadelphia contributed to this report.