(USA TODAY) -- For the first time, doctors are reporting that they have cured a child of HIV, the virus that causes AIDS.

The landmark finding, announced Sunday at an Atlanta conference, will help scientists better understand the nature of HIV, doctors say, and could potentially help HIV-positive babies in developing countries.

"I'm sort of holding my breath that this child's virus doesn't come back," says Hannah Gay, an associate professor of pediatrics at the University of Mississippi Medical Center, who treated the 2-year-old Mississippi girl. Gay says she hopes the case "will show us a way to cure other babies."

Experts note that the girl's story is unique and would not immediately lead to a cure for the 34 million people living with HIV worldwide.

The baby contracted the virus at birth -- rare today, given the success of treating pregnant women with anti-HIV drugs that have nearly eliminated mother-to-child transmission, Gay says. Doctors began treating the baby, born five weeks premature, with anti-HIV drugs the day after she was born, Gay says. She expected the girl to require lifetime medication. However, the girl and her mother stopped going to doctor's appointments when she was 18 months old. By the time they saw a doctor, the baby had been off her HIV medications for five months.

Gay was amazed to find the child not just healthy, but HIV-free. Today, 10 months after stopping treatment, there's no sign of the virus.

Gay says doctors are not sure why the girl was cured. It's possible that giving drugs so early prevented the virus from hiding in her white blood cells, which can serve as "reservoirs" of infection. These reservoirs can cause the disease to come back if patients stop their treatment.

The girl's case could have the greatest potential impact in developing countries, where lack of prenatal care fuels a much higher rate of mother-to-child transmission, says Anthony Fauci of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, which partly funded the study. Despite the excitement, Fauci says, you "have to be careful not to make too much of one case."

Doctors have definitively cured one person of HIV, Timothy Brown of San Francisco, though two others in Boston may also have been cured, Fauci says. Brown's case was unusual because he had leukemia and had a bone-marrow transplant to treat his cancer from a donor with a genetic mutation that protects against HIV. However, these procedures pose major risks to patients and cost hundreds of thousands of dollars.

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