A four-year-old Mississippi girl, who was believed to be cured of HIV, now has detectable levels of the virus, according to her doctors and U.S. officials. The finding is disappointing for the medical community as it continues to search for a cure for the thousands of children who are born infected with HIV every year.

There are about 250,000 children born every year who are infected with the virus that causes AIDS.

The so-called “Mississippi baby’s” case was brought to the attention of the medical community at a meeting in March 2013. The girl was born prematurely to an HIV-infected mother, who did not receive antiretroviral medication during pregnancy and was not diagnosed with HIV until the time of delivery.

Because of the high risk of HIV exposure, the infant received liquid, triple-drug antiretroviral treatment within 30 hours of life. Within several days, testing confirmed that the baby had been infected with HIV. The baby was discharged from the hospital and continued on liquid antiretroviral therapy after two-weeks of age.

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After 18 months on treatment, the girl reportedly ceased treatment. Then weeks later, when she did come back to the medical center where she was receiving care, she showed no signs of the virus. Since March, the child had gone 27 months without treatment and showed no evidence of the virus, until last week when the virus was found to have replicated.

Dr. Hannah Gay, a pediatric HIV specialist, who treated the baby after she was born at the Mississippi Medical Center, reportedly called the development “a punch to the gut.”

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a press statement, “Certainly, this is a disappointing turn of events for this young child, the medical staff involved in the child’s care, and the HIV/AIDS research community.”

Fauci added that the case highlights the dire need for better tools to measure resivoirs of HIV in patients, since the young girl was clearly infected from birth, though her doctors could not find any trace of the virus at a later time.

Dr. Deborah Persaud, a professor of infectious diseases at the Johns Hopkins Children’s Center in Baltimore and one of the two pediatric HIV experts involved in the ongoing analysis of the case, said in the press statement, “The fact that this child was able to remain off antiretroviral treatment for two years and maintain quiescent virus for that length of time is unprecedented. Typically, when treatment is stopped, HIV levels rebound within weeks, not years.”

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Commenting on the news, Dr. Demetre Daskalakis, an associate professor for infectious diseases at the Icahn School of Medicine at Mount Sinai in New York, told Healthline, “Although very disappointing, the loss of HIV control in this child is similar to what has been seen in studies of individuals treated for acute HIV infection who subsequently interrupt therapy. Some percentage of these individuals maintain viral suppression for a significant period of time, some longer than others. When immunologic control is lost, viral loads rebound, as they have in this child.

Continuing to understand the biology of HIV and the immune system for the goal of cure should still be high on the agenda despite this disappointment. The good news is that with antiretroviral therapy and good follow up, this child will be able to lead a healthy life.”

Fauci said, “The case of the Mississippi child indicates that early antiretroviral treatment in this HIV-infected infant did not completely eliminate the reservoir of HIV-infected cells that was established upon infection, but may have considerably limited its development and averted the need for antiretroviral medication over a considerable period. Now we must direct our attention to understanding why that is, and determining whether the period of sustained remission in the absence of therapy can be prolonged even further.”

Fauci added, “Scientifically, this development reminds us that we still have much more to learn about the intricacies of HIV infection and where the virus hides in the body. The NIH remains committed to moving forward with research on a cure for HIV infection.”