Tests made last week in the four year old girl from Mississippi indicate that it is no longer in remission, doctors say.
She seemed to be free of HIV by recent March without receiving treatment for about two years.
The news is a setback in the hope that very early treatment drugs can reverse the permanent infection.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told US media that the new results were "obviously disappointing" and had possible implications in a federal study in HIV to come.
"We'll take a good look at the study and see if he needs any change," he said.
By James Gallagher Health Editor, BBC News website
There was great hope that the "baby of the Mississippi" to live a life free of HIV.
The antiretroviral drugs can keep the virus restriction in the bloodstream, but HIV has places to hide - known as reservoirs - in the gut and brain.
If treatment is interrupted, then the virus emerges from its reservoirs and begins his attack again.
Physicians are expected to begin treatment in the early hours after birth would prevent the formation of reservoirs.
This did not appear to be the case.
This case never lead to a cure for HIV-infected adults who start treatment months or years after infection.
The child, nicknamed "Baby Mississippi" received no care with HIV during prenatal care.
Due to a high risk of infection, it began a powerful treatment for HIV only hours after the pain of childbirth.
She continued to receive treatment until 18 months, when doctors could not locate it. When she returned 10 months later, no sign of infection was evident though her mother had not given her drugs for HIV in the meantime.
Repeated tests showed no detectable HIV virus until last week. Doctors do not yet know why the virus reappeared.
The second child with HIV was given early treatment a few hours after birth in Los Angeles in April 2013.
Subsequent tests indicate that it completely cleared the virus from your body, but that child also received continuous treatment.
It is currently believed that only an adult HIV was cured.
In 2007, Timothy Ray Brown received a bone marrow transplant from a donor with a rare genetic mutation that resists HIV. He showed signs of infection for more than five years.
Translated by Rodrigo Pellegrini Sgobbi