A baby who doctors had hoped was cured of HIV is infected again, doctors said Thursday. The child, now 4, had been regularly tested for the AIDS virus and now it has not only returned, but showed signs of damaging her immune system, researchers said. "It felt very much like a punch to the gut," said Dr. Hannah Gay of the University of Mississippi, who has been treating the child. The Mississippi baby was born a little premature to a mother discovered to have HIV only when she was in labor. The baby, who doctors never named, tested positive for HIV after birth and received regular care and treatment from Gay at the University of Mississippi Medical Center. A cocktail of three drugs pushed her virus down to an undetectable level.