Late on Wednesday, Bush's spokesman, Jim McGrath, said that the former president was admitted to the ICU on Sunday at Methodist Hospital, "following a series of setbacks including a persistent fever."

McGrath says Bush is alert and conversing with medical staff, and that doctors are cautiously optimistic about his treatment.

No other details about his medical condition were provided, but McGrath says Bush is surrounded by family.

Earlier Wednesday, McGrath said a fever that kept Bush in the hospital over Christmas had gotten worse and that doctors had put him on a liquids-only diet.

A bronchitis-like cough initially brought Bush to the hospital in late November. McGrath says the cough has improved.

AP