Former President H.W. Bush is in intensive care at a hospital in Houston, his spokesman reported Wednesday.
Jim McGrath, Bush's spokesman, said the 88-year-old had suffered "a series of setbacks including a persistent fever."
"It's an elevated fever, so it's actually gone up in the last day or two," McGrath told The Associated Press. "It's a stubborn fever that won't go away."
Nevertheless, McGrath said the former president was alert and talking to medical staff.
The senior Bush was first admitted to The Methodist Hospital to treat bronchitis Nov. 7. He was released on Nov. 19 but readmitted less than a week later.
Doctors hoped he would spend Christmas at home, but decided otherwise when he developed a fever, The Houston Chronicle reported.
McGrath said Bush and his wife, Barbara, their son Neil and his wife Maria, and his grandson Pierce enjoyed Chinese food together on Christmas Day.
Two other sons, former President George W. Bush and former Florida Gov. Jeb Bush have both visited their father during his hospital stay but weren't there for Christmas.