HOUSTON (AP) — Former President George H.W. Bush has been admitted to the intensive care unit at a Houston hospital "following a series of setbacks including a persistent fever," but he is alert and talking to medical staff, his spokesman said Wednesday.

Jim McGrath, Bush's spokesman in Houston, said in a brief email that Bush was admitted to the ICU at Methodist Hospital on Sunday. He said doctors are cautiously optimistic about his treatment and that the former president "remains in guarded condition."

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

The 88-year-old has been hospitalized since Nov. 23, when he was admitted for a lingering cough related to bronchitis after having been in and out of the hospital for complications related to the illness.

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.

"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."

But he said the cough that initially brought Bush to the hospital has improved.

Bush, the oldest former U.S. president, was visited on Christmas by his wife, Barbara, his son, Neil, and Neil's wife, Maria, and a grandson, McGrath said. Bush's daughter, Dorothy, was expected to arrive Wednesday in Houston from Bethesda, Md. The 41st president has also been visited twice by his sons, George W. Bush, the 43rd president, and Jeb Bush, the former governor of Florida.

Bush and his wife live in Houston during the winter and spend their summers at a home in Kennebunkport, Maine.

The former president was a naval aviator in World War II — at one point the youngest in the Navy — and was shot down over the Pacific. He achieved notoriety in retirement for skydiving on at least three of his birthdays since leaving the White House in 1992.

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