The family had hoped Bush would have been well enough to spend Christmas at home. His cough eased, but he developed a persistent fever. His condition has since been downgraded to "guarded."
The former president has been visited by family and friends, including longtime friend James Baker III, his former Secretary of State. Bush's daughter, Dorothy, arrived Wednesday from her home in Bethesda, Md. Other visitors have included his sons George W. Bush, the 43rd president, and Jeb Bush, the former Florida governor.
Bush and his wife, Barbara, live in Houston during the winter and spend their summers at a home in Kennebunkport, Maine.
Bush, the 41st president, had served two terms as Ronald Reagan's vice president when he was elected in 1988. Four years later, after a term highlighted by the success of the 1991 Gulf War in Kuwait, he lost to Democrat Bill Clinton amid voters' concerns about the economy.
Bush was a naval aviator in World War II — at one point the youngest in the Navy — and was shot down over the Pacific. He's skydived on at least three of his birthdays since leaving the White House, most recently when he turned 85.
Bush, also a former U.S. ambassador to China and CIA director, suffers from a form of Parkinson's disease that forced him in recent years to use a motorized scooter or wheelchair for mobility.