Former President George H.W. Bush remains in a Houston intensive care ward, but he continues to improve, and his exchanges with doctors and nurses now include singing.

"The Bushes thank everyone for their prayers and good wishes and, like their doctors, are cautiously optimistic that the current course of treatment will be effective," a family statement said Friday afternoon.

Earlier, a longtime aide said Bush was unlikely to leave the Houston hospital where he's being cared for anytime soon, but he would tell well-wishers to "put the harps back in the closet."

Jean Becker said in a statement Thursday evening that the 88-year-old, who has been hospitalized for longer than a month, is receiving excellent care after a "terrible case of bronchitis which then triggered a series of complications."

Bush, the oldest living former president, has been in intensive care since Sunday. He was admitted to Methodist Hospital in Houston on Nov. 23 for treatment of what his spokesman Jim McGrath described as a "stubborn" cough. He had spent about a week there earlier in November for treatment of the same condition.

Becker, Bush's longtime Houston chief of staff, said "most of the civilized world" contacted her Wednesday after word spread that Bush had been placed in intensive care unit when physicians were having difficulty bringing a fever under control.

"Someday President George H.W. Bush might realize how beloved he is, but of course one of the reasons why he is so beloved is because he has no idea," Becker said in the at-times lighthearted statement that made multiple references to jokes and the former president's sense of humor.

She said updates about Bush's condition have been limited "out of respect for President Bush and the Bush family who, like most of us, prefer to deal with health issues in privacy." She said another factor was "because he is so beloved we knew everyone would overreact."

It's a Wonderful Life

"I hope you all know how much your love, concern and support are appreciated," Becker said.

While the president's treatment was "unequaled anywhere," she said prayers also were needed and welcomed.

"I am thinking heaven has not seen such a barrage of prayer intentions since It's a Wonderful Life," she said, referring to the classic Christmas movie.

It was hoped Bush would be well enough to spend Christmas at home. But while his cough eased, he developed a persistent fever and his condition was downgraded to "guarded."

The former president has had visits from 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.

Lost to Clinton

Bush, the 41st president, had served two terms as Ronald Reagan's vice president when he was elected in 1988 to succeed Reagan. 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.

He left New England for an oil business job in West Texas in 1948. He's also been a Republican congressman from Texas, U.S. ambassador to China and CIA director.

Bush suffers from a form of Parkinson's disease that forced him in recent years to use a motorized scooter or wheelchair for mobility.