A family spokesman said Friday that former U.S. President George H.W. Bush, who has been hospitalized for more than a month, "continues to improve" but remained in intensive care at a Texas hospital.

"The President is alert and, as always, in good spirits — and his exchanges with doctors and nurses now include singing," family spokesman Jim McGrath said in a brief statement.

Physicians remained "cautiously optimistic that the current course of treatment will be effective," McGrath added.

Bush, the oldest living former U.S. president, has been hospitalized since Nov. 23. He was moved into intensive care on Sunday for treatment of a fever following a bronchitis-related cough.

Longtime aide Jean Becker said in a statement Thursday evening that Bush likely would advise well-wishers to "put the harps back in the closet."

Becker said "most of the civilized world" contacted her Wednesday after disclosures that Bush had been placed in the intensive care unit after 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 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."

"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.

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

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 skydived on at least three of his birthdays since leaving the White House, most recently when he turned 85.

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