George HW Bush is the oldest of the four living former US presidents and uses a wheelchair.
Former US president George H.W. Bush on Wednesday was admitted to an intensive care unit in Houston, suffering from pneumonia, Bush's office said, adding that wife Barbara Bush has also been hospitalized.
The 92-year-old ex-president, who was initially hospitalized on Saturday, was moved to intensive care "to address an acute respiratory problem stemming from pneumonia," Bush's office said in a statement.
"Doctors performed a procedure to protect and clear his airway that required sedation."
He was originally admitted to Houston Methodist Hospital for shortness of breath, Bush spokesman Jim McGrath posted on Twitter.
"President Bush is stable and resting comfortably in the ICU, where he will remain for observation," the office said.
Early Wednesday, the former first lady, 91, was also admitted to the same hospital "as a precaution after experiencing fatigue and coughing," it said.
Bush, who served as president from 1989 to 1993, is the oldest of the four living former US presidents and uses a wheelchair. He has seemed frail in recent public appearances.
On January 10, he wrote President-elect Donald Trump a warm personal letter offering regrets that he and his wife would not be able to make it to Friday's presidential inauguration in Washington.
"My doctor says if I sit outside in January, it likely will put me six feet under. Same for Barbara," Bush wrote.
"So I guess we're stuck in Texas. But we will be with you and the country in spirit."
Bush is the patriarch of one of America's most prominent political dynasties and is father to former president George W. Bush (2001-2009) and former Florida governor Jeb Bush, who was a contender in the 2016 Republican presidential primary.
In July 2015, the elder Bush was treated in a Maine hospital after falling and breaking a bone in his neck. The previous December, he was admitted to Houston Methodist Hospital for breathing problems.
Bush was treated at the same facility in November 2012 for bronchitis, spending nearly two months in the hospital.
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