Former President George H.W. Bush continues to fight a stubborn fever in the intensive care unit at Houston Methodist Hospital.

"Following a series of setbacks including a persistent fever, President Bush was admitted to the intensive care unit at Methodist Hospital on Sunday where he remains in guarded condition," Bush family spokesman Jim McGrath revealed in a prepared statement. "Doctors at Methodist continue to be cautiously optimistic about the current course of treatment. The president is alert and conversing with medical staff, and is surrounded by family."

McGrath earlier told ABC affiliate KTRK that the former president was awake and joking with doctors, but had yet to respond to medication designed to reduce the fever.

Bush, 88, has been in the intensive care unit in Houston's Methodist Hospital since Sunday, and hospitalized since Nov. 23, when he was brought to the hospital with a bronchitis-like cough. A hospital statement released on Dec. 13 predicted the former president would be discharged before Christmas.

Hospital Media spokesman David Bricker told ABC News that Houston Methodist Hospital will be releasing an updated statement on Bush's condition, but could not provide a timeline for the release and added that such information would be revealed when doctors felt it was appropriate and in accordance with the wishes of the Bush family.

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President Obama reportedly was being updated on Bush's condition but hadn't spoken directly with the Bush family.

A young Navy fighter pilot during WWII and former CIA director, Bush developed a warm relationship with his successor, Bill Clinton, teaming up to raise money for Asian tsunami victims in 2004 and then again in 2005 for victims of Hurricane Katrina.