Former President George H.W. Bush is in the intensive care unit at Methodist Hospital, fighting a stubborn fever that is on the rise.
As a result, he is now on a liquids-only diet, family spokesman Jim McGrath said.
The 88-year-old Bush was moved to ICU on Sunday. Doctors continue to treat his fever with Tylenol, but still haven't nailed down a cause for the fever.
McGrath said Bush remains upbeat as he continues to receive visitors.
"All the kids are making their own plans to come back to Houston to visit him and help him rally -- rally to recovery," said McGrath.
Bush's daughter, Dorothy, arrived on Wednesday for a visit. His sons, former President George W. Bush and former Florida Gov. Jeb Bush, will be paying a visit in the coming days.
The 41st president has been hospitalized since Nov. 23 with a lingering cough caused by bronchitis. Doctors were ready to send him home after a short string of good days, but changed their minds after Bush suffered a series of setbacks, including a few low-energy days and now a stubborn fever.