A "stubborn" fever that kept former President George H.W. Bush in a hospital over Christmas has gotten worse, and doctors have put him on a liquids-only diet, his spokesman said Wednesday.

Jim McGrath, Bush's spokesman in Houston, had said earlier in the day that the fever had gone away, but he later corrected himself.

"It's an elevated fever, so it's actually gone up in the last day or two," McGrath told The Associated Press. "It's a stubborn fever that won't go away."

Doctors at Methodist Hospital in Houston have run tests and are treating the fever with Tylenol, but they still haven't nailed down a cause, McGrath said. Doctors also have put Bush on a liquid diet, though McGrath could not say why.