Former President George H W Bush is in the intensive care unit of a Houston hospital and is in "guarded condition," family spokesman Jim McGrath said on Wednesday.

"The president is alert and conversing with medical staff, and is surrounded by family," McGrath said in a statement.

"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," McGrath said. "Doctors at Methodist continue to be cautiously optimistic about the current course of treatment."

The 88-year-old was admitted to the hospital on November 23 for bronchitis.

A hospital spokesman said in mid-December that the former president was expected to be home from the hospital in time for Christmas, but that spokesman later said doctors felt that he should build up his energy before going home.

Bush has lower body Parkinsonism, which causes a loss of balance, and has used wheelchairs for more than a year, McGrath said in an email on Wednesday.

Bush, the 41st US president and a Republican, took office in 1989 and served one term in the White House. The father of former President George W Bush, also served as a congressman, ambassador to the United Nations, envoy to China, CIA director and vice president for two terms under Ronald Reagan. – Reuters