HOUSTON (AP) — Former President George H.W. Bush is being treated in the intensive care unit at a Houston hospital after suffering “a series of setbacks,” including a stubborn fever, his spokesman said.

In a brief email Wednesday, Jim McGrath, Bush’s spokesman in Houston, said the 88-year-old former leader had been admitted Sunday to the ICU at Methodist Hospital. McGrath said Bush, the oldest living former U.S. president, was alert and talking to medical staff.

He said doctors are cautiously optimistic about Bush’s treatment and that the former president “remains in guarded condition.” He said Bush was surrounded by family.