Sen. Robert Byrd (D-W.Va.) is expected to remain in the hospital for the time being as a result of a staph infection he developed while being hospitalized for an unrelated infection, his office said Monday.

“According to his doctors, Senator Byrd developed a staph infection during his initial hospitalization for treatment for a minor infection. This, in turn, has delayed his departure from the hospital at this time. Doctors have been treating him with antibiotics for the infection and he has been responding well. There has been no additional indication as to when he will be released from the hospital,— the statement from Byrd’s office said.

Byrd, 91, the oldest serving Senator, has been in the hospital since May 15. His office said at the time that he had been admitted for a minor infection.