Sen. Robert Byrd (D-W.Va.), hospitalized five weeks ago for an infection, will not be coming back to work this week, according to a statement from his office.

“Senator Byrd continues to improve but remains in the hospital while he undergoes physical therapy and treatment for a staph infection,— the statement said. “He is not expected to be in the office this week.—

Byrd, 91, is the Senate’s longest-serving Member and serves as its President Pro Tem, a leadership position that requires him to sign bills approved by Congress before heading to the White House. The statement released Monday notes the ailing Senator “is resuming some of his official duties while recuperating, including signing several enrolled bills as President pro tempore of the Senate.—

Sen. Patty Murray (D-Wash.), filling in for Byrd, will steer the fiscal 2010 Homeland Security appropriations bill on the floor later this week. Byrd chairs the Appropriations Subcommittee on Homeland Security but missed the committee’s consideration of the bill because of his extended hospital stay.

Byrd was hospitalized on May 15 for what was described as a mild infection. His office said he later developed a staph infection. His office has offered few additional details on his condition and declined to say where Byrd is receiving medical treatment.

The ailing Democrat has been admitted to the hospital a few times over the past year. Last June, he also had been treated for a minor infection.