Sen. Chuck Grassley, who became the oldest serving senator after the death of Sen. Dianne Feinstein last year, is in a Washington, DC hospital with an infection and is receiving antibiotic infusions, his office says. "He is in good spirits and will return to work as soon as possible following doctors' orders," the Iowa Republican's office said in a statement Tuesday, per Fox News. Taylor Foy, a spokesperson for the 90-year-old senator, says Grassley has been in the hospital since he went in for tests Sunday, reports the Des Moines Register. "He never likes to be away from his job, so he's in as good of spirits as he can be," says Foy, who expects Grassley to make a full recovery. (More Chuck Grassley stories.)