because a quarter of the students are already sick. the extreme measures are keeping big city hospitals busy. as abc s linsey davis reports. reporter: all day long, dr. ron walls is rushing down the hall. a squirt of hand sanitizer and he s off to battle more flu. it s going to take you two or three weeks to feel really good again. reporter: he s wearing a face mask because he can t afford to be sick. not now with brigham hospital overrun with flu case s this patient has been battling the flu for ten days now. you ve been coughing a lot? yes. what are you bringing up with the cough? reporter: while we were there, the cases mounted. so much so, the hospital sounded an all hands on deck code amber alert. it s basically a disaster notification that we use when we have a large number of things to deal with. reporter: at holy name hospital in new jersey, dr.