When I worked in CBP many years ago there was a USPHS person officing next door to one of our offices. He worked 9-5 daily M-F and never on the weekends. I usually only saw him when he came out of his office to get a cup of coffee or go home. Most of the flights carrying Vietnamese refugees and other immigrants arrived after 5 PM or on weekends. Many of these people had active TB and had never seen a bathroom. They would stop in the corridor, drop their pants and take a crap on the floor. USPHS man nowhere to be seen.