 After his residency, Katz remained in San Francisco.In 1991, he joined the San Francisco Department of Public Health (SFDPH), serving as chief of research and director of the AIDS Office, director of the Emergency Medical Services Agency and director of the department's health and safety branch.From 1997 to 2010, Katz served as the director of health and health officer for the San Francisco Department of Public Health, where he implemented the Healthy San Francisco program, which is the United States' first municipal universal health care system.