This project examines the history of the relationship of injection drug use and disease transmission in order to illuminate the public health challenges of emerging infectious diseases among isolated and hard-to-reach populations. When the link between injection drug use and the spread of AIDS was discovered in the 1980s, public health physicians and heroin addicts had known for more than five decades that infectious disease could be spread through drug users' injection practices. Yet not until that disease was AIDS did grass roots groups and public health researchers develop an effective response aimed at reducing disease transmission through syringe sharing. This book-length study will analyze the history of injection behaviors and medical knowledge of their health risks, and the history of the emergence of public health responses to blood-borne infectious disease transmitted through syringe sharing. It will analyze public health policy toward blood-borne infectious disease transmitted via syringes at the federal, state and local levels in the U.S. The states of California and Pennsylvania, and the cities of San Francisco, Philadelphia, and Pittsburgh will serve as case studies.