According to the Centers for Disease Control, injection drug use directly and indirectly accounts for more than 36% of all AIDS cases in the United States.

For decades, HIV prevention advocates have been campaigning for funding of needle-exchange programs to reduce HIV transmission rates, but have run into a wall of opposition from conservative politicians who claim needle exchange programs were unproven and, worse, that they "encouraged" drug use.

Following through on these assertions, in 1998 the U.S. Congress imposed a federal ban on funding for any program or agency that incorporated needle exchange into its AIDS prevention efforts. Republican leaders said that if researchers and advocates could prove needle exchange programs were effective and did not contribute to increased use, they would consider lifting the ban.

A survey of 81 cities around the world compared rates of HIV infection rates among injection drug users in...