of white individuals after the initiation of a police anti-drug operation. These and other findings illustrate a possible mechanism by which racial disparities in law enforcement can translate into disparities in HIV transmission. Notably, the majority (56%) of respondents reported not documenting adverse police events; those who did were 2.92 times more likely to report unauthorized syringe confiscation. These findings suggest that systematic surveillance and interventions are needed to address police interference. Causes Police interference with legal NEP operations may be partially explained by training defects. A study of police officers in an urban police department four years after the decriminalization of syringe purchase and possession in the US state of Rhode Island suggested that up to a third of police officers were not aware that the law had changed. This knowledge gap parallels other areas of public health law, underscoring pervasive gaps in dissemination. Even police officers with accurate knowledge of the law, however, reported intention to confiscate syringes from drug users as a way to address problematic substance use. Police also reported anxiety about accidental needle sticks and acquiring communicable diseases from IDUs, but were not trained or equipped to deal with this occupational risk; this anxiety was intertwined with negative attitudes towards syringe access initiatives. Training and interventions to address law enforcement barriers US NEPs have successfully trained police, especially when framed as addressing police occupational safety and human resources concerns. Preliminary evidence also suggests that training can shift police knowledge and attitudes regarding NEPs specifically and public health-based approaches towards problematic drug use in general. According to a 2011 survey, 20% of US NEPs reported training police during the previous year. Covered topics included the public health rationale behind NEPs (71%), police occupational health (67%), needle stick injury (62%), NEPs' legal status (57%), and harm reduction philosophy (67%). On average, training was seen as moderately effective, but only four programmes reported conducting any formal evaluation. Assistance with training police was identified by 72% of respondents as the key to improving police relations. Advocacy Organizations ranging from the NIH, CDC, the American Bar Association, the American Medical Association, the American Psychological Association, the World Health Organization and many others endorsed low-threshold programmes including needle exchange. Needle exchange programmes have faced opposition on both political and moral grounds. Advocacy groups including the National District Attorneys Association (NDAA), Drug Watch International, The Heritage Foundation, Drug Free Australia, and so