 A 2010 review found insufficient evidence that NSP prevents transmission of the hepatitis C virus, tentative evidence that it prevents transmission of HIV and sufficient evidence that it reduces self-reported injecting risk behaviour.It has been shown in the many evaluations of needle-exchange programmes that in areas where clean syringes are more available, illegal drug use is no higher than in other areas.Needle exchange programmes have reduced HIV incidence by 33% in New Haven and 70% in New York City.