Estimated numbers of sex workers vary from 8,000 to over 13,000 in each country of Central Asia. Sentinel Surveillance conducted with technical support from the U.S. Centers for Disease Control and Prevention (CDC) in 2007 found prevalence of HIV to be as high as 16% among sex workers in parts of Uzbekistan. Overlap and interaction between sex and injecting drug use is another feature of the HIV epidemic in the region. Risky behaviors among drug-using sex workers may be the most important engine for the spread of HIV to the general population, and require specific interventions to prevent both blood-borne and sexual transmission of HIV. Sentinel Surveillance by CDC showed that 8.2% of sex workers in Uzbekistan inject drugs and 50% of female injecting drug users in Tajikistan have provided sex services in exchange for money or food. An estimated 35% of all HIV positive women in Eastern Europe and Central Asia were infected through the use of contaminated drug injecting equipment and 50% acquired the virus through unprotected sex.