The AIDS epidemic is concentrated primarily among MSM, sex workers and their clients, and people who inject drugs. Results of a 2006 study by Bravo-Garcia et al. reported by UNAIDS indicate that sex between men accounts for 57 percent of the HIV infections. Mexico’s National Center for HIV/AIDS Prevention and Control (CENSIDA) estimates that HIV prevalence among MSM was 10 to 13.5 percent in 2006. Results from studies in 2006 by Gayet et al., Magis et al., and the Biological Behavioral Surveillance Survey conducted in Mexico showed that HIV prevalence rates among male sex workers were 25 percent in Monterrey, 20 percent in Guadalajara and Mexico City, and 12 percent in Ciudad Nezahualcóyotl.