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Response to the calculation of population attributable fractions (PAFs) of risk factors for hepatitis C transmission.

We commend Hagan et al. [1] for their important review on incidence of sexually transmitted hepatitis C virus (HCV) infection in HIV-positive men who have sex with men (MSM). With this correspondence, we wish, first, to explain how their calculation of population attributable fraction (PAF) likely leads to incorrect conclusions and, second, to explicate the transmission route of hepatitis C among HIV-positive MSM.