He and his colleagues at Mount Sinai were the first to describe a syndrome of unexpectedly rapid onset and accumulation of hepatic fibrosis after HCV infection in HIV-infected men, a syndrome that appears to resemble the rapid fibrosis progression after HCV infection in patients with other disease-mediated or iatrogenic immunosuppression. In addition to his ongoing investigation into the epidemiology and mechanism of this liver disease, the main focus of his work has been to determine the mechanisms and fluids responsible for HCV infection among men who have sex with men, and to identify and functionally define the enhanced treatment responsiveness period of early HCV to be able to identify those who will be cured with short-course therapy with interferon-free treatments.