His earlier work focused on studies of the epidemiology of tuberculosis among drug users, and on health care delivery models and behavioral and structural interventions to facilitate adherence to the TB care continuum. Recent work has focused on the delivery of other health care services (HIV, STI, HCV, HBV, others) to drug users in and out of drug abuse treatment, a qualitative and quantitative study of barriers and facilitators of HIV and HCV testing and care among ethnic minority drug users, and a “seek, test, treat and retain” intervention for high risk heterosexuals.  A prominent line of inquiry has been improving adherence to multi-step heath care interventions and care continua in a variety of settings, including extensive work with drug using populations in and out of drug abuse treatment settings. His current work focuses on the HCV care continuum. He was PI of the NIDA funded “Bridges” project, an RCT of a combined case management-motivational interviewing intervention to promote adherence to off-site referral for HCV care from methadone maintenance treatment (published in AJPH and selected for the AHRQ New Innovations Exchange). He is actively involved in a number of ongoing projects.