Dr. Johnson is an Infectious Disease Researcher at the Hines VA Hospital, Hines IL and an Emeritus Professor of Medicine at Loyola University Chicago Stritch School of Medicine. His main research interest and focus has involved the epidemiology, pathogenesis, and treatment of Clostridioides difficile infection (CDI). His work has highlighted the risk of specific antibiotic-resistant C. difficile strains to cause outbreaks in institutions that have high usage patterns of those antibiotics, the role of non-toxigenic C. difficile strains, and the importance of toxin B in the virulence of C. difficile. His clinical experience in the treatment of patients with recurrent CDI has translated into studies helping to define optimal management of these infections. He is currently the Principal Investigator of a multi-center, randomized, controlled trial within the VA Healthcare system designed to define optimal management of early recurrences of CDI.