After his internal medicine residency training, he served as Epidemic Intelligence Service (EIS) officer at the Centers for Disease Control and Prevention (CDC), where he led an outbreak investigation that resulted in the discovery of E. coli O157:H7, a major foodborne pathogen that causes bloody diarrhea. His current research work includes molecular epidemiology and pathogenesis of tuberculosis and drug-resistant bacterial infections, as well as global health focused on diseases of urban slums. He has research collaborations in Brazil, Colombia, India, Japan, China, Romania, and Bangladesh.