Resident pediatrics Children's Hospital Philadelphia, 1971—1973. Chair, community health science Aga Khan University, Karachi, Pakistan, 1993—1997. Chief epidemiology Institute Pasteur, Paris, 1997—1999.
Executive Information System officer Centers Disease Control, Atlanta, chief, special pathogens branch. Dean and professor University of Texas School Public Health, Brownsville Campus. Captain United States Public Health Service, 1973-1995, Centers for Disease Control and Prevention, Atlanta.