Medical Progress

From the Department of Microbiology, Duke University Medical Center, Durham, N.C. (T.C.D., P.C.H.); the Department of Molecular and Cellular Biology, Harvard University, Cambridge, Mass. (M.M.); the Department of Sociology, Boston College, Chestnut Hill, Mass. (J.G.); and the Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor (P.C.H.). Address reprint requests to Dr. Hanna at 1150 W Medical, 5641 MS II, Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48104, or at [email protected].