This week in the CDC Expert Commentary series on Medscape, (log in required) Dr. Susan Hocevar describes the first recognized cluster of transplant-transmitted microsporidiosis linked to a common organ donor. An estimated 1 percent of organs transplanted in the U.S. each year are suspected to harbor a disease either infection or cancer. Examples of transmitted pathogens or diseases include an array of parasites, fungi, bacteria, and viruses. The CDC depends on astute clinicians to alert public health authorities of unusual infections, including microsporidiosis. The full description of this cluster of infections was published online in the March issue of the Annals of Internal Medicine.