CYTOMEGALOVIRUS and herpes simplex, varicella–zoster, and Epstein–Barr viruses, members of the herpesvirus family, are ubiquitous agents that infect almost all human beings at some point during their lives. Infections with these viruses have been found in all populations tested, although their prevalence varies according to the age of patients at acquisition and to the geographic and socioeconomic settings. A unique characteristic of herpesvirus infections is that viral shedding may persist for weeks or months after the primary infection, as occurs with cytomegalovirus and Epstein–Barr virus. After the primary infection, latency is established and periodic episodes of reactivation can occur. Except. © 1985, Massachusetts Medical Society. All rights reserved.