Human cytomegalovirus. also known as human herpesvirus-5 or CMV is a virus in the herpes family. In most infected individuals, it is persistent, but harmless. However, it can affect the developing fetus in the uterus and can be particularly serious in a person who is immunocompromised. Estimates are that 50-80% of Americans are infected with the virus.
CMV is usually asymptomatic. In rare cases, it can cause symptoms that resemble mononucleosis.
However, in the newborn, persons with AIDS or persons on immunosuppressing drugs like transplant recipients, it can be life threatening. It is the leading infectious cause of congenital defects, affecting about 5 in every 1000 newborns with one or more defects. Any adult with an active infection is presumed to have AIDS even in the absence of a positive test as it very rarely causes symptoms in any other person without a medical history of immunosuppressant use.