Definition of CMV (cytomegalovirus)

CMV (cytomegalovirus): A virus that infects 50-85% of adults in the US by age 40 and is also the virus most frequently transmitted to a child before birth. Persons with symptoms have a mononucleosis-like syndrome with prolonged fever and mild hepatitis. Once a person becomes infected, the virus remains alive and usually dormant within that person's body for life. Recurrent disease rarely occurs unless the person's immune system is suppressed due to therapeutic drugs or disease. CMV infection is therefore a concern because of the risk of infection to the unborn baby, people who work with children, and immunodeficient people such as transplant recipients and those with HIV.

CMV is a member of the herpesvirus group, which also includes herpes simplex virus, varicella-zoster virus (which causes chickenpox) and Epstein-Barr virus (which causes infectious mononucleosis). These viruses share a characteristic ability to remain dormant within the body over a long period. Initial CMV infection, which may have few symptoms, is always followed by a prolonged, inapparent infection during which the virus resides in cells without causing detectable damage or clinical illness. Severe impairment of the body's immune system by medication or disease consistently reactivates the virus from the latent or dormant state.

Infectious CMV may be shed in the bodily fluids of any previously infected person, and thus may be found in urine, saliva, blood, tears, semen, and breast milk. The shedding of virus may take place intermittently, without any detectable signs, and without causing symptoms.

Spread of CMV is from person to person. Infection requires close contact with a person excreting the virus in their saliva, urine, or other bodily fluids. CMV can be sexually transmitted. It can also be transmitted via breast milk, transplanted organs and, rarely, blood transfusions. Although the virus is not highly contagious, it has been shown to spread in households and among young children in day care centers.

Transmission of the virus is often preventable because it is most often transmitted through infected bodily fluids that come in contact with hands and then are absorbed through the nose or mouth of a susceptible person. Therefore, care should be taken when handling children and items like diapers. Simple hand washing with soap and water is effective in removing the virus from the hands.

CMV infection without symptoms is common in infants and young children; therefore, it is unjustified and unnecessary to exclude from school or an institution a child known to be infected. Similarly, hospitalized patients do not need separate or elaborate isolation precautions.

During pregnancy when a woman becomes infected with CMV, there is a risk that the infant may be born with CMV and have CMV-related complications. On the other hand, infants and children who acquire CMV after birth have few, if any, symptoms or complications.

CMV is the most important cause of congenital viral infection in the US. For infants who are infected by their mothers before birth, two potential pictures exist:

1. Generalized infection may occur in the infant, and symptoms may range from moderate enlargement of the liver and spleen (with jaundice) to fatal illness. With supportive treatment, most infants with CMV disease survive. However, from 80% to 90% have complications within the first few years of life that may include hearing loss, vision impairment, and varying degrees of mental retardation.
2. Another 5% to 10% of infants who are infected have no symptoms at birth but subsequently have varying degrees of hearing and mental or coordination problems.

Most healthy people working with infants and children face no special risk from CMV infection. However, for women of child-bearing age who previously have not been infected with CMV, there is a potential risk to the developing unborn child (the risk is described above in the Pregnancy section). Contact with children who are in day care, where CMV infection is commonly transmitted among young children (particularly toddlers), may be a source of exposure to CMV. Since CMV is transmitted through contact with infected body fluids, including urine and saliva, child care providers (meaning day care workers, special education teachers, therapists, as well as mothers) should be educated about the risks of CMV infection and the precautions they can take. Day care workers appear to be at a greater risk than hospital and other health care providers, and this may be due in part to the increased emphasis on personal hygiene in the health care setting.

Primary (or the initial) CMV infection in the immunocompromised patient can cause serious disease. However, the more common problem is the reactivation of the dormant virus. Infection with CMV is a major cause of disease and death in immunocompromised patients, including organ transplant recipients, patients undergoing hemodialysis, patients with cancer, patients receiving immunosuppressive drugs, and HIV-infected patients. Pneumonia, retinitis (an infection of the eyes), and gastrointestinal disease are the common manifestations of disease. Because of this risk, exposing immunosuppressed patients to outside sources of CMV should be minimized. Whenever possible, patients without CMV infection should be given organs and/or blood products that are free of the virus.

Most infections with CMV are not diagnosed because the virus usually produces few, if any, symptoms and tends to reactivate intermittently without symptoms. However, persons who have been infected with CMV develop antibodies to the virus, and these antibodies persist in the body for the lifetime of that individual. A number of laboratory tests that detect these antibodies to CMV have been developed to determine if infection has occurred and are widely available. In addition, the virus can be cultured from specimens obtained from urine, throat swabs, and tissue samples to detect active infection.