Cytomegalovirus (CMV) is a virus that infects the majority of Americans. CMV infection causes the cells of some organs to enlarge and swell, but typically does not cause symptoms or illness in most people. However, the virus can trigger serious illness in pregnant women, fetuses and people with weakened immune systems.

People who are infected with CMV can pass the virus to others who come into contact with body fluids. Once the virus is inside a person’s body, it remains there for life. In most cases, it lies dormant, but it can become reactivated in people whose immune systems are compromised.

Most frequently, CMV infection occurs by the time people are 2 years old or sometime before the teenage years. It is particularly likely in children who have been in daycare or preschool settings. Between 50 percent and 80 percent of adults in the United States are infected with CMV by the age of 40, according to the U.S. Centers for Disease Control and Prevention (CDC).

CMV infection typically is most dangerous when women become infected during pregnancy and pass the virus on to their fetus. Children born with congenital CMV infection typically do not experience symptoms or health problems associated with the infection. However, 1 in 750 children born with CMV infection – or about 8,000 children annually – will have permanent disabilities as a result of this infection.

Severe symptoms are also more likely to occur in people infected with CMV who also have weakened immune systems. This includes people with HIV and AIDS. It also includes people who have undergone organ or bone marrow transplants, and who are undergoing chemotherapy treatment for cancer. Some research shows that there may be a link between CMV and other conditions, including heart disease and certain forms of cancer, such as malignant brain tumors, colon cancer and breast cancer.

CMV culturing and special DNA-detecting tests are available to check for the CMV virus. In most cases, CMV infection does not require medical treatment. However, people with weakened immune systems may benefit from use of antiviral drugs.

Maintaining good personal hygiene may help lower the risk of cytomegalovirus infection. Young children are more likely to have CMV present in their urine or saliva than are older children or adults, so people who are in close contact with young, infected children are urged to exercise caution around them. This is particularly important for women who are pregnant, but who have not yet been infected with CMV.