What is cytomegalovirus (CMV)?

Most people do not know that CMV infection is the most common cause of congenital viral infection in the United States, affecting about one to two out of 100 newborn babies.

How can you get cytomegalovirus (CMV)?

CMV may be found in body secretions, such as urine, saliva, feces, blood and blood products, breast milk, semen and cervical secretions and it can stay in these secretions for months to years after the initial infection. The principal mode of infection in adults is contact with young children in the household or in day-care centers. Close contact includes kissing and getting saliva or urine on your hands and then touching your nose or mouth. CMV may also be transmitted through sexual contact. A pregnant woman who is infected can pass the virus to her developing baby before or during labor, or during breastfeeding.

Learn about common sexually transmitted diseases

Most initial CMV infections in adults go unnoticed, although some people experience non-specific ‘flu-like’ symptoms such as fever, fatigue, sore throat, headache, decreased appetite and swelling of the lymph glands, liver and spleen. A CMV infection is usually harmless, but it can be life-threatening for people with immune problems, such as those with cancer or HIV infections. And if a person carries CMV during pregnancy it can also infect the fetus by passing across the placenta, possibly creating problems.

When you become infected with CMV for the very first time, you develop a ‘primary’ infection. Contrary to other viral infections such as German measles or chickenpox, which provide immunity for life after an infection, a previous infection with CMV prior to pregnancy does not protect you from becoming infected again or from infecting the fetus, though the chance of this happening is very small. After the primary infection you can continue to shed the virus intermittently for the rest of your life without any symptoms. This is called a ‘recurrent’ infection.

About 30-60% of all children have serologic evidence of prior infection by the time they reach school age, and about 45-85% of women in the United States have been infected with CMV prior to pregnancy and carry the antibody against CMV in their blood. Women of lower socioeconomic means have a higher chance of having been exposed to the virus than women of higher socioeconomic means.

CMV and pregnancy

About 0.2-2% of all pregnant women develop a primary infection during pregnancy, and if that happens, about one-half of the fetuses become infected. The chance of a fetal infection is higher later on in pregnancy, but a fetal infection early into a pregnancy has more severe consequences than an infection in the third trimester.

About 10-15% of all congenitally infected fetuses are born with problems such as intrauterine growth restriction (IUGR), jaundice, nonimmune hydrops, eye infections, enlargement of the liver and spleen (hepatosplenomegaly), low platelets and brain abnormalities such as microcephaly (small heads), hydrocephaly, and calcifications of the brain.

Over 90% of infected babies without symptoms at birth will have no problems, but about 10% can develop problems later on such as mental retardation, learning disabilities, eye problems, hearing loss, and other developmental problems.

How is CMV diagnosed?

The CMV blood test looks for two different kinds of antibodies: IgG antibodies signify an infection in the past, anytime between 4 weeks and many years. The IgG stays positive forever. The IgM antibody identifies more recent infections, maybe within the last months, and it usually becomes negative within months after an infection.

The diagnosis of a primary infection is usually made when someone who tested negative for the antibody in the past, now tests positive.

If IgM antibody is found in the newborn baby, that usually means the baby was infected inside the uterus, while a positive IgG has usually come from the mother and crossed the placenta. A baby can also get tested after delivery with a culture for CMV. Before delivery, a congenital infection of the fetus can be detected by doing an amniocentesis and finding a positive virus culture and/or a positive PCR test in the amniotic fluid.

At present, no specific prevention or  treatment for CMV is known. Good hand-washing may decrease your chance of getting infected, and concerns have been raised about having small children in day-care settings while mom is pregnant. Routine testing of pregnant women without any symptoms is also presently not suggested. However, if you are exposed to small children, screening for prior CMV infection before pregnancy may be indicated. We suggest that you discuss this with your doctor.

What are my risks of infecting the baby with cytomegalovirus CMV during pregnancy?

CMV infections per 10,000 pregnancies with approximate percentages: