Cytomegalovirus (CMV)

Cytomegalovirus (CMV) belongs to the herpes virus family. It’s very common, affecting people all over the world. 

For most healthy adults and children, CMV does not cause any noticeable symptoms or long-term effects. In some cases, a healthy adult or child may develop cold- or flu-like symptoms.

However, if a woman catches CMV for the first time while pregnant, particularly during early pregnancy, CMV can have long-term effects on the unborn baby. CMV infection in an unborn baby is called congenital CMV (cCMV), which means it's present from birth. 

cCMV is the second most-common cause of permanent deafness in children. (The most common reason for deafness in children is because of genetic (inherited) causes.)

Once infected by CMV, the virus usually stays in an inactive form in the body (often for life). If the immune system becomes weakened the virus can reactivate.

How is CMV spread?

CMV spreads from one person to another through close contact with bodily fluids such as urine, saliva, blood, tears, breast milk, semen, vaginal fluids and faeces (poo). You can’t catch CMV from being in the same room as a person who has the infection.

CMV can also be spread through transplants and transfusions through a donor with either an active or past infection. Patients receiving transplants or transfusions are more susceptible because of their weakened immune systems.

Pregnant women often catch CMV through close contact with young children. You can prevent the spread of CMV by:

• washing your hands regularly (particularly after nappy changes)
• avoiding eating leftover food, drinking from the same cup or sharing utensils with young children
• avoiding kissing young children on the mouth.

There is currently no vaccine to prevent cCMV, but researchers are working to create one. 

What is congenital cytomegalovirus (cCMV)?

When a pregnant mother is infected with CMV for the first time, the virus can be transmitted across the placenta to her unborn baby. This is especially likely to happen during early pregnancy. CMV infection in an unborn baby is called congenital CMV (cCMV), which means it's present from birth. cCMV is the most common infection transmitted from mothers to their unborn children, affecting approximately 1000 babies a year.

Around 90% of babies born with cCMV don’t exhibit any obvious or visible symptoms of the virus. This is called asymptomatic cCMV. Around 10% of babies with cCMV will display signs of the virus at birth. This is called symptomatic cCMV. These symptoms can include:

• chorioretinitis (retinal inflammation)
• optic atrophy (optic nerve damage)
• cataracts (clouding of the eye lens)
• neurological disorders
• problems with other organs.

When might deafness happen?

Babies with cCMV might be born deaf, or they might lose their hearing later in life. Most cCMV-related deafness develops within the first four years of life, which can affect speech and language development. There is a very small possibility that young people with cCMV might become deaf in their teenage years.

Deafness is more common in babies with symptomatic cCMV. For newborns with asymptomatic cCMV, around 10 to 15% will go on to lose their hearing in the future. Some children whose deafness is caused by cCMV will have progressive or late-onset deafness, which means they lose more hearing as they get older. 

Children with cCMV should have regular hearing tests so that any changes in hearing are picked up early and help is offered quickly.

What type of deafness does cCMV cause?

cCMV causes sensorineural deafness, which affects the cochlea (inner ear). This type of deafness is permanent and can affect one or both ears.  

cCMV may cause unilateral deafness (deafness in one ear). This is more common in children with asymptomatic (showing no other symptoms) cCMV. Some children may develop deafness in the other ear later. Sometimes a child’s hearing may go up and down (fluctuate). Research is being carried out to try to understand how cCMV affects hearing and how this damage might be prevented.

cCMV may also affect the balance organs in a child’s inner ear, their hearing nerve, or more rarely their ability to interpret sound (auditory processing disorder (APD)). Children with cCMV may also experience glue ear, which causes temporary conductive deafness.

Hearing tests

Babies with a degree of deafness at birth are usually picked up by newborn hearing screening. They will have Auditory Brainstem Response (ABR) testing to confirm the degree and nature of deafness. Babies with confirmed cCMV should be offered ABR testing before 4 weeks of age.

Regular hearing tests are crucial for children with cCMV to detect any changes in hearing early. A child may not have noticeable problems with their hearing initially, especially if the deafness is affecting one ear.

All children with cCMV should have hearing tests regularly in early childhood to detect deafness. Hearing tests should be done:

• every three to six months in the first year
• every six to nine months until the age of three
• every year until the age of six.

There is a very small possibility that children with cCMV might lose their hearing during their teenage years. If a child is not likely to report a change in hearing themselves, for example because they have additional needs, they should continue to have regular hearing tests until the age of 11 or 12.

How is cCMV diagnosed?

Sometimes, signs of cCMV may be detected before a baby is born, often during an ultrasound scan. In such cases, tests for the infection may be offered to the pregnant mother.

Following birth, cCMV may be suspected in children who exhibit symptoms such as deafness. Early diagnosis is crucial because treatment is most effective during the first four weeks of life.

If you suspect your newborn child has CMV, you can request urine and saliva swab tests, or a blood test if your child is older.

Testing a sample of urine, saliva or blood within the first three weeks of a child’s life is the standard way of confirming cCMV. In some areas, this test may be offered alongside to all babies who do not pass the newborn hearing screen. A positive test for CMV helps diagnose cCMV if taken within the first three weeks of life. However, a negative result doesn’t completely rule out CMV.

Confirming cCMV becomes more challenging in children older than three weeks. If a child tests positive for CMV after they're three weeks old, it will be unclear whether the infection occurred before or after birth. Newborn blood spot testing can provide valuable insights in such cases. This test, offered to all UK newborns, checks for rare illnesses.

For children over a year old, antibody tests are reliable. A negative result suggests that the child has not had CMV, while a positive result indicates exposure to CMV. This test will not show whether the child had CMV before or after birth. The newborn blood spot test can help to clarify this. 

If your child is infected with CMV after birth, this is called 'perinatal CMV' (if they're under four weeks old), or 'acquired CMV' (if they're more than four weeks old). Perinatal and acquired CMV is not known to cause deafness. 

Treatment for cCMV

Babies younger than four weeks old who show signs of symptomatic cCMV, and babies with cCMV who've been identified as deaf, may be offered antiviral drugs to stop the virus from multiplying.

Further support

If your family is affected by cCMV, you're not alone. Your family, friends, teachers, and health professionals can get information from CMV Action. If your deaf child also has visual impairment, you can get support from Sense.

Some families with children affected by cCMV may be eligible for Disability Living Allowance (DLA).

Last reviewed: April 2024