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Cytomegalovirus (CMV)

Photo: Congenital CMV causes about 10% to 20% of permanent deafness in children in the UK

CMV belongs to the herpes virus family. It’s very common, affecting people all over the world. Despite there being very little public awareness, CMV is more common than many other conditions associated with deafness such as Down’s syndrome, spina bifida, toxoplasmosis and cystic fibrosis.

Many of us will have had CMV by the time we’re 40 years old. Sometimes CMV can cause cold or flu-like symptoms but often the infection has no symptoms so we may not know we’ve had it. 

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.

Who can get CMV?

The CMV infection can cause illness in anyone with a weak immune system, such as an unborn baby. CMV infection in an unborn baby is called congenital CMV (congenital means present from birth).

Congenital CMV (cCMV) causes about 10% to 20% of permanent deafness in children in the UK and is the leading cause of non-hereditary deafness. There is currently no vaccine to prevent cCMV, but researchers are working on one.

If you have the CMV infection as a child or adult, this is called 'acquired CMV'. If a baby has a CMV infection in the first month of life, this is called 'perinatal CMV'. Acquired and perinatal CMV is not known to cause childhood deafness.

How is CMV spread?

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.

A pregnant mother infected with the CMV virus for the first time can transmit it across the placenta to her unborn baby. The majority of these babies will not have any problems.

When might deafness happen?

Half of all children with deafness caused by cCMV have a degree of deafness at birth and this may be picked up following newborn hearing screening. The other half go on to develop deafness after birth and will have had no problems identified on their newborn hearing screen.

Most deafness caused by cCMV develops during the first three years of life and so may affect speech and language development.

Some children born with cCMV may develop deafness later in childhood.

It’s important that children with cCMV have regular hearing tests so that any changes in hearing are picked up early and help is offered quickly. If you suspect your new-born child has CMV, you can request urine and saliva swab tests, or a blood test if your child is older.

What type of deafness does cCMV cause?

cCMV causes sensorineural deafness. This type of deafness is permanent and can affect one or both ears. Half of the children whose deafness is caused by cCMV will have progressive or late onset deafness (becoming worse over time).

cCMV may cause unilateral deafness (deafness in one ear). This is more common in children with asymptomatic (showing no other symptoms) cCMV, and some 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 CMV 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.

You can find more information in our factsheet Congenital cytomegalovirus and deafness