Cytomegalovirus (CMV)

When a pregnant person is infected with CMV for the first time, the virus can be transmitted across the placenta to the unborn baby. This is especially likely to happen during early pregnancy. cCMV is the most common infection transmitted from mothers to their unborn children. It affects approximately 1,000 babies a year.

Around 90% of babies born with cCMV do not show any obvious or visible symptoms of the virus. This is called asymptomatic cCMV. Around 10% to 15% of newborns with asymptomatic cCMV will go on to lose some degree of hearing in the future.

Around 10% of babies with cCMV show signs of the virus at birth. This is called symptomatic cCMV. Deafness is more common in babies with symptomatic cCMV.

Symptoms of cCMV vary. They may include:

• a rash

• low birth weight
• yellowing of the skin and the whites of the eyes ('jaundice')

• seizures (fits)

• a smaller head than usual (microcephaly)

• problems with the eyes

• problems with the liver and spleen

• deafness in one or both ears

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

Babies younger than 4 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.

CMV spreads from one person to another through close contact with bodily fluids. You cannot catch CMV from being in the same room as a person who has the infection.

CMV can also be spread through organ transplants and blood transfusions through a donor who has either an active or past infection.

Pregnant people often catch CMV through close contact with young children. Everyone 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.

Babies with cCMV might be born deaf, or they might lose their hearing later in life. Most cCMV-related deafness develops within the first 4 years of life.

There is a very small possibility that children with cCMV might become deaf in their teenage years.

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.

cCMV causes sensorineural deafness. Sensorineural deafness happens when there is a fault in the inner ear or the auditory nerve that carries sound signals to the brain. Sensorineural deafness is permanent.

cCMV usually affects the cochlea. In some children, the hearing nerve can be affected, causing auditory neuropathy spectrum disorder (ANSD).

cCMV may cause unilateral deafness (deafness in one ear). This is more common in children with asymptomatic cCMV. They may also develop deafness in the other ear later on. Sometimes, their hearing may also 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.

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.

It's important that children with cCMV have regular hearing tests, so that any changes in hearing are picked up early. A child with cCMV may not have noticeable problems with their hearing initially, especially if the deafness is affecting one ear.

Hearing tests should be done:

• every 3 to 6 months in the first year
• every 6 to 9 months until the age of 3
• every year until the age of 6

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.

Sometimes, signs of cCMV may be detected during an ultrasound scan before a baby is born. In such cases, the pregnant mother might be offered a test for CMV.

Following birth, cCMV may be suspected in children who show symptoms such as deafness. CMV treatment is most effective during the first 4 weeks of life. It’s important that CMV is identified as soon as possible.

If you suspect your newborn baby has CMV, you can ask your doctor about CMV testing.

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, saliva swab tests may be offered to all babies who do not pass the newborn hearing screen.

A positive test for CMV helps diagnose cCMV if taken within the first 3 weeks of life. However, a negative result doesn’t completely rule out CMV.

Confirming cCMV is more challenging in children older than 3 weeks. If a child tests positive for CMV after they're 3 weeks old, it will be unclear whether the infection occurred before or after birth.

In the UK, blood spot testing (sometimes called the ‘heel prick test’) is offered to all newborn babies to check for rare illnesses. This test can be used to help find out whether a baby with CMV was infected before or after they were born.

For children over a year old, antibody tests are reliable. A negative result suggests that the child has not had CMV. 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 4 weeks old) or 'acquired CMV' (if they're more than 4 weeks old). Perinatal and acquired CMV are not known to cause deafness.