Neil Bauman, Ph.D.
© November, 2017
Introduction to Cytomegalovirus
Perhaps you have never heard of cytomegalovirus (CMV), but the chances are, this virus has already infected your body. By age 40, between 50% and 80% of adults in the United States have already been infected by the cytomegalovirus. (1) This incidence increases to 91% in people 80 and older. (2) Even in children, the incidence of CMV infection is high. About 36% of children between the ages of 6 and 11 have already had a CMV infection. (2)
The cytomegalovirus (sie-toe-MEG-ah-low-vie-rus) is a member of the herpes family of viruses. As such, it is a close relative of the viruses that cause chickenpox and infectious mononucleosis (mono). Furthermore, like other herpes viruses, once CMV is in your body, it stays there for the rest of your life. (1)
Although CMV infects people of all ages, most children and adults infected with CMV will have no symptoms, or might develop only a mild mononucleosis-like illness. (2) This is because if your immune system is healthy, it usually keeps the virus under control.
Once a person is infected, the virus becomes latent. However, it may reactivate at any time in the future. (2) If you have a weakened immune system, the cytomegalovirus can reactivate and cause serious health problems including hearing loss.
The most serious problems with the cytomegalovirus occurs in children, especially in babies infected with the cytomegalovirus before they are even born. This is called congenital CMV. Congenital cytomegalovirus is a public health problem because it is so common. One in every 200 babies born already is infected with CMV. (3)
Hearing Loss Due to Cytomegalovirus
You may be surprised to learn that sensorineural hearing loss (SNHL) is the most common health problem in babies born with congenital CMV. About 21% of all permanent hearing loss at birth is due to congenital CMV. (3)
However, not all hearing loss from congenital CMV occurs at birth. Approximately 33% to 50% of sensorineural hearing loss due to congenital CMV infection occurs after the newborn period. By four years of age, 25% of childhood hearing loss is due to congenital CMV infection” (3), and by five years of age, nearly one in three children have already been infected with CMV. (4)
One study reported that 8% of all CMV-infected children identified with sensorineural hearing loss had a hearing loss of 30 dB or greater at 6 years of age. This included 11% of children who were asymptomatic at birth and 36% of children who were symptomatic at birth. (2)
In another study using stored, dried umbilical cord samples from children with various levels of hearing loss, here is what researchers found.
- In children with moderately-severe to profound bilateral sensorineural hearing losses (>55 dB), 16% had congenital CMV infections.
- In children with severe sensorineural hearing losses; 15% were found to have congenital CMV infections.
- In children with profound bilateral sensorineural hearing losses (>90 dB), 22% were identified with congenital CMV infections. (2)
Hearing loss from congenital CMV infections can occur in just one ear, or in both ears, and can vary from mild to profound. (2)
Furthermore, about 50% of the children born with sensorineural hearing losses following congenital CMV infections will have further hearing loss in the future. (3)
Another characteristic of CMV-related hearing loss is fluctuating hearing loss. (Incidentally, this fluctuating loss is not caused by concurrent middle ear infections.) Fluctuating hearing loss may only occur in one ear; it may occur at all, or just a few frequencies; or it may occur in both ears if a child has bilateral hearing loss. “About 30% to 50% of children with CMV-related hearing loss will have fluctuating loss.” (3)
Hearing losses resulting from CMV infections do not have unique audiometric configurations. Thus, you cannot tell a person has hearing loss from a CMV infection just by looking at their audiogram. (2)
How does the cytomegalovirus damage hearing? It is thought that a CMV infection may directly damage the hair cells and supporting structures in the inner ear. Another possibility is that the body’s inflammatory responses to CMV in the inner ear may damage the auditory apparatus resulting in hearing loss. However, neither of these possibilities fully explains why hearing loss from CMV infections is progressive and may occur several years after birth. (2) This is still unknown and needs more research to reveal the reason why.
Differences between Asymptomatic or Symptomatic Hearing Losses
When babies are born with cytomegalovirus, they may have no obvious symptoms of the virus (asymptomatic), or they may have symptoms of CMV right from birth (symptomatic). Here is what you can expect in these two cases.
Asymptomatic at Birth
Of all babies born with the cytomegalovirus in their bodies, roughly 90% will be asymptomatic and will show no obvious or visible symptoms of the virus. You can expect these children to live healthy lives and grow and develop normally. (5)
However, the remaining 10% or so (One study put this figure at 8.7%. ) of babies born with asymptomatic congenital CMV will develop hearing loss—either from birth, or later in life.
If this is your child’s situation, you should carefully monitor his hearing, even if he passed his newborn hearing screening because he could develop hearing loss in the next few years. In fact, “hearing loss can progress over months to several years, throughout childhood, adolescence, and even into young adulthood.” (5)
Incidentally, if hearing loss occurs in asymptomatic children, it will usually begin in one ear, and then may progress to severe or profound hearing loss in one or both ears.” (5)
A study that compared the differences in hearing loss between children born with asymptomatic congenital CMV to children who were not infected with CMV revealed some interesting things.
- At age 18, those who were born with congenital CMV had an incidence of sensorineural hearing loss of 25%. The incidence of sensorineural hearing loss in the controls was only 8%.
- The risk of developing sensorineural hearing loss after age 5 among those born with asymptomatic congenital CMV was not different from uninfected children.
- Delayed-onset hearing loss and the progression of sensorineural hearing loss among children with asymptomatic congenital CMV infections continued to occur throughout adolescence.
- The prevalence of severe to profound bilateral sensorineural hearing loss among those born with asymptomatic congenital CMV was 2%. Such children would be candidates for cochlear implants. (6)
Symptomatic at Birth
Roughly 10% of babies born with congenital cytomegalovirus will show obvious symptoms of CMV right from birth. Such symptoms include “small size, jaundice, a “blueberry muffin” skin rash and/or an enlarged liver or spleen. These babies may also have a small head size (microcephaly) and may have problems with their blood cell counts and low platelets.” (5)
In addition, “approximately 75% of these babies will have signs of brain involvement and may experience major challenges as they grow, including problems with hearing, vision, nutrition, growth, cognition, learning, and motor/muscle tone.” (5)
Unfortunately, up to 75% of the babies born with symptomatic congenital CMV will have hearing loss. (5) (One study put this figure at 41%. )
In almost all such children, hearing loss will progress throughout the course of their lives. Therefore, if this is your child’s situation, you should make sure she has regular periodic hearing evaluations throughout her life to detect any changes in hearing loss so she can be fitted with appropriate amplification (hearing aids or cochlear implants). (5)
Testing for Hearing Loss Due to Cytomegalovirus
If your new-born baby fails its newborn hearing screening, you have to act quickly if you want to know whether his hearing loss was the result of the cytomegalovirus or not. You only have a 2 to 3 week window from birth when lab tests of your baby’s urine or saliva can determine whether your baby’s hearing loss was the result of CMV or not. Once three weeks have passed, the only way to identify CMV as the cause of hearing loss is to detect the DNA of the CMV virus in dried blood samples from the first 3 weeks of life or from the dried umbilical cord (assuming blood or the umbilical cord were saved). (7)
Hearing loss may occur soon after birth, or it may develop later in childhood. (4) Late-onset hearing loss can occur throughout the first several years of life. (3) Since 59% of the children diagnosed with sensorineural hearing loss at 6 years of age had not been identified with a hearing loss by 12 months of age, it is obvious that children with CMV infections need frequent and routine audiological evaluations until they are 5 or 6 years old, if not longer. (2)
Note that in all cases of late-onset sensorineural hearing loss, since it was not yet present, the hearing loss could not have been detected through newborn hearing screening. That is why it is critical that periodic audiometric testing be done for at least six years.
At any time, if you are concerned that your child’s hearing has deteriorated because of the progressive nature of CMV-related hearing loss, don’t delay. Schedule your child for appropriate audiological evaluations. Immediate evaluation and treatment of your child’s hearing loss gives him the best chance of keeping up with his peers. (2)
(1) Cytomegalovirus Infections. 2017. MedlinePlus. https://medlineplus.gov/cytomegalovirusinfections.html.
(2) Ross, Danielle, and Fowler, Karen. 2008. Cytomegalovirus: A Major Cause of Hearing Loss in Children. The ASHA Leader, May 2008, Vol. 13, 14-17. http://leader.pubs.asha.org/article.aspx?articleid=2291965.
(3) Fowler, Karen B. DrPH. Targeted Screening for Cytomegalovirus and Hearing Loss. Hearing Journal: October 2017 – Volume 70 – Issue 10 – pp 10,11.
(4) Centers for Disease Control and Prevention. 2016. Cytomegalovirus (CMV) and Congenital CMV Infection. https://www.cdc.gov/cmv/overview.html.
(5) National CMV Foundation. 2017. Congenital CMV Outcomes. https://www.nationalcmv.org/congenital-cmv/outcomes.aspx.
(6) Lanzieri, Taliana M. et. al. 2017. Hearing Loss in Children with Asymptomatic Congenital Cytomegalovirus Infection. Pediatrics. http://pediatrics.aappublications.org/content/early/2017/02/14/peds.2016-2610.
(7) CMV and Hearing Loss. 2017. Success for Children with Hearing Loss. https://successforkidswithhearingloss.com/for-professionals/cmv-and-hearing-loss/.