BCCHR’s Ask an Expert Series
While congenital cytomegalovirus infection (cCMV) is a major cause of childhood hearing loss, intellectual disability and cerebral palsy, only a minority of people have heard of it.
Dr. Soren Gantt, a pediatric infectious disease specialist and director of clinical research at BC Children’s Hospital and associate professor in the faculty of medicine at the University of British Columbia, talks about the prevalence of cCMV, how it’s detected and what can be done to avoid transmission.
Q: How prevalent is cCMV?
About half of all adults in Canada have this virus. In lower-income countries, almost everyone’s infected. People with the virus often don’t know they carry it. When they first get infected, they may experience mild or flu-like symptoms, or they may not even notice anything. Then they live with the infection the rest of their lives but the virus rarely causes any problems.
But, if babies are infected during pregnancy, CMV can be devastating. One in every 200 babies born in Canada has CMV infection present at birth, and, of those, about 20 per cent will have some kind of permanent disability.
CMV harms more children than all of the diseases we currently screen newborns for combined. It’s the most common congenital infection in the world.
Q: How is CMV transmitted to babies?
An infected mother can pass the virus to her baby before, during or after birth, but problems only happen when the baby is infected before birth (congenital infection). Babies are very often infected after birth through breast milk or saliva, but they don’t get sick. Infection of the baby before birth occurs when a woman gets infected, or re-infected, with CMV during pregnancy. The most common way this happens is when a woman has contact with saliva or urine from an infected child, who shed high levels of virus.
Q: Why is early detection a challenge?
Very, very rarely does a baby with congenital CMV infection look sick enough or have symptoms that are specific enough to make clinicians test for it, so the vast majority of infected babies are missed. Additionally, the majority of kids who develop hearing loss from congenital CMV will not be identified by a newborn hearing screening, because hearing loss most often starts after a baby leaves the hospital.
At a minimum, early diagnosis alerts clinicians to watch infected babies very carefully for hearing loss and other developmental problems. This information makes early interventions possible. Some babies would also be eligible for treatment with antiviral medicine to improve their outcomes.
Q: Why is intervention important?
Identifying children that develop hearing loss early is enormously important. Kids with hearing loss where there’s no early intervention never achieve the same educational or professional outcomes as their hearing peers. If you intervene early with hearing aids or cochlear implants or speech-language therapy, kids have totally normal outcomes. They may not hear normally, but they communicate just as well and do just as well in school.
Q: How is congenital CMV detected?
Testing saliva or urine of a baby at birth is the best way to diagnose congenital CMV infection. The dried blood spots that are collected from every baby when they’re born are a potential way to diagnose congenital CMV. The problem is they’re less sensitive than saliva or urine, so it’s not the ideal way to screen. Effective screening catches everyone. Saliva is easy to collect with a swab of the newborn’s mouth, whereas urine can be messy or difficult to collect from a diaper.
Q: You led an international study that was recently published in the Journal of Clinical Microbiology that evaluated Alethia, the first product approved by the FDA to detect the virus in newborns’ saliva. Why was this study important?
Alethia allows pretty much any birthing hospital or moderate complexity lab setting to do CMV testing, and do it using saliva. A nurse could swab a newborn’s mouth and have the results within an hour. Our study found this commercial test is sensitive and specific. It finds cases of CMV where there is one and it doesn’t find them falsely when there isn’t one. It may not be the right platform to test every baby born in B.C. or elsewhere, but it’s a big step in the right direction to be able to expand testing and identify these babies and get them the appropriate care.
At BC Children’s Hospital, Dr. David Goldfarb, Dr. Vijay Gadkar and Dr. Peter Tilley have developed another test using saliva that is available for newborns province-wide. So anybody in B.C. who’s worried that a baby might have CMV can do a saliva swab and send it to the lab here at BC Children’s and BC Women’s. We’re also continually working on developing cheaper, faster tests. We’re hoping to develop a test that takes less than an hour to process and costs less than $5 per test, which would be quite cheap for this.
Q: What can a pregnant woman do to avoid contracting CMV?
CMV is primarily transmitted through saliva and urine from other young children. Similar to the prevention of transmission of other viruses, pregnant women should practice good hand washing. They should also avoid sharing saliva with small children, for example by sharing cups or spoons or kissing on the lips.
Q: What can parents do if they’re worried their baby may have congenital CMV?
A parent should share their concern with a physician to see whether their child should be tested.