The obscure virus that causes some children to go deaf

Sarah Percy had never heard of cytomegalovirus, until her daughter Camden was diagnosed with profound deafness in her right ear, aged three.

It was picked up on a routine trip to the audiologist, and further tests showed it had been caused by the virus, otherwise known as CMV, contracted when Camden was a baby.

"We did beat ourselves up that maybe we'd missed something, but talking to lots of doctors it's really easy to miss kids' hearing - they just make do," Percy said.

For healthy adults and children, CMV is usually harmless. But when it's passed to an unborn baby during pregnancy, it can cause children to develop hearing loss, vision impairment, developmental delays, epilepsy, cerebral palsy, learning difficulties, feeding challenges, and other lifelong disabilities.

Known as congenital CMV (cCMV), it affects about one in 200 babies globally and is one of the leading causes of childhood hearing loss.

But because testing for the virus was not routinely done at birth, Percy worried there were many cases caused by the virus without parents or doctors ever realising it.

"One of the most difficult things about cCMV is that it can hide in plain sight," she said. "A child can appear completely healthy, pass their newborn checks, and then develop hearing loss or other challenges months or years later."

Percy was frustrated by a lack of awareness of the virus and its effects - even among medical professionals.

Simple hygiene measures, like hand washing and not sharing food, drink or utensils with young children, or parents putting their children's dummies in their own mouths, could help prevent the spread of CMV.

Percy said there was a balance to be struck between increasing awareness, while acknowledging pregnancy was already a stressful time filled with things to do differently and things to avoid. But, she said, ultimately knowledge was power.

Health NZ's Dr Jacqui Lunday, national chief of allied health, scientific and technical, said early detection and diagnosis did improve outcomes for children with congenital cytomegalovirus, as it led to earlier treatment.

But, routine testing was not currently done in New Zealand, which was "consistent with current international practice".

She said all babies were offered a free hearing test in their first month of life, and children found to have congenital hearing loss might be tested for cCMV after receiving the diagnosis.

Percy said in Camden's case, her infant hearing test came back normal - the deafness came on later.

Lunday explained a child with confirmed cCMV at birth, but who passed their newborn hearing screening, would undergo regular testing until the age of at least four, to catch late onset or progressive hearing loss.

"We acknowledge there is more to do to understand and improve consistency of testing and treatment for this condition," she said.

Work underway towards infant testing

There is currently no approved or licensed vaccine for CMV anywhere in the world, although several are being evaluated in clinical trials.

Genevieve Choi, a PhD candidate in audiology at the University of Auckland, is working on feasibility study for introducing routine CMV testing for infants diagnosed with sensorineural hearing loss - a practice standard in places like the UK for 15 years, but not yet routine in New Zealand.

The study is currently operating across three New Zealand hospitals - one large, one medium, and one small.

The first test was a urine PCR test, the preferred validated method in New Zealand. If the urine sample was positive, they would then do a dried blood spot test.

Choi said for infants with confirmed sensorineural hearing loss, knowing if CMV was the cause is critical, as roughly half of those infants experienced further sudden drops in hearing levels.

Early diagnosis would allow clinicians to monitor their hearing closely and consider cochlear implants, to make sure the child continuted their auditory and language learning during a critical neurodevelopmental window.

Choi said the evidence showed CMV was more prevalent among Māori and Pacific children, and any screening or treatment programme must keep that in mind.

Camden's robot ear

Camden's family made the decision to self-fund a cochlear implant, an electronic hearing device that is hardwired into the brain to transmit audio signals directly.

Now, aged six, Camden proudly sports what her family calls "her robot ear".

Percy said they received conflicting advice on whether to go down that route - the arguments against it were the invasive surgery, the creation of a visible difference (the implant) which might lead to anxiety or embarrassment for Camden, and ultimately, they were told children with hearing loss in one ear tended to get by just fine.

But the arguments in its favour won out, Percy said. Deafness caused by CMV could sometimes progress to deafness in both ears, she said, and if that happened, at least now Camden would be used to her implant.

Camden decorated it with stickers - this week, it was Taylor Swift - and wore it with pride.

Through it, Camden could take phone calls and stream the audio from television shows or music straight to it. It had taken a while to get used to decoding speech, Percy said, but now she could understand whole conversations.

"We definitely wanted it to be like a fun thing and make it like, this is awesome, this is like a superpower no one else gets," Percy said.