Covid-19 and hearing loss: A new study explores an auditory mystery

The link between contracting Covid-19 and losing one’s taste and smell is well established.

However, new research and anecdotal reports suggest Covid-19’s attack on the senses may go beyond those senses — extending to the ability to hear.

Not everyone who becomes sick with Covid-19 will experience hearing loss, and not all experiences of hearing loss will be the same. However, certain themes do link some patient stories.

For example, a 45-year-old man with asthma developed a severe case of Covid-19 for which he had to be intubated. After extubation, he developed sudden hearing loss and tinnitus in one ear. According to the case report published in October, “he had no previous history of hearing loss or ear pathology.”

Meanwhile, in October, a 42-year-old woman named Meredith Harrell recounted to CNN a moment when she was walking from her backyard to her house. Her right ear started to ring. Other than the ringing, she couldn’t hear anything out of her right ear. She took a Covid-19 test and was positive, but other than the hearing loss in her right ear, she didn’t have any symptoms. While steroids have helped some people recover their hearing after Covid-19, they didn’t work for Harrell.

Cases like these have prompted researchers from the Manchester Centre for Audiology and Deafness to review all the case studies of Covid-associated hearing loss they can find and warn the public of the possible link. They published their findings Monday in the International Journal of Audiology.

The background — Early in the pandemic, the Manchester team looked through published studies to see if there was a robust connection between hearing loss and Covid-19.

However, in the chaos of the pandemic’s onset, there were few good quality studies on the subject. Now, a year into the pandemic, that’s changed. And while more studies need to be done to confirm these early findings, members of the study team tell Inverse they believe hearing loss — and the development of tinnitus or vertigo — could be the result of contracting Covid-19.

This wouldn’t be unprecedented. While we’re all familiar with losing our sense of taste and/or smell when we have a cold, viruses can do the same to our hearing. Measles, Mumps, Rubella, West Nile, and HIV are just a few of the viruses that have been shown to affect our auditory abilities.

Now, early research suggests we might be able to add SARS-CoV-2 — the virus that causes Covid-19 — to that list.

Covid-19 and hearing loss

Reviewing roughly 60 studies of “audio-vestibular” problems in people with confirmed cases of Covid-19. (The “vestibular system” is just the name of the collection of little sensors in our ear that help us keep our balance.) The findings, published Monday in the International Journal of Audiology, suggest that as many as 15 percent of people diagnosed with Covid-19 report having audio-vestibular symptoms.

The most commonly reported hearing issue was tinnitus--characterized by hearing a sound when none is there. The American Tinnitus Association (ATA) says that this is most often characterized by a ringing in the ear, but can also be a “buzzing, hissing, whistling, swooshing or clicking” in the ear. According to the Centers for Disease Control, it’s estimated that 10 percent of adults in the United States have experienced tinnitus lasting at least five minutes in the past year.

After reviewing the available studies, the researchers from Manchester estimate that the prevalence of tinnitus among Covid-19 patients is 14.8 percent. While they caution that many of the reports they reviewed are based on self-reported accounts, other reports jibe with what was found, suggesting tinnitus is a common symptom of “long-Covid.” This is the condition where people still experience symptoms weeks and even months after the virus has cleared their body.

The next most common auditory symptom associated with Covid-19 is hearing loss. The Manchester researchers estimate the prevalence of hearing loss during or after Covid-19 is 7.6 percent. In some cases, hearing may be restored after treatment with steroids but — as was the case of the 45-year-old with asthma and Meredith Herrell — this isn’t always the case.

Co-author Kevin Munro, a professor at the University of Manchester, tells Inverse it’s unclear how long Covid-19 induced hearing loss lasts.

“We know that there are reports of tinnitus and hearing loss improving over time in some individuals but don’t yet have data to say what percentage is temporary and what percentage is permanent,” Munro says.

Vertigo, also known as dizziness, was slightly less common than hearing loss in the analysis. The researchers estimate vertigo occurs in about 7.2 percent of cases.

Why does Covid-19 affect hearing?

For now, we only have hypotheses. Without more and better studies, scientists can’t know exactly why hearing might be affected by Covid-19.

However, Munro and colleagues do posit some potential mechanisms by which this could be happening:

• Cochleitis (inflammation of the cochlea, the spiral tube that forms part of the inner ear) or neuritis (inflammation of a nerve) caused by “viral involvement of the inner ear or the vestibulocochlear nerve.”
• Cross-reactions where “antibodies or t-cells misidentify inner ear antigens as the virus, leading to accidental damage of the inner ear.”
• Vascular disorders: Our cochlea and semicircular ear canals have no collateral blood supply and are vulnerable to ischemia, or restricted blood supply. We know Covid-19 can result in blood clots and other coagulation abnormalities.
• Immune-mediated: Hearing loss could result from the production of too many pro-inflammatory cytokines, as often seen in cytokine storms in severe cases of Covid-19.

Considering how many people have contracted Covid-19 and how few of those people have experienced hearing loss, there are lots of unanswered questions.

“There have been around 10 reports of sudden hearing loss associated with Covid-19,” Munro says.

“If it really is Covid-19 that is causing these sudden hearing losses, the overall number of people with sudden hearing loss should be higher than previous years. We don’t have the answer yet.”

What comes next — Munro and co-author Ibrahim Almufarrij argue what’s really needed are clinical and diagnostic studies, as their conclusions are based on surveys and case reports. This is all that’s available to them at this time.

But Munro says they’re working on it. “Our new study, which is just about to start, will involve a comprehensive assessment in people with and without Covid-19,” he says. They hope will provide the answer to questions like:

• What is the prevalence of ear problems and how does it differ between people admitted to hospital with Covid-19 and other health conditions?
• What part of the ear is damaged and how severe is the damage?
• Are there associations between other health conditions, treatment for Covid-19, and severity of ear problems?

“We hope to have the answer later this year,” he says.

While the researchers’ current findings may change once we have more data, what we do know — that this virus may cause significant hearing damage —should be taken seriously.

“Covid-19 is not just a respiratory disease,” Munro says. “It affects many parts of the body and this may include hearing.”