TORONTO -- In an overview of studies, researchers from the University of Manchester and the U.K.'s National Institute for Health Research suggest there may be a link between COVID-19 and hearing loss, sparking calls for further studies about the long-term effects of the disease on the auditory system.
"There is an urgent need for a carefully conducted clinical and diagnostic study to understand the long-term effects of COVID-19 on the auditory system," study co-author Kevin Munro said in a press release.
"It is also well-known that viruses such as measles, mumps and meningitis can cause hearing loss; little is understood about the auditory effects of the SARS-CoV-2 virus."
The research, published last Monday in the International Journal of Audiology, looked at data from 56 studies involving participants that tested positive for COVID-19 and had experienced hearing loss, tinnitus and vertigo.
According to the research, there were 17 case reports and one case series involving 28 patients that reported hearing loss as a possible COVID-19 symptom. Of these, 14 patients reported sensorineural hearing loss, which involves damage to the inner ear. Nine reported conductive hearing loss, which is caused by damage in the middle or outer ear. One patient reported mixed hearing loss, is a combination of both sensorineural and conductive hearing loss.
From this data, researchers estimate hearing loss to affect 7.6 per cent of COVID-19 patients.
The researchers also found 14 patients in 11 case reports had developed tinnitus, characterized by ringing sounds in the ears. The researchers estimate that this affects 14.8 per cent of COVID-19 patients.
The prevalence of vertigo among COVID-19 patients was also estimated to be 7.2 per cent, based on 10 patients in nine case reports that described vertigo symptoms.
However, the research is not without its limitations. The researchers note that the studies they examined relied on self-reported questionnaires and medical records rather than hearing tests. It also wasn't clear in half the studies that the patients were describing a new symptom, given that hearing loss has existed long before COVID-19.
"Though the evidence is of varying quality, more and more studies are being carried out so the evidence base is growing. What we really need are studies that compare COVID-19 cases with controls, such as patients admitted to hospital with other health conditions," said study co-author Ibrahim Almufarrij in a news release.
The research adds to a growing body of evidence linking COVID-19 and hearing problems.
In November 2020, another U.K. study surveying over 3,000 people with tinnitus found that 40 per cent of those who had experienced COVID-19 symptoms saw worsening tinnitus symptoms.
Another study from July 2020, also published by Munro and his team, examining 138 COVID-19 patients, found 13 per cent of patients reported tinnitus symptoms eight weeks after being discharged from hospital.
