Study: Incidence of hearing loss following COVID-19 among young adults in South Korea: a nationwide cohort study. Image Credit: Jaromir Chalabala / Shutterstock

A major study finds that COVID-19 triples the risk of hearing loss in young adults, highlighting an urgent need to investigate the long-term effects of the virus on auditory health amid concerning new evidence of sudden sensorineural hearing loss among those infected.

In a recent study published in the journal eClinicalMedicine, researchers from South Korea conducted a population-based study among young adults to determine the association between coronavirus disease 2019 (COVID-19) and hearing loss, including sudden sensorineural hearing loss.

Background

The COVID-19 pandemic affected over 775 million individuals worldwide and resulted in over seven million deaths. The post-infection sequelae, commonly known as long coronavirus disease (long COVID), continues to impact a significant portion of the individuals who recovered from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. Furthermore, the symptoms of long COVID impact various organ systems, such as the cardiovascular, gastrointestinal, pulmonary, renal, and neural systems.

Studies have reported cases of sensorineural hearing loss and sudden sensorineural hearing loss associated with COVID-19, which suggests an impact of COVID-19 on the brainstem. This also indicates that hearing loss could be one of the non-specific COVID-19 symptoms.

Viral and bacterial meningitis, where meningeal inflammation is believed to spread to the cochlea, has been reported to cause sudden hearing loss. Numerous recent cases among young adults have suggested that hearing loss could be a serious COVID-19-associated public health issue, and it is vital to study this association at a population scale to account for confounding factors.

About the study

In the present study, the scientists used data from the Korea Disease Control and Prevention Agency’s COVID-19 registry and the National Health Insurance Service database to obtain information on diagnoses of COVID-19, as well as types, dates, and vaccination doses.

The insurance service database provided a wide range of data, including sociodemographic factors, health examination results, outpatient visits, hospitalization and prescription records, and medical treatments.

The study only included young adults between the ages of 20 and 38 and excluded all individuals with a hearing loss history. The exposure in the study was SARS-CoV-2 infection confirmed using real-time reverse-transcriptase polymerase chain reaction (rRT-PCR) analysis of oro- or nasopharyngeal swabs.

The outcomes examined in the study consisted of composite hearing loss based on the International Statistical Classification of Diseases Tenth Revision codes. Sudden sensorineural hearing loss was the secondary outcome examined in the study. To determine the risk of sudden sensorineural hearing loss, follow-ups were conducted until a diagnosis of hearing loss, death, or end of the study.

Hearing loss was determined based on the inability to hear sounds below 25 decibels, and sudden sensorineural hearing loss was diagnosed based on the rapid development of hearing loss below 30 decibels within 72 hours.

Factors such as age, sex, household income, and COVID-19 vaccination status were included as covariates. Additional covariates included body mass index, fasting serum glucose levels, systolic blood pressure, alcohol consumption, smoking status, and physical activity levels.

The researchers performed various statistical and sensitivity analyses to determine the association between SARS-CoV-2 infections and an increased risk of hearing loss or sudden sensorineural hearing loss among young adults while accounting for all the demographic, physiological, and lifestyle-related covariates.

Results

The study found that the risk of hearing loss or sudden sensorineural hearing loss was higher after a SARS-CoV-2 infection among young adults. Compared to individuals who never had COVID-19, those who recovered from COVID-19 were at a 3.44 times higher risk of hearing loss and a 3.52 times higher risk of sudden sensorineural hearing loss.

Even after adjusting for covariates linked to lifestyle and metabolic factors, the association was significant. The researchers also discussed some proposed hypotheses explaining the association between SARS-CoV-2 infections and hearing loss.

The inner ear is believed to be susceptible to viruses, and infections from viruses belonging to Paramyxoviridae and Herpesviridae families, as well as from hepatitis, influenza, and Lassa viruses, have been linked to neurological symptoms such as sudden sensorineural hearing loss, along with facial paralysis and anosmia. Additionally, viral infections can also damage the perilymphatic and cochlear tissue, which has previously been observed in cases of cochleitis and cochlear nerve neuritis.

Murine model studies where mice were infected with the herpes simplex virus showed evidence of hearing loss after the viral infection. The infection of epithelial cells inside the stria vascularis of the cochlear duct, the death of uninfected cells, and the apoptosis of cells infected in the organ of Corti are believed to contribute to hearing loss.

Other studies have also reported the persistence of SARS-CoV-2 in the ear long after recovering from the initial infection, suggesting that the virus’s ability to remain in tissues for the long term could be an underlying reason for hearing loss.

Conclusions

Overall, the findings suggested a significant association between COVID-19 and the development of hearing loss in young adults. However, the researchers believe that limitations such as the absence of objective audiological data, the retrospective study design, and the inability to generalize these findings to broader populations warrant careful interpretation of these results and necessitate further research on the subject.