In December 2019, novel coronavirus infection occured which spread around the world, many manifestions were reported by mulitcenter study. A year after the outbreak of COVID-19, Wang et al. [1] and Shi et al. [2] reported that the clinical presentation of COVID-19 mainly includes fever, fatigue, cough, and anorexia. According to recent statistics, there were more than 590 million cases worldwide by August 2022, of which 6 million died [3]. As the cases accumulate and progress, long-term sequelae have been reported in addition to the symptoms initially seen. That was called by post-acute sequelae of COVID-19 [4] in the United States, commonly referred to as long COVID [5]. Carfi et al. [6] reported that 87.4% of hospitalized patients with COVID-19 had at least one sequelae at a mean of 60.3 days after symptom onset.

In Europe, multicenter study to investigate the occurrence of dysphonia in mild-to-moderate COVID-19 patients was done and 26.8% of patients had the dysphonia which appear in patients with a more severe clinical COVID-19 presentation [7]. When there was severe COVID-19 cases who had pneumonia or acute respiratory distress syndrome, patients have difficulty to not only in the inspiratory phase of respiration but also in the expiratory phase. Since the energy source for speech is provided by the air expelled from the lungs, if both respiratory phases do not have proper functioning it may cause voice disorder [8,9].

Gölaç et al. [10] evaluated several voice-related parameters using Computerzied Speech Lab (CSL). Recovering patients from COVID-19 showed significantly lower maximum phonation time (MPT), increased Voice Handicap Index-10 scores, decreased scores of Voice-Related Quality of Life questionnaire. But there was no difference in other voice parameters between the study and the control group.

While previous studies have investigated dysphonia and voice changes in COVID-19 patients, research focusing on sex-specific differences and longitudinal recovery patterns remains limited. Furthermore, most studies have been conducted in Western populations, leaving gaps in understanding the unique vocal characteristics of East Asian patients, including South Koreans. This study is the first to report on voice changes by gender and duration of infection in Korean COVID-19 patients. It analyzes the prevalence of voice-related symptoms, gender differences in acoustic parameters, and temporal recovery patterns of voice function.

A COVID-19 patient is defined as a person who has been confirmed to be infected based on the test criteria for COVID-19 diagnosis or a person who shows symptoms of COVID-19 and has been identified and diagnosed by a physician as positive through a rapid antigen test (for experts) or an emergency screening test (approved for emergency use).

Acoustic analysis was conducted using the CSL (Model 4500 b, KayPENTAX Elemetrics Corporation, Lincoln Park, NJ, USA). The following parameters, including F0, jitter, shimmer, noise-to-harmonics ratio (NHR), speaking fundamental frequency (SFF), and MPT, were utilized for analysis. The GRBAS ratings of patients were assessed by the same speech-language pathologist. To evaluate auditory perceptual parameters, two questionnaires were utilized: the Korean version of the Voice Handicap Index-30 (KVHI-30) and the Korean version of the Voice-Related Quality of Life (KVQOL). These questionnaires were employed to assess the impact of voice disorders on individuals’ quality of life and their perceived handicap related to their voice, respectively.

The inclusion criteria for research subjects in this study were adults aged 18 years or older who had been diagnosed with COVID- 19 and released from isolation, understood the study contents, voluntarily agreed to participate, confirmed voice changes, and had no issues with the disability questionnaire (KVHI-30, KVQOL) and voice analysis test. Exclusion criteria for the study included individuals who declined participation, had a history of voice disease or surgery causing voice abnormalities, had congenital laryngeal disease, or had difficulty with voice and breathing due to structural problems other than vocal cords.

The final number of participants who met the inclusion criteria was 85. Participants were then divided into a male and a female group. The average age of the 85 COVID-19 confirmed patients was 31 years old (range: 26.0–45.5), with 35 males and 50 females. The most common accompanying symptoms were dysphonia (24.7%), cough (10.6%), sputum (9.4%), and sore throat (7.1%). Among the participants, 66 individuals (77.9%) were non-smokers, 12 (14.0%) were current smokers, and 7 (8.1%) were former smokers. Additionally, 44 participants (51.2%) had occupations that involved significant voice usage, and 83 participants (96.5%) received the COVID-19 vaccination. There were three cases of reinfection with COVID-19 (3.5%), and the average duration between the date of the experiment and the date of diagnosis was 92.0 days (range: 38–127).

Voice production is a complex process that relies on the coordinated functioning of the respiratory and neurological systems. Dysfunction in these systems can result in voice disorders [12]. COVID-19 can significantly impact the respiratory system, potentially leading to conditions such as pneumonia and acute respiratory distress syndrome. Moreover, common COVID-19 symptoms like coughing, sore throat, runny nose, sneezing, and vomiting are closely related to the anatomical structures involved in voice production [9]. Consequently, COVID-19 infection, which may cause airflow and structural issues in the vocal folds, often results in voice changes and related concerns among affected individuals.

In a meta-analysis of eight papers, it was reported that dysphonia was present in 70% of cases when symptoms were assessed using multiple-choice options in COVID-19 patients [13]. Dysphonia, identified as an otorhinolaryngological complication of COVID-19, is frequently mentioned in the literature as a condition associated with mechanical ventilation and coughing during the infection, primarily affecting the lower respiratory system. In our study, dysphonia was the most prevalent accompanying symptom, observed in 24.7% of participants, followed by cough (10.6%), sputum (9.4%), and sore throat (7.1%). Notably, KVHI-30 scores demonstrated a strong correlation with the overall symptom burden (r=0.62, p<0.01), particularly in patients experiencing dysphonia and chronic cough. These findings highlight the significant impact of COVID-19 on voice-related symptoms and underscore the importance of addressing vocal impairments during recovery.

Among the participants, 12 were current smokers, 7 were former smokers, and 44 (51.2%) were voice professionals whose occupations required significant vocal use. Smoking status and voice professional status were not associated with voice changes in post-COVID-19 patients. Laryngoscopic findings revealed unilateral vocal fold paralysis in 2 male patients (5.7% of male participants). This suggests that the neurotropic effects of COVID- 19 infection may contribute to vocal fold paresis. These findings align with the hypothesis that SARS-CoV-2 can affect the peripheral nervous system, potentially leading to laryngeal neuropathy and subsequent vocal fold paralysis.

One study conducted a comparison of acoustic parameters between the COVID-19 group and the control group, revealing notable differences between the two cohorts. Specifically, the COVID-19 group exhibited higher values for parameters such as the standard deviation of F0, jitter, shimmer, and the difference between the first and second harmonic amplitude (H1H2). Conversely, the patient group demonstrated lower values for NHR, cepstral peak prominence, and MPT compared to healthy individuals. These findings suggest that COVID-19 can significantly impact the acoustic characteristics of voice production, indicating potential vocal abnormalities and dysfunctions in individuals affected by the virus [14]. In this study, similar to prior research, comparisons using the KVHI-30 and KVQOL revealed voice-related deterioration in COVID-19 patients. Notably, female patients exhibited significantly higher voice-related handicap scores (KVHI-30 total score: 22.1 vs. 8.3, p<0.001) and poorer voice-related quality of life (KVQOL total score: 80.5 vs. 91.7, p=0.002) compared to males. These disparities may be linked to anatomical and hormonal differences between sexes. Female vocal folds are shorter in length and have thinner mucosal layers, rendering them more vulnerable to inflammation. COVID-19-related laryngeal edema may exacerbate this vulnerability, leading to reductions in acoustic parameters such as F0 and SFF. This anatomical vulnerability aligns with prior findings in Korean populations [11]. Estrogen plays a critical role in modulating mucosal elasticity and hydration. Fluctuations in estrogen levels, particularly during menstrual cycles or menopause, may delay vocal fold recovery in females. This hypothesis is supported by studies demonstrating prolonged voice recovery times in women with hormonal imbalances [14]. The combined effects of anatomical and hormonal factors may explain the greater perceived vocal handicap and reduced quality of life observed in female post-COVID-19 patients. These findings underscore the need for sex-specific vocal rehabilitation strategies, particularly for women with persistent dysphonia.

Our study revealed significant changes in voice parameters among male and female post-COVID-19 patients, highlighting sex-specific differences in vocal outcomes. Among male patients, jitter (p=0.013) and shimmer (p=0.016) were significantly elevated compared to healthy controls, suggesting incomplete glottic closure and potential microtrauma to the vocal folds. These findings align with prior studies indicating that COVID-19-induced coughing can lead to mechanical stress on the vocal folds, contributing to submucosal hemorrhage and edema.

In female patients, shimmer showed a significant increase (p=0.003), while jitter did not differ significantly (p=0.064). This persistent elevation in shimmer may reflect residual irregularities in vocal fold vibration, potentially caused by prolonged laryngeal inflammation or neuropathy. These results suggest the need for long-term follow-up using laryngoscopic evaluations to monitor recovery and identify lingering vocal abnormalities.

Our findings are consistent with Asiaee et al. [14], which reported increased jitter, shimmer, and reduced MPT in COVID-19 patients. Similarly, Lechien et al. [7] observed a higher prevalence of voice disorders among female patients, which aligns with our data showing significantly higher KVHI-30 scores in females compared to males (p<0.001). However, our study identified a unique finding: male patients exhibited an increase in SFF (+9.2%, 124.37 Hz vs. normative value of 113.8 Hz). This result contrasts with Western studies [10], where no significant changes in SFF were reported among male patients post-COVID-19 infection. This discrepancy may be attributed to anatomical differences in vocal fold length between Korean and Western populations, emphasizing the need for further research on race-specific variations in vocal physiology.

Based on these results, treatment strategies for voice disorders in post-COVID-19 patients may differ by gender. For male patients, proton pump inhibitors can be prescribed to prevent laryngeal irritation, while antitussive medications can be used to reduce mechanical stress on the vocal folds caused by chronic coughing. For female patients, vocal hygiene education focusing on adequate hydration and vocal rest can help minimize shimmer irregularities. Additionally, voice therapy, such as resonant voice training, can be implemented to improve vocal fold vibratory stability and facilitate recovery.

Females demonstrated significant SFF recovery 90 days postinfection (post-90 days: 202.86 Hz vs. pre-90 days: 170.87 Hz, p=0.047), approaching normal values, while males exhibited no significant temporal changes in SFF. This recovery trend in females likely reflects the gradual resolution of laryngeal edema over time. Additionally, MPT increased over time in male patients but showed a non-significant decrease in female patients. These findings align with a previous study by Gölaç et al. [10], which reported improvements in MPT and acoustic parameters 3 months after COVID-19 infection. However, the observed recovery trend in SFF after 90 days is a novel finding that has not been previously reported in the literature.

This study has several limitations. First, it was conducted at a single institution with a relatively small sample size of 85 patients, which may limit the statistical power and generalizability of the findings. To address this, future multicenter studies with larger datasets are recommended to validate the results and provide broader insights. Second, the study lacked pre-COVID-19 voice data for comparison, which restricted the ability to directly assess voice changes caused by COVID-19 infection. The inclusion of pre-infection voice data in future research would allow for a more comprehensive evaluation of the impact of COVID-19 on voice characteristics.

This study provides novel insights into the prevalence and characteristics of voice-related symptoms among South Korean post-COVID-19 patients, emphasizing the impact of the disease on vocal function and quality of life. Our findings revealed significant sex-specific differences in voice parameters, with males exhibiting elevated jitter and shimmer, suggesting incomplete glottic closure and potential microtrauma to the vocal folds. In contrast, females demonstrated a persistent increase in shimmer and significantly poorer KVQOL, likely influenced by anatomical and hormonal factors. These results underscore the need for tailored therapeutic approaches, such as antitussive medications for males and vocal hygiene education and voice therapy for females.

In conclusion, this study emphasizes the significant impact of COVID-19 on voice production, with notable sex-specific differences and recovery patterns. These findings provide a foundation for developing targeted rehabilitation strategies to improve vocal outcomes in post-COVID-19 patients.