National representative analysis of unilateral hearing loss and hearing aid usage in South Korea.

A definitive study on the prevalence of adult unilateral hearing loss and hearing aid rehabilitation is lacking in Korea. The purpose of our study was to investigate the prevalence of adult unilateral hearing loss and the factors associated with hearing aid use in patients with unilateral hearing loss in South Korea. We obtained data from 2009 to 2012 from the Korea National Health and Nutrition Examination Surveys (KNHANES), a cross-sectional, nationwide and population-based survey in the Republic of Korea. We analyzed the prevalence and associated factors of unilateral hearing loss and hearing aid adoption by univariable and multivariable analysis. Unilateral hearing loss was defined as pure tone average ≥ 41 dB in the worse hearing ear, and < 41 dB in the other ear assessed at 0.5, 1.0, 2.0, and 3.0 kHz. From 2009 to 2012, 33,252 individuals participated in the KNHANES. Among them, the number of patients with unilateral hearing loss was 1632 (5.55%) and the prevalence of hearing aid adoption in unilateral hearing loss was 1.56%. We also compared the factors between hearing aid users and non-users. Occupational status (OR 3.759, 95% CI 1.443-9.804), the hearing threshold in the better ear (OR 1.088, 95% CI 1.029-1.151), and hearing threshold in the worse ear (OR 1.031, 1.005-1.058) were found to affect the adoption of hearing aids. The prevalence of noise exposure at work in hearing aid users was significantly lower than the prevalence of noise exposure at work in those with no hearing aid. The prevalence of hearing aid use in patients with unilateral hearing loss in Korea is very low compared to other countries. Public health education is needed to increase public awareness of unilateral hearing loss, hearing aid adoption and its continued usage. Auditory rehabilitation should be actively recommended to patients with unilateral hearing loss.

Introduction

Sensorineural hearing loss (SNHL) affects approximately 1 in 500 newborns [1]. Unilateral hearing loss (UHL) is often not detected until early grade school and affects approximately 0.1%–3.0% of children [2]. The true incidence of UHL has been difficult to determine because many patients with UHL exhibit normal speech and language development [3, 4].

Bilateral hearing loss that occurs with aging is known to be associated with dementia and falls [5, 6]. Little is known about associations between morbidity and UHL. Recent studies suggest that in children UHL is associated with cognitive impairment and poor school performance [7, 8]. Lieu [7] reported that in school-age children UHL was associated with an increased likelihood of grade failures, and that speech and language delays may occur. A meta-analysis performed by Purcell et al. [8] suggested that children with UHL have lower full-scale IQ and performance IQ than children with normal hearing. These studies indicate the importance of auditory rehabilitation in the deficient ear in children with UHL.

Auditory deprivation is one reason why patients with UHL use hearing aids. Auditory deprivation can progress systematically over time and is associated with the reduced availability of acoustic information [9]. Many studies suggest that unilateral deprivation during early development can reorganize the central auditory representation of the two ears, resulting in a stronger representation of the better hearing ear and weaker representation of the other ear. These changes lead to a persistent aural preference for one ear, as demonstrated by asymmetric speech comprehension when each ear is tested separately [10-12]. Therefore, hearing aid use is important in patients with UHL. Notably, however, no study has investigated the prevalence of UHL and hearing aid adoption and use in South Korea. Most previous epidemiologic studies of UHL have focused on children. Golub et al. [13] recently analyzed big data derived from the USA and reported that the prevalence of UHL in that country was 7.2% but only 2.0% of Americans with UHL were using hearing aids. The Korea National Health and Nutrition Examination Survey (KNHANES) makes big data available for investigating diseases and aspects of health and nutrition. In the present study, the prevalence of UHL in participants aged ≥ 12 years in South Korea was investigated, as were factors associated with hearing aid use in South Koreans with UHL.

Materials and methods

KNHANES and the study population

Data were obtained from the 2009–2012 KNHANES and thus the study involved the secondary analysis of a large data-set. The KNHANES is a cross-sectional, nationwide, population-based survey designed to assess national health and nutrition levels accurately that has been conducted by the Division of Chronic Disease Surveillance under the Korea Centers for Disease Control and Prevention since 1998. It is composed of three different components; a health interview, a physical examination, and a nutrition survey. Every year 10,000–12,000 individuals in approximately 4000 households are selected from a panel to represent the population using a multistage clustered and stratified random sampling method that is based on Korean national census data. Since the Korean Society of Otolaryngology-Head and Neck Surgery began to participate in the survey in 2008, it has included otolaryngologic interviews and examinations performed by well-trained otolaryngologists in a mobile unit containing an endoscopic system and audio booth. Survey sample weights are used in all analyses to generate estimates that are representative of the non-institutionalized civilian Korean population. A detailed description of the KNHANES data collection methods has been published previously [14, 15]. All participants in the KNHANES provided written informed consent prior to undertaking the survey. The present study was approved by the relevant institutional review board (file ID 2019-09-024), and that board waived the need for informed consent due to the retrospective nature of the study and the lack of any personally identifiable information in the study.

Hearing survey and otologic examination

Pure tone audiograms were conducted in participants aged ≥ 12 years who were eligible for the survey. Only air conduction thresholds were measured. Data from the otolaryngologic survey and examinations were evaluated, including tympanic membrane perforation, hearing loss, dizziness, and vestibular dysfunction. Potential associations between factors derived from the basic health examination and interview and UHL and hearing aid use were assessed. To determine the prevalence of tympanic membrane perforation and cholesteatoma, as well as the retraction pocket and otitis media with effusion, an ear examination was conducted with a 4-mm 0-degree angled rigid endoscope attached to a charge-coupled device camera in all participants. Pure tone audiograms were measured by a trained otolaryngologist using an automatic audiometer (GSI SA-203; Entomed Diagnostics AB, Lena Nodin, Sweden) in a soundproof booth. Pure tone thresholds were obtained independently at 6 frequencies in each ear; 0.5, 1.0, 2.0, 3.0, 4.0, and 6.0 kHz. Pure-tone average (PTA) was calculated as the average threshold at 0.5, 1.0, 2.0, and 3.0 kHz in accordance with the recommendations of the American Academy of Otolaryngology-Head and Neck Surgery [16]. UHL was defined as a PTA hearing level ≥ 41 dB in one ear and < 41 dB in the other. UHL was deemed to be not present if the PTA was ≥ 41 dB in both ears. With regard to their use of hearing aids participants were asked “Do you use hearing aid(s)?”, and the response options were “yes”, “yes, but rarely”, and “no”. Hearing aid adoption was deemed to be present in subjects who answered “yes” or “yes, but rarely”, which means currently active or rarely used, respectively. Hearing aid use was deemed to be present in subjects who answered “yes”, which means currently used actively.

Statistical analysis

The prevalence of UHL was calculated and reported as a weighted percentage with standard error. In the univariable analysis, the Rao-Scott Chi-square test and logistic regression analysis were used to test associations between UHL and potentially related factors in complex sampling design. In multivariable analysis, adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were calculated via logistic regression analysis. To reflect the national population estimates, sample weights were applied in all analyses. Statistical analysis was performed using SAS version 9.4 (SAS Institute, Cary, NC, USA). All p values were two-sided, and p < 0.05 was deemed to indicate statistical significance.

Results

Prevalence of UHL and hearing aid adoption

A total of 33,252 individuals participated in the KNHANES from 2009–2012. Of these, the number of participants with UHL was 1,632 (weighted percentage of 5.55%, standard error 0.23). PTA ≥ 41 dB and < 55 dB, PTA ≥ 55 dB and < 70 dB, and PTA ≥ 70dB accounted for 56.86%, 21.89%, and 21.25% respectively. The prevalence of UHL in the eight different age groups are shown in Table 1. In the Rao-Scott Chi-Square test, there was a significant correlation between age group and hearing level in participants with UHL (p < 0.0001).

Table 1

Prevalence of unilateral hearing loss in South Korea by age group in participants over 12 years old (n = 1623).

Values expressed as a weighted percentage (standard errors).

	PTA results
	≥41 dB, <55 dB	≥55 dB, <70 dB	≥70 dB	overall
Age (years)
12–19	1.29 (0.48)	1.27 (0.58)	7.50 (1.87)	2.60 (0.58)
20–29	4.51 (1.26)	5.10 (1.99)	4.78 (1.74)	4.70 (0.89)
30–39	5.08 (1.06)	6.31 (2.02)	12.88 (3.05)	7.01 (1.15)
40–49	8.48 (1.27)	10.88 (2.68)	17.57 (3.04)	10.94 (1.15)
50–59	21.82 (1.86)	24.88 (3.10)	21.83 (3.02)	22.49 (1.40)
60–69	25.33 (1.84)	24.17 (2.70)	18.49 (2.45)	23.62 (1.35)
70–79	26.60 (1.81)	20.81 (2.55)	14.22 (2.16)	22.71 (1.37)
80-	6.74 (1.33)	6.89 (1.50)	2.72 (0.86)	5.94 (0.82)
overall	56.86 (1.87)	21.89 (1.38)	21.25 (1.74)

UHL, unilateral hearing loss defined as pure tone average ≥ 41 dB in the worse hearing ear, and < 41 dB in the other ear assessed at 0.5, 1.0, 2.0, and 3.0 kHz

In participants with UHL, the prevalence of hearing aid adoption was 1.56% (standard error 0.37). Bilateral PTAs in hearing aid adopters with UHL are shown in Table 2. There was no hearing aid adoption when the hearing threshold in the better ear was < 20 dB, and hearing aids were adopted when the hearing threshold in the better ear was > 20 dB. Hearing aid adoption in the worse ear was more common in participants with a hearing threshold in the better ear of 30–40 dB than it was in participants with a hearing threshold in the better ear of 20–30 dB.

Table 2

Bilateral pure-tone average of hearing aid adopters with unilateral hearing loss.

Values expressed as a weighted percentage (standard errors).

PTA of better ear	PTA of worse ear
	≥ 41 dB, < 55 dB	≥ 55 dB, < 70 dB	≥ 70 dB
≤ 20dB	0	0	0
> 20dB, ≤ 30 dB	13.78 (9.90)	62.22 (22.99)	44.20 (18.36)
> 30 dB, ≤ 40 dB	86.22 (9.90)	37.78 (22.99)	55.80 (18.36)

UHL, unilateral hearing loss defined as pure tone average ≥ 41 dB in the worse hearing ear, and < 41 dB in the other ear assessed at 0.5, 1.0, 2.0, and 3.0 kHz

Factors associated with hearing aid adoption

Univariable and multivariable logistic regression analyses were performed to identify factors associated with hearing aid adoption. In univariable analysis occupational status (OR 3.759, 95% CI 1.443–9.804), the hearing threshold in the better ear (OR 1.088, 95% CI 1.029–1.151), and hearing threshold in the worse ear (OR 1.031, 1.005–1.058) were significantly associated with hearing aid adoption. In multivariable logistic regression analyses occupational status (OR 3.750, 95% CI 1.441–9.763), hearing threshold in the better ear (OR 1.088, 95% CI 1.029–1.151), and hearing threshold in the worse ear (OR 1.031, 95% CI 1.005–1.058) were significantly associated with hearing aid adoption (Table 3). There were no calibration parameters other than those shown in the table.

Table 3

Univariable and multivariable analyses of factors associated with hearing aid adoption with unilateral hearing loss.

Variables	Categories	Univariable analysis		Multivariable analysis
		Odds Ratio (95% CI)	p-value	Odds Ratio (95% CI)	p-value
Age		1.005 (0.966, 1.046)	0.8075
Sex	Male	ref	-
	Female	0.506 (0.192, 1.334)	0.1683
Income	Lower	ref	-
	Lower middle	0.982 (0.247, 3.899)	0.8592
	Upper middle	1.042 (0.279, 3.894)	0.9602
	Upper	1.258 (0.346, 4.575)	0.7001
Education level	<Elementary school	ref	-
	Middle school	0.644 (0.183, 2.265)	0.8268
	High school	1.519 (0.507, 4.551)	0.0891
	College or higher	0.270 (0.033, 2.189)	0.2101
Occupational status	No	ref	-	ref	-
	Yes	3.433 (1.402, 8.409)	0.0070*	3.750 (1.441, 9.763)	0.0068*
Marriage status	Yes	ref	-
	No	2.532 (0.506, 12.669)	0.2583
Difficulty in hearing	No	ref	-
	Yes	.	.
Tinnitus	Yes	ref	-
	No	0.856 (0.327, 2.240)	0.7520
Anxiety about tinnitus	No	ref	-
	Yes	2.813 (0.623, 12.695)	0.1785
Noise exposure during work	No	ref	-
	Yes	1.000 (0.222, 4.496)	>.9999
TM perforation in worse ear	No	ref	-
	Yes	0.754 (0.128, 4.454)	0.7555
Cholesteatoma in worse ear	No	ref	-
	Yes	1.012 (0.172, 5.934)	0.9897
Otitis media with effusion in worse ear	No	ref	-
	Yes	< .001 (< .001, < .001)	< .0001
Chronic otitis media	No	ref	-
	Yes	1.125 (0.392, 3.228)	0.8260
Dizziness	No	ref	-
	Yes	< .001 (< .001, < .001)	< .0001
Perception of stress	No	ref	-
	Yes	0.569 (0.171,1.900)	0.3596
Depression mood ≥ 2 weeks	No	ref	-
	Yes	0.655 (0.156, 2.754)	0.5634
Smoking	No	ref	-
	Yes	1.724 (0.633, 4.480)	0.2640
Hearing threshold in better ear		1.088 (1.033, 1.146)	0.0014*	1.088 (1.029, 1.151)	0.0031*
Hearing threshold in worse ear		1.031 (1.006, 1.056)	0.0140*	1.031 (1.005, 1.058)	0.0195*

UHL, unilateral hearing loss defined as pure tone average ≥ 41 dB in one ear, and < 41 dB in the other ear assessed at 0.5, 1.0, 2.0, and 3.0 kHz

The independent variables of the multivariable logistic regression model included the occupational status, the hearing threshold in the better ear, and the hearing threshold in the worse ear.

Factors associated with hearing aid use

The prevalence of hearing aid use was 0.86% (standard error 0.28) in participants with UHL, and it was 55.31% (standard error 11.97) in participants who reported initial hearing aid adoption. To identify factors associated with hearing aid use, t-tests and Chi-square tests were performed to compare hearing aid users and non-users. In that analysis noise exposure at work was associated with hearing aid use (Table 4). The prevalence of noise exposure at work in the hearing aid users was 3.61%, which was significantly lower than the prevalence of noise exposure at work in the hearing aid non-users (27.93%; p = 0.0240). None of the other factors analyzed were statistically significant.

Table 4

Comparison between hearing aid users and non-users with unilateral hearing loss.

Values expressed as weighted percentage (standard errors).

Variables	Categories	Uilateral hearing loss	Non-users	Users	p-value
Age		58.14 (0.77)	64.41 (7.26)	57.62 (6.64)	0.3496
Sex	Male	51.35 (1.51)	80.71 (12.10)	55.59 (16.22)	0.2142
	Female	48.65 (1.51)	19.29 (12.10)	44.41 (16.22)
Income	Lower	32.40 (1.56)	30.15 (16.49)	32.53 (15.55)	0.3353
	Lower middle	24.92 (1.51)	16.46 (10.18)	28.80 (16.77)
	Upper middle	21.76 (1.62)	11.33 (10.73)	27.36 (13.90)
	Upper	20.91 (1.55)	42.06 (18.23)	11.31 (6.98)
Education level	<Elementary school	43.30 (1.78)	24.25 (14.85)	62.50 (16.54)	-
	Middle school	15.54 (1.08)	13.02 (9.27)	8.06 (5.99)
	High school	28.21 (1.56)	62.73 (16.39)	24.22 (16.85)
	College or higher	12.95 (1.30)	-	5.22 (5.22)
Occupation	No	53.62 (1.68)	78.20 (11.59)	77.39 (10.95)	0.9586
	Yes	46.38 (1.68)	21.80 (11.59)	22.61 (10.95)
Marriage status	Yes	91.03 (1.28)	100.00 (-)	70.95 (16.74)	-
	No	8.97 (1.28)	-	29.05 (16.74)
Difficulty in hearing	No	54.98 (1.95)	100.00 (-)	100.00 (-)	-
	Yes	45.02 (1.95)	.	.
Tinnitus	Yes	35.37 (1.58)	57.59 (16.94)	47.52 (16.39)	0.6638
	No	64.63 (1.58)	42.41 (16.94)	52.48 (16.39)
Anxiety about tinnitus	No	54.96 (2.82)	13.45 (13.30)	38.57 (23.13)	0.2845
	Yes	45.04 (2.82)	86.55 (13.30)	61.43 (23.13)
Noise exposure during work	No	13.78 (1.23)	27.93 (17.72)	3.61 (3.73)	0.0240*
	Yes	86.22 (1.23)	72.08 (17.72)	96.39 (3.73)
TM perforation in worse ear	No	39.43 (4.58)	.	76.66 (21.73)	-
	Yes	60.57 (4.58)	100 (-)	23.34 (21.73)
Cholesteatoma in worse ear	No	58.51 (4.50)	100 (-)	23.34 (21.73)	-
	Yes	41.49 (4.50)	-	76.66 (21.73)
Otitis media with effusion in worse ear	No	90.07 (2.35)	100.00 (-)	100.00 (-)	-
	Yes	9.93 (2.35)	.	.
Chronic otitis media	No	82.31 (1.47)	74.89 (13.71)	70.24 (15.49)	0.8178
	Yes	17.69 (1.47)	25.11 (13.71)	29.76 (15.49)
Dizziness	No	92.50 (2.27)	100.00 (-)	100.00 (-)	-
	Yes	7.50 (2.27)	.	.
Perception of stress	No	74.31 (1.47)	92.24 (7.66)	68.66 (15.99)	0.1458
	Yes	25.69 (1.47)	7.76 (7.66)	31.34 (15.99)
Depression mood ≥ 2 weeks	No	82.68 (1.14)	100.00 (-)	72.16 (15.77)	-
	Yes	17.32 (1.14)	.	27.84 (15.77)
Smoking	No	47.82 (1.64)	72.97 (13.90)	53.34 (17.01)	0.3703
	Yes	52.18 (1.64)	27.03 (13.90)	46.66 (17.01)
Hearing threshold in better ear		24.58 (0.50)	31.07 (1.15)	35.48 (1.15)	0.0726
Hearing threshold in worse ear		57.39 (0.69)	58.98 (7.06)	64.67 (5.69)	0.9117

UHL, unilateral hearing loss defined as pure tone average ≥ 41 dB in one ear, and < 41 dB in the other ear assessed at 0.5, 1.0, 2.0, and 3.0 kHz

Discussion

In the present study conducted in South Korea, the prevalence of UHL determined via KNHANES data was 4.91%. This is lower than the prevalence of 7.9%–13.3% in the general population [17, 18] and the prevalence of UHL was 7.2% in the US [13]. Although it was not possible to distinguish SNHL from conductive hearing loss, most patients with UHL had normal tympanic membranes and it was concluded that most of them had SNHL. However, our definition of UHL was > 40 dB, which is different from the previously cited studies, which used > 25 dB to define UHL. Thus, we cannot make direct comparisons.

In the present study, in participants with UHL, the prevalence of hearing aid adoption was 0.86% and the prevalence of hearing aid use was 1.56%. Hearing aid use prevalence of 14.2% in the USA [19] and 21.5% in the United Kingdom have been reported [20]. Those studies were based on patients aged > 50 years or 40 years with bilateral hearing loss, whereas the participants in the current study were aged ≥ 12 years. Golub et al. [13] reported that the prevalence of hearing aid use in people with UHL was 2.0% in the USA and that the reason why it was much lower than that in people with bilateral hearing loss was unawareness of disability. Public health insurance systems may also affect hearing aid use. In European countries such as the United Kingdom, France, and Denmark hearing aid-related expenses are covered by public health insurance [21]. In the USA the use of hearing aids has steadily increased, and most of this growth has been attributed to the provision of free hearing aids that can be obtained via the Department of Veterans Affairs, or the availability of low-cost hearing aids via the internet [22]. In South Korea hearing aid-related expenses are not covered by the government health insurance system however, and the average price of hearing aids is relatively high with reference to the national income per capita.

Occupational status, the hearing threshold in the better ear, and hearing threshold in the worse ear were associated with hearing aid adoption in the present study. Patients with UHL may not feel discomfort in their daily life. If they attend meetings or are required to spend time in a noisy environment however, problems can arise from UHL. Patients with UHL experience difficulty with sound localization and speech recognition in noisy environments [23]. Additionally, their co-workers may have problems communicating with them. Hearing aid use in the work-place can evidently increase productive hearing capacity and enhance the ability to communicate with others [24, 25].

People who adopt hearing aids tend to have more severe hearing loss in both the better ear and the worse ear than non-adopters. In a previous investigation, the severity of hearing loss was a major determinant of hearing aid adoption [26]. In another study people with severely restrictive hearing thresholds reported greater amounts of hearing aid use per day, and higher levels of satisfaction with their hearing aids [27]. In comparison with objectively measured severity of hearing loss, a self-perceived degree of hearing impairment was reportedly a stronger determinant of hearing aid adoption in many studies [28, 29]. In the present study, however, difficulty hearing was not statistically significantly associated with hearing aid adoption.

Noise exposure during work was the only factor that was significantly associated with hearing aid use in the present study. Hearing aid users were exposed to less noise at work than non-users. In noisy environments patients with hearing impairment can be free from noise without hearing aids. Unlike bilateral SNHL, it is thought that patients with unilateral SNHL have a lower need for hearing aids and that it is not necessary to wear hearing aids even in noisy situations. There have been recent advances in hearing aid technology. Specifically, noise reduction systems have been incorporated into hearing aids to improve the signal-to-noise ratio and listening comfort. These advances may have resulted in improved noise tolerance in hearing aid users.

The current study had some limitations. The KNHANES data it utilized were acquired from 2009–2012 and thus were ≥ 7 years old, and hearing aid technology has advanced rapidly in the last 5 years. With regard to financial considerations, in November 2015 the hearing aid subsidy provided by government health insurance in Korea was raised to KRW 1,310,000. As a result, hearing aid adoption and use may have increased since the 2009–2012 KNHANES was conducted. Second, the KNHANES defined UHL as a PTA hearing level ≥ 41 dB in one ear and < 41 dB in the other, whereas other studies defined UHL as a PTA hearing level > 25 dB. Another study limitation is that the KNHANES questionnaire components pertaining to hearing aids are not detailed, thus the scope for analyzing factors associated with the adoption and use of hearing aids was restricted. Notably, however, the present study was based on a very large national cross-sectional survey of a representative sample based on Korean national census data, and by design, the study had the capacity to reliably determine the prevalence of UHL and overall hearing aid use.

In conclusion, the prevalence of hearing aid use in patients with UHL is very low in South Korea compared to other countries. Public health education is needed in an effort to increase public awareness of UHL and hearing aid adoption and continued use, and auditory rehabilitation should be actively recommended to patients with UHL.

2 Jan 2020

PONE-D-19-32331

Big data analysis of unilateral hearing loss and hearing aid use in South Korea

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Reviewer #1: 1. REVIEWER SUMMARY: This is a report of unilateral hearing loss prevalence and also hearing aid use in South Korea. It uses the KNHANES, which should be representative of the actual population through sample weighting. Reporting of accurate, unbiased prevalence statistics is very important. While this has been done, for example, in the US, it is important to replicate in other countries because prevalence may differ. This study contains these important data, but there are a number of limitations detailed below. For example, multivariable regression was used but there was no obvious mention of what the variables were that were adjusted for in the model, which is critical information. In addition, the definition of unilateral hearing used a 40 dB cutoff, which is different from other papers that were mentioned in the discussion. While the authors are free to chose whatever defintion they wish, they should (a) justify the definition and (b) not make comparisons to studies that use a different definition unless they explicitly discuss this.

2. UNIQUE ASPECTS: There have been a few studies on hearing loss prevalence using the KNHANES that were not mentioned. For example: https://www.ncbi.nlm.nih.gov/pubmed/25216153 and https://www.ncbi.nlm.nih.gov/pubmed/28196098 . Both, in fact, reported unilateral hearing loss, although different definitions may have been used. This should be mentioned.

3. STUDY DESIGN: Cross-sectional

4. WRITING STYLE: Mostly understandable English. Abstract needs proofreading by a native English speaker. Many wording issues, mostly in the abstract:

Line 37-38. What does "occupation presence" mean. Does that mean having an occupation (i.e., "working")?

Line 34. Do not begin a sentence with And.

Lines 40-42 "In comparison of hearing aid users and non-users, noise exposure during work in hearing aid users was significantly lower than hearing aid non-users." Needs rewording.

Lines 42-43. "The prevalence of hearing aid use in patients with unilateral hearing loss in South Korea is very low compared as other countries." Do you mean that the low use is similar to other countries? In that case, you want to write "comparable to". Otherwise it should be "compared with" or "compared to".

Line 43-45. "Public health education is needed for increased insight and auditory rehabilitation for unilateral hearing loss should be recommended actively." Needs rewording.

Lines 104-106. "To determine the prevalence of tympanic membrane perforation and cholesteatoma, including retraction pocket and otitis media with effusion" Needs rewording. Retraction pockets and otitis media with effusion are not types of tympanic membrane perforations or cholesteatoma.

5. SPECIFIC COMMENTS:

Big data is sort of a buzz word. This is a relatively big dataset, but there are many studies that use KNHANES or the US NHANES and they normally don't use the term big data, I would at least remove from the title. You could maybe replace with something like "Nationally representative" to indicate it wasn't just based on a single hospital's audiology clinic.

Line 26-27. Do you mean lacking in South Korea? There are other studies using population-level data, e.g., reference #13.

Line 48-51. You state the incidence of unilateral hearing loss and then in the next sentence state that the true incidence is not known. In between, you should explain the limitations of the existing methods, i.e., why they are not accurate.

Line 57. It is Purcell, not Percell.

Line 113-115. Your definition of PTA >= 41 dB for hearing loss is different from many of the recent American epidemiology papers which use >=26 dB. As I am familiar, 25-40 dB is often considered mild hearing loss, which is still hearing loss. How you define hearing loss is a matter of debate and certainly varies. I would place your definition of unilateral hearing loss in the abstract to make this clear (i.e., >= 40 dB PTA at 0.5, 1, 2, 3 KHz in the worse hearing ear). I would also place this definition as a footnote in all of your tables.

I would recommend not double-spacing the tables so they are not spread across four pages (i.e., Table 3).

Table 1. You present categories, but the total data. It would be helpful to have an overall column that is not divided into a severity category. i.e, >=41 dB. It would also be helpful to have an age >= 12 row to represent "any age."

Line 121. It seems you presented the prevalence of UHL with standard eror, not 95% CI (e.g., tables 1, 2, 4)

Line 170. "In multivariable logistic regression..." You have to state what the other variables that you adjusted for were! This should also be clear in Table 3, e.g., in a footnote. This should also be in the methods.

The Table title and results text (and methods) should all match and reflect what was actually done. E.g., Table 3 title states the outcome is hearing aid adoption or cochlear implantation. The results and methods text do not mention cochlear implantation. In fact, nowhere else in the paper is cochlear implant mentioned as far as I see.

I am very confused by the different method used to assess factors associated with hearing aid use versus factors associated with hearing aid adoption. Hearing aid use and hearing aid adoption are VERY similar, with the later also including people who have a hearing aid but rarely use them. Why do you use regression to look for variables associated with hearing aid adoption, but then you use T-tests or Chi-squared tests for variables associated with hearing aid use.

Lines 193-197. This is very important. If you are comparing your findings of unilateral hearing loss to other papers measuring hearing loss, your definitions must be the same! You cite ref #16 Agrawal but she used >25 dB to define hearing loss, but you used >40 dB. Those will lead to VERY different numbers! Also ref #13 Golub et al used > 25 dB. I think ref #17 Chia et al also used >25 dB.

The similarity of the terms hearing aid use and hearing aid adoption is a little confusing. In the results and the discussion, I would clarify that use means something like current active use. And adoption means something like current active or rare use.

Methods - you must define how all variables were measured. This includes all variables in the table. For example, how was noise exposure during work measured and what does it even mean? It can mean extremely loud noise such as explosions or factory noise. This could injure your hearing. It can also mean background noise like people talking. This would not injure your hearing but can make hearing with a mild hearing loss more difficult.

Line 249 "In conclusion, the prevalence of hearing aid use in patients with UHL is very low in South Korea compared to other countries." This is your key concluding statement, but I am not sure I can trust it because your definition of UHL may be different from the studies you compared to (see above)

Reviewer #2: � Line 8; This article did not focus on congenital UHL. So, introduction like this is inappropriate.

� Line 63; What does “development” mean? Development of what?

� Line 100; Why did you exclude children younger than 12 years-old?

� Line 113-4; Was this definition of PTA suitable for UHL or asymmetric HL? General criteria for “hearing loss” is 26dBHL. 40dBHL is used as the criteria of “disabling hearing loss”, NOT “hearing loss” for adults. The criteria of “disabling hearing loss” is 30dBHL for children. Please, provide the reference of authors’ criteria for UHL. I think that authors should have used other term rather than UHL if they insisted on the 40dBHL-criteria.

� Line 142-3; Authors told that they analyzed the hearing use in people with UHL, but their data concluded the hearing aid was more used in asymmetric HL. How do you think about my point-out?

� To identify the factors associated with hearing aid adoption, logistic regression analyses were performed. But to identify factors associated with hearing aid use, t-tests and Chi-square tests were performed. Why did you use different statistical methods?

� Table 1; What was the “weighted percentage”? On what was it weighted?

� Table 2; Why was PTA average of better ear classified into {≤ 20dB}, {> 20dB, ≤ 30 dB} and {> 30 dB, ≤ 40 dB}?

� Table 2; please, rewrite the data correctly.

� Table 3; Cochlear implantation? What is this?

**********

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Reviewer #2: No

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9 Feb 2020

February 10, 2020

Joerg Heber

Editor

PLOS ONE

Dear Dr Heber,

Please consider our revised manuscript, “National representative analysis of unilateral hearing loss and hearing aid usage in South Korea”, for publication in PLOS One

We appreciate the interest that the editors and reviewers have taken in our manuscript and the constructive criticism they have given. We have addressed the major concerns of the reviewers. We have also included a point-by-point response to the reviewers in addition to making the changes in the manuscript. Changes to the text in the manuscript are marked in red. Our main findings remain unchanged.

This manuscript has not been published or presented elsewhere in part or in entirety and is not under consideration by another journal. The study design was approved by the appropriate ethics review board. We have read and understood your journal’s policies, and we believe that neither the manuscript nor the study violates any of these. There are no conflicts of interest to declare.

Bo Gyung Kim, MD, PhD

Department of Otorhinolaryngology-Head and Neck Surgery, Soonchunhyang University College of Medicine

Address: 170 Jomaru-ro, Wonmi-gu, Bucheon 14584, Korea

Tel: +82-32-621-6951

Fax: +82-32-621-5018

E-mail: bgkim@schmc.ac.kr

Submitted filename: Response_letter_final.docx

Click here for additional data file.

23 Mar 2020

PONE-D-19-32331R1

National representative analysis of unilateral hearing loss and hearing aid usage in South Korea

PLOS ONE

Dear Kim,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please carefully review all recommendations for revision in the original submission and re-submission.  While the authors did address the comments in their response, a number of critical clarifications were not incorporated into the revised manuscript.  The reviewer for revised submission has very carefully pointed out some essential changes that clarify how the current manuscript differs in some definitions from others in the literature, and how variables in their analysis were defined in KHANES data.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #1: (No Response)

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The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

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Reviewer #1: (No Response)

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Reviewer #1: (No Response)

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for the revisions and the detailed responses to my comments. Several of my comments from the prior submission remain unaddressed in the manuscript. In general, when a reviewer has a comment that requires a clarification, they would like the clarification to be inside the manuscript, not just in the response to reviewer comments. If the reviewer had a question, then many readers may have the same question.

1. NEW COMMENTS. (Line numbers refer to the new submission version with tracked changes)

Line 42 "...noise exposure at work in users with no hearing aid" should be "...noise exposure at work in those with no hearing aid"

2. PRIOR COMMENTS that were not addressed by modifications to the manuscript. NOTE that line numbers here refer to the **first submission**) Your comments are denoted by >>. My new comments are denoted by >>>

Line 26-27. Do you mean lacking in South Korea? There are other studies using population- level data, e.g., reference #13.

>>Of course, several studies have been published, such as reference # 13, however, there are very few studies on the use of UHL and hearing aids in Korea as well as in other countries, compared to studies on bilateral SNHL.

>>>Thank you, I understand. Please make this more clear in the manuscript by rewording the first sentence of the abstract to add "in Korea" to the end of this current sentence: "A definitive study on the prevalence of adult unilateral hearing loss and hearing aid rehabilitation is lacking."

Line 113-115. Your definition of PTA >= 41 dB for hearing loss is different from many of the recent American epidemiology papers which use >=26 dB. As I am familiar, 25-40 dB is often considered mild hearing loss, which is still hearing loss. How you define hearing loss is a matter of debate and certainly varies. I would place your definition of unilateral hearing loss in the abstract to make this clear (i.e., >= 40 dB PTA at 0.5, 1, 2, 3 KHz in the worse hearing ear). I would also place this definition as a footnote in all of your tables.

>>Thank you for your valuable comment and suggestion. Many studies define unilateral hearing loss as PTA >= 26 dB. However, the KNHANES defined unilateral hearing loss as PTA >=41 dB. Moreover, the prevalence of unilateral hearing loss in our study is much lower than other studies, which define unilateral hearing loss as PTA >=25 dB. If we change the definition of PTA >=26dB rigidly, there would be no one who used a hearing aid.

>>>Thank you for the explanation. You justify why you use >=40 dB. I understand this. However, because this is not the worldwide standard definition of hearing loss, I recommend doing this (repeated from above): Place your definition of unilateral hearing loss in the abstract to make this clear (i.e., >= 40 dB PTA at 0.5, 1, 2, 3 KHz in the worse hearing ear). I would also place this definition as a footnote in all of your tables."

Line 170. "In multivariable logistic regression..." You have to state what the other variables that you adjusted for were! This should also be clear in Table 3, e.g., in a footnote. This should also be in the methods.

>>The independent variables of the multivariable logistic regression model are the occupational status, the hearing threshold in the better ear, and the hearing threshold in the worse ear. There are no calibration parameters other than those shown in the table. In the univariable analysis results, the significant variables were considered as independent variables of the multivariable analysis. Among the five variables that were significant in univariable analysis, otitis media and dizziness were difficult to estimate due to an insufficient number of patients.

>>>I understand. Often in multivariable regression, there are other variables that are non-significant (i.e., pontential confounders). Since all 3 variables you describe are significant, it is not clear that you did not include any other variables in the model. To make this clear, at the end of the sentence "In multiple logistic regression..." please insert another sentence and explain that there were no other variable present in the multivariable model. Please also, like I said, put this information in the methods and in a Table 3 footnote.

Lines 193-197. This is very important. If you are comparing your findings of unilateral hearing loss to other papers measuring hearing loss, your definitions must be the same! You cite ref #16 Agrawal but she used >25 dB to define hearing loss, but you used >40 dB. Those will lead to VERY different numbers! Also ref #13 Golub et al used > 25 dB. I think ref #17 Chia et al also used >25 dB.

>>As mentioned earlier, the KNHANES defined unilateral hearing loss as PTA >=41 dB. Moreover, the prevalence of unilateral hearing loss in our study is much lower than other studies, which define unilateral hearing loss as PTA >=25 dB. If we change the definition of PTA >=26dB rigidly, there would be no one who used a hearing aid. The criteria are less strict than other studies, but with lower prevalence, we believe our results are meaningful.

>>>Thank you and I understand why you used >40 dB: you had no choice because this is what KHANES used. However, please modify the text here to explain that your definition of hearing loss is different from the papers you are comparing it to. The following statement is completely misleading without an explanation: "In the present study conducted in South Korea, the prevalence of UHL determined via KNHANES data was 4.91%. This is lower than the prevalence of 7.9%–13.3% in the general population [16, 17] and the prevalence of UHL was 7.2% in the US [13]." You must insert a sentence here to say something like: "However, our definition of hearing loss was >40 dB which is different from the previously cited studies, which used >25 dB to define hearing loss. Thus we can not make direct comparisons."

Methods - you must define how all variables were measured. This includes all variables in the table. For example, how was noise exposure during work measured and what does it even mean? It can mean extremely loud noise such as explosions or factory noise. This could injure your hearing. It can also mean background noise like people talking. This would not injure your hearing but can make hearing with a mild hearing loss more difficult.

>>We used the data obtained from the 2009-2012 KNHANES. Participants were asked for the presence of noise but there was no query on the degree of noise.

>>>Thank you. Please address my comment. Please define how all the variables were measured or defined, briefly according to the KHANES manual, in the methods. If there is no room, place this in a supplement or a reference to the KHANES manual.

**********

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Reviewer #1: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

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7 Apr 2020

We thank you and the reviewers for your thoughtful suggestions and insights. The manuscript has benefited from these insightful suggestions. I look forward to working with you and the reviewers to move this manuscript closer to publication in Plos One.

The manuscript has been rechecked and the necessary changes have been made in accordance with the reviewers’ suggestions. This included editing the entire document for readability and organization. Additions to the manuscript are marked with red text. The responses to all comments have been prepared and attached herewith.

Thank you for your consideration. I look forward to hearing from you.

Submitted filename: 2ndrevision_responseletter.docx

Click here for additional data file.

8 Apr 2020

National representative analysis of unilateral hearing loss and hearing aid usage in South Korea

PONE-D-19-32331R2

Dear Dr. Kim,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

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Clifford R. Hume, MD PHD

Academic Editor

PLOS ONE

13 Apr 2020

PONE-D-19-32331R2

National representative analysis of unilateral hearing loss and hearing aid usage in South Korea

Dear Dr. Kim:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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on behalf of

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PLOS ONE