PEDIATRICS Vol. 109 No. 5 May 2002, pp. 987-988
Noise-Induced Hearing Loss
To the Editor—Niskar et al’s 1 estimate of 5.2 million US children with noise-induced threshold shifts (NITS) was unexpectedly high for a condition known primarily as an occupational hazard. It was particularly surprising that 1 out of 12 of the youngest children, aged 6–11, already had NITS. Some other study findings were also remarkable. NITS generally occurs in both ears; yet 85% of the children with NITS were only affected in 1 ear. NITS typically occurs at 4 kHz, yet in this study only 24% of NITS involved 4 kHz, while >3 times as many cases (76%) involved 6 kHz. These unexpected findings (ie, the large prevalence estimate, the predominance of unilateral NITS, and the concentration of threshold shifts at 6 kHz) can be largely explained by a methodologic flaw.
Noise-induced threshold shift, as the term suggests, is a change in hearing level threshold (HLT) attributable to noise. Correspondingly, the standard operational definition entails a difference in HLT between baseline and follow-up audiograms covering a period with documented noise exposure. 1 Niskar et al were unable to use this definition because their database included neither baseline audiograms nor noise exposure data. Given these limitations, the authors substituted the presence of a "notch" or "dip" on the audiogram at 3, 4, or 6 kHz as a proxy measure.
Serious questions have previously been raised about this choice. Sataloff 3 observed that a notch is not sufficient evidence to diagnose NITS because numerous other medical conditions also produce notches. Mostafapour et al 4 found that presence of a notch among students did not correlate with any source of noise exposure including personal listening devices, home stereos, or firearms. Another study found no association between notches and noise exposure among electrical workers. 5
These findings suggest that the false-positive rate in the study by Niskar et al may have been substantial. Some misclassification may be attributable to medical conditions besides noise-induced hearing loss that also produce notches. 2 In addition, many notches, particularly those at 6 kHz, may reflect 2 statistical factors, systematic measurement error and statistical variation, rather than hearing pathology. In a study of carefully screened, young adults free of hearing pathology and hazardous noise exposure, Lutman and Davis 6 found mean HLTs above audiometric zero at all standard frequencies. Among these higher than expected HLTs, the mean value of 15.4 dB at 6 kHz was the outlier. Studies in children have also reported higher average HLTs at 6 kHz than at other frequencies. 7,8 Lutman and Davis 6 concluded that the current standard of hearing, ISO 389, requires adjustment at 16 kHz.
Systematic overestimation of HLTs for 6 kHz could appear as notches on some audigrams. For example, based on the data of Lutman and Davis, 6 an audiogram with mean HLTs of 15.4 dB at 6 kHz and 3.1 dB at 1 kHz would appear to have an 11.3-dB notch at 6 kHz. Statistical variation at 6 kHz was large enough (SD, 7.6 dB) so that within 1 standard deviation of the mean, notches would be about 19 dB. This would be more than enough to meet Niskar’s criterion of 15 dB. 1
Lutman and Davis 5 have traced the origin of the overestimation bias in HLT at 6 kHz to the process used to develop the current standard of "normal" hearing, International Organization for Standardization (ISO) 389. The results of Niskar’s study may represent some of the pitfalls into which this problem may lead. Fully 76% of the cases of NITS involved 6 kHz. If these involved included spurious 6-kHz notches, the unexpectedly high prevalence of NITS in young children may be greatly overstated. The very low percentage of bilateral notches also fits this explanation. If the notches were mainly random events produced by measurement bias and statistical variation, rather than noise exposure, with a probability of 1 in 8 (the study NITS rate), then chance predicts that the percentage of cases with notches in 2 ears would be 13%, quite similar to Niskar’s report of 15%. The potential impact of hearing standards and statistical variation on measurement of NITS can be greatly reduced by adhering to the definition used in occupational safety regulations. The difference between a baseline and follow-up audiogram for the same frequency is independent of the standard of hearing and less subject to statistical variation than comparing one frequency with others. In addition, as Sataloff 6 observed, the diagnosis of NITS should not be made without a history of exposure to noise.
Jesse Green, PhD
Hoffman-LaRoche
Nutley, NJ, USA
REFERENCES
1.
Niskar AS, Kieszak SM, Holmes AE, Esteban E, Rubin C, Brody DJ. Estimated prevalence of noise-induced hearing threshold shifts among children 6 to 19 years of age: The Third National Health and Nutrition Examination Survey, 1988–1994, United States.
Pediatrics.2001; 108
:40
–43
2. Occupational Safety and Health Administration. Occupational Noise Exposure. Criteria for a Recommended Standard.Washington, DC: US Department of Labor, Occupational Safety and Health Administration;1998 . DHHS (NIOSH) Publ. No.98 –126
3. Sataloff RT. The 4,000-Hz audiometric dip. Entechnology.1980; 59 :251 –257[Medline]
4. Mostafapour S, Lahargoue K, Gates G. Noise-induced hearing loss in young adults: the role of personal listening devices and other sources of leisure noise. Laryngoscope.1998; 108 :1832 –1839[CrossRef][Medline]
5.
McBride DI, Williams S. Audiometric notch as a sign of NIHL.
Occup Environ Med.2001; 58
:46
–51
6. Lutman ME, Davis AC. The Distribution of hearing threshold levels in the general population aged 18–30 years. Audiology.1994; 33 :327 –350[Medline]
7. Haapaniemi J. The hearing threshold levels of children at school age. Ear Hear.1996; 76 :469 –477
8. Roberts J. Hearing levels of children of children by demographic and socioeconomic characteristics. National Health Survey.1972 (111):Series 11
In Reply—
We thank Dr Green for his comments on our article. We agree that our data do not provide a diagnosis of noise-induced hearing loss (NIHL). In the "Discussion" section of our article, we explained that our results were suggestive of noise-induced hearing threshold shifts (NITS) but that a diagnosis of NIHL could not be confirmed because the Third National Health and Nutrition Examination Survey did not include an extensive noise exposure history, baseline audiometric testing data, or follow-up audiometric testing data. 1 In the "Discussion" section we also acknowledged that other causes could explain an audiometric notch configuration but that the specific notch criteria used were most likely attributable to noise. 1–4 Our analysis did not find ototoxic medication usage to be a confounder in this study.
Dr Green references studies by Mostafapour et al 5 and McBride and Williams 6 to suggest that there is no association between noise exposure and audiometric notch configurations. In the study of Mostafapour et al, 5 a small convenience sample of adult volunteers completed a subjective noise history that was limited by recall bias and lacked sound level measurements. Mostafapour et al 5 acknowledge that an association of a notch with firearm noise exposure could not be evaluated because hearing protection was worn during firearm use. McBride and Williams’ 6 study of 357 adults showed that firearm use was significantly associated (odds ratio = 4.25; 95% confidence interval 1.28–14.1) with a notch at 4 kHz. Recent publications show asymetrical and unilateral noise notches to be associated with firearm use among children. 7,8
Green references Lutman and Davis 9 to support the possibility of systematic overestimation of hearing level thresholds at 6 kHz for the current International Organization for Standardization (ISO) standard. Green suggests that our NITS criteria in combination with statistical variation would result in misclassification because Lutman and Davis 9 report a mean of 15.4 dB at 6 kHz (with a standard deviation of 7.6 dB) and a mean of 4.1 dB at 1 kHz, which would appear as a 11.3-dB notch at 6 kHz. However, our American National Standards Institute (ANSI) standard data show the right ears to have a mean of 4.1 dB with a standard error (SE) of 0.1 at 1 kHz and a mean of 9.1 dB (SE: 0.2) at 6 kHz, which would appear as a 5.0-dB notch at 6 kHz. The left ears showed a mean of 4.8 (SE: 0.4) at 1 kHz and a mean of 10.1 (SE: 0.3) at 6 kHz, which would appear as a 5.3-dB notch at 6 kHz. These notches do not meet our NITS criteria. Our analysis suggests that 6 kHz is an important frequency to watch for in children 6 to 19 years of age. 1
Several distinctions need to be noted between Green’s references and our study. Green’s main references include analyses of data collected using ISO-calibrated audiometers. 5,9,10 However, our data were collected using ANSI-calibrated audiometers. 1 There is a difference of approximately 2 dB at 6 kHz between the ISO and ANSI standard. 11 In addition, our study reports findings from a nationally representative large sample of children, but most of Green’s references describe findings from small convenience samples of adults. 5,6,9
Green suggests that occupational NIHL definitions are appropriate for children, but these definitions are developed for use in workman’s compensation and adult handicap ratings. 4,12 Child-specific physiologic factors need to be considered when evaluating pediatric audiometric configurations. 13,14 Children’s psychosocial and educational factors can be impacted by their hearing status. 15,16 Thus, the adult occupational functional definition of nonreversible NIHL may not be appropriate for children. Our study provides conservative estimates of suggestive NITS among children 6 to 19 years of age. NITS is preventable, and these findings support the need for the development, research, and application of child-specific prevention methods to benefit children. 1
Amanda Sue Niskar, RN, BSN, MPH
Stephanie M Kieszak, MA, MPH
Emilio Esteban, DVM, MBA, PhD
Carol Rubin, DVM, MPH
Centers for Disease Control and Prevention
Atlanta, GA, USA
Alice E Holmes, PhD, CCC-A
University of Florida
Gainesville, FL, USA
Debra J Brody, MPH
Centers for Disease Control and Prevention
Hyattsville, MD, USA
REFERENCES
1. Niskar AS, Kieszak SM, Holmes AE, Esteban E, Rubin C, Brody DJ. Estimated prevalence of noise-induced hearing threshold shifts among children 6 to 19 years of age: the Third National Health and Nutrition Examination Survey, 1988–1994, United States. Pediatrics.2001; 108 :40 –43
2. Sataloff RT. The 4,000-Hz. Audiometric dip. Entechnology.1980; 59 :251 –257
3. Katz J, ed. Handbook of Clinical Audiology. Baltimore, MD: Williams & Wilkins;1994 :20 –21, 283–291, 534–551, 627
4. US Department of Health and Human Services, Centers for Disease Control and Prevention. Criteria for a Recommended Standard: Occupational Noise Exposure—Revised Criteria 1998. Cincinnati, OH: US Department of Health and Human Services, Centers for Disease Control and Prevention;1998
5. Mostafapour SP, Lahargoue K, Gates GA. Noise-induced hearing loss in young adults: the role of personal listening devices and other sources of leisure noise. Laryngoscope.1998; 108 :1832 –1839
6. McBride DI, Williams S. Audiometric notch as a sign of NIHL. Occup Environ Med.2001; 58 :46 –51
7. Holmes AE, Kaplan HS, Phillips RM, Kemker FJ, Weber FT, Isart FA. Screening for hearing loss in adolescents. Lang Speech Hear Serv Sch.1997; 28 :70 –75
8. Royster JD. Audiometric monitoring phase of HCP. In: Berger EH, et al, editors. The Noise Manual. Fairfax, VA: American Industrial Hygiene Association Press;2000 :455 –516
9. Lutman ME, Davis AC. The distribution of hearing threshold levels in the general population aged 18–30 years. Audiology.1994; 33 :327 –350
10. Haapaniemi JJ. The hearing threshold levels of children at school age. Ear Hear.1996; 17 :469 –477[Medline]
11. American National Standards Institute. Specifications for audiometers (ANSI S3.6-1996). New York, NY: American National Standards Institute;1996
12.
American Academy of Otolaryngology, Committee on Hearing and Equilibrium, American Council of Otolaryngology, Committee on the Medical Aspects of Noise. Guide for the evaluation of hearing handicap.
JAMA.1979; 241
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13. Berglund B, Lindvall T, eds. In: The World Health Organization WHO Healthy Cities Programme. Community noise. Arch Cent Sensory Res.1995; 2 :1 –195
14. Hellstrom PA. The relationship between sound transfer functions and hearing levels. Hear Res.1995; 88 :54 –60[CrossRef][Medline]
15. Bess FH. The minimally hearing-impaired child. Ear Hear.1985; 6 :43 –47[Medline]
16. Crandell CC. Speech recognition in noise by children with minimal degrees of sensorineural hearing loss. Ear Hear.1993; 14 :210 –216[Medline]
PEDIATRICS (ISSN 1098-4275). ©2002 by the American Academy of Pediatrics
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