Hearing Impairment Among Noise-Exposed Workers — United States, 2003–2012 | MMWR

Hearing Impairment Among Noise-Exposed Workers — United States, 2003–2012 | MMWR

MMWR Weekly Vol. 65, No. 15 April 22, 2016

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Hearing Impairment Among Noise-Exposed Workers — United States, 2003–2012

Weekly / April 22, 2016 / 65(15);389–394

Summary

What is already known about this topic?

Hearing loss is prevalent in the United States, especially among noise-exposed workers.

What is added by this report?

This is the first known study to quantify the disability-adjusted life years attributable to hearing impairment for noise-exposed U.S. workers, and to estimate the prevalence at each level of hearing impairment by industry sector.

What are the implications for public health practice?

Prevention, early detection, and intervention to preclude additional hearing loss are essential to reducing worker disability caused by hearing impairment.

Elizabeth A. Masterson, PhD1; P. Timothy Bushnell, PhD2; Christa L. Themann, MA3; Thais C. Morata, PhD3 (View author affiliations)

Hearing loss is the third most common chronic physical condition in the United States, and is more prevalent than diabetes or cancer (1). Occupational hearing loss, primarily caused by high noise exposure, is the most common U.S. work-related illness (2). Approximately 22 million U.S. workers are exposed to hazardous occupational noise (3). CDC compared the prevalence of hearing impairment within nine U.S. industry sectors using 1,413,789 noise-exposed worker audiograms from CDC’s National Institute for Occupational Safety and Health (NIOSH) Occupational Hearing Loss Surveillance Project (4). CDC estimated the prevalence at six hearing impairment levels, measured in the better ear, and the impact on quality of life expressed as annual disability-adjusted life years (DALYs), as defined by the 2013 Global Burden of Disease (GBD) Study (5). The mining sector had the highest prevalence of workers with any hearing impairment, and with moderate or worse impairment, followed by the construction and manufacturing sectors. Hearing loss prevention, and early detection and intervention to avoid additional hearing loss, are critical to preserve worker quality of life.

The NIOSH Occupational Hearing Loss Surveillance Project collects de-identified audiograms* for U.S. workers (4) who were tested to comply with regulatory requirements because of high occupational noise exposure, defined as ≥85 decibels on the A-scale (dBA).† Audiometric service providers and others that perform worker testing agreed to share these data with NIOSH. A cross-sectional retrospective cohort analysis was conducted using the last audiogram completed for each worker during 2003–2012. Audiograms missing necessary fields or with other quality issues, having hearing threshold values that suggested testing errors, or displaying attributes unlikely to be primarily caused by occupational exposures, were excluded (4). Industries were classified using the 2007 North American Industry Classification System.§

The prevalences of six severity levels of hearing impairment were calculated for workers in each industry sector using the audiometric definitions from the GBD Study (Table 1) (5), except that workers in this sample who had hearing aids did not wear them during testing. DALYs representing the number of healthy years lost per 1,000 workers each year were calculated by industry sector using the GBD Study disability weights (Table 1).¶Tinnitus information required to calculate the DALYs was not available in the NIOSH Occupational Hearing Loss Surveillance Project sample and was estimated using results from previous studies (6,7).**

The final sample included 1,413,789 audiograms for workers employed by 25,908 U.S. companies during 2003–2012. Among 99% of audiograms for which information on the worker’s sex was available, 78% were recorded for males and 22% for females. A greater percentage of males had any hearing impairment (14%) than did females (7%), and the prevalence and severity of impairment increased with age (Table 2) for both sexes. Among all industries, 13% of noise-exposed workers had any impairment and 2% had moderate or worse impairment (Table 3). Workers with hearing impairment were represented in all industry sectors, with sharply decreasing numbers of workers with higher levels of impairment. The mining sector had the highest prevalence of workers with any impairment (17%) and with moderate or worse impairment (3%), followed by the construction sector (any impairment = 16%, moderate or worse impairment = 3%), and the manufacturing sector (14% and 2%). The public safety sector, which includes police protection, fire protection (including wildland firefighters), corrections, and ambulance services, had the lowest prevalence of workers with any impairment (7%).

Across all industries, 2.53 healthy years were lost annually per 1,000 noise-exposed workers (Table 3). Mild impairment accounted for 52% of all healthy years lost and moderate impairment accounted for 27%. Workers in the mining and construction sectors lost 3.45 and 3.09 healthy years per 1,000 workers, respectively. Overall, 66% of the sample worked in the manufacturing sector and represented 70% of healthy years lost by all workers. Public safety workers lost 1.30 healthy years per 1,000 workers, the fewest among all workers.

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Discussion

Findings of increasing prevalence with age and a higher prevalence among males were expected and consistent with other research (2,4,8). Industry results highlight the high prevalence of hearing loss within the noise-exposed working population and the need for continued prevention efforts, especially in the mining, construction, and manufacturing sectors. The proportion of mining sector employees exposed to hazardous noise (76%) was the highest in any sector (3), and studies have consistently indicated elevated risks for occupational hearing loss within this sector (2,4). Occupational hearing loss risks have also been established within the construction sector (2,4); however, current noise regulations do not require audiometric testing for construction workers (2). Without testing to identify workers losing their hearing, intervention might be delayed or might not occur. Although a comparatively smaller percentage of manufacturing workers are noise-exposed (37%), this sector accounts for the most noise-exposed workers in the United States (3), and, as expected, the largest number of workers with hearing impairment. Some manufacturing sub-sectors, such as wood product, apparel, and machinery manufacturing, have been found to have occupational hearing loss risks as high as those in the mining and construction sectors (4). Another study using earlier GBD Study hearing impairment definitions also found the heaviest burdens of hearing impairment were in the mining, construction, and manufacturing sectors, indicating the most healthy years were lost in these sectors (8).

Approximately 78% of the healthy years lost were attributable to mild or moderate hearing impairment. Preventing any occupational hearing loss is the best way to reduce worker hearing impairment over a lifetime, because even mild-to-moderate impairment during working years can culminate in more healthy years lost during retirement. Prevention also has short-term benefits; persons with even mild hearing loss experience reduced audibility (loudness), reduced dynamic range of hearing (the difference between the softest and loudest perceptible sounds), and increased listening fatigue (2). They also often experience difficulties understanding speech, especially in the presence of background noise (2). Other effects include degraded communication (2), cognitive decline (9), and depression (2).

In the general population, the prevalence of impairment also sharply decreases at higher levels of impairment, and severe impairment is not typically caused exclusively by noise. Some workers with a substantial hearing impairment might transfer away from noisy jobs because of difficulties communicating in noisy environments, or from jobs where hearing is critical for productivity and safety. For example, although the public safety sector had fewer older workers (lowering the prevalence), hearing impairment might have resulted in attrition because of the hearing-critical nature of many occupations in this sector (2).

The findings in this report are subject to at least seven limitations. First, this was a convenience sample and might not be representative of all noise-exposed workers tested in the United States. Second, not all noise-exposed workers are tested in the United States, especially in industries with high proportions of mobile or temporary workers, such as the construction and agriculture sectors. Third, in the absence of additional information, such as medical records, hearing impairment caused by occupational exposures can only be inferred. However, this inference was strengthened by studying exposed workers and excluding audiograms indicating nonoccupational exposures. Fourth, GBD Study disability weights were developed using international surveys asking respondents to compare life limitations posed by different health conditions, and to compare the value of preventing certain health conditions to the value of preventing death (5); respondents might not be able to appreciate the impact a disability can have on quality of life if they do not have that disability. Fifth, GBD Study audiometric definitions for impairment levels are conservative, with stringent requirements to reach even mild impairment. In addition, no impairment is identified when there is a total loss of hearing in one ear, and the impairment in the other ear can be lessened by hearing aid use. These limitations might have lowered impairment estimates, and worker impairment might be higher than reported here. Sixth, workers in the Occupational Hearing Loss Surveillance Project who wear hearing aids did not wear them during testing. However, few persons wear hearing aids during working years (9), so no adjustments were made for hearing aid use. Finally, no information was available on other conditions, so healthy years lost because of hearing impairment were not adjusted for comorbidities (5).

Occupational hearing loss is a permanent but entirely preventable condition with today's hearing loss prevention strategies and technology (2). Concurrent with prevention efforts, early detection of hearing loss by consistent annual audiometric testing, and intervention to preclude further loss (e.g., refitting hearing protection, training), are critical. Although lost hearing cannot be recovered, workers can benefit from clinical rehabilitation, which includes fitting hearing aids, learning lip-reading, and adopting other compensation strategies to optimize hearing. Study results support beginning rehabilitation at a mild level of hearing impairment. Prevention, and early detection, intervention, and rehabilitation, might greatly improve workers’ quality of life (2,9).

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Acknowledgments

Jia Li, William Murphy, National Institute for Occupational Safety and Health, CDC; audiometric service data providers.

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Corresponding author: Elizabeth A. Masterson, emasterson@cdc.gov, 513-841-4291.

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1Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, CDC; 2Office of the Director, National Institute for Occupational Safety and Health, CDC; 3Division of Applied Research and Technology, National Institute for Occupational Safety and Health, CDC.

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References

1. Blackwell DL, Lucas JW, Clarke TC. Summary health statistics for US adults: National Health Interview Survey, 2012. Vital health statistics, series 10, no. 260. Atlanta, GA: National Center for Health Statistics, CDC; 2014. http://www.cdc.gov/nchs/data/series/sr_10/sr10_260.pdf
2. Themann CL, Suter AH, Stephenson MR. National research agenda for the prevention of occupational hearing loss—part 1. Semin Hear 2013;34:145–207. CrossRef
3. Tak S, Davis RR, Calvert GM. Exposure to hazardous workplace noise and use of hearing protection devices among US workers—NHANES, 1999–2004. Am J Ind Med 2009;52:358–71.CrossRef PubMed
4. Masterson EA, Tak S, Themann CL, et al. Prevalence of hearing loss in the United States by industry. Am J Ind Med 2013;56:670–81. CrossRef PubMed
5. Global Burden of Disease Study 2013 Collaborators. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2015;386:743–800. CrossRef PubMed
6. Masterson EA, Themann CL, Luckhaupt SE, Li J, Calvert GM. Hearing difficulty and tinnitus among US workers and non-workers in 2007. Am J Ind Med 2016;59:290–300. CrossRefPubMed
7. World Health Organization. WHO methods and data sources for global burden of disease estimates 2000–2011. Global health estimates technical paper WHO/HIS/HSI/GHE/2013.4. Geneva, Switzerland: World Health Organization; 2013. http://www.who.int/healthinfo/statistics/GlobalDALYmethods_2000_2011.pdf
8. Nelson DI, Nelson RY, Concha-Barrientos M, Fingerhut M. The global burden of occupational noise-induced hearing loss. Am J Ind Med 2005;48:446–58. CrossRef PubMed
9. Chien W, Lin FR. Prevalence of hearing aid use among older adults in the United States. Arch Intern Med 2012;172:292–3. CrossRef PubMed

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* Audiograms are the results of hearing tests.

† Decibel is a unit of measure of the intensity (or loudness). The A-scale is used because it corresponds better to the sound intensities perceived by the human ear at low frequencies.

§ North American Industry Classification System (NAICS) codes range from two-digit to six-digit numbers and industry specificity increases with each digit (https://www.census.gov/eos/www/naics/).

¶ For morbid conditions, such as hearing impairment, the burden over a one-year period is represented by a “disability weight” between 0 and 1, representing life limitations as a lost fraction of a year of healthy life. Because the most recent audiograms for workers were used to characterize hearing impairment, the DALY results are an estimate of the annual number of DALYs per 1,000 workers in the year of the last audiogram, and a minimum estimate of DALYs in following years. Thus, the DALY results are estimates of the annual DALYs per 1,000 workers as of 2012, the last year included in the analysis.

** Tinnitus prevalences were estimated using results for U.S. noise-exposed workers with daily or more frequent tinnitus comorbid with hearing loss (http://onlinelibrary.wiley.com/doi/10.1002/ajim.22565/epdf) and proportions of the general population experiencing daily tinnitus by GBD Study level of hearing impairment (http://www.who.int/healthinfo/statistics/GlobalDALYmethods_2000_2011.pdf). Tinnitus prevalence estimates for each level of hearing impairment severity for the DALYs calculations were as follows: mild (18.40%); moderate (26.58%); moderately severe (28.61%); severe (55.79%); profound (56.42%); and complete (47.97%).