Self-Reported Hearing Loss Among Workers Potentially Exposed to Industrial Noise -- United States

Noise-induced loss of hearing has been recognized as an occupational health problem since the 18th century (1). Occupational deafness is an irreversible, sensorineural condition that results from damage to the nerve cells of the inner ear. Recent estimates from surveys indicate that between 7.4 and 10.2 million people work at sites where the level of noise presents an increased risk of hearing loss (85 decibels (dBA) or higher) (2). During the period 1978-1987, an estimated $835 million was paid in workers' compensation claims for occupationally induced hearing impairment (3).

To assess the prevalence of hearing-loss symptoms among adult workers in the United States, investigators from the National Institute for Occupational Safety and Health (NIOSH) recently analyzed data collected during the 1971 and 1977 National Health Interview Surveys (NHIS) conducted by the National Center for Health Statistics (NCHS) (4,5). NHIS is a continuing household survey of a stratified probability sample of the civilian, noninstitutionalized U.S. population. Members of some 42,000 households, comprising approximately 120,000 persons, are interviewed each year to obtain information about health status. Thus, NHIS serves as a database for national estimates of prevalence of various health conditions in the U.S. population. The survey is also useful for following health trends in this population. For this study, the prevalence of self-reported hearing loss was obtained for all persons over 17 years of age who were in the labor force at the time of interview. The Gallaudet Scale, a well-validated, self-rating hearing scale consisting of seven questions, was used to evaluate the degree of hearing impairment (6). Unilateral hearing loss, which was involved in about half of the cases, was excluded.

Data from the 1972-1974 National Occupational Hazard Survey (NOHS) were used to classify worksites by noise level (7). NOHS was conducted by NIOSH from 1972 to 1974 on a probability sample of approximately 5,000 workplaces across the United States (7). The survey provides information on potential exposures of workers to chemical and physical agents. These data identified industries and occupations in which employees are exposed to continuous noise.*

Some degree of hearing loss was reported by 3.2% of all NHIS respondents. Self-reported hearing loss was higher among adults working in industries with potential exposure to industrial noise than among those working in industries without such potential exposures. NHIS data were then analyzed with the data collected independently during NOHS. Stratifying NHIS data on self-reported hearing loss by the noise levels reported in NOHS shows that self-reported hearing loss increases with age, and that, within age groups, it is consistently greater for noisy industries.

The percentage and number of workers exposed to noise and the percentage of self-reported hearing loss in 31 broad industrial categories were estimated from the NOHS and the NHIS (Table 1). Industries in the manufacturing sector had the highest prevalence of noise exposure (overall exposure rate, 37%).

Results of the NHIS on self-reported hearing loss among workers 17 years of age or older were divided into three groups: 1) persons with light exposure, or those working in industries where less than 10% of the employees were estimated by NOHS to be exposed to noise at greater than or equal to85 dBA; 2) persons with moderate exposure, or those employed in industries where 10%-24% of the workers receive such exposure; and 3) persons with heavy exposure, or those employed in industries where greater than or equal to25% of the workers receive such exposure. These data were further stratified into three age groups: 17-44 years, 45-54 years, and greater than or equal to55 years. A comparison of these groups showed that the prevalence of self-reported hearing loss among white males** increased with both age and increasing exposure to industrial noise (Figure 1). Reported by: Surveillance Br, Div of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health; Div of Health Interview Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: Current findings indicate that occupational exposure to noise is a widespread problem that has a substantial impact on the prevalence of hearing loss among the working population. Exposure to intense noise causes hearing loss that may be temporary or permanent. Temporary hearing loss, also called auditory fatigue, may occur after only a few minutes of exposure to intense noise and is reversible after a period of time away from the noise. However, when exposure to excessive noise occurs over a period of months or years, only partial recovery of hearing may be possible.

NIOSH has identified noise-induced hearing loss as one of ten leading work-related diseases and injuries (8). A national strategy for the prevention of such hearing loss will be included in a NIOSH publication entitled Proposed National Strategies for the Prevention of Leading Work-Related Diseases and Injuries, Part II, which is to be published soon. The three main recommendations for preventing hearing loss among workers are 1) developing technology that will substitute quiet processes for noisy ones; 2) controlling the noise of existing processes; and 3) developing hearing conservation programs, including proper use of personal protective equipment.

The existing Occupational Safety and Health Administration standard for occupational exposure to noise specifies a maximum permissible exposure level of 90 dBA for 8 hours, with higher levels allowed for shorter durations (9). After a review of epidemiologic and laboratory data, NIOSH has proposed a limit of 85 dBA (10). Recommended or required levels vary depending on the number of hours of exposure during the work day (Table 2).

The study presented here demonstrates the practical value of linking information from an exposure surveillance survey (NOHS) with information from a survey that measures health status on a national level (NHIS). By identifying associations between potential environmental and occupational exposures and self-reported adverse health outcomes, it is possible to develop a better focus for research studies. When conducting large studies or assessing the impact of prevention strategies at the national level, such self-reported measures of adverse health outcomes may be more practical than actual testing.

A comparison of the current results with future studies that use data from similar surveys will permit an evaluation of overall progress toward the prevention of work-related hearing loss. As intervention strategies are applied successfully, there should be no differential hearing loss between workers in industries with low, medium, or high noise levels. Improvement should be evident first in the younger age groups and later among older employees.

References

1. Ramazzini B. Diseases of workers (De morbis artificum, 1713). Trans. Wilmer Cave Wright. New York: Hafner Publishing, 1964:231,437. 2. Simpson M, Bruce R. Noise in America: the extent of the noise

problem. Washington, DC: Bolt, Beranek, and Newman, 1981; BBN report no. 3318R. 3. Ginnold RE. Occupational hearing loss. Workers' compensation under

state and federal programs. Washington, DC: Environmental Protection Agency, 1979; EPA report no. 550/9-79-101. 4. Wilder CS. Prevalence of selected impairments, United

States--1971. Rockville, Maryland: National Center for Health Statistics, 1975; DHEW publication no. (HRA)75-1526. (Vital and health statistics: data from the National Health Survey; series 10; no. 99). 5. Feller BA. Prevalence of selected impairments, United

States--1977. Hyattsville, Maryland: National Center for Health Statistics, 1981; DHEW publication no. (HRA)81-1562. (Vital and health statistics: data from the National Health Survey; series 10; no. 134). 6. Ries PW. Hearing ability of persons by sociodemographic and health

characteristics: United States. Hyattsville, Maryland: National Center for Health Statistics, 1982; DHHS publication no. (PHS)82-1568. (Vital and health statistics: data from the National Health Survey; series 10; no. 140). 7. National Institute for Occupational Safety and Health. National

Occupational Hazard Survey. 3 volumes. Rockville, Maryland: National Institute for Occupational Safety and Health, 1974, 1977, 1978; DHEW publication nos. (NIOSH)74-127, 77-213, 78-114. 8. Centers for Disease Control. Leading work-related diseases and

injuries--United States. MMWR 1983;32:24-6,32. 9. Office of the Federal Register. Code of federal regulations:

labor. Washington, DC: Office of the Federal Register, National Archives and Records Administration, 1986. (29 CFR 1910.95). 10. National Institute for Occupational Safety and Health. Criteria

for a recommended standard . . . occupational exposure to noise. Rockville, Maryland: National Institute for Occupational Safety and Health, 1972; DHEW publication no. (HSM)73-11001. *Occupational exposure to noise was assessed by an industrial hygienist who determined the effect of noise on employees in the workplaces surveyed by NOHS. Workers were considered to be exposed if the noise level was measured or estimated to be greater than or equal to85 dBA, irrespective of the number of hours of daily exposure. **Results for other races are not shown because there were too few nonwhite males in the NHIS samples to provide reliable estimates after stratification of the data. No effect was seen for women, possibly because of the small number of women employed in industries with high noise levels.

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