CAOHC Newsletter: UPDATE

NIOSH Announces First Results from Occupational Hearing Loss Surveillance Project

Elizabeth Masterson, PhD, CPH, COHC

Greetings from the National Institute for Occupational Safety and Health (NIOSH)! Some new and exciting public health surveillance efforts for occupational hearing loss (OHL) have been underway and we would like to share our progress, future plans and the results from our first study. The NIOSH OHL Surveillance Project began in 2009 to establish a national repository for occupational hearing loss data and to conduct surveillance and research of this common occupational illness. During this project we have partnered with 14 audiometric service providers (which we will refer to as providers) and collected nearly nine million audiograms, many of which were conducted before 2000, allowing for historical trends to be examined. None of the audiograms contain personal identifying information. We also developed quality assurance methods to identify and remove from analyses audiograms with quality deficiencies or hearing loss consistent with non-occupational exposures. These characteristics included unlikely threshold values, negative slope indicating excessive background noise during testing, and large inter-aural differences (>40 dB). The North American Industry Classification System (NAICS) was used to identify the industry, and a NAICS code was assigned to each audiogram (U.S. Census Bureau, 2012). NAICS codes can range from two-digit to six-digit numbers, and industry specificity increases with each digit.

It is important to define a few of the concepts in public health surveillance. Surveillance is “the systematic collection, analysis, and dissemination of health-related information for the purposes of prevention or control of disease or injury” (Halperin & Howard, 2011). Surveillance is vital to hearing loss prevention. It allows us to establish baseline estimates for hearing loss within various industries, including the prevalence, which is the total number or percent of workers with hearing loss, and the incidence, which is the number of new cases of hearing loss. Without a starting point, we cannot identify progress or the need for improvement. Surveillance also allows us to identify high risk groups, guide prevention and research efforts, and evaluate the success or failure of interventions.

Our first manuscript using this data was recently submitted for publication in a peer-reviewed journal. We examined the prevalence (or percent) of workers with hearing loss by industry for 1,122,722 workers. We also estimated prevalence ratios indicating the risk for hearing loss for workers in each industry compared with workers in a reference industry. Our reference industry was Couriers and Messengers (NAICS 492). Workers from the entire range of industry categories in the United States were represented in our sample. Hearing loss was defined using the NIOSH definition of material hearing impairment, which is a pure-tone average threshold across frequencies 1,000, 2,000, 3,000 and 4,000 Hz of 25 dB or more in either ear (National Institute for Occupational Safety and Health [NIOSH], 1998).

In our sample, approximately 18% of workers had material hearing loss, which included 21% of males and 8% of females. Male workers were over two-and-a-half times more likely to have hearing loss than female workers. The percent of workers with hearing loss increased with age, from 3% among workers ages 18-25 to 56% among workers ages 56-65. We adjusted each prevalence ratio (our risk estimate) by age group, gender, geographical region and provider. The manuscript included prevalence and risk estimates for hearing loss for all industries at the two-digit NAICS level of specificity, focused on mining, construction and manufacturing at the three-digit NAICS level of specificity, and provided a targeted look at high-risk industries at the four-digit NAICS level. Here we present new results for NAICS industry sectors, which are larger groupings of industries (please see Table 1).

Table 1. Estimated Prevalence and Adjusted Prevalence Ratios for Hearing Loss (HL) by Industry Sector, 2000 - 2008 (N = 1,122,722)
Industry Sector (NAICS 2007 Code)	n	Prevalence of HL in % (95% CI)	Prevalence Ratio* (95% CI)
Agriculture, Forestry, Fishing and Hunting (11)	4,309	16.22 (15.12-17.32)	1.51 (1.43-1.61)
Mining, Quarrying, and Oil and Gas Extraction (21)	3,232	27.01 (25.48-28.54)	1.60 (1.52-1.68)
Construction (23)	29,639	23.48 (23.00-23.96)	1.56 (1.52-1.61)
Manufacturing (31-33)	739,964	19.81 (19.72-19.90)	1.46 (1.43-1.50)
Wholesale and Retail Trade (42, 44-45)	79,724 18.90	(18.63-19.17)	1.44 (1.40-1.48)
Transportation, Warehousing and Utilities (48, 491, 493, 22)	46,172	17.10 (16.76-17.44)	1.27 (1.23-1.30)
Healthcare and Social Assistance (62)	3,966	18.36 (17.16-19.57)	1.21 (1.14-1.29)
Services (51-56, 61, 71-72, 81, 92)	102,824	18.45 (18.21-18.69)	1.34 (1.31-1.37)
Couriers and Messengers (492) (reference group)	112,892	8.29 (8.13-8.45)	reference group
*PRs were adjusted for gender, age group, geographical region and provider. CI = 95% confidence interval

Overall, the three industry sectors with the highest prevalence percentages (Table 1, third column) of workers with hearing loss were 1) Mining, Quarrying, and Oil and Gas Extraction (27%), 2) Construction (23%), and 3) Manufacturing (20%). The percentage of workers with hearing loss in the reference industry was 8%. When adjusted for age group, gender, geographical region and provider, the risks for workers developing hearing loss (Table 1, fourth column) were highest in the 1) Mining, Quarrying, and Oil and Gas Extraction, 2) Construction, and 3) Agriculture, Forestry, Fishing and Hunting sectors. The risks for workers developing hearing loss in these sectors were 60%, 56% and 51% higher, respectively, than the risk for workers in the reference industry.

The higher percentages of workers with hearing loss and the elevated risks for developing hearing loss in the Mining, Construction and Manufacturing sectors are consistent with other studies (Engdahl, & Tambs, 2010; Tak & Calvert, 2008; Rubak et al., 2006). We included a detailed breakdown of the industries within these sectors in the manuscript. While we did not focus on the industries within the Agriculture, Forestry, Fishing and Hunting sector, the high risk associated with this sector overall indicates that a targeted analysis of hearing loss within this sector may be needed. It should be noted that NAICS codes are economic classifications and may not group together workers with similar noise and ototoxic chemical exposures. At the industry sector level, disparate types of workers within each industry are likely grouped together.

Our study used a novel approach for data collection by partnering with providers rather than individual companies. This allowed NIOSH to collect millions of de-identified audiograms from thousands of workplaces across the country while protecting the identities of workers, companies and providers. We also used the results of audiograms to determine hearing loss rather than survey responses and excluded audiograms with data quality issues. We believe these efforts greatly improved the accuracy of the results. We hope that you will check out the NIOSH study once it is published.

The project is continuing full speed ahead. NIOSH is still actively partnering with providers willing to share their audiometric data with NIOSH. We are building a web page for the project. In addition, three other manuscripts are also currently in development. One provides estimates of the incidence of hearing loss by industry. Another compares the self-reported use of hearing protection for workers with and without hearing loss. Finally, the third manuscript estimates the prevalence of workers with standard threshold shifts, by industry, in comparison with the prevalence of workers with NIOSH-recommended significant threshold shifts. A standard threshold shift is indicated when there is a 10 dB increase in the average of the 2,000, 3,000 and 4,000 Hz threshold values, in either ear, from the baseline audiogram to the current audiogram. An optional age correction can also be applied. A significant threshold shift is indicated if there is a 15 dB increase in any of the threshold values for frequencies 500, 1,000, 2,000, 3,000, 4,000, or 6,000 Hz, in either ear, from the baseline audiogram to the current audiogram. This increase must be present on a subsequent audiogram and no age correction is applied.

If you have any questions about the NIOSH OHL Surveillance Project or are interested in partnering with us, please contact Liz Masterson at OHLSurveillance@cdc.gov or (513) 841-4291. Thank you!

The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the Centers for Disease Control and Prevention/the National Institute for Occupational Safety and Health.

Mini-Bio/Affiliation

Elizabeth A. Masterson is an epidemiologist in the Surveillance Branch of the National Institute for Occupational Safety and Health, Cincinnati, Ohio.

References

Engdahl, B. and Tambs, K. (2010). Occupation and the risk of hearing impairment -- results from the Nord-Trondelag study on hearing loss. Scandinavian Journal of Work, Environment & Health, 36(3), 250-257.

Halperin. W. and Howard, J. (2011). Occupational epidemiology and the National Institute for Occupational Safety and Health. Morbidity and Mortality Weekly Report, 60(04), 97-103.

National Institute for Occupational Safety and Health (1998). Criteria for a recommended standard: Occupational noise exposure: Revised criteria 1998 (DHHS [NIOSH] Publication No. 98-126). U.S. Dept. of Health and Human Services, Centers for Disease Control and Prevention, Cincinnati, OH: U.S. Government Printing Office.

Rubak, T., Kock, S. A., Koefoed-Nielsen, B., Bonde, J. P., and Kolstad, H. A. (2006). The risk of noise-induced hearing loss in the Danish workforce. Noise & Health, 8(31), 80-87.

Tak, S., and Calvert, G. M. (2008). Hearing difficulty attributable to employment by industry and occupation: An analysis of the National Health Interview Survey - United States, 1997 to 2003. Journal of Occupational and Environmental Medicine, 50(1), 46-56.

U.S. Census Bureau (2012). North American Industry Classification System. Retrieved February 28, 2012 from http://www.census.gov/eos/www/naics/.