NORA Manufacturing Sector Strategic Goals
927ZBCM - Determining the Work Relatedness of Hearing Loss
Principal Investigator (PI)
Primary Goal Addressed
Secondary Goal Addressed
Attributed to Manufacturing
The goal of this project is to improve the ability to detect noise-induced hearing losses. This will be accomplished by demonstrating the viability of 8 kHz as an audiometric test frequency. This, in turn, will lead to an improved ability to detect 6 kHz noise notches. This is important because recent data has demonstrated noise notches occur most commonly at 6 kHz. The outcome of this research is expected to lead to recommendations, policies, and standards that call for 8 kHz to be adopted as a required test frequency in hearing conservation audiometric monitoring protocols.
The study approach will be designed to obtain hearing thresholds on a cross section of adult males and females in their 3rd, 4th, 5th and 6th decades of life.
The number of subjects to be tested will be approximately 600. To obtain comparative reliability measures, multiple repeat audiograms will be obtained. This will include immediate retests (as recommended by NIOSH) to determine the existence of a significant change in hearing threshold. It will also include multiple retests on different days. In addition to 8 kHz, current standard audiometric test frequencies (500, 1000, 2000, 3000, 4000, and 6000 Hz) will also be tested. A total of 6000 audiograms will be obtained. During year one NIOSH with input from its U.S. Army partners will develop a protocol, obtain HSRB approval, and prepare a statement of work for a contract to collect data. During year two the contract will be awarded and data collection will begin. Data collection will continue throughout year 3 and will be completed by year four, and NIOSH will analyze the results. NIOSH will then collaborate with its partners to develop recommendations for practical solutions that address an Institute of Medicine recommendation that the Department of Defense include 8 kHz in its audiometric test protocol. These solutions should be equally applicable to the general hearing loss prevention community. For example, by demonstrating the reliability of 8 kHz hearing thresholds, NIOSH will be able to update its 1998 criteria document to include new, well-supported recommendations to adopt 8 kHz as a required test frequency. As a consequence, this may lead to a change in the procedure for testing the hearing of every American worker at risk of occupational hearing loss. It may also lead to a reconciliation between American and international protocols for conducting hearing conservation audiometric monitoring.
This project will determine the reliability of standard audiometric test frequencies currently required by OSHA, MSHA, and the DoD (500 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz, and 6000 Hz). Additionally, it will measure the reliability of 8000 Hz. Reliability will be measured as a function of same day and between day repeated measures. Audiometric thresholds also will be evaluated as functions of gender, ethnicity, and age. The goal is to provide a definitive comparative analysis of the reliability of audiometric test frequencies from 500 Hz to 8 kHz. The immediate outcome will be to establish that 8 kHz is as reliable as other audiometric test frequencies currently required in hearing conservation audiometric monitoring protocols. The intermediate outcome will be the adoption of 8 kHz by professional certifying organizations (e.g., CAOHC, AAA, and ASHA) as the standard of practice for measuring workers' hearing. This is expected to lead to revised hearing conservation regulations and standards. Application of methods which enable early identification of noise-induced hearing loss will lead to a long term outcome of reduced incidence and severity of noise-induced occupational hearing loss.
This effort will develop improved audiometric methods for detecting a 6 kHz notch by demonstrating the viability of 8 kHz as a standard test frequency. As such, the proposed effort would be consistent with the recent National Academies review of the NIOSH Hearing Loss Research portfolio and its recommendation that NIOSH continue its efforts to improve hearing loss prevention programs, particularly through research that would have a substantial impact in this arena.
Noise-induced hearing loss has traditionally been characterized by a "notch" at 4 kHz (i.e., the hearing at 4 kHz is worse than at the adjacent frequencies of 3 and 4 kHz). Should the "notch" occur at 3 kHz, it would be identifiable because hearing would be tested at adjacent frequencies (i.e., 2 kHz and 4 kHz). Thus, one can see that without testing at 8 kHz, it would not be possible to determine the presence or absence of a notch at 6 kHz. Worse yet, without testing at 8 kHz, a 6 kHz notch would mimic the appearance of age-related hearing loss (presbyacusis). Because audiologists and occupational hearing conservation technicians are currently taught to look for a 4 kHz notch, it is likely that a noise-induced hearing loss manifested by a 6 kHz notch would be misdiagnosed as presbyacusis. Unfortunately in OSHA, MSHA, and DOD mandated hearing conservation programs, 6 kHz is the highest required test frequency. There is resistance to incorporating 8 kHz as a standard test frequency because of a widely held belief that it is not possible to obtain reliable 8 kHz hearing thresholds. This belief is not substantiated by data. Nevertheless, it has assumed an unwarranted acceptance among the audiological community as being true.
Adding 8 kHz to the audiometric test protocol will (1) enable 6 kHz noise notches to be identified, and thereby improve our ability to detect and measure noise-induced hearing loss, (2) greatly facilitate our ability to determine work-relatedness of a given hearing loss, and (3) reduce the likelihood that noise-induced hearing loss is misdiagnosed. This will lead to a long-term outcome of reduced occupational hearing loss. This effort supports Goal #4 in the Manufacturing sector (reduce the incidence and severity of work-related illness and injury. It supports Goal #4 in the Construction sector Reduce hearing loss among construction workers by increased use of noise reduction solutions, practices, and hearing conservation programs by the construction community. It supports Goal # 2 in the Mining sector (reduce noise-induced hearing loss) and Intermediate Goal 2.3 Empower workers to acquire and pursue more effective hearing conservation action. It also supports Strategic Goal #4 of the NIOSH hearing loss research program, Identify and Develop Best Practices for Identifying Workers at Risk of Occupational Hearing Loss, and specifically Intermediate Goal 4.1: Development of the most effective audiometric test protocol.