Acoustic trauma from continuous noise: Minimum exposures, issues in clinical trial design, and comments on magnetic resonance imaging exposures.

Acoustic trauma (AT) is permanent hearing loss after a single noise exposure. A few human cases resulting from continuous, i.e., nonimpulsive noise, have been reported as reviewed by Ward [(1991). "Hearing loss from noise and music," presented at Audio Engineering Society, New York, October 4-8]. This paper updates that review by examining 11 cases in nine reports, from 1950 to 2006, with the intention of determining minimum exposures that may cause AT, including the potential risk of exposure to noise from magnetic resonance imaging machines. Diffuse-field related levels above 120 dBA for 10 s or more, or above 130 dBA for 2-3 s (values well above OSHA's unprotected exposure limits), can lead to AT. These cases appear to represent a susceptible fraction of the population, because much more intense exposures (e.g., 130 dBA for 32 min) have been tolerated by groups of volunteers who suffered only temporary threshold shifts. AT from continuous noise is unlikely to occur in OSHA-compliant hearing conservation programs, and probably rare enough in the general civilian population that clinical trials of drugs aimed at treating it are unlikely to be practical. AT from impulse noise, such as gunfire, which is specifically not the topic of the current work, is more amenable to clinical trials, especially in military settings.

Kids Nowadays Hear Better Than We Did: Declining Prevalence of Hearing Loss in US Youth, 1966-2010.

OBJECTIVES/HYPOTHESIS: To investigate factors associated with hearing impairment (HI) in adolescent youths during the period 1966-2010. STUDY DESIGN: Cross-sectional analyses of US sociodemographic, health, and audiometric data spanning 5 decades. METHODS: Subjects were youths aged 12 to 17 years who participated in the National Health Examination Survey (NHES Cycle 3, 1966-1970; n = 6,768) and youths aged 12 to 19 years in the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994; n = 3,057) and NHANES (2005-2010; n = 4,374). HI prevalence was defined by pure-tone average (PTA) ≥ 20 dB HL for speech frequencies (0.5, 1, 2, and 4 kHz) and high frequencies (3, 4, and 6 kHz). Multivariable logistic models were used to estimate the odds ratio (OR) and 95% confidence interval (CI). RESULTS: Overall speech-frequency HI prevalence was 10.6% (95% CI: 9.7%-11.6%) in NHES, 3.9% (95% CI: 2.8%-5.5%) in NHANES III, and 4.5% (95% CI: 3.7%-5.4%) in NHANES 2005 to 2010. The corresponding high-frequency HI prevalences were 32.8% (95% CI: 30.8%-34.9%), 7.3% (95% CI: 5.9%-9.0%), and 7.9% (95% CI: 6.8%-9.2%). After adjusting for sociodemographic factors, overall high-frequency HI was increased twofold for males and cigarette smoking. Other significant risk factors in NHANES 2005 to 2010 included very low birth weight, history of ear infections/otitis media, ear tubes, fair/poor general health, and firearms use. CONCLUSIONS: HI declined considerably between 1966 to 1970 and 1988 to 1994, with no additional decline between 1988 to 1994 and 2005 to 2010. Otitis media history was a significant HI risk factor each period, whereas very low birth weight emerged as an important risk factor after survival chances improved. Reductions in smoking, job-related noise, and firearms use may partially explain the reduction in high-frequency HI. Loud music exposure may have increased, but does not account for HI differences. LEVEL OF EVIDENCE: NA Laryngoscope, 129:1922-1939, 2019.

Occupational Noise-Induced Hearing Loss.

: Occupational hearing loss is preventable through a hierarchy of controls, which prioritize the use of engineering controls over administrative controls and personal protective equipment. The occupational and environmental medicine (OEM) physician plays a critical role in the prevention of occupational noise-induced hearing loss (NIHL). This position statement clarifies current best practices in the diagnosis of occupational NIHL.

Cost-Effective Hearing Conservation: Regulatory and Research Priorities.

Hearing conservation programs (HCPs) mandated by the US Occupational Safety and Health Administration (OSHA) cost about $350/worker/year. Are they cost-effective? A cross-sectional model of the US adult population with and without HCPs incorporates (1) the American Medical Association's method for estimating binaural hearing impairment and whole-person impairment; (2) the model of the International Organization for Standardization (ISO) for estimating both age-related and noise-induced hearing loss; and (3) an acceptable cost of $50,000 per quality-adjusted life year. The ISO model's outputs were audiometric thresholds for groups of people with different age, sex, and noise exposure history. These thresholds were used to estimate cost per quality-adjusted life year saved for people in HCPs with different noise exposure levels. Model simulations suggest that HCPs may be cost-effective only when time-weighted average (TWA) noise exposures are ≥ 90 dBA. Enforcing existing regulations, requiring engineering noise control at high exposure levels, and using new methods that can document hearing protection device performance could improve cost-effectiveness. If the OSHA action level remains at 85 dBA-TWA, reducing the permissible exposure limit to the same level would simplify management and slightly improve cost-effectiveness. Research should evaluate employer compliance across industries, determine whether workers currently excluded from HCP regulations are at risk of noise-induced hearing loss, and develop cost-effective HCPs for mobile workers in construction, agriculture, and oil and gas drilling and servicing. Research on HCP cost-effectiveness could be extended to incorporate sensitivity analyses of the effects of a wider range of assumptions.

Declining Prevalence of Hearing Loss in US Adults Aged 20 to 69 Years.

Importance: As the US population ages, effective health care planning requires understanding the changes in prevalence of hearing loss. Objective: To determine if age- and sex-specific prevalence of adult hearing loss has changed during the past decade. Design, Setting, and Participants: We analyzed audiometric data from adults aged 20 to 69 years from the 2011-2012 cycle of the US National Health and Nutrition Examination Survey, a cross-sectional, nationally representative interview and examination survey of the civilian, noninstitutionalized population, and compared them with data from the 1999-2004 cycles. Logistic regression was used to examine unadjusted, age- and sex-adjusted, and multivariable-adjusted associations with demographic, noise exposure, and cardiovascular risk factors. Data analysis was performed from April 28 to June 3, 2016. Interventions: Audiometry and questionnaires. Main Outcomes and Measures: Speech-frequency hearing impairment (HI) defined by pure-tone average of thresholds at 4 frequencies (0.5, 1, 2, and 4 kHz) greater than 25 decibels hearing level (HL), and high-frequency HI defined by pure-tone average of thresholds at 3 frequencies (3, 4, and 6 kHz) greater than 25 decibels HL. Results: Based on 3831 participants with complete threshold measurements (1953 men and 1878 women; mean [SD] age, 43.6 [14.4] years), the 2011-2012 nationally weighted adult prevalence of unilateral and bilateral speech-frequency HI was 14.1% (27.7 million) compared with 15.9% (28.0 million) for the 1999-2004 cycles; after adjustment for age and sex, the difference was significant (odds ratio [OR], 0.70; 95% CI, 0.56-0.86). Men had nearly twice the prevalence of speech-frequency HI (18.6% [17.8 million]) as women (9.6% [9.7 million]). For individuals aged 60 to 69 years, speech-frequency HI prevalence was 39.3% (95% CI, 30.7%-48.7%). In adjusted multivariable analyses for bilateral speech-frequency HI, age was the major risk factor (60-69 years: OR, 39.5; 95% CI, 10.5-149.4); however, male sex (OR, 1.8; 95% CI, 1.1-3.0), non-Hispanic white (OR, 2.3; 95% CI, 1.3-3.9) and non-Hispanic Asian race/ethnicity (OR, 2.1; 95% CI, 1.1-4.2), lower educational level (less than high school: OR, 4.2; 95% CI, 2.1-8.5), and heavy use of firearms (≥1000 rounds fired: OR, 1.8; 95% CI, 1.1-3.0) were also significant risk factors. Additional associations for high-frequency HI were Mexican-American (OR, 2.0; 95% CI, 1.3-3.1) and other Hispanic race/ethnicity (OR, 2.4; 95% CI, 1.4-4.0) and the combination of loud and very loud noise exposure occupationally and outside of work (OR, 2.4; 95% CI, 1.4-4.2). Conclusions and Relevance: Adult hearing loss is common and associated with age, other demographic factors (sex, race/ethnicity, and educational level), and noise exposure. Age- and sex-specific prevalence of HI continues to decline. Despite the benefit of delayed onset of HI, hearing health care needs will increase as the US population grows and ages.

Commentary on the regulatory implications of noise-induced cochlear neuropathy.

OBJECTIVE: A discussion on whether recent research on noise-induced cochlear neuropathy in rodents justifies changes in current regulation of occupational noise exposure. DESIGN: Informal literature review and commentary, relying on literature found in the authors' files. No formal literature search was performed. STUDY SAMPLE: Published literature on temporary threshold shift (TTS) and cochlear pathology, in humans and experimental animals, as well as the regulations of the US Occupational Safety and Health Administration (OSHA). RESULTS: Humans are less susceptible to TTS, and probably to cochlear neuropathy, than rodents. After correcting for inter-species audiometric differences (but not for differences in susceptibility), exposures that caused cochlear neuropathy in rodents already exceed OSHA limits. Those exposures also caused "pathological TTS" (requiring more than 24 h to recover), which does not appear to occur with human broadband noise exposure permissible under OSHA. CONCLUSION: It would be premature to conclude that noise exposures permissible under OSHA can cause cochlear neuropathy in humans.

Is this STS work-related? ISO 1999 predictions as an adjunct to clinical judgment.

BACKGROUND: Physicians and audiologists are often asked to decide whether standard threshold shifts (STSs) are work-related; epidemiological data can inform these decisions. METHODS: Predictions of ISO (2013) for both age-related and noise-induced threshold shifts, for the 2, 3, and 4 kHz average used in calculating OSHA STSs, are presented, in tables, graphs, and an Excel spreadsheet calculator. Specifically, the ISO 1999 model estimates age-related thresholds based on age and sex; it estimates noise-induced threshold shifts based on noise level and duration. It specifies that to estimate the final hearing thresholds for a person of given percentile, age, sex, and noise exposure, the expected age-related threshold is to be added to the expected noise-induced threshold shift. Examples show how these data can predict the relative contributions of aging and occupational noise to an STS. RESULTS: Early-career STSs, especially with high levels of noise exposure, are more likely to be primarily noise-induced. After the first decade of exposure, most STSs will be primarily age-related. CONCLUSION: Given a worker's age, sex, and occupational noise exposure history, ISO 1999 estimates of the expected contributions of aging and noise can supplement clinical judgment.

Age correction in monitoring audiometry: method to update OSHA age-correction tables to include older workers.

OBJECTIVES: The US Occupational Safety and Health Administration (OSHA) Noise Standard provides the option for employers to apply age corrections to employee audiograms to consider the contribution of ageing when determining whether a standard threshold shift has occurred. Current OSHA age-correction tables are based on 40-year-old data, with small samples and an upper age limit of 60 years. By comparison, recent data (1999-2006) show that hearing thresholds in the US population have improved. Because hearing thresholds have improved, and because older people are increasingly represented in noisy occupations, the OSHA tables no longer represent the current US workforce. This paper presents 2 options for updating the age-correction tables and extending values to age 75 years using recent population-based hearing survey data from the US National Health and Nutrition Examination Survey (NHANES). Both options provide scientifically derived age-correction values that can be easily adopted by OSHA to expand their regulatory guidance to include older workers. METHODS: Regression analysis was used to derive new age-correction values using audiometric data from the 1999-2006 US NHANES. Using the NHANES median, better-ear thresholds fit to simple polynomial equations, new age-correction values were generated for both men and women for ages 20-75 years. RESULTS: The new age-correction values are presented as 2 options. The preferred option is to replace the current OSHA tables with the values derived from the NHANES median better-ear thresholds for ages 20-75 years. The alternative option is to retain the current OSHA age-correction values up to age 60 years and use the NHANES-based values for ages 61-75 years. CONCLUSIONS: Recent NHANES data offer a simple solution to the need for updated, population-based, age-correction tables for OSHA. The options presented here provide scientifically valid and relevant age-correction values which can be easily adopted by OSHA to expand their regulatory guidance to include older workers.

Does occupational noise cause asymmetric hearing loss?

OBJECTIVE: Determine whether occupational noise exposure increases audiometric asymmetry. DESIGN: Audiograms were performed on 2044 men from the Occupational Noise and Hearing Survey, representing four groups based on preliminary screening (for previous noise exposure, otologic history, and otoscopy) and current occupational noise exposure. The effects of current noise exposure on audiometric asymmetry were tested using ANCOVA, with binaural average thresholds as covariates. RESULTS: There were no significant differences in asymmetry attributable to current occupational noise exposure. RESULTS: Occupational noise exposure does not usually cause or exacerbate audiometric asymmetry.

Exchange rates for intermittent and fluctuating occupational noise: a systematic review of studies of human permanent threshold shift.

OBJECTIVE: The aim of this study was to review the literature regarding human noise-induced permanent threshold shift and to determine whether the observed data agreed with the predictions of two different exchange rates (ERs). DESIGN: An initial list of possibly relevant studies included those cited by authors who endorsed the 3 dB ER, as well as studies in personal files, studies retrieved by a MEDLINE search, and the reference lists of all of these. Criteria for relevance were designed to ensure that exposures were sufficiently intermittent or fluctuating that effective exposure levels based on the 3 dB (LAeq8h) and 5 dB (time-weighted average [TWA]) ERs would differ by at least 1 dB, that at least one of these metrics could be estimated, and that audiometric data were available for groups of defined age, sex, and exposure. Relevant studies were reviewed in detail, and their audiometric data were compared with the predictions of the ISO-1999/ANSI S3.44 model. RESULTS: Nine relevant studies were identified. For six articles, the reported hearing levels were substantially less than would have been predicted from LAeq8h. In each of these cases, TWA would have predicted lower hearing levels than LAeq8h and would have better fit the observed data. In three cases it was not possible to say which ER would have better fit the observed data. CONCLUSIONS: The 3 dB ER systematically overestimates the risk of noise-induced hearing loss for intermittent or fluctuating noise. The 5 dB ER appears to be more accurate, but also overestimates risk, particularly for exposures above 100 dBA.

A new standardized format for reporting hearing outcome in clinical trials.

The lack of an adequate standardized method for reporting level of hearing function in clinical trials has hampered the ability of investigators to draw comparisons across studies. Variability in data reported and presentation format inhibits meta-analysis and makes it impossible to accumulate the large patient cohorts needed for statistically significant inference. Recognizing its importance to the field and after a widely inclusive discussion, the Hearing Committee of the American Academy of Otolaryngology-Head and Neck Surgery endorsed a new minimal standard for reporting hearing results in clinical trials, consisting of a scattergram relating average pure-tone threshold to word recognition score. Investigators remain free to publish their hearing data in any format they believe is interesting and informative, as long as they include the minimal data set to facilitate interstudy comparability.