Studies have been focused on population-based cohorts in the United States and Europe. A planned six-year study of hearing impairment in the United States began in April 1999, the Fourth National Health and Nutrition Examination Survey (NHANES IV), 1999-2004. The Epidemiology, Statistics and Data System Branch has collaborated with staff of the National Institute for Occupational Safety and Health (NIOSH) in developing the protocol and data collection instruments for this study of US adults, 20 to 69 years of age. This study of pure-tone hearing thresholds via examinations in sound- treated booths and responses to questionnaires on difficulties with hearing (and tinnitus), has been implemented by the National Center for Health Statistics (NCHS) as part of a larger multifaceted examination and interview survey. This year Branch staff participated in several planning meetings and reviewed results from the pilot testing of the hearing component. Adjustments in the study protocol were made to reduce the time required for the hearing examination, which remains the single longest component administered in the mobile examination centers (MECs). Throughout the study, there will be two different examination teams and MECs (specially equipped trailers) deployed in randomly-selected communities. No hearing tests for a national sample of the US population has been conducted since NHANES I, 1971-1975. We have also analyzed data from the Hispanic Health and Nutrition Examination Survey (HHANES), 1982- 1984. This project was designed for an audiologist conducting research in the Branch through the NIDCD Partnership Program. The focus was on risk factors for hearing impairment in males and, especially, for a dip at 4000 Hz, the location of the noise notch. This region of the audiogram is most sensitive to damage from long- term exposure to loud noise. A total sample of 1,847 Hispanic men (Cuban-American, Mexican-American, and Puerto Rican), aged 15-75 years, was available for study. Data consisted of responses to a detailed household interview, conducted in either English or Spanish, and a comprehensive physical examination that included air conduction pure-tone threshold audiometric examinations. Hearing threshold levels were obtained at 500, 1000, 2000, and 4000 Hz in each ear. Pure-tone averages (PTA) were calculated by averaging thresholds at 500, 1000, and 2000 Hz frequencies, the standard speech frequencies. Overall hearing impairment was defined as a PTA greater than 20 dB hearing level (HL) in the better ear. A 4000 Hz dip was defined as a greater than 15 dB difference between the pure- tone threshold at 4000 Hz and the PTA in the better hearing ear. In addition, to be considered a dip, the threshold at 4000 Hz in the better ear had to exceed 20 dB HL. Several potential risk factors: occupation, education, overall health assessment, smoking history, and service in the armed forces were evaluated. Logistic regression analysis was used to determine estimates of odds ratios (OR) and 95% confidence intervals (CI) for these estimates. Analyses were stratified within the 3 different Hispanic groups in accordance with NCHS recommendations since the samples were obtained from 3 separate geographic locations in the US. A significant association was found between occupation and presence of a 4000 Hz dip in both younger (15-44 years) and older (45-75 years) Mexican-American subjects. In the younger group, the association was strongest for agricultural workers, while for the older group, the association was strongest for those employed in construction or as machine operators. Lower educational levels also tended to be associated with the 400 Hz dip. Sample sizes were too small for theother Hispanic groups to produce comparable findings, although trends were similar for those employed in the construction trades. Analyses have continued this year of a large cohort of adults in an hearing examination study conducted in Nord Trondelag, Norway as part of a larger health examination study (HUNT-96). NIDCD and the Norwegian Public Health Institute jointly supported this study. The primary focus of analyses this year has been on comparing otoacoustic emissions results with pure-tone thresholds on a sample of subjects who completed both tests. A paper describing these findings has been completed and submitted for publication. In addition, we have evaluated the contribution of several known risk factors for hearing impairment using a nested case-control design. Subjects with hearing loss and matched controls completed a detailed follow-up questionnaire on exposures to occupational and recreational noise, and on other factors known to contribute to hearing impairment. For example, familial hearing loss (siblings or parents with hearing loss) and report of frequent childhood ear infections (otitis media) yielded significantly increased risks for hearing impairment in multivariate models for both male and female subjects. Results from these analyses will be presented in November at a meeting of the Acoustical Society of America in Columbus, Ohio. We have also begun collaborating with Danish researchers who have conducted population-based health interview studies on adult twin subjects. Using structural equation analyses suitable for twin samples, we have estimated the hereditability of reported hearing loss to be 45-52%. A paper describing the findings for the oldest subjects, 75 years of age or older, is in preparation.
| Janusauskas, A; Marozas, V; Engdahl, B et al. (2001) Otoacoustic emissions and improved pass/fail separation using wavelet analysis and time windowing. Med Biol Eng Comput 39:134-9 |
| Christensen, K; Frederiksen, H; Hoffman, H J (2001) Genetic and environmental influences on self-reported reduced hearing in the old and oldest old. J Am Geriatr Soc 49:1512-7 |
