Analyses have been conducted with data from the Nord Trondelag (NT) Hearing Study, part of a larger health examination study in NT county, located in the middle of Norway. The first report of findings was based on 45,920 adults (70% of subjects eligible for the hearing exam). Norwegian investigators obtained hearing thresholds from each ear at standard pure-tone frequencies (.25, .5, 1, 2, 3, 4, 6, and 8 kHz) using semi- portable, dismountable sound-attenuation booths. For epidemiologic analyses, hearing loss (HL) is defined as greater than 25 dB, and moderate-to-severe hearing loss (MHL) as greater than 40 dB, based on pure-tone averages of thresholds at .5, 1, and 2 kHz in the speech frequency range. Also analyzed were responses to questionnaires on health, lifestyle, medical, and occupational histories of the subjects. For example, 45% of males and 15% of females, aged 35-74 years, reported exposures of 5 or more hours per week to loud noises at work. Logistic regression models have been used to estimate relative risks for many potential risk factors for HL or MHL. Analyses were performed for the whole sample adjusting for age of subjects and, separately, by stratifying age into younger (20-44 years) and older (55-74 years) subjects. The relation of unadjusted logit rates of HL to age differed between males and females, showing greater HL at an earlier age for males, which was related to the increased occupational noise exposure of males. Both younger and older subjects showed increased risks of HL (and MHL) related to tinnitus (ringing in ears), history of frequent otitis media in childhood, and having familial HL or first-degree relatives with known HL. In multi-variable logistic regression analyses, exposure to noise at work and increased exposure to impulse noise (e.g., firearms use) were both highly significant for HL in older subjects. Also, 43% of subjects found to have MHL reported they had no prior knowledge of a hearing loss. We have concluded that interventions, based on knowledge of avoidable risk factors, could significantly increase the number of quality years of life without major hearing loss. A six-year, population-based study of hearing impairment in the United States, based on the next National Health and Nutrition Examination Survey (NHANES IV), is just beginning. We coordinated the protocol development of both a hearing and balance examination (modified Romberg) component for NHANES, together with colleagues at NIOSH and NCHS. A stratified random sample of U.S. adults, oversampled for African-American and Hispanic race/ethnicity, will have hearing and balance examinations conducted in mobile examination centers which move to communities throughout the U.S.
| 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 |
