Hearing loss induced by noise, ear infections, and head injuries: results from the Nord-Trøndelag Hearing Loss Study.

Pure-tone audiometry was administered to the adult population in Nord-Trøndelag County, Norway, 1995-97. The 51,975 participants also provided questionnaire information about occupational and leisure noise exposure, previous ear infections, and head injury. Values averaged over both ears were calculated for low (250 and 500 Hz), middle (1 and 2 kHz) and high frequencies (3, 4, 6 and 8 kHz). The aim was to estimate the magnitude of hearing loss associated with various types of exposure by age and sex. Noise, ear infections and head injury explained 1-6% of the variance in hearing loss (varying with age, sex, and frequency range), in addition to what could be explained by age alone (30-58%). Only moderate effects of noise could be detected among women. The upper tenth percentile regarding occupational noise among men older than 44 years had on average an 8-9-dB high-frequency loss, adjusted for other predictors. Exposure to impulse noise (hunting, sports shooting) caused a 7-8-dB high-frequency loss in the same group. No significant effects of frequent use of personal stereo players or regular attendance at discotheques or rock concerts could be demonstrated. There were clear effects of recurrent ear infections and head injury.