An epidemiological study regarding the hearing acuity of residents in the area with high level of aircraft noise: results of hearing tests conducted in the vicinity of Kadena Air Base]

Hearing tests, primary and secondary, were conducted in two communities vicinal to Kadena US Air Base in Okinawa from May 1996 to July 1998. The noise exposure expressed in WECPNL as designated by the Defense Facilities Administration Agency ranged from 85 to 95 and above. A total of 2035 subjects aged between 25 and 69 years inclusive were considered eligible for inclusion in this study and among them 137 males and 206 females underwent the primary test. Before the test, subjects were asked about hearing difficulty, tinnitus, otological anamnesis and past experience of noise exposure at work and/or hobbies. The primary test was a pure tone audiometry using the ascending method of limits with 5 dB step at 7 test frequencies of 0.5 to 8 kHz. Forty individuals who were judged to have possible noise induced hearing loss were sent to Okinawa Chubu Hospital as subjects for the secondary test. The secondary test consisted of pure tone audiometry with 1 dB step at 9 test frequencies with the addition of 3 kHz and 6 kHz to the primary test frequencies, a Short Increment Sensitivity Index (SISI), test, tympanometry and audioscan audiometry. Based on test findings 12 subjects were considered to have noise induced hearing loss. The examiners interviewed the 12 subjects again to confirm that they had not experienced habitual or repeated intense noise exposure other than aircraft noise exposure around their homes. The geographical distribution of the subject's residences showed their proximity to the airfield, which strongly suggests that the cause of hearing loss may be exposure to aircraft noise from Kadena Air Base.