Navy hearing Conservation Program: Threshold shifts in enlisted personnel, 1995-1999

Military Medicine, Jan 2002 by Bohnker, Bruce K

This study presents audiometric information from 54,057 Navy enlisted personnel in the Navy and Marine Corps Hearing Conservation Program database from 1995 to 1999. The purpose was to compare current threshold shift patterns for Navy enlisted population with historical literature and review programmatic effectiveness issues. The data suggest that 82% of the population did not display significant threshold shift (STS) on the "annual" and "termination" audiograms, which increased to 94% after the "follow-up 2" examination. Compared with historical data, STS rates were significantly lower for the most junior enlisted personnel (E 1-E3) (odds ratio = 0.34, p = 0.00, 95% confidence interval = 0.30-0.39) but not significantly different for more senior enlisted personnel (odds ratio = 0.96, p = 0.22, 95% confidence interval = 0.90-1.03). STS rates did not appear to correlate with expected "high" and "low" noise exposure Navy enlisted occupations. This suggests further investigation to readdress the possible risk factors other than noise intensity/duration.

Introduction

Occupation-related hearing loss has been a long-standing Navy concern, leading to Navy Medicine establishing a Hearing Conservation Program in 1955.' Subsequently, program oversight became a responsibility of the Chief of Naval Operations in 1979,23 although Navy Medicine continues to manage the program. Exposure to hazardous sound levels continues to be the Navy's most prevalent occupational health risk, with an estimated 350,000 military and civilian personnel enrolled in the Hearing Conservation Program.

Several authors have addressed Navy hearing conservation issues, although they have been hindered by small size and limited sampling from the entire Navy enlisted population. In 1978, the Naval Aerospace Medical Research Laboratory (NAMRL) in Pensacola, Florida, reviewed hearing status for about 4,000 Navy enlisted personnel by obtaining copies of audiograms.4 In 1985, Gwin and Lacroix presented information on hearing status for approximately 500 members of the submarine force in Groton, Connecticut.5 In 1990, the Navy Environmental Health Center replicated the NAMRL study on hearing loss for selected Navy enlisted classifications.' Although limited, the NAMRL and Navy Environmental Health Center studies established the length of service/hearing loss correlation and suggested that certain rates exhibited a greater prevalence of hearing loss. In 1995, Wolgemuth et al. reviewed the effectiveness of the Navy program using data from 1987 to 1990, based on about 12,000 records available from inspections of afloat units.' That analysis represents the best available historical information on hearing in the Navy population, although it was limited to East Coast afloat units. Recently, the Occupational and Environmental Medicine Directorate of the Navy Environmental Health Center created the Navy and Marine Corps Hearing Conservation Database, which allows more detailed analysis of hearing issues. Using that database, we have chosen to update those previous studies on Navy enlisted personnel both afloat and ashore and to make some assessments of program effectiveness and priorities.

The Navy uses the Department of Defense standard hearing conservation audiogram form (DD 2216), which has four test categories: (1) 90-day, (2) annual, (3) termination, and (4) other. In addition, the categories follow-up 1 and follow-up 2 are used for personnel who have demonstrated a significant threshold shift (STS) and are returned for further evaluation after a period of removal from noise. The Department of Defense has defined an STS as a change in hearing, in either ear, between the current hearing thresholds and baseline or revised reference thresholds of 15 dB at the frequencies of 1,000, 2,000, 3,000, and 4,000 Hz.8 Additionally, an average change of _ 10 dB or greater at the frequencies of 2,000, 3,000, and 4,000 Hz is considered an STS. Personnel displaying an STS are followed up by standardized protocol under the supervision of an operational/occupational audiologist or an occupational and environmental medicine physician.9 It should be noted that the Navy's definition of potentially harmful "noise" includes desirable sound level exposure greater than 84 dB and not just unwanted sound," which is the classic definition of noise.

Data Collection and Analysis

The Occupational and Environmental Medicine Directorate at the Navy Environmental Health Center (Norfolk, Virginia) has overall management responsibility for the Navy Hearing Conservation Program. Copies of monitoring audiograms were submitted by Navy medical field activities throughout the 1990s as part of programmatic oversight. To assess program effectiveness, a Navy and Marine Corps Hearing Conservation Program Database was created in 1999. Because of funding limitations, a sampling plan was used with an initial 20% sampling rate that was increased to 25% after about 15,000 records were keyed to ensure an adequate sample size. A total of 152,590 records from 1995 to 1999 were keyed into the database. These records included Navy and Marine Corps enlisted, officer, and civilian employees. This report will present the results from 54,057 Navy enlisted personnel, consisting of 92% men and 8% women.