DOUGLAS BADZIK
Hearing loss in US Army aviators, comparing 2005 to 2001
Occupational and Environmental Medicine, MPH
Preceptor: William Daniell, MD, MPH
Introduction: Noise induced hearing loss is the most common occupational disease in the United States. Army pilots, greater than 95% of whom fly helicopters, are at particular risk due to the open environment of the aircraft, with unprotected cockpit noise levels reaching 105 dB. Previous studies evaluating hearing loss in aviators demonstrated an association between exposure to aircraft noise and hearing loss; however, few studies have looked specifically at helicopters and none have evaluated what additional risks are associated with a war time environment of on-going combat operations. These risks may include increased training time at home garrison, physical stressors associated with deployment to a combat zone, exposure to high impulse noise from ordinance explosions and weapons fire, exposure to ototoxic agent, and altered use of hearing protection.
Objective: To determine the risk of U.S. Army aviators acquiring hearing loss if exposed to an environment of on-going combat operation (2002-2005) compared to aviators without this exposure (1998-2001).
Methods: A retrospective cohort study was conducted with 3,802 U.S. Army aviators on active flight status. The exposure cohort (2005) was 2,050 aviators who were on flight status 2001-2005 with a flight physical in 2005 which included a pure tone audiogram. The non-exposure cohort (2001) was 1,752 aviators who were on flight status 1998-2001 with a flight physical in 2001. Standard and significant threshold shifts were determined by calculating the difference in hearing thresholds in the respective 2005 and 2001 audiograms from baseline audiograms that were obtained 3-6 years earlier. Both OSHA and U.S. Army (USA) criteria were used to determine if a standard or significant threshold shift (STS) had occurred.
Results: The prevalence of STS in the 2001 cohort by OSHA and USA criteria was 6.1% and 13.7% respectively compared to 11.6% and 23.8% for the 2005 cohort. Using logistic regression, it was determined that the 2005 cohort was approximately 2.5 times more likely to have a STS compared to the 2001 cohort.
Conclusion: U.S. Army aviators exposed to an environment of on-going combat operation were 2.5 times more likely to experience hearing loss compared to aviators who were not. Focused research needs to be conducted to determine what factors contributed to this increased risk so systems can be implemented to further protect the hearing of these aviators.
The views and opinions expressed are those of the authors and should not be construed as representing the official position of the Department of the Army, Department of Defense, or the US government.
