Retrospective cohort study of pure tone audiometry hearing changes from ototoxic metals and solvents, continuous noise, and impulse noise exposures at Hill Air Force Base from 2005 to 2019

This retrospective cohort epidemiological study investigated the relative risks of hearing loss associated with ototoxicants in combination with noise exposure. Utilizing United States Department of Defense (DoD) industrial hygiene and hearing conservation data, this research expanded on a 2020 study conducted on Tinker Air Force Base (AFB), Oklahoma, applying a similar methodology to Hill AFB, Utah, adding 893 evaluated individuals. Grouped into twelve exposure combinations with a minimum of 3 years of exposure duration, the study assessed various hearing loss indicators, including DoD Significant Threshold Shift (STS) and National Institute for Occupational Safety and Health (NIOSH) STS. Ototoxic substances consistently elevated relative risk (RR) compared to noise-only exposure groups, but none reached significance at the 95% confidence level. Incorporating Hill AFB to findings from Tinker AFB (n = 2,372) revealed exposure groups with a RR greater than one for developing a NIOSH STS were significant at the 95% confidence level, with the greatest RR coming from the metal, solvent, continuous noise exposure group in the left ear at 2,000 Hz (RR = 2.25; 1.96-2.57). Logistic regression modeling identified age and audiogram duration between first and last audiogram (as a surrogate for duration of exposure) as significant independent variables for hearing loss indicator development prediction.