"Retrospective Cohort Study of Pure Tone Audiometry Hearing Changes fro" by Zachary I. Johnson

Date of Award

3-2024

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Systems Engineering and Management

First Advisor

Jeremy M. Slagley, PhD

Abstract

This retrospective cohort epidemiological study investigated the relative risks of hearing loss associated with ototoxicants in combination with noise exposure. Utilizing Department of Defense (DoD) industrial hygiene and hearing conservation data, this research expanded on a 2020 thesis conducted on Tinker Air Force Base (AFB), applying a similar methodology to Hill AFB, adding 893 evaluated individuals. Grouped into twelve exposure combinations with a minimum of three years of exposure duration, the study assessed various hearing loss indicators, including DoD Standard Threshold Shift (STS) and 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 as significant independent variables for hearing loss indicator development prediction. Results further suggest potential limitations in the DoD Hearing Conservation Program's ability to capture hearing risk from ototoxic substance exposure.

AFIT Designator

AFIT-ENV-MS-24-M-137

Comments

A 12-month embargo was observed for posting this work on AFIT Scholar.

Distribution Statement A, Approved for Public Release. PA case number on file.

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