Longitudinal changes in hearing threshold levels for noise-exposed military personnel

Military personnel are exposed to variable and sometimes very high noise in their professional environment. The aim of this study is to evaluate through a longitudinal study if our hearing conservation program has to be adapted to consider specific interventions for subgroups of our military population still subject to a higher risk of hearing loss.

We conducted a retrospective longitudinal study in 2015-2016 to describe the evolution of hearing threshold levels of military personnel as measured during periodic audiometric screening over a period of 6 years (2009-2014) after the implementation of our hearing conservation program. A linear mixed model explored the relationship of pure-tone average (PTA) on 3, 4 and 6 KHz with probability of noise exposure, gender, age at baseline, time since baseline, hearing loss at baseline and ear.

For 18,672 military individuals, our results show a small but statistically significant increase of 0.08 dB per year in PTA on 3, 4 and 6 KHz over the 6-year period that is consistently decelerating as a function of time. An additional annual increase of hearing thresholds due to higher age and moderate and high probability of exposure to noise was also found.

No major adaptation of our hearing conservation program is required but efforts should be strengthened to better evaluate and counsel older individuals and subjects exposed to noise regarding avoidance of noise and correct use of personal hearing protection.