Recovery patterns and influencing factors of temporary threshold shifts in occupational noise-exposed workers

Abstract

Noise-induced hearing loss represents a significant global occupational health issue. Understanding the recovery patterns of temporary threshold shift (TTS) is crucial for early intervention. This longitudinal study enrolled 140 occupational noise-exposed workers and conducted serial audiological assessments over one week to characterize multi-frequency TTS recovery trajectories and explore influencing factors. The results showed that the highest prevalence of TTS occurred at 6 kHz (81.4%), followed by 4 kHz (72.1%). Recovery was frequency-dependent: low-frequency hearing thresholds (0.5-1 kHz) returned to baseline within 72.2 h in more than 85% of participants, while recovery at high frequencies (4-6 kHz) was comparatively slower. Longer occupational noise exposure (>10 years), male, and higher noise level (≥85 dB(A)) were each associated with delayed recovery. Notably, although more than 80% of participants showed substantial hearing recovery within 72.2 h, complete recovery across all frequencies required up to one week, this suggests that the current mandated 48-h pre-audiometry rest period may be insufficient to assess full auditory recovery. We recommend extending this rest period to 72 h, with a follow-up confirmatory test one week after exposure, to provide a more evidence-based approach for occupational hearing protection protocols.