Uncharted territory — an audiometric surveillance program for seafarers

BACKGROUND: Occupational noise exposure causes noise-induced hearing loss (NIHL). The International Maritime Organization Code on Noise Levels on Board Ships includes audiometric surveillance as an optional measure for monitoring auditory thresholds over time. The Occupational Safety and Health Administration (OSHA) standard threshold shift (STS) criterion is widely used for surveillance. A standard threshold shift can occur due to aging, illness, cumulative exposure to noise and ototoxic agents, or test-retest variability. To the authors' knowledge, this is the first service implementation and evaluation study of an audiometric surveillance program among seafarers in marine transport. MATERIAL AND METHODS: In addition to pre-existing noise controls compliant with industry standards, an audiometric surveillance program was implemented across a fleet of hydrocarbon transport ships for a multinational population of 745 noise-exposed seafarers. Audiometry was conducted during seafarers' periodic fitness examinations, and the OSHA STS criterion was used to identify threshold shifts. RESULTS: After 1 year, 542 seafarers had baseline audiograms, and 85 had both a baseline audiogram and at least one subsequent audiogram. Nine cases of STS were detected (11%). CONCLUSIONS: Audiometric surveillance in international marine transport is feasible and can be used to verify the effectiveness of risk controls for NIHL among seafarers. The observed incidence of STS is unlikely to reflect true hearing loss over the short follow-up period, and is more likely caused by test-retest variability. It is at the upper end of the predicted variability from clinical and industrial audiometry studies, although higher test-retest variability and STS rates have been reported in naval operations. High test-retest variability in an itinerant workforce presents a challenge when verifying the effectiveness of noise controls. Although individual audiometric surveillance remains important, aggregate population-level surveillance data may provide a more robust indicator of risk control effectiveness across the workforce. Further research on the epidemiology of NIHL and the performance of audiometric testing among seafarers is needed.