Interventions to prevent occupational noise induced hearing loss.

BACKGROUND Millions of workers worldwide are exposed to noise levels that increase their risk of hearing impairment. Little is known about the effectiveness of hearing loss prevention interventions. OBJECTIVES To assess the effectiveness of non-pharmaceutical interventions for preventing occupational noise exposure or occupational hearing loss compared to no intervention or alternative interventions. SEARCH STRATEGY We searched the Cochrane Ear, Nose and Throat Disorders Group Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library issue 4, 2008); PubMed; EMBASE; CINAHL; Web of Science; BIOSIS Previews; Cambridge Scientific Abstracts; NIOSHTIC, CISDOC and mRCT to 15 December 2008. SELECTION CRITERIA Randomised controlled trials, controlled before-after studies and interrupted time series (ITS) of non-clinical hearing loss prevention interventions under field conditions among workers exposed to noise. DATA COLLECTION AND ANALYSIS Two authors (EK, JV) independently assessed study eligibility and trial quality and extracted data. MAIN RESULTS Twenty-one studies were included. One study evaluated a strategy to reduce noise exposure. Fourteen studies with 75,672 participants evaluated hearing loss prevention programmes (HLPPs), and six studies with 169 participants evaluated hearing protection. The overall quality of studies was low.One ITS study evaluated the effect of new legislation in reducing noise exposure. It found that the median noise level decreased by 27.7 dB(A) (95% confidence interval (CI) -36.1 to -19.3 dB) with a change in trend in time of -2.1 dB per year (95% CI -4.9 to 0.7).A hearing protection study in army recruits compared those exposed to impulse noise with non-exposed recruits. The odds ratio (OR) for hearing loss was 3.0 (95% CI 1.1 to 8.0) despite hearing protection. In four studies, workers in a HLPP had a 0.5 dB HL greater hearing loss at 4 kHz than non-noise exposed workers (95% CI -0.5 to 1.7). In one study, the hazard ratio of hearing loss was 3.8 (95% CI 2.7 to 5.3) for workers exposed to noise compared to non-exposed workers.In three studies, a high quality HLPP had a lower risk of hearing loss than lower quality programmes.Noise attenuation ratings of hearing protection under field conditions were consistently lower than the ratings provided by the manufacturers. AUTHORS' CONCLUSIONS There is low quality evidence that legislation can reduce noise levels in workplaces.The effectiveness of hearing protection devices depends on their proper use. There is contradictory evidence that HLPPs are effective in the long-term. Even though case studies show that substantial reductions can be achieved, there is no evidence that this is realised in practice. Better implementation and reinforcement is needed.Better evaluations of technical interventions and long-term effects are needed. Audiometric and noise measurement data are potentially valuable for such studies.