Interventions to prevent occupational noise induced hearing loss - hearing loss prevention programmes

There is contradictory evidence that hearing loss prevention programmes in work places prevent noise-induced hearing loss.

A Cochrane review included 29 studies. Eleven studies (n=3725) evaluated effects of personal hearing protection devices and 17 studies (n=84 028) effects of hearing loss prevention programmes (HLPPs). Four studies used a randomised design, one study used a quasi-randomised design with alternation, two studies used an interrupted time-series (ITS) design and all remaining studies used a form of controlled before-after (CBA) design. In most studies only men were included or there were mostly male workers at the workplaces that were studied.

Effects on noise exposure

• Engineering interventions following legislation: One interrupted time-series (ITS) study found that new legislation in the mining industry reduced the median personal noise exposure dose in underground coal mining by 27.7 percentage points (95% CI -36.1 to -19.3 percentage points) immediately after the implementation of stricter legislation. This roughly translates to a 4.5 dB(A) decrease in noise level. The intervention was associated with a favourable but statistically non-significant downward trend in time of the noise dose of -2.1 percentage points per year (95% CI -4.9 to 0.7, 4 year follow-up).
• Engineering intervention case studies: Twelve studies, describing 107 uncontrolled case studies of immediate reductions in noise levels of machinery ranging from 11.1 to 19.7 dB(A) as a result of purchasing new equipment, segregating noise sources or installing panels or curtains around sources. However, the studies lacked long-term follow-up and dose measurements of workers, and we did not use these studies for our conclusions.
• Hearing protection devices: In general hearing protection devices reduced noise exposure on average by about 20 dB(A) in one RCT and 3 controlled before-after studies (CBA) (n=57). Two RCTs showed that, with instructions for insertion, the attenuation of noise by earplugs was 8.59 dB better (95% CI 6.92 dB to 10.25 dB) compared to no instruction (2 RCTs, n=140 participants).
• Administrative controls: information and noise exposure feedback: On-site training sessions did not have an effect on personal noise-exposure levels compared to information only in one cluster-RCT after 4 months' follow-up (MD 0.14 dB; 95% CI -2.66 to 2.38). Another arm of the same study found that personal noise exposure information had no effect on noise levels (MD 0.30 dB(A), 95% CI -2.31 to 2.91) compared to no such information (n=176 participants).

Effects on hearing loss

• Hearing protection devices: Two studies compared the effect of different devices on temporary threshold shifts at short-term follow-up but data were insufficient for analysis. In 2 CBA studies there was no difference in hearing loss from noise exposure above 89 dB(A) between muffs and earplugs at long-term follow-up (OR 0.8, 95% CI 0.63 to 1.03). In another CBA study wearing hearing protection more often resulted in less hearing loss at very long-term follow-up.
• Combination of interventions: hearing loss prevention programmes: One cluster-RCT found no difference in hearing loss at 3- or 16-year follow-up between an intensive HLPP for agricultural students and audiometry only. One CBA study found no reduction of the rate of hearing loss (MD -0.82 dB per year, 95% CI -1.86 to 0.22) for a HLPP that provided regular personal noise exposure information compared to a programme without this information. In 4 very long-term studies that better use of hearing protection devices as part of a HLPP decreased the risk of hearing loss compared to less well used hearing protection in HLPPs (OR 0.40, 95% CI 0.23 to 0.69). Other aspects of the HLPP such as training and education of workers or engineering controls did not show a similar effect. In 3 long-term CBA studies, workers in a HLPP had a statistically non-significant 1.8 dB (95% CI -0.6 to 4.2) greater hearing loss at 4 kHz than non-exposed workers and the confidence interval includes the 4.2 dB which is the level of hearing loss resulting from 5 years of exposure to 85 dB(A). In addition, of 3 other CBA studies that could not be included in the meta-analysis, 2 showed an increased risk of hearing loss in spite of the protection of a HLPP compared to non-exposed workers and one CBA did not.

Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment, high drop-out rate, lack of information on the implementation level of the prevention measures), inconsistency (heterogeneity in study designs) and indirectness (most studies were retrospective, mostly men were included).

Ədəbiyyat

1. Tikka C, Verbeek JH, Kateman E et al. Interventions to prevent occupational noise-induced hearing loss. Cochrane Database Syst Rev 2017;7():CD006396.