Cochrane method for systematic review and meta-analysis of interventions to prevent occupational noise-induced hearing loss – abridged

Revisão sistemática e metanálise Cochrane de intervenções para prevenção de perda auditiva ocupacional induzida por ruído – abreviada

Christina Tikka Jos Verbeek Erik Kateman Thais Catalani Morata Wouter Dreschler Silvia Ferrite About the authors

ABSTRACT

Purpose

Assess the effect of non-pharmaceutical interventions at work on noise exposure or occupational hearing loss compared to no or alternative interventions.

Research strategies

Pubmed, Embase, Web of Science, OSHupdate, Cochrane Central and Cumulative Index to Nursing and Allied Health Literature (CINAHL) were searched.

Selection criteria

Randomized Controlled Trials (RCT), Controlled Before-After studies (CBA) and Interrupted Time-Series studies (ITS) evaluating engineering controls, administrative controls, personal hearing protection devices, and hearing surveillance were included. Case studies of engineering controls were collected.

Data analysis

Cochrane methods for systematic reviews, including meta-analysis, were followed.

Results

29 studies were included. Stricter legislation can reduce noise levels by 4.5 dB(A) (very low-quality evidence). Engineering controls can immediately reduce noise (107 cases). Eleven RCTs and CBA studies (3725 participants) were evaluated through Hearing Protection Devices (HPDs). Training of earplug insertion reduces noise exposure at short term follow-up (moderate quality evidence). Earmuffs might perform better than earplugs in high noise levels but worse in low noise levels (very low-quality evidence). HPDs might reduce hearing loss at very long-term follow-up (very low-quality evidence). Seventeen studies (84028 participants) evaluated hearing loss prevention programs. Better use of HPDs might reduce hearing loss but other components not (very low-quality evidence).

Conclusion

Hearing loss prevention and interventions modestly reduce noise exposure and hearing loss. Better quality studies and better implementation of noise control measures and HPDs is needed.

Keywords:
Noise-Induced Hearing Loss; Occupational Noise; Hearing Protective Devices; Systematic Review; Meta-Analysis

RESUMO

Objetivo

Avaliar o efeito de intervenções no trabalho sobre a exposição ao ruído ou a perda auditiva em comparação com ausência ou intervenções alternativas.

Estratégia de pesquisa

Buscas em Pubmed, Embase, Web of Science, OSHupdate, Cochrane Central e CINAHL.

Critérios de seleção

Incluídos ensaios clínicos randomizados (ECR), estudos controlados pré/pós-intervenção (ECPPI) e estudos de séries temporais interrompidas (SIT) avaliando controles de engenharia, administrativos, equipamentos de proteção auditiva (EPAs) e vigilância auditiva. Coletados estudos de caso de engenharia.

Análise dos dados

Cochrane para revisões sistemáticas, incluindo metanálise.

Resultados

Foram incluídos 29 estudos. Legislação mais rigorosa pode reduzir níveis de ruído em 4,5 dB(A) (evidência de qualidade muito baixa). Controles de engenharia podem reduzir imediatamente o ruído (107 casos). Onze ECR e ECPPI (3.725 participantes) avaliaram EPAs. Treinamento para inserção do EPA reduz a exposição ao ruído no acompanhamento de curto prazo (evidência de qualidade moderada). Protetores tipo concha podem ter desempenho melhor do que protetores de inserção em níveis altos de ruído, mas piores em níveis mais baixos (evidência de qualidade muito baixa). EPAs podem reduzir a perda auditiva no acompanhamento de muito longo prazo (evidência de qualidade muito baixa). Dezessete estudos (84.028 participantes) avaliaram programas de prevenção de perdas auditivas. Um melhor uso do EPA pode reduzir a perda auditiva, mas outros componentes não (evidência de qualidade muito baixa).

Conclusão

As intervenções para prevenção da perda auditiva reduzem modestamente a exposição ao ruído e a perda auditiva. Estudos de melhor qualidade e melhor implementação de medidas de controle de ruído e EPA são necessários.

Descritores:
Perda Auditiva Provocada por Ruído; Ruído Ocupacional; Dispositivos de Proteção Auditiva; Revisão Sistemática; Metanálise

INTRODUCTION

Worldwide millions of workers are exposed to noise levels that increase their risk of hearing disorders(11 Forouzanfar MH, Afshin A, Alexander LT, Anderson HR, Bhutta ZA, Biryukov S, et al. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015. Lancet. 2016;388(10053):1659-724. http://dx.doi.org/10.1016/S0140-6736(16)31679-8. PMid:27733284.
http://dx.doi.org/10.1016/S0140-6736(16)...
). While hearing loss prevention programs (HLPPs) are mandatory in many countries, the reportedly continuing high rate of occupational noise-induced hearing loss (NIHL) casts doubt upon their effectiveness(22 Nelson DI, Nelson RY, Concha-Barrientos M, Fingerhut M. The global burden of occupational noise-induced hearing loss. Am J Ind Med. 2005;48(6):446-58. http://dx.doi.org/10.1002/ajim.20223. PMid:16299704.
http://dx.doi.org/10.1002/ajim.20223...
). Moreover, the broad range of interventions included in HLPPs makes it difficult to appraise the most effective strategy. A systematic review of studies that evaluated interventions to reduce occupational exposure to noise or to decrease occupationally induced hearing loss is therefore warranted. This paper summarizes the main results of the second update of the Cochrane review originally published in 2009.

Purpose

To assess the effectiveness of non-pharmaceutical interventions for preventing occupational noise exposure or occupational hearing loss compared to no or alternative interventions.

Research strategy

This is an abridged version of the second update of a Cochrane Review originally published in 2009 based on the methods originally described in the review protocol(33 Kateman E, Verbeek JH, Morata T, Coolsma B, Dreschler W, Sorgdrager B. Interventions to prevent occupational noise-induced hearing loss. Cochrane Database Syst Rev. 2017;7:CD006396. http://dx.doi.org/10.1002/14651858.CD006396.pub4.
http://dx.doi.org/10.1002/14651858.CD006...
). Systematic searches were conducted combining search words for the occupational setting, exposure, interventions, and effects on noise or hearing loss. No restrictions on language were used, publication year or publication status and were searched Pubmed, Embase, Web of Science, OSHupdate, Cochrane Central and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases up until September 2016 (search history in Appendix 1 and Appendix 2). To determine which studies fulfilled the inclusion criteria, pairs of the review authors independently scanned the titles and abstracts of every record retrieved from the databases. Full articles were retrieved for further eligibility assessment.

Data were independently extracted for each included study and resolved discrepancies by discussion. A standard form to extract information about was used: study design, randomisation methods, setting, participants, interventions, outcome measures, follow-up, and adverse events. To assess whether HLPPs are as good as not being exposed, it had to be made an assumption about the minimal clinically relevant hearing loss. Hearing loss was associated with exposure to 85 dB(A) as the minimum amount of damage that should be avoided by the interventions. Based on International Organization for Standardization (ISO) 1990(44 ISO: International Organization for Standardization. ISO 4869-1: Acoustics - Hearing Protectors - Part 1: Subjective method for the measurement of sound attenuation. Geneva: ISO; 1990.), the amount of hearing loss after five years of exposure to 85 dB(A) was calculated for the median, 10th and 90th percentile would be 4.2 dB, 2.1 dB and 6.1 dB, respectively. This is equivalent to a mean of 4.2 dB hearing loss and represents clinically relevant hearing loss(55 Hozo SP, Djulbegovic B, Hozo I. Estimating the mean and variance from the median, range and the size of a sample. BMC Medical Research Methodology. 2005;5:1-13. http://dx.doi.org/10.1186/1471-2288-5-13.
http://dx.doi.org/10.1186/1471-2288-5-13...
). This means, the 95% CI from meta-analysis results on hearing loss can include zero, but not 4.2 to assure

that the protected and non-exposed groups are equivalent(66 Piaggio G, Elbourne DR, Altman DG, Pocock SJ, Evans SJ, CONSORT Group. Reporting of non-inferiority and equivalence randomised trials. JAMA. 2006;295(10):1152-60. http://dx.doi.org/10.1001/jama.295.10.1152. PMid:16522836.
http://dx.doi.org/10.1001/jama.295.10.11...
).

Selection criteria

We included studies that 1) used a randomised controlled, controlled before-after, or interrupted time-series study design, 2) included workers exposed to noise levels greater than 80 dB(A), 3) concerned interventions aimed at reduction of noise exposure to prevent NIHL, and 4) used noise exposure or NIHL as an outcome. Case studies on the effects of engineering control interventions without a control group could be included. The results of case studies for the conclusions of the review, as the study design did not fulfil our inclusion criteria, were not used.

Data analysis

Eight authors of recent studies were contacted regarding missing or unclear information and were obtained additional data from three(77 Davies H, Marion S, Teschke K. The impact of hearing conservation programs on incidence of noise-induced hearing loss in Canadian workers. Am J Ind Med. 2008;51(12):923-31. http://dx.doi.org/10.1002/ajim.20634. PMid:18726988.
http://dx.doi.org/10.1002/ajim.20634...

8 Joy G, Middendorf PJ. Noise exposure and hearing conservation in US coal mines, a surveillance report. J Occup Environ Hyg. 2007;4(1):26-35. http://dx.doi.org/10.1080/15459620601067209. PMid:17162478.
http://dx.doi.org/10.1080/15459620601067...
-99 Rabinowitz PM, Galusha D, Kirsche SR, Cullen MR, Slade MD, Dixon-Ernst C. Effect of daily noise exposure monitoring on annual rates of hearing loss in industrial workers. Occup Environ Med. 2011;68(6):414-8. http://dx.doi.org/10.1136/oem.2010.055905. PMid:21193566.
http://dx.doi.org/10.1136/oem.2010.05590...
).

When authors reported results separately for participant groups(1010 Pell S. An evaluation of hearing conservation program - a five-year longitudinal study. Am Ind Hyg Assoc J. 1973;34(2):82-91. http://dx.doi.org/10.1080/0002889738506811. PMid:4715098.
http://dx.doi.org/10.1080/00028897385068...
,1111 Adera T, Amir C, Anderson L. Use of comparison populations for evaluating the effectiveness of hearing loss prevention programs. Am Ind Hyg Assoc J. 2000;61(1):11-5. http://dx.doi.org/10.1202/0002-8894(2000)061<0011:UOCPFE>2.0.CO;2. PMid:10772609.
http://dx.doi.org/10.1202/0002-8894(2000...
) we combined these following the Cochrane Handbook for Systematic Reviews of Interventions guidance(1212 Deeks JJ, Higgins JPT, Altman DG. Analysing data and undertaking meta-analyses. In: Higgins JPT, Green S, editors. Cochrane handbook for systematic reviews of interventions version 5.1.0 [Internet]. United Kingdom: The Cochrane Collaboration; 2011. Chapter 9 [cited 2019 May 26]. Available from: handbookcochraneorg). In two studies, multiple interventions were compared with one control group. To avoid using the same control group data more than once, the control group was split into three(1313 Muhr P, Månsson B, Hellström PA. A study of hearing changes among military conscripts in the Swedish army. Int J Audiol. 2006;45(4):247-51. http://dx.doi.org/10.1080/14992020500190052. PMid:16684706.
http://dx.doi.org/10.1080/14992020500190...
) or two(1414 Seixas NS, Neitzel R, Stover B, Sheppard L, Daniell B, Edelson J, et al. A multi-component intervention to promote hearing protector use among construction workers. Int J Audiol. 2011;50(Suppl 1):s46-56. http://dx.doi.org/10.3109/14992027.2010.525754. PMid:21091403.
http://dx.doi.org/10.3109/14992027.2010....
) equal subgroups that were subsequently combined in the meta-analysis.

To evaluate the risk of bias, the quality criteria presented by Ramsay et al.(1515 Ramsay CR, Matowe L, Grilli R, Grimshaw JM, Thomas RE. Interrupted time series designs in health technology assessment: lessons from two systematic reviews of behavior change strategies. Int J Technol Assess Health Care. 2003;19(4):613-23. http://dx.doi.org/10.1017/S0266462303000576. PMid:15095767.
http://dx.doi.org/10.1017/S0266462303000...
) for ITS studies was used. For RCTs and cohort studies, the internal validity items by Downs and Black(1616 Downs SH, Black N. The feasibility of creating a checklist for the assessment of the methodological quality both of randomised and non-randomised studies of health care interventions. J Epidemiol Community Health. 1998;52(6):377-84. http://dx.doi.org/10.1136/jech.52.6.377. PMid:9764259.
http://dx.doi.org/10.1136/jech.52.6.377...
) were used that are mostly congruent with the Cochrane 'Risk of bias' tool(1717 Higgins JPT, Altman DG, Sterne JAC. Assessing risk of bias in included studies. In: Higgins JPT, Green S, editors. Cochrane handbook for systematic reviews of interventions version 5.1.0 [Internet]. United Kingdom: The Cochrane Collaboration; 2011. Chapter 8 [cited 2019 May 26]. Available from: handbookcochraneorg). We defined studies’ overall risk of bias as low if they scored more than 50% of the maximum score.

Sufficiently homogeneous studies, regarding interventions, participants, settings and outcomes in a meta-analysis, were combined. When results were statistically heterogeneous according to the I2 statistic, a random-effects model for the meta-analysis was used. A sensitivity analysis to assess the influence of risk of bias on the pooled effect sizes was conducted.

We deemed change in hearing level at 4 kHz and Standard Threshold Shifts (STS) as similar outcome measures for hearing effects and calculated Standardized Mean Differences (SMD) to enable combination of both measures in the meta-analysis(1818 Chinn S. A simple method for converting an odds ratio to effect size for use in meta-analysis. Stat Med. 2000;19(22):3127-31. http://dx.doi.org/10.1002/1097-0258(20001130)19:22<3127::AID-SIM784>3.0.CO;2-M. PMid:11113947.
http://dx.doi.org/10.1002/1097-0258(2000...
). For easing interpretation, we transformed the pooled SMDs back to a mean change in hearing level in dB using the median standard deviation of the included studies.

The Grading of Recommendation, Assessment, Development and Evaluation (GRADE) approach to rate the quality of the evidence for each outcome was followed. The grading is based on study design, risk of bias, consistency, directness (generalisability), precision and publication bias across all studies(1919 Balshem H, Helfand M, Schünemann HJ, Oxman AD, Kunz R, Brozek J, et al. GRADE guidelines: 3. Rating the quality of evidence. J Clin Epidemiol. 2011;64(4):401-6. http://dx.doi.org/10.1016/j.jclinepi.2010.07.015. PMid:21208779.
http://dx.doi.org/10.1016/j.jclinepi.201...
). Overall quality is considered high for RCTs and low for observational studies and can be further reduced or upgraded(2020 Cuello-Garcia CA, Morgan RL, Brozek J, Santesso N, Verbeek J, Thayer K, et al. A scoping review and survey provides the rationale, perceptions, and preferences for the integration of randomized and nonrandomized studies in evidence syntheses and GRADE assessments. J Clin Epidemiol. 2018;98:33-40. http://dx.doi.org/10.1016/j.jclinepi.2018.01.010. PMid:29452221.
http://dx.doi.org/10.1016/j.jclinepi.201...
) (Table 1).

Table 1
Assessment of quality of evidence (GRADE)

Ratings are interpreted as: 1) high-quality evidence is unlikely to change, moderate-quality evidence; 2) further research is likely to have an impact and may change estimates, low-quality evidence; 3) further research is very likely to have an important impact, and very low-quality evidence provides very uncertain effects estimates.

The results for the most important comparisons in 'Summary of Findings' (SoF) were presented tables.

RESULTS

29 studies (Figure 1, Table 2, Appendix 1, Appendix 2)(77 Davies H, Marion S, Teschke K. The impact of hearing conservation programs on incidence of noise-induced hearing loss in Canadian workers. Am J Ind Med. 2008;51(12):923-31. http://dx.doi.org/10.1002/ajim.20634. PMid:18726988.
http://dx.doi.org/10.1002/ajim.20634...

8 Joy G, Middendorf PJ. Noise exposure and hearing conservation in US coal mines, a surveillance report. J Occup Environ Hyg. 2007;4(1):26-35. http://dx.doi.org/10.1080/15459620601067209. PMid:17162478.
http://dx.doi.org/10.1080/15459620601067...

9 Rabinowitz PM, Galusha D, Kirsche SR, Cullen MR, Slade MD, Dixon-Ernst C. Effect of daily noise exposure monitoring on annual rates of hearing loss in industrial workers. Occup Environ Med. 2011;68(6):414-8. http://dx.doi.org/10.1136/oem.2010.055905. PMid:21193566.
http://dx.doi.org/10.1136/oem.2010.05590...

10 Pell S. An evaluation of hearing conservation program - a five-year longitudinal study. Am Ind Hyg Assoc J. 1973;34(2):82-91. http://dx.doi.org/10.1080/0002889738506811. PMid:4715098.
http://dx.doi.org/10.1080/00028897385068...
-1111 Adera T, Amir C, Anderson L. Use of comparison populations for evaluating the effectiveness of hearing loss prevention programs. Am Ind Hyg Assoc J. 2000;61(1):11-5. http://dx.doi.org/10.1202/0002-8894(2000)061<0011:UOCPFE>2.0.CO;2. PMid:10772609.
http://dx.doi.org/10.1202/0002-8894(2000...
,1313 Muhr P, Månsson B, Hellström PA. A study of hearing changes among military conscripts in the Swedish army. Int J Audiol. 2006;45(4):247-51. http://dx.doi.org/10.1080/14992020500190052. PMid:16684706.
http://dx.doi.org/10.1080/14992020500190...
,1414 Seixas NS, Neitzel R, Stover B, Sheppard L, Daniell B, Edelson J, et al. A multi-component intervention to promote hearing protector use among construction workers. Int J Audiol. 2011;50(Suppl 1):s46-56. http://dx.doi.org/10.3109/14992027.2010.525754. PMid:21091403.
http://dx.doi.org/10.3109/14992027.2010....
,2121 Adera T, Donahue AM, Malit BD, Gaydos JC. An epidemiologic method for assessing the effectiveness of hearing conservation programs using audiometric data. Mil Med. 1993;158(11):698-701. http://dx.doi.org/10.1093/milmed/158.11.698. PMid:8284053.
http://dx.doi.org/10.1093/milmed/158.11....

22 Berg RL, Pickett W, Fitz-Randolph M, Broste SK, Knobloch MJ, Wood DJ, et al. Hearing conservation program for agricultural students: short-term outcomes from a cluster-randomised trial with planned long-term follow-up. Prev Med. 2009;49(6):546-52. http://dx.doi.org/10.1016/j.ypmed.2009.09.020. PMid:19800914.
http://dx.doi.org/10.1016/j.ypmed.2009.0...

23 Brink LL, Talbott EO, Burks JA, Palmer CV. Changes over time in audiometric thresholds in a group of automobile stamping and assembly workers with a hearing conservation program. Am Ind Hyg Assoc J. 2002;63(4):482-7. http://dx.doi.org/10.1080/15428110208984737. PMid:12486782.
http://dx.doi.org/10.1080/15428110208984...

24 Erlandsson B, Hakanson H, Ivarsson A, Nilsson P. The difference in protection efficiency between earplugs and earmuffs. An investigation performed at a workplace. Scand Audiol. 1980;9(4):215-21. http://dx.doi.org/10.3109/01050398009076356. PMid:7466283.
http://dx.doi.org/10.3109/01050398009076...

25 Gosztonyi RE Jr. The effectiveness of hearing protective devices. J Occup Med. 1975;17(9):569-80. PMid:1165499.

26 Hager WL, Hoyle ER, Hermann0 ER. Efficacy of enforcement in an industrial hearing conservation program. Am Ind Hyg Assoc J. 1982;43(6):455-65. http://dx.doi.org/10.1080/15298668291410035. PMid:7113926.
http://dx.doi.org/10.1080/15298668291410...

27 Heyer N, Morata TC, Pinkerton LE, Brueck SE, Stancescu D, Panaccio MP, et al. Use of historical data and a novel metric in the evaluation of the effectiveness of hearing conservation program components. Occup Environ Med. 2011;68(7):510-7. http://dx.doi.org/10.1136/oem.2009.053801. PMid:21059594.
http://dx.doi.org/10.1136/oem.2009.05380...

28 Horie S. Improvement of occupational noise-induced temporary threshold shift by active noise control earmuff and bone conduction microphone. J Occup Health. 2002;44(6):414-20. http://dx.doi.org/10.1539/joh.44.414.
http://dx.doi.org/10.1539/joh.44.414...

29 Huttunen KH, Sivonen VP, Poykko VT. Symphony orchestra musicians’ use of hearing protection and attenuation of custom-made hearing protectors as measured with two different real-ear attenuation at threshold methods. Noise Health. 2011;13(51):176-88. http://dx.doi.org/10.4103/1463-1741.77210. PMid:21368443.
http://dx.doi.org/10.4103/1463-1741.7721...

30 Lee-Feldstein A. Five-year follow-up study of hearing loss at several locations within a large automobile company. Am J Ind Med. 1993;24(1):41-54. http://dx.doi.org/10.1002/ajim.4700240105. PMid:8352292.
http://dx.doi.org/10.1002/ajim.470024010...

31 Meyer GD, Wirth DB. An evaluation of the U.S. Air Force’s detailed follow-up audiometric examination program. Mil Med. 1993;158(9):603-5. http://dx.doi.org/10.1093/milmed/158.9.603. PMid:8232998.
http://dx.doi.org/10.1093/milmed/158.9.6...

32 Moshammer H, Kundi M, Wallner P, Herbst A, Feuerstein A, Hutter HP. Early prognosis of noise-induced hearing loss. Occup Environ Med. 2015;72(2):85-9. http://dx.doi.org/10.1136/oemed-2014-102200. PMid:25063775.
http://dx.doi.org/10.1136/oemed-2014-102...

33 Muhr P, Johnson AC, Skoog B, Rosenhall U. A demonstrated positive effect of a hearing conservation program in the Swedish armed forces. Int J Audiol. 2016;55(3):168-72. http://dx.doi.org/10.3109/14992027.2015.1117662. PMid:26754548.
http://dx.doi.org/10.3109/14992027.2015....

34 Nilsson R, Lindgren F. The effect of long term use of hearing protectors in industrial noise. Scand Audiol Suppl. 1980;(Suppl 12):204-11. PMid:6939090.

35 Pääkkönen R, Lehtomaki K, Savolainen S. Noise attenuation of communication hearing protectors against impulses from assault rifle. Mil Med. 1998;163(1):40-3. http://dx.doi.org/10.1093/milmed/163.1.40. PMid:9465571.
http://dx.doi.org/10.1093/milmed/163.1.4...

36 Pääkkönen R, Kuronen P, Korteoja M. Active noise reduction in aviation helmets during a military jet trainer test flight. Scand Audiol Suppl. 2001;52(52):177-9. http://dx.doi.org/10.1080/010503901300007452. PMid:11318460.
http://dx.doi.org/10.1080/01050390130000...

37 Park MY, Casali JG. A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors. Hum Factors. 1991;33(6):693-714. http://dx.doi.org/10.1177/001872089103300606. PMid:1800294.
http://dx.doi.org/10.1177/00187208910330...

38 Reynolds JL, Royster LH, Pearson RG. Hearing conservation programs (HCPs): the effectiveness of one company’s HCP in a 12-hr work shift environment. Am Ind Hyg Assoc J. 1990;51(8):437-46. http://dx.doi.org/10.1080/15298669091369907. PMid:2392973.
http://dx.doi.org/10.1080/15298669091369...

39 Royster LH. An evaluation of the effectiveness of two different insert types of ear protection in preventing TTS in an industrial environment. Am Ind Hyg Assoc J. 1980;41(3):161-9. http://dx.doi.org/10.1080/15298668091424546. PMid:7395724.
http://dx.doi.org/10.1080/15298668091424...

40 Salmani Nodoushan M, Mehrparvar AH, Torab Jahromi M, Safaei S, Mollasadeghi A. Training in using earplugs or using earplugs with a higher than necessary noise reduction rating? A randomized clinical trial. Int J Occup Environ Med. 2014;5(4):187-93. PMid:25270008.

41 Simpson TH, Stewart M, Kaltenbach JA. Early indicators of hearing conservation program performance. J Am Acad Audiol. 1994;5(5):300-6. PMid:7987019.
-4242 Moshammer H, Kundi M, Wallner P, Herbst A, Feuerstein A, Hutter HP. Author response: comments on TTS as a predictor of noise-induced hearing loss. Occup Environ Med. 2015;72(2):160-1. http://dx.doi.org/10.1136/oemed-2014-102644. PMid:25406475.
http://dx.doi.org/10.1136/oemed-2014-102...
) were included. One study evaluated legislation to reduce noise exposure in a 12-year ITS analysis. Thirteen studies with 3725 participants evaluated effects of personal HPDs (three RCTs and ten CBAs). Fifteen studies with 84,028 participants evaluated effects of HLPPs (two RCTs and thirteen CBAs).

Figure 1
Study flow diagram
Table 2
Overview of study characteristics

While the participants in all studies were described as being exposed to noise at work, these descriptions were often based on measurement methods that were not clearly described. We assumed that the noise exposure was higher than 80 dB(A).

Noise-exposed participants worked in construction, mining, manufacturing, agriculture, forestry, military, an orchestra, unspecified company or in various workplaces. One study did not describe workplaces(4040 Salmani Nodoushan M, Mehrparvar AH, Torab Jahromi M, Safaei S, Mollasadeghi A. Training in using earplugs or using earplugs with a higher than necessary noise reduction rating? A randomized clinical trial. Int J Occup Environ Med. 2014;5(4):187-93. PMid:25270008.).

In most studies, only men were included or there were mostly male workers at the workplaces studied.

Most studies scored poorly on all aspects of the risk of bias checklist (Figure 2) and only six studies scored an overall low risk of bias(1313 Muhr P, Månsson B, Hellström PA. A study of hearing changes among military conscripts in the Swedish army. Int J Audiol. 2006;45(4):247-51. http://dx.doi.org/10.1080/14992020500190052. PMid:16684706.
http://dx.doi.org/10.1080/14992020500190...
,2222 Berg RL, Pickett W, Fitz-Randolph M, Broste SK, Knobloch MJ, Wood DJ, et al. Hearing conservation program for agricultural students: short-term outcomes from a cluster-randomised trial with planned long-term follow-up. Prev Med. 2009;49(6):546-52. http://dx.doi.org/10.1016/j.ypmed.2009.09.020. PMid:19800914.
http://dx.doi.org/10.1016/j.ypmed.2009.0...
,2828 Horie S. Improvement of occupational noise-induced temporary threshold shift by active noise control earmuff and bone conduction microphone. J Occup Health. 2002;44(6):414-20. http://dx.doi.org/10.1539/joh.44.414.
http://dx.doi.org/10.1539/joh.44.414...
,2929 Huttunen KH, Sivonen VP, Poykko VT. Symphony orchestra musicians’ use of hearing protection and attenuation of custom-made hearing protectors as measured with two different real-ear attenuation at threshold methods. Noise Health. 2011;13(51):176-88. http://dx.doi.org/10.4103/1463-1741.77210. PMid:21368443.
http://dx.doi.org/10.4103/1463-1741.7721...
,3737 Park MY, Casali JG. A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors. Hum Factors. 1991;33(6):693-714. http://dx.doi.org/10.1177/001872089103300606. PMid:1800294.
http://dx.doi.org/10.1177/00187208910330...
,4040 Salmani Nodoushan M, Mehrparvar AH, Torab Jahromi M, Safaei S, Mollasadeghi A. Training in using earplugs or using earplugs with a higher than necessary noise reduction rating? A randomized clinical trial. Int J Occup Environ Med. 2014;5(4):187-93. PMid:25270008.).

Figure 2
Risk of bias summary for included studies

The effect of engineering interventions (following legislation) on noise exposure was evaluated in one ITS study. The study(88 Joy G, Middendorf PJ. Noise exposure and hearing conservation in US coal mines, a surveillance report. J Occup Environ Hyg. 2007;4(1):26-35. http://dx.doi.org/10.1080/15459620601067209. PMid:17162478.
http://dx.doi.org/10.1080/15459620601067...
) 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% Confidence Interval (CI) -36.1 to -19.3 percentage points) immediately after the implementation of stricter legislation (Table 3). 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, four-year follow-up, very low-quality evidence).

Table 3
SoF table – Stricter legislation (noise exposure)

Additionally, 12 case studies were collected reporting on 107 uncontrolled studies of engineering control interventions(4343 Azman AS, Yantek DS, Alcorn LA. Evaluations of a noise control for roof bolting machines. Min Eng. 2012;64(12):64-70. PMid:26251555.

44 Caillet J, Marrot F, Unia Y, Aubourg PA. Comprehensive approach for noise reduction in helicopter cabins. Aerosp Sci Technol. 2012;23(1):17-25. http://dx.doi.org/10.1016/j.ast.2012.03.004.
http://dx.doi.org/10.1016/j.ast.2012.03....

45 Cockrell TW Jr, Balanay JAG, Dawkins W. Engineering control of noise from 4-roll calender operations in tire manufacturing. J Occup Environ Hyg. 2015;12(9):D193-200. http://dx.doi.org/10.1080/15459624.2015.1043053. PMid:25921237.
http://dx.doi.org/10.1080/15459624.2015....

46 Golmohammadi R, Giahi O, Aliabadi M, Darvishi E. An intervention for noise control of blast furnace in steel industry. J Res Health Sci. 2014;14(4):287-90. PMid:25503285.

47 HSE: Health and Safety Executive. Sound solutions for the food and drink industries: reducing noise in food and drink manufacture. USA: HSE; 2013. 77 p. HSG232.

48 Küpper T, Jansing P, Schöffl V, Van Der Giet S. Does modern helicopter construction reduce noise exposure in helicopter rescue operations? Ann Occup Hyg. 2013;57(1):34-42. PMid:23006816.

49 Maling GC Jr, Wood EW, Lotz G, Lang WW. Reducing employee noise exposure in manufacturing: best practices, innovative techniques, and the workplace of the future. USA: Institute of Noise Control Engineering; 2016.

50 Morata T, Hayden C, Driscoll D, Stephenson CM, Clegg PM, Afanuh S. Preventing hazardous noise and hearing loss during project design and operation. Workplace design solutions. USA: National Institute for Occupational Safety and Health; 2015.

51 Pan J, Paurobally R, Qiu XJ. Active noise control in workplaces. Acoust Aust. 2016;44(1):45-50. http://dx.doi.org/10.1007/s40857-015-0035-2.
http://dx.doi.org/10.1007/s40857-015-003...

52 Thompson JK. Noise control of large mining machines. In: 44th International Congress and Exposition on Noise Control Engineering – INTERNOISE; 2015 Aug 9-12; San Francisco, California. Proceedings. Reston: Institute of Noise Control Engineering; 2015.

53 Wilson P. Top 10 noise control techniques: 2015. Acoust Aust. 2016;44(1):33-43. http://dx.doi.org/10.1007/s40857-015-0039-y.
http://dx.doi.org/10.1007/s40857-015-003...
-5454 HSE: Health and Safety Executive. A recipe for safety: health and safety in food and drink manufacture. USA: HSE; 2015. HSG252.). In most cases(4141 Simpson TH, Stewart M, Kaltenbach JA. Early indicators of hearing conservation program performance. J Am Acad Audiol. 1994;5(5):300-6. PMid:7987019.), authors evaluated design changes, followed by installing damping material and silencers(2121 Adera T, Donahue AM, Malit BD, Gaydos JC. An epidemiologic method for assessing the effectiveness of hearing conservation programs using audiometric data. Mil Med. 1993;158(11):698-701. http://dx.doi.org/10.1093/milmed/158.11.698. PMid:8284053.
http://dx.doi.org/10.1093/milmed/158.11....
), purchasing new equipment(1717 Higgins JPT, Altman DG, Sterne JAC. Assessing risk of bias in included studies. In: Higgins JPT, Green S, editors. Cochrane handbook for systematic reviews of interventions version 5.1.0 [Internet]. United Kingdom: The Cochrane Collaboration; 2011. Chapter 8 [cited 2019 May 26]. Available from: handbookcochraneorg), using enclosures(1515 Ramsay CR, Matowe L, Grilli R, Grimshaw JM, Thomas RE. Interrupted time series designs in health technology assessment: lessons from two systematic reviews of behavior change strategies. Int J Technol Assess Health Care. 2003;19(4):613-23. http://dx.doi.org/10.1017/S0266462303000576. PMid:15095767.
http://dx.doi.org/10.1017/S0266462303000...
), installing acoustic panels and curtains(1313 Muhr P, Månsson B, Hellström PA. A study of hearing changes among military conscripts in the Swedish army. Int J Audiol. 2006;45(4):247-51. http://dx.doi.org/10.1080/14992020500190052. PMid:16684706.
http://dx.doi.org/10.1080/14992020500190...
), and maintenance only(77 Davies H, Marion S, Teschke K. The impact of hearing conservation programs on incidence of noise-induced hearing loss in Canadian workers. Am J Ind Med. 2008;51(12):923-31. http://dx.doi.org/10.1002/ajim.20634. PMid:18726988.
http://dx.doi.org/10.1002/ajim.20634...
). Types of jobs, when reported, included operating machines and driving vehicles. The effect of the intervention was measured as change in absolute noise levels in 87 of the 107 cases and as personal noise exposure for workers in 27 cases.

Studies showed 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, studies lacked long-term follow-up, a control group, and in some cases the outcome was evaluated by an acoustical consultant or an employee at the firm where the intervention was evaluated and a conflict of interest was apparent (14 cases).

The review found no effects for administrative controls on environmental noise exposure. On-site training sessions giving instructions for HPD use and noise control techniques (sound barriers and distance) did not have an effect on personal environmental noise-exposure levels compared to information only in one cluster-RCT after four months' follow-up (Mean Difference (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 (176 participants, low-quality evidence) (Table 4).

Table 4
SoF table – Training plus exposure information versus training (noise exposure)

HPDs reduced noise exposure on average over various frequencies measured by about 20 dB(A) in one RCT and three CBAs (57 participants, low-quality evidence). There was moderate-quality evidence that personal instructions for inserting earplugs into the ear canal have a considerable effect on the noise attenuation of the devices with an 8.6 dB (95% CI 6.9 to 10.3) higher protection averaged across frequencies (two RCTs(3737 Park MY, Casali JG. A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors. Hum Factors. 1991;33(6):693-714. http://dx.doi.org/10.1177/001872089103300606. PMid:1800294.
http://dx.doi.org/10.1177/00187208910330...
,4040 Salmani Nodoushan M, Mehrparvar AH, Torab Jahromi M, Safaei S, Mollasadeghi A. Training in using earplugs or using earplugs with a higher than necessary noise reduction rating? A randomized clinical trial. Int J Occup Environ Med. 2014;5(4):187-93. PMid:25270008.), 140 participants) (Table 5).

Table 5
SoF table – Earplugs with instruction versus no instruction (noise exposure)

The effects of HPDs on hearing loss were measured in short and long-term follow-up studies. Authors of two studies compared different devices and measured temporary threshold shifts at short-term follow-up but reported insufficient data for analysis. In two CBA studies, the authors found no difference in hearing loss from noise exposure above 89 dB (A) between earmuffs and earplugs at long-term follow-up (Odds Ratio (OR) 0.8, 95% CI 0.63 to 1.03, very low-quality evidence) (Table 6). The long-term evaluation of the effect of earmuffs versus earplugs on hearing loss showed that earmuffs might perform better than earplugs in high noise levels, but worse in low noise levels (very low-quality evidence).

Table 6
SoF table – Earmuffs versus earplugs (hearing loss)

Authors of another CBA study found that wearing HPDs more often resulted in less hearing loss at very long-term follow-up (very low-quality evidence).

Studies also evaluated the effects of the combination of interventions in a hearing loss prevention programmes on noise exposure and hearing loss. One RCT found no significant effect in lowering noise level with the use of noise level indicators plus basic information or plus intensive information compared to basic information only at two- and four-months follow-up. The noise level decreased 0.32 dB more in the control group at two months (95% CI -2.44, 3.08) but 0.14 dB more in the intervention group at four months (95%CI -2.66 to 2.38). Neither were statistically significant. Also, the comparison of intensive versus basic information showed no significant differences in noise levels at two (-1.7dB, 95% CI -1.24 to 4.64) and four months (0.3 dB, 95% CI -2.31 to 2.91).

One cluster-RCT found no difference in hearing loss at three- or 16-year follow-up between an intensive HLPP for agricultural students and audiometry only (moderate-quality evidence) (Table 7). 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 program that did not provide such information (Table 8).

Table 7
SoF table - HLPP versus audiometry (hearing loss)
Table 8
SoF table - HLPP with exposure information versus HLPP without (hearing loss)

There was very low-quality evidence in four long-term studies, that better use of HPDs as part of a HLPP decreased the risk of hearing loss compared to less well used HPDs in HLPPs (OR 0.40, 95% CI 0.23 to 0.69) (Table 9).This could not be shown for worker training, audiometry alone or noise monitoring by very low- and moderate-quality evidences. More individualized information on daily noise exposure as part of a HLPP showed favourable but non-significant effects on hearing loss in one study.

Table 9
SoF table - Better implemented versus less well-implemented HLPP (hearing loss)

In the meta-analysis of four long-term CBA studies the difference in mean changes in hearing level at 4 kHz was 0.53 dB (95%CI -0.53 to 1.68)(1010 Pell S. An evaluation of hearing conservation program - a five-year longitudinal study. Am Ind Hyg Assoc J. 1973;34(2):82-91. http://dx.doi.org/10.1080/0002889738506811. PMid:4715098.
http://dx.doi.org/10.1080/00028897385068...
,2525 Gosztonyi RE Jr. The effectiveness of hearing protective devices. J Occup Med. 1975;17(9):569-80. PMid:1165499.,2626 Hager WL, Hoyle ER, Hermann0 ER. Efficacy of enforcement in an industrial hearing conservation program. Am Ind Hyg Assoc J. 1982;43(6):455-65. http://dx.doi.org/10.1080/15298668291410035. PMid:7113926.
http://dx.doi.org/10.1080/15298668291410...
,3030 Lee-Feldstein A. Five-year follow-up study of hearing loss at several locations within a large automobile company. Am J Ind Med. 1993;24(1):41-54. http://dx.doi.org/10.1002/ajim.4700240105. PMid:8352292.
http://dx.doi.org/10.1002/ajim.470024010...
). We performed a sensitivity-analysis and left out one study(1010 Pell S. An evaluation of hearing conservation program - a five-year longitudinal study. Am Ind Hyg Assoc J. 1973;34(2):82-91. http://dx.doi.org/10.1080/0002889738506811. PMid:4715098.
http://dx.doi.org/10.1080/00028897385068...
) that had a high risk of bias due to a 10-year age difference between the intervention and the non-exposed group, which could explain a difference of 7dB hearing thresholds (calculated based on ISO 1990(44 ISO: International Organization for Standardization. ISO 4869-1: Acoustics - Hearing Protectors - Part 1: Subjective method for the measurement of sound attenuation. Geneva: ISO; 1990.)). Sensitivity analysis results showed 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 (very low-quality evidence, Table 10). The confidence interval includes a possible hearing loss of 4.2 dB which is similar to the level of hearing loss resulting from five years of exposure to 85 dB(A), which means workers might still be at risk of a clinically relevant hearing loss.

Table 10
SoF table - HLPP versus non-exposed workers (hearing loss)

In addition, out of three other CBA studies that could not be included in the meta-analysis, two showed an increased risk of hearing loss in spite of the protection of a HLPP compared to non-exposed workers(1313 Muhr P, Månsson B, Hellström PA. A study of hearing changes among military conscripts in the Swedish army. Int J Audiol. 2006;45(4):247-51. http://dx.doi.org/10.1080/14992020500190052. PMid:16684706.
http://dx.doi.org/10.1080/14992020500190...
,3838 Reynolds JL, Royster LH, Pearson RG. Hearing conservation programs (HCPs): the effectiveness of one company’s HCP in a 12-hr work shift environment. Am Ind Hyg Assoc J. 1990;51(8):437-46. http://dx.doi.org/10.1080/15298669091369907. PMid:2392973.
http://dx.doi.org/10.1080/15298669091369...
) and one CBA did not(3333 Muhr P, Johnson AC, Skoog B, Rosenhall U. A demonstrated positive effect of a hearing conservation program in the Swedish armed forces. Int J Audiol. 2016;55(3):168-72. http://dx.doi.org/10.3109/14992027.2015.1117662. PMid:26754548.
http://dx.doi.org/10.3109/14992027.2015....
).

DISCUSSION

We could not find any controlled studies, in which technical measures to reduce workers’ noise exposures were evaluated at the company level. Some argue that control groups are not necessary because the effect can be measured immediately(5555 Glasziou P, Chalmers I, Rawlins M, McCulloch P. When are randomised trials unnecessary? Picking signal from noise. BMJ. 2007;334(7589):349-51. http://dx.doi.org/10.1136/bmj.39070.527986.68. PMid:17303884.
http://dx.doi.org/10.1136/bmj.39070.5279...
). On the other hand, the measurement of noise levels in real working life can be biased by many operational and environmental factors. To address this issue, we systematically collected case studies. The immediate results of those studies are similar to those of HPDs. Noise control can potentially make HPDs in workplaces unnecessary, along with other components of hearing conservation programs. However, for most case studies, it was unclear if the measured reductions also effected personal noise level exposure. Other case studies measured personal noise exposure of workers but did not report measurement protocols and the personal effect remains uncertain. Moreover, long-term follow-up is missing and it is unclear if these are lasting solutions. Many potential biases in the uncontrolled studies would be remediated by the use of control groups, better reporting of noise measurement protocols and long-term follow-up measurements.

No studies evaluated the effectiveness of recommendations from occupational health services, national agencies or occupational health professionals to reduce noise levels. Regulations regarding noise at work can make it difficult to challenge current practice in experiments.

For immediate effects of HPDs, we restricted our inclusion criteria to field studies among workers and excluded studies that made use of volunteers or were carried out in the laboratory. All excluded studies showed a benefit of extra instruction compared to less or no instruction(5656 Franks JR, Murphy WJ, Johnson JL, Harris DA. Four earplugs in search of a rating system. Ear Hear. 2000;21(3):218-26. http://dx.doi.org/10.1097/00003446-200006000-00005. PMid:10890730.
http://dx.doi.org/10.1097/00003446-20000...

57 Merry CJ, Sizemore CW, Franks JR. The effect of fitting procedure on hearing protector attenuation. Ear Hear. 1992;13(1):11-8. http://dx.doi.org/10.1097/00003446-199202000-00005. PMid:1541368.
http://dx.doi.org/10.1097/00003446-19920...

58 Toivonen M, Pääkkönen R, Savolainen S, Lehtomäki K. Noise attenuation and proper insertion of earplugs into ear canals. Ann Occup Hyg. 2002;46(6):527-30. PMid:12176767.
-5959 Williams W. Instruction and the improvement of hearing protector performance. Noise Health. 2004;7(25):41-7. PMid:15703148.). The increase in attenuation was similar to that found in our review. We only included studies that compared different devices worn by the same workers because the evaluation depends to a great extent on the wearer. That criterion excluded a great number of studies that evaluated different devices worn by different workers, but provided us with more reliable results.

Researchers who intended to evaluate a HLPP did not clearly define its implementation, which is especially important in studies comparing HLPPs. It is unclear if the results are applicable in other settings and what measures were taken in addition to HPDs (e.g. training).

The risk of bias was high (especially for long-term evaluation studies) because most studies were set up retrospectively and it is difficult to control confounders. Individual factors, such as skills necessary to correctly use HPDs or age, have an important effect on the outcome but only some studies used randomisation to ensure no baseline differences. Consequently, there is a need for better quality evidence. It has often been argued that randomisation of workers or workplaces is not possible but two studies that evaluated a HLPP (or components thereof) showed that randomisation was feasible, even in difficult sectors such as construction(1414 Seixas NS, Neitzel R, Stover B, Sheppard L, Daniell B, Edelson J, et al. A multi-component intervention to promote hearing protector use among construction workers. Int J Audiol. 2011;50(Suppl 1):s46-56. http://dx.doi.org/10.3109/14992027.2010.525754. PMid:21091403.
http://dx.doi.org/10.3109/14992027.2010....
,2222 Berg RL, Pickett W, Fitz-Randolph M, Broste SK, Knobloch MJ, Wood DJ, et al. Hearing conservation program for agricultural students: short-term outcomes from a cluster-randomised trial with planned long-term follow-up. Prev Med. 2009;49(6):546-52. http://dx.doi.org/10.1016/j.ypmed.2009.09.020. PMid:19800914.
http://dx.doi.org/10.1016/j.ypmed.2009.0...
). Evidence from more RCTs would eventually yield much higher-quality information on the effectiveness of hearing loss prevention programs.

Even though, we made significant efforts to search databases that would contain grey literature seeing that we did not go through conference proceedings. It is therefore possible that we missed retrospective cohort studies or controlled noise-reduction studies.

Publication bias could play a role in the results of the evaluation studies of HLPPs, with four of the studies being funded or carried out by people employed by the company responsible for the intervention, who could possibly have an interest in publishing studies demonstrating a preventative effect of HLPPs(1313 Muhr P, Månsson B, Hellström PA. A study of hearing changes among military conscripts in the Swedish army. Int J Audiol. 2006;45(4):247-51. http://dx.doi.org/10.1080/14992020500190052. PMid:16684706.
http://dx.doi.org/10.1080/14992020500190...
,3333 Muhr P, Johnson AC, Skoog B, Rosenhall U. A demonstrated positive effect of a hearing conservation program in the Swedish armed forces. Int J Audiol. 2016;55(3):168-72. http://dx.doi.org/10.3109/14992027.2015.1117662. PMid:26754548.
http://dx.doi.org/10.3109/14992027.2015....
).

Other authors drew similar conclusions to our review but mostly applied less systematic approaches.

One review located 22 studies that evaluated the field performance of many different types of HPDs worn by different workers(6060 Berger EH, Franks JR, Behar A, Casali JG, Dixon-Ernst C, Kieper RW, et al. Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of subject-fit data. J Acoust Soc Am. 1998;103(2):665-72. http://dx.doi.org/10.1121/1.423236. PMid:9479749.
http://dx.doi.org/10.1121/1.423236...
,6161 Berger EH, Franks JR, Lindgren F. International review of feld studies of hearing protector attenuation. In: Axelsson A, Borchgrevink HM, Hamernik RP, Hellstrom P-A, Henderson D, Salvi RJ, editors. Scientific basis of noise-induced hearing loss. USA: George Thieme Verlag; 1996. p. 361-77.). The inclusion criteria of these studies were essentially different from ours because only studies comparing devices among the same subjects were included. However, the conclusions from all these studies are in agreement: under field conditions the noise attenuation of HPDs is much less than under laboratory conditions.

Another review concluded that the evidence from long-term evaluation studies does not support HLPPs’ effectiveness(6262 Dobie RA. Prevention of noise-induced hearing loss. Arch Otolaryngol Head Neck Surg. 1995;121(4):385-91. http://dx.doi.org/10.1001/archotol.1995.01890040011002. PMid:7702811.
http://dx.doi.org/10.1001/archotol.1995....
), but the search for studies was not systematic. The review included five studies, of which four were also included in this review. His conclusions for the effectiveness of HLPPs are similar to ours.

Authors from other studies reviewed occupational NIHL data(6363 Borchgrevink HM. Does health promotion work in relation to noise? Noise Health. 2003;5(18):25-30. PMid:12631433.), evaluated the quality of HLPPs in companies(6464 Daniell WE, Swan SS, McDaniel MM, Camp JE, Cohen MA, Stebbins JG. Noise exposure and hearing loss prevention programmes after 20 years of regulations in the United States. Occup Environ Med. 2006;63(5):343-51. http://dx.doi.org/10.1136/oem.2005.024588. PMid:16551755.
http://dx.doi.org/10.1136/oem.2005.02458...
), or performed a narrative review directed at the mining sector alone(6565 McBride DI. Noise-induced hearing loss and hearing conservation in mining. Occup Med (Lond). 2004;54(5):290-6. http://dx.doi.org/10.1093/occmed/kqh075. PMid:15289584.
http://dx.doi.org/10.1093/occmed/kqh075...
). All studies concluded either that HLPPs are ineffective, or programs are commonly incomplete and miss noise control interventions.

There is very low-quality evidence that implementation of stricter legislation can reduce noise levels in workplaces. Case studies showed promising effects of engineering control on noise reduction at immediate follow-up but controlled studies and evaluation of the long-term effects are missing. It is unclear if results can be replicated in other workplaces and what the long-term effects are.

Under field conditions the average noise reduction of HPDs is lower than indicated ratings provided by the manufacturers. There is moderate-quality evidence that training of proper insertion of earplugs significantly reduces noise exposure at short-term follow-up but long-term follow-up is still needed.

There is very low-quality evidence that the better use of HPDs as part of HLPPs reduces the risk of hearing loss, whereas for other program components of HLPP we found no effect. The absence of conclusive evidence should not be interpreted as evidence of lack of effectiveness. Rather, it means that further research is very likely to have an important impact.

Future studies should use randomised design for HPDs or comparisons of different HLPPs or single programme components, or different levels of implementation in a cluster-randomised design. The ITS design has potential for evaluating HLPPs because much data is collected routinely.

CONCLUSION

Hearing loss prevention interventions modestly reduce noise exposure and hearing loss. Better quality studies and better implementation of noise control measures and HPDs is needed.

Disclaimer

The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

Appendix 1   Search strategy for CENTRAL

#1 MeSH descriptor Noise, Occupational explode all trees with qualifier: PC #2 noise AND (reduction OR abatement OR diminishment OR elimination OR “engineering controls” OR “administrative controls”) #3 “hearing loss prevention” OR “hearing conservation” OR “hearing surveillance” #4 “ear protective device” OR “ear protective devices” OR “hearing protective device” OR “hearing protective devices” OR “hearing protector” OR “hearing protectors” OR “hearing protection” OR “ear muffs” OR “ear plugs” OR “ear defenders” #5 (“noise reduction” AND “protective equipment”) #6 MeSH descriptor Noise, Occupational explode all trees #7 “protective equipment” #8 (#6 AND #7) #9 (#1 OR #2 OR #3 OR #4 OR #5 OR #8)

2016

#10 (#9) limited to publication year from 2008

Appendix 2   Search strategies for other databases

ACKNOWLEDGEMENTS

We would like to thank the Dutch Ministry of Social Affairs and Employment, Stichting Arbouw, and the Cochrane Editorial Unit for the grants received to complete and update the review in 2009, 2012, and 2017. In addition, we would like to thank Jani Ruotsalainen from Cochrane Work and Jenny Bellorini from Cochrane ENT for their support. We also thank Bas Sorgdrager who contributed to an earlier version of the full review.

  • Study conducted at the Cochrane Work Review Group, Finnish Institute of Occupational Health, Kuopio - Pohjois-Savo, Finland
  • Financial support: nothing to declare.

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Publication Dates

  • Publication in this collection
    03 Apr 2020
  • Date of issue
    2020

History

  • Received
    23 May 2019
  • Accepted
    10 Sept 2019
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