Occupational Medicine 2015;65:238–244 Advance Access publication 10 March 2015 doi:10.1093/occmed/kqu214

Noise-induced hearing loss and combined noise and vibration exposure A. Turcot, S. A. Girard, M. Courteau, J. Baril and R. Larocque Institut national de santé publique du Québec, 945 avenue Wolfe, Québec G1V 5B3, Canada. Correspondence to: A. Turcot, Institut national de santé publique du Québec, 945 avenue Wolfe, Québec G1V 5B3, Canada. Tel: +1 418 650 5115, ext 5207; fax: +1 418 654 3134; e-mail: [email protected]

Aims

To determine whether hearing impairment is worse in noise-exposed workers with VWF than in workers with similar noise exposures but without VWF.

Methods

The Quebec National Institute of Public Health audiometric database was used in conjunction with work-related accident and occupational diseases data from the Quebec workers’ compensation board to analyse differences in audiometry results between vibration-exposed workers in the mining and forestry industries and the overall source population, and between mining and forestry workers with documented VWF and those without VWF. The International Organization for Standardization (ISO) 7029 standards were used to calculate hearing loss not attributable to age.

Results

15 751 vibration-exposed workers were identified in an overall source population of 59 339. Workers with VWF (n  =  96) had significantly worse hearing at every frequency studied (500, 1000, 2000 4000 Hz) compared with other mining and forestry workers without VWF.

Conclusions This study confirms previous findings of greater hearing loss at higher frequencies in workers with VWF, but also found a significant difference in hearing loss at low frequencies. It therefore supports the association between combined noise and hand-arm vibration (HAV) exposure and NIHL. Key words

Forestry workers; mining workers; noise; noise-induced hearing loss; vibration; vibration-induced white finger.

Introduction Workers exposed to hand–arm vibration (HAV) from the use of vibrating tools are also frequently exposed to high levels of noise [1,2]. Forestry workers with vibration white finger (VWF) tend to present with more severe hearing loss than their co-workers without VWF, with the hearing loss being more pronounced at higher frequencies [3–10]. Pyykkö et al. [9] found that workers with VWF had greater hearing loss than vibration- and noise-exposed workers without VWF. However, he found that the permanent hearing loss in workers exposed to noise and vibration did not exceed the permanent loss from exposure to noise only. This may suggest that VWF is a marker of individual susceptibility to noise-induced hearing loss (NIHL) without the vibration conferring increased risk of hearing

loss from noise exposure [11]. Palmer et al. [12] observed that hearing impairment was about twice as common in women and men who reported finger blanching, even among those who had never been exposed to HAV. This lends further support to the hypothesis that finger blanching and hearing impairment may have similar underlying, and predisposing, pathophysiological mechanisms, though the exact nature of this relationship remains poorly understood. However, an experimental study has supported the hypothesis that the combination of HAV and noise aggravates noise-induced temporary threshold shift more than noise exposure alone [13]. A recent study among workers in heavy engineering also supports an association between combined exposure to noise and HAV and NIHL [14]. The objective of this study was to ascertain whether hearing impairment in noise-exposed workers is more

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Background While there is a wide body of literature addressing noise-induced hearing loss (NIHL) and hand– arm vibration syndrome (HAVS) independently, relatively few studies have considered the combined effects of noise and vibration. These studies have suggested an increased risk of NIHL in workers with vibration white finger (VWF), though the relationship remains poorly understood.

A. TURCOT ET AL.: NIHL AND NOISE AND VIBRATION EXPOSURE  239

pronounced in those with documented VWF than those without VWF, while also considering the broader question of whether hearing loss differs significantly between workers in industries traditionally considered as having high HAV exposure versus industries in which the primary exposure would be expected to be noise alone.

Methods

Table 1.  Description of the population

Source population Forestry + mining Forestry Mining Source pop. − (forestry + mining) Cases (VWF)

Number of workers, n

Mean age at the audiometric examination (years)

Mean number of years in noisy environment

Presence of tinnitus, n (%)

Number (%) of compensable workers according to QWCB criterion

Number (%) of workers compensated by QWCB

59 339 15 757 8526 7231 43 582

39.9 40.4 39.0 42.2 39.7

15.8 16.1 14.0 18.7 15.6

4151 (7) 1124 (7) 401 (5) 723 (10) 3027 (7)

8730 (15) 2491 (16) 1147 (13) 1344 (19) 6239 (14)

3986 (7) 1093 (7) 491 (6) 602 (7) 2893 (7)

96

44.8

22.3

25 (26)

45 (47)

20 (21)

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The source population in this study was a cohort of workers aged 25–64 who had at least one audiometric examination in the Quebec National Institute of Public Health mobile audiometric laboratory between 1983 and 1996. This database has been used and described in another study [15]. This cohort comprised 59 339 male workers from a wide range of industry sectors with a documented history of occupational noise exposure of 80 dBA (Laeq 8 h) or greater. The study population was a subset of this cohort comprising 15 757 mining and forestry workers, these industries being chosen as workers in industries associated with both HAV and noise exposure [16,17]. The comparison group consisted of all non-forestry and nonmining workers of the source population (n = 43 582). Examinations were individually conducted in accordance with the methods specified by the International Organization for Standardization (ISO) 6189 (1983) since using these methods under standardized conditions, while controlling for potential confounding by exposure dose and age-related hearing loss, produces highly reproducible hearing threshold measurements [18,19]. Hearing loss was calculated by air conduction at 500, 1000, 2000 and 4000 Hz, taken individually or jointly, depending on the analysis. Occupational ambient noise levels were measured by occupational health professionals from the Quebec public health network. Noise exposure levels were grouped into two categories: Laeq 8 h ≥90 and

Noise-induced hearing loss and combined noise and vibration exposure.

While there is a wide body of literature addressing noise-induced hearing loss (NIHL) and hand-arm vibration syndrome (HAVS) independently, relatively...
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