In the period 2005 – 2009, the Labour Inspection Authority received a total of 7 888 reports on work-related hearing loss. Altogether 40 % of these reports concerned employees older than 55 years. This is fairly consistent with a corresponding study from the Norwegian continental shelf (petroleum installations), in which 44 % of the reports pertained to employees older than 55 years (13). Hearing loss develops over time, and will not always manifest itself until additional age-related changes develop in parallel. The relative attribution of ageing and occupation to hearing loss is difficult to evaluate (14). Changes in industrial structure, technological development and better primary prevention over the last 20 – 30 years may have reduced the risk of work-related hearing loss.
Only 4 % of the reports concerned women. This corresponds poorly with the gender distribution in terms of exposure to noise in Norwegian working life. Noise exposure and hearing loss in women employees have been described as an underestimated problem also in the EU (15). A Belgian study showed that while the proportion of women who were exposed to noise in the workplace was half that of men, only 1 % of all cases of hearing loss that were recognised as an occupational injury included women (16).
The situation in Norway is identical. According to Statistics Norway’s living conditions survey from 2009, half as many women as men (7 % vs 14 %) were exposed to loud noise at work, and nearly half as many women as men (2 % vs 5 %) reported to suffer from work-related hearing loss. (6). However, no women were granted compensation from NAV for permanent occupational injury because of hearing loss in the period 2004 – 2007 (7). Our study shows that the doctors’ report to the Labour Inspection Authority fails to capture work-related hearing loss in women.
Only 2 % of the reports concerned tinnitus (ICD-10 H 93.1). Similarly, a low proportion of tinnitus was found in a Finnish study where work-related tinnitus was not reported when hearing loss was also present (17). Tinnitus was mentioned in no more than 4 % of the reports on work-related hearing loss, while it was evident in nearly 90 % of the cases (17). For many, tinnitus is a serious consequence of exposure to noise, but the problem largely fails to appear in the reports to the Labour Inspection Authority.
The distribution of the reports by industry largely accords with known facts on exposure to noise and hearing loss in Norwegian working life. Three of the four industries that had the highest reporting incidence for hearing loss in this study (mining, manufacturing and construction) also had the highest proportion of employees who were exposed to noise (20 – 25 %) according to Statistics Norway’s living conditions survey from 2009 (6). In the HUNT studies, the prevalence of age-adjusted hearing loss was highest in occupations that are common in these three industries (4). The ten occupations with the highest number of reports (Figure 3) in our material largely correspond to those occupations in which the highest number of cases of work-related hearing loss was reported in the 2009 living conditions survey, and also to those occupations in which the HUNT studies detected the largest average hearing loss (4, 6).
For the primary industries, however, the proportion and reporting incidence are both low in our material, despite the fact that the exposure to noise may be considerable. In Statistics Norway’s living conditions survey for 2009, altogether 12 % of employees in agriculture and aquaculture reported to suffer from work-related hearing loss, compared to 4 % of all employees (6). The primary industries include agriculture, forestry and fishery, but in our study agriculture accounts for 75 % (n = 155) of the reports. An occupational health service is not mandatory for agriculture, pursuant to the Working Environment Act. A voluntary scheme for this industry (the HSE service for agriculture) covers no more than approximately 12 000 of the total of 50 000 agricultural enterprises. In agriculture, a large proportion of workers are self-employed people who are not automatically included in public occupational injury benefit and insurance schemes. They thus stand to gain no financial benefit from being diagnosed with work-related hearing loss, and this most likely explains the low reporting incidence.
We also compared the age distribution of those reported by industry with the age distribution of self-reported work-related hearing loss in the 2009 living conditions survey (6). Figure 2 shows that the proportion of those under 40 years who report to suffer from work-related hearing loss in the living conditions survey is for the most part higher than the corresponding proportion in the reports submitted to the Labour Inspection Authority. This difference varies by industry. It is smaller in the construction industry (23 % vs 20 %) than in the transport sector (22 % vs 11 %) and retail trade (43 % vs 22 %).
The age distribution of those reported by industry may indicate that the follow-up in the form of hearing tests for younger employees exposed to noise is less effective in the transport sector and retail trade than in the construction industry. A large proportion of the employees in retail trade are women, and only parts of this industry are obligated to provide occupational health services. These are two issues that according to our observations reduce the likelihood of hearing loss being captured by the system of reporting to the Labour Inspection Authority.
In the construction industry the prevalence of hearing loss in young employees may also be greater than is indicated by the reporting incidence in this study. In a questionnaire survey undertaken by IRIS (International Research Institute of Stavanger) among 456 employees in this industry with an average age of 34 years, altogether 29 % reported reduced hearing because of exposure in the workplace (18). A number of international studies indicate that young employees in exposed industries such as construction have measurable hearing loss that requires early detection and preventive intervention (14, 19).
Primary prevention on the basis of the doctor’s report to the Labour Inspection Authority can be undertaken after the inspectorate has issued an injunction for a mapping of the noise exposure (if there is doubt regarding the risk) or noise reduction (level or time of exposure). The doctor’s hearing loss report may also provide a basis for an injunction for secondary prevention if the employee needs follow-up because of vulnerability to the hazardous effects of noise. For example, a relocation may be necessary.
About 52 % of the reports to the Labour Inspection Authority pertained to previous exposure. Hearing tests undertaken after the employment relationship and exposure have ceased may clarify the individual employee’s claim to compensation from national and private insurance, but provide little information of value to the labour inspectorate. However, if the report states that the enterprise in question continues to have a noise problem, this information may provide grounds for an injunction for primary prevention that will benefit other employees.
The occupational health physicians account for 85 % of all reports concerning hearing loss. Even in industries that are obligated to provide occupational health services, less than half of the enterprises are likely to comply with this obligation, according to figures from inspections undertaken by the Labour Inspection Authority in 2010. Many industries that are not obligated to provide occupational health services may have employees who are exposed to hazardous noise. In addition to the primary industries, this applies also to other industries such as the entertainment business and retail trade. Employers are obligated to ensure that hearing tests are performed, irrespective of their obligation to provide occupational health services (Regulations on performance of work in enterprises with exposure to noise). Judging by the reports submitted to the Labour Inspection Authority, however, hearing tests are very rarely undertaken by doctors other than occupational health physicians.
If the doctors suspects that there is an association between the patient’s tinnitus or hearing loss and noise in the workplace, this constitutes sufficient grounds for reporting. The threshold for reporting ought to be low. The purpose of the reporting system is not to measure «the scope of the problem», as many seem to believe, but to obtain information on possible risk factors and the need for preventive efforts. The criticism that has been raised regarding the lack of specificity in the reporting system clearly disregards this fact (20).
General practitioners could ask about the patient’s occupational history and undertake a simple hearing test such as whispering voice test (Box 1) (21). This is similar to when completing a health certificate for a driving licence (22). Studies have shown that when appropriately applied, the whispering test remains a useful tool for diagnosing hearing loss (23) – (25). A whispering test combined with an occupational history may reveal a need for an examination by a specialist and audiometry, but a report to the Labour Inspection Authority does not require detailed examinations.
Whispered voice test for a simple hearing test (21)
The doctor stands at an arm’s length (0.6 m) behind the seated patient and whispers a combination of numbers and letters (e.g. 4-k-2). The patient is then asked to repeat the sequence.
The doctor should quietly exhale before whispering to ensure as quiet a voice as possible.
If the patient answers correctly, his/her hearing is deemed normal. If the patient gives a wrong answer, the test is repeated with another combination of numbers and letters.
The patient’s hearing is deemed normal if at least three of six possible numbers or letters are repeated correctly.
The doctor must stand behind the patient to prevent lip-reading.
Each ear is tested individually, starting with the ear with better hearing. The patient blocks the other ear by occluding the auditory canal with a finger and rubbing the tragus in a circular motion. The other ear is assessed similarly with a different combination of numbers and letters.
A strength of this study is the authors’ familiarity with internal practices for registration and follow-up in the Labour Inspection Authority and the inspectorate’s internal inspection data at the aggregate level (compliance with the Act on enterprise health services). A weakness is that the information communicated in the reports on noise exposure and work-related hearing loss by age, gender and industry cannot be compared to noise exposure and audiometry data. Available national data are mainly based on self-reported information from surveys (Statistics Norway’s living conditions survey from 2009).