Objective To report the annual incidence of occupational diseases (ODs) in economic sectors in The Netherlands.
Methods In a 5-year prospective cohort study (2009–2013), occupational physicians were asked to participate in a sentinel surveillance system for OD notification. The inclusion criteria for participation were (1) covering a population of employees, (2) reporting the economic sectors and the size of their employee population and (3) willingness to report all diagnosed ODs. In this study, an OD was defined as a disease with a specific clinical diagnosis that was predominantly caused by work-related factors. The economic sectors (n=21) were defined according the NACE (Nomenclature des Activités Économiques dans la Communauté Européenne) classification.
Results In a total working population of 514 590 employees, 1782 ODs were reported over 12 months in 2009. The estimated annual incidence for any OD was 346 (95% CI 330 to 362) per 100 000 worker-years. Of all the ODs, mental diseases were reported most frequently (41%), followed by musculoskeletal (39%), hearing (11%), infectious (4%), skin (3%), neurological (2%) and respiratory (2%) diseases. The four economic sectors with the highest annual incidences per 100 000 workers were construction (1127; 95% CI 1002 to 1253), mining and quarrying (888; 95% CI 110 to 1667), water and waste processing (832; 95% CI 518 to 1146) and transport and storage (608; 95% CI 526 to 690).
Conclusion ODs are reported in all economic sectors in The Netherlands. Up to 91% of all ODs are mental, musculoskeletal and hearing diseases. Efforts to increase the effective assessment of ODs and compliance in reporting activities enhance the usability of incidence figures for the government, employers and workers.
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What this paper adds
In The Netherlands occupational diseases are reported but incidence rates are lacking.
A sentinel surveillance system with motivated occupational physicians is a feasible approach to estimate the incidence rates of occupational diseases in economic sectors.
Up to 91% of all medically reported occupational diseases are mental, musculoskeletal and hearing diseases.
Annual incidence rates of occupational diseases could be helpful for selecting and prioritising activities to prevent work-related diseases.
Preventing occupational diseases begins with the assessment of occupational demands and their effects on the health of workers.1 Research activities to evaluate the health and safety risks of occupational demands are conducted frequently in various jobs and economic sectors. However, research activities concerning the effects of occupational demands on workers' health are conducted less often.2
In The Netherlands, occupational physicians (OPs) are obligated to report occupational diseases (ODs) to the Netherlands Center for Occupational Diseases (NCOD). In contrast to most other countries, no financial compensation system exists for diagnosed ODs in The Netherlands. Therefore, an information system to keep employers and employees alert and to detect and prevent ODs is important. Incidence figures for various economic sectors seem to be a promising way to prioritise regulatory and preventive actions. A sentinel surveillance system with a group of motivated OPs was piloted3 and seemed a feasible approach to obtain incidences of ODs in the various economic sectors by assessing both the population of workers and all reported ODs, details of which are lacking in the Dutch National Registry which provides only absolute numbers of cases. Therefore, the main objective of this sentinel surveillance system is to determine the incidence rates of medically reported ODs in The Netherlands in various economic sectors on an annual basis with a sample group of motivated OPs. This report examines the annual incidence rates of ODs for 2009.
A 5-year dynamic prospective cohort (2009–2013) of active Dutch registered OPs was established to determine annually (1) the number of reported ODs and (2) the size and type of workers' population at risk.
OPs: recruitment, training and feedback
Dutch registered OPs with known email addresses (n=1773) were asked by the NCOD to participate in a sentinel surveillance system for the notification of ODs. The inclusion criteria for participation were (1) covering a population of employees, (2) reporting the economic sectors and size of their employee population and (3) willingness to register all diagnosed ODs. Education (free professional training on diagnosing ODs), facilitation (website, help desk and guidelines) and information (newsletters) were provided to enhance the quality and compliance of reporting ODs.
ODs: reported variables
An OD is defined as a disease for which the work-related fraction is >50%. The NCOD (http://www.occupationaldiseases.nl) has developed evidence-based guidelines for the assessment of the most frequently reported ODs. A guideline consists of two parts: a clinical case definition of the disease and disease-specific exposure criteria. These exposure criteria are defined in terms of the intensity, frequency and/or duration of specific occupational demands, such as lifting more than 10 kg at least 10 times a day. Exposure criteria are based on a systematic review of the scientific literature and are reported in a criteria document.
Each worker diagnosed with an OD is anonymously reported to the NCOD and the following information is recorded in a database: disease or pathology with clinical diagnosis, demographic characteristics (age, gender), exposure (information on physical, chemical, biomechanical and psychosocial factors), occupation, economic sector and consequences for work ability. The category of economic sector is based on the 21 main economic sectors described in the Statistical Classification of Economic Activities in the European Community.4
The data reflected a Poisson distribution with ODs as events during a fixed period of time (2009). Parameter calculation was based on Poisson counting. Incidence figures and their 95% CIs were determined for each economic sector by calculating the ratio of the number of reported ODs per economic sector and the worker-years for each participating OP during 2009. The unit of worker-years was used because each 6-month period of notifications of ODs and worker-years was corrected for changes in the participation of OPs. OPs ending their participation before July 1 were considered to have no participation, and those ending between July 1 and December 31 were considered to have participated only during the first 6 months of 2009. New participants between January 1 and July 1 were considered participants only during the last 6 months of 2009.
In 2009, 189 OPs, covering 514 590 employees over 21 economic sectors, participated in the sentinel surveillance system for the notification of ODs. Of these 189 OPs, 176 participated for an entire year and 13 participated for 6 months. Three OPs ended their participation during 2009 for various reasons (too busy, no employee organisation or personal reasons). Eighty-one per cent of the OPs reported at least one OD, with a mean of 12 ODs (range 1–81). The coverage of the economic sectors varied from 563 worker-years for the mining and quarrying sector to 119 330 worker-years for the health sector.
Medically reported ODs
Of all medically reported ODs, mental diseases were reported most frequently (41%, n=738; incidence (I): 143, 95% CI 133 to 154) followed by musculoskeletal diseases (39%, n=693; I: 135; 95% CI 125 to 145), hearing diseases (11%, n=194; I: 38, 95% CI 32 to 43), infectious diseases (4%, n=67; I: 13; 95% CI 10 to 16), skin diseases (3%, n=55; I:11; 95% CI 8 to 14), neurological diseases (2%, n=36; I:7; 95% CI 5 to 9) and respiratory diseases (2%, n=34; I:7; 95% CI 4 to 9).
Table 1 shows the annual incidence per 100 000 worker-years of ODs categorised into 21 economic sectors for 2009. In total, 1782 incident cases of ODs were registered over 12 months. For 17 cases of ODs the economic sector was unknown. The estimated year incidence in 2009 for any OD was 346 (95% CI 330 to 362) per 100 000 worker-years. The highest annual OD incidences by economic sector were 1127 (95% CI 1002 to 1253) in the construction sector, 888 (95% CI 110 to 1667) in the mining and quarrying sector, 832 (95% CI 518 to 1146) in the water and waste processing sector and 608 (95% CI 526 to 690) in the transport and storage sector.
ODs are reported in all economic sectors in The Netherlands. Up to 91% of all ODs are mental, musculoskeletal and hearing diseases, which is comparable to other European countries such as the UK.5 Efforts to increase the validity of the assessment of ODs and to improve compliance in the reporting activities of OPs could further enhance the usability of incidence figures. Employers and employees are interested in indications of where work-related health and safety problems can be expected, whereas governments focus on reliable OD statistics.6
Validity of medically reported OD incidences
In most cases, the medically reported ODs by an OP are based on a worker's self-report through a structured anamnesis and the opportunity to obtain additional information via clinical examination and tests. However, knowledge and the use of evidence-based case definitions and exposure assessment are equally important to increase the validity of the assessment of ODs. A sentinel surveillance system with a group of motivated and trained OPs7 is a strategy for estimating the annual incidence of ODs to counterbalance the under-reporting of ODs due to OPs' lack of knowledge or motivation to report ODs. The strength of this sentinel project is the extra source of information, between individual clinical case reports and epidemiological studies, on the incidence of medically reported ODs. However, the incidence rates for a number of economic sectors should be interpreted with caution because of the small number of cases as reflected in large CIs. Additional research is needed to detect ODs among populations of workers who have no access to OPs (eg, flexible workers or self-employed workers), who do consult other physicians (eg, family physicians or medical specialists) or who have diseases for which the attributed fraction of occupational factors is difficult to assess on an individual basis (eg, cardiovascular diseases) to identify the potential occupational causes of diseases.
Implications for preventive activities
Knowledge of the incidence of ODs in economic sectors is a starting point for preventive actions. The ultimate goal of registration activities is the prevention of ODs through the selection and implementation of interventions aimed at reducing exposure to biomechanical, environmental and psychosocial occupational demands among at-risk working populations in various economic sectors. In The Netherlands, the regulation of asbestos, research on prognostic factors for chronic solvent-induced encephalopathy8 and skin protection in nursing work9 are examples of (national) activities to prevent ODs. It is recommended that information about incidence rates of ODs should be used to increase the quality of governmental regulation regarding prevention, risk inventories and subsequent evaluations by employers and implement job-specific workers' health surveillance.
However, a reduction in exposure to job demands does not a priori result in a similar reduction in the risk of the onset or worsening of work-related diseases10 or ODs. Moreover, many of the instruments used by OPs, ergonomists, occupational hygienists and psychologists to assess job demands are not based on scientific evidence regarding an increased risk of ODs. Therefore, in The Netherlands, evidence-based occupational disease guidelines have been developed for mental, musculoskeletal, hearing, infectious, skin, respiratory and neurological diseases.11 12 In addition to their instrumental assistance to assess ODs, these guidelines contain evidence-based exposure criteria for ODs that might be useful for practitioners when assessing high job demands and prioritising preventive measures.
Funding This work was supported by the Dutch Ministry of Social Affairs and Employment.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.