Comparison of national statistics on occupational diseases - experiences from the EODS 1995 pilot data

Karjalainen, Antti

Senior Scientist / Department of Epidemiology and Biostatistics / Finnish Institute of Occupational Health / Topeliuksenkatu 41 aA / FIN-00250 Helsinki / Finland

INTRODUCTION

Incidence of occupational diseases is frequently used as an indicator of the state of occupational health. An occupational disease is not characterised merely by the disease itself, but by a combination of a disease and an exposure, as well as an association between these two. There are three basic options to collect data on incidence or prevalence of occupational diseases: (a) cases accepted by compensation authorities, (b) cases reported by physicians' judgement as of occupational origin, and (c) cases reported by the diseased individuals' judgement as of occupational origin. These three approaches are based on different judgements of causality and consequently result in different incidence or prevalence rates and different distributions of diseases and symptoms that are reported. It has been pointed out that it is advisable not to rely on only one source of information when surveillance of health and safety at work is concerned ¹.

Various Commission Recommendations, Council Resolutions and publications have addressed the reporting of occupational diseases in the Member States of the European Community ^2,3,4,5. These documents also underlined the need to initiate work on the harmonisation of statistics on occupational diseases and the need to improve the available data. They also recommend that Member States should ensure as far as possible that all cases of occupational disease are reported. In this framework a Working Group on the harmonisation of European statistics on occupational diseases was established and it carried out a detailed investigation of current practices in the 12 Member States in 1992. The investigation revealed great differences in national social security and compensation systems. The expert group first discussed a suggestion that a system of reporting of occupational disease by doctors should be put in place in all member states, and form the basis of comparative data. This was considered impractical by most member states. Furthermore, such systems would be heavily influenced by the existing administrative systems for dealing with occupational disease, and would therefore not escape from the difficulties created by the differences between these systems. The group agreed that it was better to approach the problem directly, by drawing data from the existing systems on as similar basis as possible. This would enable the extent of differences to be clearly documented, and the sources of non-comparability to be explored. The group concluded that a pilot study was needed to assess the comparability of the data drawn from the existing systems.

This paper summarises the experiences of the EODS (European Occupational Disease Statistics) pilot study which was funded by the European Commission. Following a Call for tender the evaluation work was assigned to an external evaluation team from the Finnish Institute of Occupational Health in co-operation with a technical subcommittee established by Eurostat. The evaluation was performed in 1998 and the detailed results of the EODS pilot study have been published ⁶.

EODS METHODOLOGY

Data for the reference year 1995 on recognised occupational diseases were collected in co-operation with Eurostat and the responsible bodies of the 15 member states for 31 items taken from the European Schedule of Occupational Diseases ⁴. Questionnaire data on recognition criteria and statistical data on recognised cases were collected. Further information on the coverage and recognition criteria was collected with a questionnaire. The evaluation had the following aims:

1. To assess the degree of comparability of the pilot data.

2. To assess the strengths and weaknesses of the pilot data.

3. To propose changes to improve the available data.

The case data covered 8 variables: country, age, gender, reference number of the European Schedule, diagnosis, occupation, economic activity of the employer and disability. The data did not cover the entire working population for some member states and for some member states it did not represent recognised cases. Questionnaire data on the coverage of the Occupational Diseases systems were completely or partly available for 13 member states. An additional questionnaire was used to clarify the inclusion criteria of mild diseases in general, coding of the medical diagnosis and specific recognition and inclusion criteria of six selected items. To calculate incidence rates, data from the 1995 Labour Force Survey were used to build reference populations that would correspond to the workforce that is covered by the compensation scheme from which the data on occupational diseases were retrieved.

EODS RESULTS

There were 57414 cases of occupational disease of the 31 selected items. The ten most frequent occupational diseases were noise-induced hearing loss (18419 cases), allergic or irritative skin disease (8767), respiratory allergy (4543), silicosis (4381), asbestosis (3894), paralysis of nerves due to pressure (3392), osteoarticular diseases of the hand and wrist due to mechanical vibration (2539), angioneurotic diseases due to mechanical vibration (2454), diseases of the periarticular sacs due to pressure (2305) and mesothelioma (1446).

The main factors restricting comparability were: (1) Definition of the reference population, (2) Varying inclusion criteria, (3) The coding of the medical diagnosis and (4) Differences in the recognition of mild cases.

(1) Definition of the reference population. Self-employed and family workers are not covered similarly by the national compensation schemes. The proportion of such workers varies between industries and countries. In 1995 self-employed workers accounted for 15 % of the total workforce in EU, ranging from 8 % in Denmark to 34 % in Greece. The proportion of family workers ranged from 0.5 to 12 %, i.e. self-employed and family workers represent 9 to 46 % of the total workforce in the member states. In Agriculture the proportion of such workers ranges from 49 to 88 % and in construction from 7 to 39 %. For an accurate definition of the reference population, the member states should estimate the coverage of their national system by industry and occupation. For diseases with a long latency time, it is difficult to build comparable industry-specific reference populations and the rates should preferably be calculated only for the total workforce. For example a reasonably high number of cases of silicosis still occur in past miners in some member states where most of the mining activities have already ceased, i.e. the current number of miners is low.

(2) Inclusion criteria. There was variation in what types of diseases are accepted and were included for many of the 31 items. For example, all 15 member states had included occupational asthma into respiratory allergies, while 8 of them had included also cases of allergic rhinitis and cases of allergic alveolitis into that item. Similarly all member states had included cases with pulmonary fibrosis into asbestosis, while 10 member states had also included cases with bilateral diffuse thickening of pleura and 7 member states cases of bilateral pleural plaques into asbestosis. These problems are mainly resolved by a more detailed coding of the medical diagnosis, but the inclusion criteria should also be clearly defined. For example, how the allergic and irritative bronchial responses are included into asthma under the general item of Respiratory allergies in the European Schedule of Occupational Diseases.

(3) Coding of the medical diagnosis. A more detailed classification of the diagnosis is needed. A draft list was proposed according to the ICD-classification of WHO ⁷ and this draft will further be processed according to questionnaire information. A detailed coding with clearly defined inclusion criteria will enable comparison of the national statistics for those subcategories, which are similarly recognised in the member states. See examples in the previous chapter.

(4) Recognition of mild cases. To ensure effective prevention and adequate medical follow-up at individual level, some member states recognise occupational diseases at an early stage, when they do not yet cause any disability in medical terms, while some member states only recognise cases with a certain minimum level of disability. This is well illustrated when comparing the limits which are used by the Member States when accepting noise-induced hearing loss as an occupational disease (Table 1). Some member states recognise hearing loss only if the degree of hearing capacity (audiogram) has been reduced at least 50 dB while some member states recognise it even if the degree of hearing capacity is reduced less than 15 dB if the person has been exposed to excessive noise at work and the reduction pattern in the audiogram is typical (no financial compensation is usually paid for such cases, but the exposure has to be reduced). The recognition of mild cases makes it difficult to directly compare the total incidence rates for most of the occupational diseases. The future data set should contain both incident cases and cases which were recognised earlier but became more severe during the reference year. With an adequate coding of the nature of the case and the respective degree of disability, a higher degree of comparability would be achieved.

Table 1. The threshold value for decrease of hearing capacity (audiogram) which is used for accepting a case of hearing loss as an occupational disease in EU member states ⁶.

* The data from The Netherlands and Sweden did not represent recognised cases. The threshold for recognition is therefore not applicable

DISCUSSION

Based on the EODS pilot data evaluation, improvements of data collection were proposed to solve the problems 1-4 presented in the previous chapter. In addition, it was recommended to collect more information concerning the role of the concept of occupational disease in the social security system in general and the specific recognition criteria of different occupational diseases.

Strengths of the data. Data on recognised cases of occupational disease represent a high degree of causality. They also provide detailed information on exposure and on medical and social consequences. Such data can be used in prevention and evaluation of the impact of the problem. It is very difficult if not impossible to collect such data on a continuous and more or less nation-wide basis otherwise than from the national occupational disease recognition systems. Interestingly, when the effect of the varying inclusion criteria for severity and type of disease was eliminated by comparing the industry-specific incidence rates after adjustment for the national incidence rate in the pilot data, it could be concluded that the risk industries identified by the national systems and the incidence rate ratios were quite similar in the member states for those items in which the number of cases allows for statistical comparisons. For example the incidence rate of occupational asthma in manufacture of food and food products was clearly more than the average incidence rate of occupational asthma in all member states. This is probably mostly due to baker’s asthma which seems to represent an occupational health problem in all member states.

Weaknesses of the data. After the above-mentioned improvements in the data collection, two general restrictions remain: (a) The data on recognised occupational diseases reflect not only the occurrence of such diseases, but inevitably also the way in which the concept of an occupational disease has been integrated into the social security system. This integration determines the (legal and financial) motivation of the patient, the physician, and the employer to notify cases and the motivation of social security authorities and respective bodies to allocate them under the coverage of the normal social security or to define them as occupational diseases. Even for severe diseases, e.g. mesothelioma or asthma, the reporting rate is likely to be low, if the financial level of social security is not affected by the decision. (b) The EODS pilot data indicate that underreporting is probable even for some classical occupational diseases. E.g. recognised cases of occupational mesothelioma represent only a small fraction of the total cases of mesothelioma in some member states. On the other hand it is quite clear that statistics on recognised cases do not rapidly identify new health problems because the causality has to be first proven scientifically.

The above constraints have to be remembered when data from compensation schemes are used for establishing priorities for prevention. The preventive aspect of the compensation schemes seems to vary, i.e. whether the system mainly compensates existing disability of the individual or whether an early identification of mild cases and the respective elimination of further risk is enhanced, up to a level which obliges the person to abstain from the risk in order to get compensation. In both of these extreme cases, the general responsibility for the prevention probably lies on the labour protection authorities, while in the latter one some prevention (and rehabilitation) at individual level is integrated into the occupational disease compensation scheme.

The European Schedule of Occupational Diseases is a mixture of categories defined by exposure and categories defined by disease. This causes problems for statistical comparison and use of the data. These can be solved if the medical diagnosis and the exposure are coded as separate variables in the future data collection. For many of the specific items of the European Schedule, the number of cases is low (e.g. diseases caused by manganese or compounds thereof), while the bulk of the cases fall into non-specific categories (e.g. skin ailments in general). Some categories contain both cases due to old exposures (cancer) and recent exposures (allergy), which is not optimal for the evaluation of preventive needs (e.g. diseases caused by chromium and compounds thereof).

Overall, the evaluation of the EODS pilot data identified many problems of comparability which can be avoided with improvements in the data collection. These improvements should be implemented to generate a harmonised data collection for that part of the work-related disease burden which is similarly dealt by the national compensation schemes. The evaluation also underlines, however, that alternative ways of data collection have to be explored to evaluate that part of the work-related disease burden which is not identified by the recognition systems because of (1) underreporting of causal occupational diseases or (2) legal constraints regarding the degree of causality.

REFERENCES

• 1. Report III. Statistics of occupational injuries. 16th International Conference of Labour Statisticians. ILO, Geneva, Switzerland 1998.
• 2. Council Resolution on safety, hygiene and health at work, 88/C28/01, OJ No. C 28 of 3/2/1988 and Council Resolution on the transposition and application of community social legislation, 95/C 168/01, OJ No. C 168 of 4/7/1995
• 3. Recommendations of the Commission to the Member States concerning the adoption of a European schedule of occupational diseases, 2188/62/EEC and 66/462/EEC, Official Journal, No. 81 of 31/8/1962, and No. 147 of 9/8/1966.
• 4. Recommendations of the Commission to the Member States concerning the adoption of a European schedule of occupational diseases, 90/326/EEC, Official Journal, No. 160 of 26/6/1990.
• 5. Information notices on diagnosis of occupational diseases. EUR 14768 EN. European Communities, Luxembourg 1997.
• 6. 6 . Karjalainen A, Virtanen S. European statistics on occupational diseases Evaluation of the 1995 pilot data. Eurostat Working Papers 3/1999/E/n2. Eurostat, Luxembourg, 1999.
• 7. International Statistical Classification of Diseases and Related Health Problems. Tenth revision (ICD10). WHO, Geneva, Switzerland 1992.