ABSTRACT
The purpose of the study was to obtain new data on the causes, development, prevalence and nature of occupational multimorbidity in the nickel industry workers. We extracted data from the register of occupational disease and intoxication cases in the population of the Murmansk region and the Krasnoyarsk Territory in 2007–2021. In 2007–2021, 24.6% of nickel industry workers with newly diagnosed occupational diseases developed a multimorbid pathology. Its prevalence rose from 0% in 2007 to 83.3% in 2021, and the number of occupational diseases increased by 3.17 times. Two diagnoses were found in 66 (14.9%), three in 22 (5.0%), four in fifteen (3.4%), five in eleven (2.5%), and six in three (0.7%) employees. Respiratory and musculoskeletal diseases were the most prevalent disorders, accounting for 31.5% and 23.0% of cases, respectively. Occupational multimorbidity resulted from the increased combined exposure to occupational hazards, outdated technological processes, and the working conditions in the finished product cleaners and crane operators. Multimorbid diseases can be better prevented with improvement in working conditions and better quality of periodic medical examinations.
Introduction
Health status of the working population is one of the most important indicators of social well-being, since damage to health in the workplace, including occupational disease, can reach 5% of the total gross national product. Therefore, the populational quality and standard of living is assessed also by the number of people with a newly diagnosed occupational disease [Citation1–3]. However, not only the number of persons with occupational pathology matters, but also the number of- nosologies newly diagnosed in one employee. Currently, two and (or) more concurrent chronic diseases in a patient can be classified in a number of ways, including comorbidity, polymorbidity and multimorbidity [Citation4–6]. Despite terminological differences, concurrent diseases in one patient are highly prevalent in Russia and other countries, especially in patients with low socio-economic status [Citation7,Citation8]. Such comorbidity has been associated with medical and social consequences, including increased risk of hospitalisation, temporary and permanent disability, mortality, decreased quality of life, and high medical costs [Citation9–13].
In recent years, a significant increase in the number of concurrent occupational diseases in one employee in the Russian Arctic has been reported and was also classified as “occupational multimorbidity” [Citation14]. This fully applies to the Russian nickel industry, mainly located in the Krasnoyarsk Territory and the Murmansk Region [Citation15]. Nickel industry workers are exposed to many hazards, including various nickel compounds, cobalt, arsenic, sulphur and silica, as well as work with increased physical demands in the unfavourable workplace climate [Citation16–18]. Nickel compounds as a major exposure in this industry exhibit cytotoxic, allergenic and carcinogenic effects for the respiratory, nervous, reproductive and endocrine systems, skin, blood cells and other structures [Citation19–24]. These workers usually exhibit a number of diseases including respiratory, musculoskeletal, nervous system, skin, reproductive disease and malignant neoplasms. Some of these health disorders are officially considered occupational, whereas the others are not considered occupational diseases in the Russian Federation [Citation25–30].
Unlike general medicine, this phenomenon has not yet attracted the attention of occupational medicine doctors and occupational safety specialists, yetremaining undoubtedly important [Citation14]. However, as in general medicine, multimorbidity in the occupational medicine reflects the unfavourable disease, which manifests with the spread of pathology beyond the target organ to other organs and systems resulting associated with occupational hazards. The purpose of the study was to obtain new data on the development, prevalence and nature of occupational multimorbidity in the nickel industry workers.
Materials and methods
We extracted data from the register of occupational disease and intoxication cases (Appendix No. 5, order of the Russian Ministry of Health dated 28/05/2001) of the population of the Murmansk region and the Krasnoyarsk Territory (within the Russian Arctic) in 2007–2021. The Russian ministry of health database includes all cases of newly diagnosed and officially registered cases of occupational diseases during each year, claimed by the occupational doctors’ panels in each region of the Federation. The list of occupational diseases and the associated occupational hazards is dictated by the Order of the Ministry of Health of Russia No. 417 of 27.04.2012. In total, the list of occupational diseases comprises 800 diagnoses.
Of these, nickel compounds can cause foundry fever, acute and chronic rhinitis, pharyngitis, laryngitis, tracheitis, bronchitis, chronic obstructive pulmonary disease, pneumosclerosis, nasal septum erosion (perforation), malignant neoplasms, chronic toxic encephalopathy, cardiomyopathy, nephropathy, and anaemia. Fibrogenic aerosols mainly cause various types of pneumoconioses, chronic bronchitis and bronchial asthma. Polyneuropathy of the upper and lower extremities, compression mononeuropathy, carpal tunnel syndrome, neuropathy of the median, ulnar, radial, supra-scapular nerves, reflex and compression syndromes, radiculopathy, chronic myofibrosis and osteoarthritis are most often found in the workplaces with increased work demands. Hand-arm and whole-body vibration cause the vibration disease, whereas noise is associated with noise-induced hearing loss.
Data on the occupational hazards in the nickel industry workplaces along with their measured exceedance are usually obtained from the special working conditions attestation procedure conducted by the state-licenced control organisations. It is carried out at least once every 5 years or in case of technology change. In addition, data on the quarterly departmental monitoring of air pollution in the industrial premises, including chemicals and fibrogenic aerosols are available. Working conditions attestation procedure in the Russian nickel industry along with the conventional grading of occupational hazards classes in the industry can be found in our previously published papers [Citation18,Citation26].
We then compared work conditions, including occupational hazards and technological attributes with the number of occupational diseases in a single nickel production worker when the newly diagnosed occupational disease was claimed alone or in combination. The choice of one and the leading hazard and one and the leading technological circumstance of each case of the disease is dictated by the joint decision of hygienists and occupational doctors’ panel. This information is available from the Russian Ministry of Health database, mentioned above.
Data were analysed using Microsoft Excel 2016. Numerical data in the text and tables are presented as absolute values, percentage, arithmetic mean and standard error of it (M±m). We considered statistical difference significant at p < 0.05.
Results
In 2007–2021, 657 occupational diseases were newly detected in 444 employees of nickel production enterprises in the Russian Arctic, including 355 (80.0%) men and 89 (20.0%) women with the mean age 53.0 ± 0.3 years and the mean work experience in the industry 25.3 ± 0.4 years.
Occupational diseases were associated with six hazards, led by chemicals, primarily nickel compounds. Compared with chemicals, increased work physical demands was 3 times less likely to be a cause of health disorders, noise was 5 times less likely, fibrogenic aerosols were 8 times less likely, whereas hand-arm and whole-body vibration explained only a few cases. In 99% of cases, hazards could affect workers because of outdated technological processes, equipment design flaws and outdated industrial sanitary installations. The other circumstances were not significant ().
Table 1. Conditions for occupational pathology.
Respiratory diseases were almost half of all diagnoses (). Injuries, intoxication and other external causes, as well as musculoskeletal and ear diseases (noise effects on inner ear) were 2.5–3.5 times less prevalent. Nervous system, malignant neoplasms and skin diseases were classified as the fifth through the seventh ranks in the overall structure. Malignant neoplasms (n = 30) with an unfavourable prognosis are particularly important for the nickel industry [Citation23–25]. This group did not differ from other employees in terms of age (52.3 ± 1.2 years), length of service (25.1 ± 1.1 years) and sex (men − 83.3%, women − 16.7%). In 17 (56.7%) cases, malignant process was caused by nickel, nickel oxide, nickel sulphide, a mixture of nickel compounds in the form of matte, nickel concentrate, recycled dust of sewage treatment installations (the short-term maximum permissible concentration (MPC) for nickel is 0.05 mg/m3). In 13 (43.3%) cases, nickel salts in the form of hydroaerosol were recognised as the cause of the disease (the short-term MPC for nickel is 0.005 mg/m3). 14 employees, MPC was exceeded 2.1–5.0-fold, in 8 employees 5.1–10.0-fold, in 3 employees 10.1–50.0-fold, and in 5 employees more than 50-fold. MPC exceedance was due to equipment design flaws (n = 9), outdated sanitary installations (n = 5) and outdated technological processes (n = 16). Detected neoplasms were localised in the bronchi and lungs (n = 12), stomach (n = 6), kidneys (n = 4), larynx (n = 4), nasal cavity (n = 2) with the remaining one case in the oral cavity and one more in the bones.
Table 2. Structure of occupational pathology.
The most common nosologies were associated with the exposure to nickel compounds, including chronic bronchitis, chronic intoxication and bronchial asthma; noise, including sensorineural hearing loss; and labour severity, including radiculopathy.
We found significant fluctuations in the number of occupational diseases detected annually for the first time (from 3 to 79 cases) and patients with occupational pathology (from 3 to 78 people) during the last fifteen years. In general, both tended to decrease, showing downward trend, but more pronounced in relation to the number of employees ().
Figure 1. Annual number of newly diagnosed occupational diseases and workers with occupational pathology in 2007–2021.
At the time of the initial occupational diagnosis, one occupational disease was observed in 327 (73.6%) employees, who were included in the first group. The second group was formed of 117 (26.4%) workers, who were multimorbid. Of these, two diseases were diagnosed in 66 (14.9%), three in 22 (5.0%), four in fifteen (3.4%), five in eleven (2.5%) and six in three (0.7%) workers. During the first five years of the observation, the number of sick persons and diseases was about the same, as opposed to the last 5 years, when several diagnoses were found in one employee. There was no occupational multimorbidity in 2007, which contrasts 2021, when 83.3% of employees had more than one diagnosis. On average, there were 1.48 ± 0.05 diseases in one employee in 2007–2021, growing 3.17-fold within 15 subsequent years ()
Figure 2. Growing number of occupational disease diagnoses per employee from 2007 till 2021.
What were the causes of multimorbid occupational pathology and what were its clinical differences? When compared to the first group, workers in the second group were older (54.4 ± 0.6 and 52.5 ± 0.3 years, p = 0.005) and worked longer (26.8 ± 0.7 and 24.8 ± 0.4 years, p = 0.013); however, the number of occupational diseases in one employee was not associated with age or work duration at the time of initial diagnosis (). There were more women in the second group (28.2% and 17.1%, р = 0.011), but no difference was found in the number of diagnoses between females (3.06 ± 0.21 cases) and males (2.74 ± 0.12 cases) (р = 0.188).
Table 3. Age, length of service and number of occupational diseases per employee.
One occupational hazard was associated with a multimorbid occupational disease in only 29 (24.8%) workers, including chemicals in 25 cases and labour intensity in 4 cases. In the remaining 88 (75.2%) employees, the multimorbid occupational pathology was associated with a combination of 2–4 hazards. The contribution of chemicals and fibrogenic aerosols fell with the simultaneous increase of labour severity, as opposed to their structure in the first group. When the circumstances of occupational pathology were considered, outdated sanitary facilities were most meaningful in the first group, contrasting with the outdated technological processes in the second group ().
Table 4. Occupational hazards and circumstances for occupational pathology.
The prevalence of multimorbid occupational pathology was associated with the worker’s position, and in this analysis, we only included positions with more than ten workers. Multimorbidity was observed in 56.3% of finished products cleaners, 50.0% of crane operators, 34.5% of hydrometallurgists, 23.3% of repairmen, 22.6% of electrolysis workers, 22.2% of foremen, 19.4% of smelters and 8.3% of electricians. Final product cleaners multimorbidity was more prevalent compared to repairmen (p = 0.016), electrolysis workers (p = 0.009), foremen (p = 0.042), smelters (p = 0.004) and electricians (p = 0.008). Similarly, multimorbidity prevalence in crane operators exceeded those of repairmen (p = 0.015), electrolysis workers (p = 0.006), smelters (p = 0.002) and electricians (p = 0.012).
The occupational disease structure differed between the two groups. Workers with one diagnosis had a higher proportion of respiratory diseases and malignant neoplasms, whereas multimorbid patients had more diseases attributed to “Injuries, intoxications and other external causes”, musculoskeletal and nervous systems ().
Table 5. Occupational diseases categories.
Chronic bronchitis was the most common disease in the first group (48.0%) with much lower prevalence of sensorineural hearing loss (12.8%), chronic nickel and other metals intoxication (9.5%), bronchial asthma (7.0%) and radiculopathy (3.4%). In workers with multimorbid pathology, the most common diagnoses were chronic nickel and other metals intoxication (22.1%), bronchial asthma (13.9%), sensorineural hearing loss (12.4%) and mono-polyneuropathy (7.9%).
In case of two diseases detected in one employee, a combination of chronic nickel intoxication with bronchial asthma (23.5%) or noise-induced hearing loss (22.1%) were most often found. In the case of three simultaneous diseases, chronic nickel intoxication and bronchial asthma were most often combined with noise-induced hearing loss (22.7%) or with diseases of the upper respiratory tract (18.2%). When four, five or six occupational diseases were combined in one person, there was no clear predominance of any of them.In workers with malignant tumours, multimorbidity was observed in only 5 out of total 30 cases. Sensorineural hearing loss was the second disease in two cases, whereas bronchial asthma, chronic laryngitis and polyneuropathy were the concurrent diagnoses in one case each.
Discussion
The current study of the multimorbid occupational pathology in nickel industry workers has established a number of facts that deserve attention and discussion. Firstly, with initially no cases of occupational multimorbidity in 2007, already 83.3% of employees had it in 2021. Secondly, we found a 3.17-fold increase in the number of occupational diseases newly diagnosed in one employee time over the past 15 years (2007–2021). Thirdly, workers with newly diagnosed multimorbid pathology were older and attained more years of service, as well as with a greater proportion of women among them. Fourth, multimorbid pathology in 75% of cases was associated with the combination of 2–4 occupational hazards, with prevailing chemicals and labour severity. Fifth, multimorbid occupational disease showed larger proportion of chronic metal intoxication, diseases of the musculoskeletal and nervous systems, as well as smaller proportions of respiratory diseases and malignant neoplasms.
The presented facts yield the most probable causes of multimorbid occupational disease in nickel industry workers. Firstly, that was increased work duration, which is directly associated with increased exposure occupational hazards. The employee’s willingness to extend employment cannot be justified, since it entails worse health effects [Citation31,Citation32]. Secondly, this reflects failure of periodic medical examinations to accurately verify health status of an employee [Citation33]. Such examination fails to ascertain the best time for safe employment or contract termination in harmful working conditions. The reason for such inefficiency may be both poor diagnostic equipment and their insufficient training in early occupational diagnosis [Citation34]. Thirdly, multimorbid pathology is a consequence of the combined effects of several hazards, which is mainly due to outdated technological processes. The highest prevalence of multimorbidity among cleaners and crane operators coincides with the data that these workers are most prone to occupational disease [Citation18]. In general, all these data indicate the need to improve working conditions and workers’ personal and collective protection.
The higher prevalence of multimorbid pathology in women necessitates further research. One explanation is the predominance of women (70.6%) in the groups of crane operators, in which the level of multimorbidity is 50.0%. Another explanation is hypothesised greater sensitivity of the females to nickel production hazards, which leads to the spread of pathological changes beyond the target organs, such as upper respiratory tract and bronchi [Citation35]. Seldom diagnosed occupational multimorbidity in workers with malignant tumours is probably explained by a specific approach practiced by doctors assuming that detecting one serious disease with an unfavourable prognosis to receive appropriate compensation is sufficient.
We note that the Order of the Ministry of Social Development of Russia dated 27.04.2012 No. 417n “On approval of the list of occupational diseases”, which reserves the diagnosis of chronic intoxication with nickel and its compounds, including such manifestations as chronic bronchitis, chronic obstructive pulmonary disease, pneumofibrosis and nasal septum erosion, may have affected the number of diagnosed diseases in nickel production workers, and that was a limitation of our study.
Conclusion
This is the first study to demonstrate that 24.6% of nickel industry workers with newly identified occupational diseases had a multimorbid disease (2–6 diagnoses) with worse prognosis. Its prevalence increased from 0% in 2007 to 83.3% in 2021. Occupational multimorbidity is associated with an increase in exposure to a combination of occupational hazards, primarily chemicals and increased work physical demands, outdated technological processes, and working conditions of such occupations as finished products cleaners and crane operators. Respiratory (31.5%) and musculoskeletal (23.0%) diseases are the most common in a multimorbid combination. Multimorbid diseases can be better prevented with improvement in working conditions and better quality of periodic medical examinations, which will allow to timely associate employees’ health status with the occupational hazards in the workplace.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
All data relevant to this manuscript are in the body of the manuscript.
Additional information
Funding
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