S.A. Syurin, MD, DrMedSci.,

Kola Research Laboratory for Occupational Health (Kirovsk, Russia)

ON THE PREVALENCE OF CHRONIC RESPIRATORY DISEASES IN THE POPULATION OF MURMANSK REGION

Introduction. Chronic bronchopulmonary diseases (CBPD) are rated among global priority health and social problems due to their increasing prevalence and magnitude of economic losses [1]. According to many epidemiological studies chronic bronchitis (CB) and chronic obstructive pulmonary disease (COPD) are detected in 1-10%, and asthma - in 1-18% of the total adult population [1, 3, 4, 6]. Despite their high prevalence, it is a universally recognized fact that CBPD are not timely and completely diagnosed, particularly COPD. Thus, according to the Ministry of Health of Russia in 2003, there were approximately 1 million patients with COPD, whereas according to the epidemiological studies their number was expected to be over 11 million [2]. Improvement of the quality of diagnostic work in Russia led to an increase in the number of patients with CB, COPD and emphysema to 2.4 million, and asthma - to 1.4 million people in 2007 [4, 6]

The aim of the study was a comparative investigation of the CBPD prevalence rates obtained according to the attendance rates at the health care facilities of the Murmansk region, and in the surveys of industrial workers during periodic medical examinations.

Materials and methods. In 2008-2010, 8125 industrial workers underwent annual medical examinations targeted at the determination of respiratory diseases prevalence in the adult working population. The surveyed persons were employees of the largest industrial companies in the mining and metallurgical complex of the Kola North located in five administrative districts of Murmansk region. Working conditions at all enterprises created an increased risk of CBPD due to air pollution and adverse parameters of workplace microclimate.

Of the total number of 2313 surveyed employees of the Kola Mining and Metallurgical Company (Kola MMC) 841 persons were engaged in underground mining of copper-nickel ore at the "Severny" mine in the town of Zapolyarny, Pechenga district. The larger part of Kola MMC workforce were employed in electrolytic production of nickel (1028 persons), carbonyl production of nickel (188 persons), pyrometallurgical and electrolytic production of copper (595 persons) and in the auxiliary shops of the company (502 persons) at the "Severonikel" plant in the town of Monchegorsk. Of the 4492 surveyed employees of JSC "Apatite" 3021 workers carried out mining of apatite ore in 2 surface and 2 underground mines. Another 801 and 790 persons were engaged in transportation and enrichment of apatite ore, respectively. All production facilities of JSC "Apatite" are located in the towns of Kirovsk and Apatity. Among the examined workers there were also 479 employees of the Kandalakshsky aluminum plant (the town of Kandalaksha) who were engaged in electrolytic production of aluminum (309 persons) and in service shops (170 persons).

Data on the CBPD prevalence in Murmansk region in 2009 were obtained from the Statistical Book "Morbidity of Murmansk region population. 2005-2009".

The results. Analysis of the total CBPD prevalence rates showed substantial variation of indicators in the territorial-administrative units of the Murmansk region and the lack of correlation between the prevalence rates of CB, COPD and asthma. Thus, at the same time Pechenga district experienced the highest CB prevalence rate and the lowest COPD prevalence rate although these two diseases have similar etiology and pathogenesis. The minimum asthma prevalence was found in Kandalaksha, and the maximum - in Monchegorsk. The maximum and minimum territorial prevalence rates of CB differed 4.15 times, COPD - 2.70 times, asthma - 2.90 times. The prevalence of respiratory diseases was not associated with the current territorial industry. With the same type of mining and chemical manufacturing in the Kirovsk-Apatity area, CB prevalence in Kirovsk was 1.79 times higher, and asthma - 1.29 times lower than in Apatity.

For the integrated assessment of CBPD prevalence we have ranked the five studied areas. The highest prevalence for each nosological form was estimated as five points, and the lowest - as one point. In accordance with aggregate number of points, the most favorable epidemiological situation on CBPD was detected in Kandalaksha (6 points). The ranking of other administrative districts was as follows: Pechenga (8 points), Apatity (9 points), Monchegorsk (10 points) and Kirovsk (12 points). In general, regional indicators in Murmansk region, in comparison with the federal level, significantly differed only in CB prevalence, which was two times lower than in the country (Table 1).

Table 1

Totall CBPD prevalence in administrative districts of Murmansk
  region, in Murmansk region in general and in Russian Federation in 2009 (%)

Administrative unit	CB	COPD	Asthma
Town of Apatity	0,39	0,80	1,19
Town of Kandalaksha	0,64	0,43	0,60
Town of Kirovsk	0,70	0,89	0,92
Town of Monchegorsk	0,60	0,68	1,74
Pechenga district	1,62	0,33	0,71
Murmansk region	0,72	0,50	0,98
Russian Federation	1,47	0,61	0,82

The CB and COPD prevalence rates did not differ significantly in various groups of surveyed industrial workers. At the same time the prevalence of asthma ranged substantially from 2.71% (Kandalakshsky aluminum plant) to 0.61% (“Severny” mine of Kola MMC). A similar cumulative scoring of morbidity rates showed the most favorable epidemiological situation among employees of JSC "Apatite" (4 points). Next position, in keeping with the degree of deterioration, was taken by “Severny” mine of Kola MMC (6 points). The plant "Severonikel" of Kola MMC and Kandalakshsky aluminum plant (10 points) showed the worst results (Table 2).

Comparison of CBPD morbidity rates (calculated from the number of persons who sought medical assistance in the local health care facilities) of the adult population in the five studied territorial administrative units and CBPD prevalence rates in employees of mining and metallurgical enterprises (active detection health disorders during medical examinations) revealed sharp differences on the two nosological forms: CB and COPD. The CB and COPD prevalence rates in workers of industrial enterprises were 14.7 and 3.98 times higher (respectively) than the official figures. Prevalence of asthma in the two compared groups of population was not significantly different.

Table 2

Totall CBPD prevalence in industrial workers in 2008-2009 (%)

Enterprise	CB	COPD	Asthma
JSC "Apatite"	9,85	1,95	0,81
"Severonikel" plant Kola MMC	11,35	2,56	1,42
"Severny" mine Kola MMC	10,18	2,21	0,61
Kandalakshsky aluminum plant	14,61	2,09	2,71
The average for the four enterprises	10,59	1,99	1,06

Discussion. An analysis of official statistics showed chaotic distribution of the CBPD prevalence rates in the adult population in five administrative-territorial formations of Murmansk region. It also showed no signs of local influence of non-ferrous metallurgy enterprises on respiratory health of the population within their locations. This is contrary to the results of previous studies that have proven that working conditions and environmental changes due to production of nickel and aluminum substantially increase the risk of COPD, CB [2] and asthma [5].

It is important that medical examinations of employees of mining and metallurgical companies reveal a significantly higher CB and COPD prevalence rates compared with the adult population of the region as a whole. This fact, which at first glance seems obvious, requires explanation. The most obvious argument is that characteristic for the mining and metallurgical industry hazards of work and labor process substantially increase the risk of respiratory pathology. For example, the prevalence of COPD in smoking metallurgical workers with long experience can reach 35.1% [2]. However, it is known that the CBPD prevalence in employees of enterprises with hazardous working conditions is also influenced by factors with opposite effect. There are at least two such factors. First, a pre-employment medical examination, which places a barrier for access to professions with hazardous working conditions for those with chronic respiratory diseases. This creates the effect of a «healthier worker», than the population of the area as a whole. The second factor is the well-known phenomenon of concealment of disease symptoms during medical examinations («underreporting») due to socio-economic reasons. It arises because of the fear to lose or to have only limited access to higher paying jobs with harmful working conditions.

Taking into account the above, it appears that a more likely reason for the differences found in the CBPD prevalence rates is a way of getting information. Official statistics use the data from health care institutions, mainly derived from the information about requests for medical attention. Of course, these statistics can not be complete. Official data are often an order of magnitude lower than in epidemiological studies because it does not include information about the initial stages of diseases which do not require treatment-seeking and issuing of temporary disability certificates. In contrast, a complex clinical and functional examination during periodical medical examinations helps detect early stages of respiratory disorders. Also, this occurs in those cases when for some reasons (including the above mentioned social reasons), the employee hides truthful information about his (her) health status. Medical and social importance of early stages of CBPD consists in poor predictability of their potential transfer (without proper prevention measures) into diseases with severe clinical manifestations and poor prognosis of medical interventions [3, 6].

There should be an explanation for the lack of significant differences in the asthma prevalence according to official statistics and medical examinations of industrial workers. Probably in health care settings cases of asthma are recorded better than that of CB and COPD. On the other hand, three factors may reduce asthma prevalence in employees exposed to hazardous working conditions. First, it is detection of asthma cases at the stage of pre-employment medical examination, which is a contraindication to beginning professional carrier in a wide range of occupations linked to workplace hazards. Secondly, it is deliberate hiding of mild asthma cases by employees («underreporting»). These cases can not be identified with the help of diagnostic facilities available in the standard and targeted medical examination. Third, it is the known phenomenon of resignations of workers with symptoms of workplace asthma (both diagnosed and undiagnosed asthma patients) which remain unregistered according to official health statistics. The impact of these three factors may result in a falsely reduced asthma prevalence rate in industrial workers.

Conclusion. From practical and scientific points of view, there is a need to clarify CBPD prevalence in the population of Murmansk region. Such information can be obtained through a targeted clinical and functional examination of a representative group of adult population, including industrial employees with hazardous workplace conditions.

References

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2. Chronic obstructive pulmonary disease: a practical guide for physicians / ed. A.G. Chuchalin. - M., 2004 [in Russian]..

3. Guidelines for the diagnosis, treatment and prevention of asthma / ed. A.G. Chuchalin. – M., 2005 [in Russian]..

4. Leshchenko I.V. Key questions of early treatment of chronic obstructive pulmonary disease. Consilium Medicum. 2008; 10: 46-50 [in Russian]..

5. Vasilieva O.S. Occupational asthma: clinical variants and diagnosis. Pulmonologiay. 2005; 5: 61-68 [in Russian].

6. Yemelianov A.V., Sergeeva G.R. Asthma: How to improve long-term outcomes? Consilium Medicum. 2010; 12: 80-84 [in Russian].