Spirometry and respiratory disease risk factors in firefighters in Almaty

Introduction

The profession of a firefighter is characterized by a high probability of contact with harmful factors, even despite the use of modern respiratory protection [1]. International publications contain numerous studies on the impact of occupational hazards in the workplace of a firefighter on the indicators of external respiratory function and the risk of developing certain respiratory diseases [2][3]. There are also separate hygienic studies of the concentration of harmful pollutants in the air [4–8]. However, the issue of the state of external respiratory function assessed by spirometry remains understudied, and single studies provide contradictory results.

Chronic obstructive pulmonary disease (COPD) is one of the most common human diseases and is the fourth cause of death because of the widespread occurrence of its risk factors and steadily progressing course [9]. Air pollution, including smoking, both active and passive (exposure to secondhand smoke), occupational hazards, and atmospheric air pollution are some of the most studied causes of this disease [9]. Approximately, every tenth inhabitant of the planet will get COPD during their life depending on the place of residence, the severity of the influence of risk factors, and other factors [10]. In Kazakhstan, the overall prevalence of COPD, verified by modern spirometry standards, was studied only in the largest city of the country Almaty [11], while the quality of spirometry, the degree of its use, timeliness of new cases detection, quality of treatment and adherence to treatment, and disease control remain completely unstudied.

Exposure to smoke, dust, gases, and steam in the workplace is an established and one of the most common risk factors for COPD, as well as several other respiratory diseases. According to the largest systematic review of the damage from these occupational exposures in the occurrence of respiratory pathology, the population attributable risk of developing COPD from them can reach 14%, and chronic bronchitis — 13% [12]. According to international publications, this issue was insufficiently studied in the countries of the former Soviet Union. Only a few studies paid proper attention to the role of occupational factors in the development of this disease, and the diagnosis was confirmed accordingly [13].

The aim of the study was to assess respiratory complaints and indexes of external respiratory function, as well as individual risk factors of respiratory diseases in employees of the firefighting service of Almaty.

Materials and Methods

The authors conducted a cross-sectional study of the indicators of pulmonary function, as well as selected indicators of respiratory health in employees of the Almaty City Fire Department as part of the annual periodic medical examination. Such periodic medical examination of employees of the fire protection service is conducted once a year at the polyclinic of the Department of Internal Affairs of the city of Almaty and is regulated by the relevant decree of the authorized body. This paper provides the results of the annual medical examination of workers in 2020. The study was approved by the Bioethics Committee of Al-Farabi Kazakh National University, and each employee signed a written informed consent to participate in the study. All employees of the city firefighting service referred by the HR for medical examination were included in this survey; however, some of those who were temporarily on a long business trip in other regions or on vacation were not included in the study.

Each employee was offered a questionnaire that included basic demographics (year of birth, sex, address, place of residence (city or region)), occupational history (total work experience, length of service in the fire department, current position), questions on respiratory disease risk factors, respiratory disease symptoms, and respiratory anamnesis. The questionnaire comprised 23 questions. The risk group included such risk factors as cigarette smoking, exposure to secondhand tobacco smoke, use of solid fuel for home heating and (separate question) for cooking, physical activity level, and alcohol use. The authors assessed smoking status using three questions (“Have you ever smoked cigarettes?”, “Do you smoke?”, and “Do you smoke daily?”) to place the participant in one of four categories (never smoker, former smoker, occasional smoker, and daily smoker). In addition, daily smokers had to specify the average number of cigarettes smoked per day and years of the smoking experience.

Physical activity levels were assessed with two questions: “Do you walk 10,000 steps or 6 kilometers every day, including weekends?” and “Do you do any sports or physical activity at least 3 times a week regularly?” Alcohol consumption was assessed by the question “Choose the answer that best describes your level of alcohol consumption”. A separate section of the questionnaire was devoted to identifying typical respiratory complaints. The authors used the CAT (COPD Assessment Test) questionnaire, which comprises eight questions to rate the severity of each individual symptom on a scale of 0 to 5, with a total score ranging from 0 to 40. This questionnaire is widely used to assess the severity of complaints and symptom burden in chronic respiratory disease patients, e.g., to stratify COPD patients into groups A, B, C, and D in the Global Initiative for COPD (GOLD) documents [9]. Thus, patients with a total score greater than 10 are usually considered to have “many symptoms”. To assess dyspnea severity, the authors also used the GOLD-recommended Modified Medical Research Council (mMRC) questionnaire, which consists of only one question and allows a choice of five answer choices. Previous diagnoses of chronic bronchitis, asthma, COPD, and allergic rhinitis were identified by the question “Has a doctor ever diagnosed you with...?”.

Assessment of pulmonary function, or spirometry or spirography, was performed in the morning after blood sampling, before the examination by doctors of various specialties, on the device MAS-2C made by Belintelmed (Republic of Belarus). Patients were advised not to smoke for at least 2 hours before the examination, and the examination was performed after 10 minutes of rest. At least three identical vital capacity (VC) maneuvers and three forced vital capacity (FVC) maneuvers were performed with reproducibility of less than 100 ml, according to the latest recommendations of the European Respiratory Society and the American Thoracic Society [14]. The authors calculated actual values of VC, FVC, and forced expiratory volume in the first second (FEV1), which were then divided by the proper values calculated using the GLI-2012 set of proper values based on the patient’s sex, height, and age. The main indicator of obstructive syndrome presence in this study was considered to be a decrease in FEV1/FVC less than a low level of normal (LLN), which allows a more balanced assessment of obstruction presence in comparison with the criterion of FEV1/FVC<70%. If a patient was found to have a decrease in FEV1/FVC below the threshold value, a bronchodilatation test was performed with 300 µg salbutamol. If the value remained below the threshold value (negative bronchodilatation test) after the test, the patient was classified as having obstructive syndrome.

During the analysis of the obtained data, the distribution of all data sets was checked for compliance with the law of normal distribution. If the data were distributed normally, parametric tests were used to describe and analyze it; otherwise, nonparametric tests were used. In the first case, the data in the tables are presented as mean with standard deviation, and in the second case — as median with interquartile range (IQR). The authors used Student’s test to determine the probability of difference when comparing two sets of normally distributed data. Non-normally distributed data were analyzed using the Mann-Whitney test. To compare three or more groups, the authors used analysis of variance or the Kruskal-Wallis test, respectively. Binary variables were described as the percentage of the total number of observations in the group, and the χ² test for contingency tables was used to compare the groups. The differences with p<0.05 were considered statistically significant. All calculations were performed in the NCSS-2021 program.

Results

A total of 1,379 employees of the Almaty city fire department of various specialties were included in the study. Of them, 1,259 were men (91%). The age of the study participants was 19 to 49 years old, with a significant predominance of younger individuals. Females were significantly older than males (Table 1). Men also differed from women in most of the demographic and lifestyle factors studied. The total work experience ranged from 0.1 to 35 years, with a median value of 5 years. At the same time, the relatively short length of work experience was mainly because of the predominance of men at the beginning of their working life. Because there was a strong correlation between age and total work experience (r=0.92) and fire department work experience (r=0.89), the authors included only one of these variables (age) in further analysis.

Overall, 41% of workers smoked in the study group. There were significantly more daily smokers among males than females (43% vs. 16%, respectively), and there were more women who had never smoked. Among daily smokers, the median number of cigarettes smoked per day was 7 (IQR 2-10), and the smoking experience was 5 (IQR 3-10) years. The number of smoked cigarettes per day (7 (IQR 3-11.5) for women and 7 (IQR 4-10) for men) and smoking history (6 (IQR 4-15) years for women and 5 (IQR 3-10) years for men) did not differ when comparing smokers of the two sexes. It should be noted that the vast majority of those surveyed were exposed to secondhand smoke at work or at home. One quarter used solid fuel for heating, but only 57% exercised regularly (3 times a week or more).

Since there were significant differences between men and women in most demographic indicators, including the professional structure, further analysis was conducted only in the group of males. Of the 1,259 male firefighters, 64% were firefighters, senior firefighters, squad leaders, unit chiefs, and their deputies. One-fifth of those surveyed were drivers and driving instructors. Workers in other professions accounted for only 16%. The number of points for the answer to the first question of the CAT questionnaire ranged from 0 to 4, to the second question — from 0 to 3, i.e., the severity of respiratory symptoms in the surveyed group was minimal. The median value of the first and second questions for the entire group was 0 (IQR 0-0), which can be interpreted as the absence of any respiratory symptoms in the overwhelming majority of the examined workers. There were no statistically significant differences between the groups. The severity of dyspnea was also minimal: the total mMRC score ranged from 0 to 1, with a median value of 0 (IQR 0-0), also without differences between groups.

Only 108 workers (9%) had seasonal allergies (Table 2). None of the 1,259 workers had a history of asthma, 2% had previous chronic bronchitis, and only 1% had allergic rhinitis. When comparing the groups according to actual values of FEV1 and FVC, there was a statistically significant decrease in individuals of the third group in both cases (not directly involved in firefighting) compared to firefighters and fire truck drivers. By height and gender composition (all men) (two of the three factors determining the proper values of the actual values of spirometric parameters), this group did not differ from the other two. Pulmonary function values of firefighters who were exposed to aerosol in the workplace were comparable to those who did not face harmful factors. In general, the prevalence of obstructive ventilation disorder in the studied groups was low: only 2% of workers were found to have lower FEV1/FVC less than LLN.

Discussion

This study is the first generalization of the examination of firefighting service personnel of Almaty. All employees at the annual periodic medical examination underwent high-quality spirometry and an analysis of the association with respiratory history. Low severity of respiratory complaints was detected in the examined employees of the fire department. Bronchial obstruction was established only in 2% of the employees according to the criterion of the decreased post-bronchodilation value of the FEV1/FVC index. Risk factors for respiratory diseases, such as smoking, exposure to secondhand smoke, and use of solid fuel for cooking, were quite common. This study allowed the authors to identify individuals at risk of COPD when exposed to a set of occupational factors for dynamic monitoring as part of periodic medical examinations.

Firefighters and other firefighting service workers are a special category of employees with a significant combination of harmful factors in the workplace. Thus, the most significant factor in this category was the inhalation of aerosol as a combustion product during firefighting [15][16]. Stress [17][18] and occupational burnout [19], as well as other psychosocial effects of the production process, were also important. Despite numerous studies of this category of workers, the issues of occupational pathology and risk factors remain insufficiently studied. Assessment of the rate of the annual decrease in FEV1 and the risk of COPD in firefighters needs further investigation.

In general, the prevalence of bronchial obstruction as a spirometric criterion of COPD in the studied group of male firefighters was very low, not exceeding 2%. Given the high level of exposure to respiratory aerosol, the expected prevalence of COPD should be higher than in the general population, which was 6.4% among men in the age group of 18 years and older, according to a population study of Almaty city residents [11]. A decrease in the detection of this pathology among firefighters, despite approximately the same prevalence of smoking, may be because of the so-called healthy worker effect, described in the literature in workers of various professions [20][21].

The results of a study of the severity of respiratory complaints in firefighters compared to other groups were controversial. The very low prevalence of respiratory complaints in this study is not supported by studies conducted in other countries [22][23]. The studies of the pulmonary function parameters in firefighters also provide heterogeneous results [24]. Differences in the severity of respiratory complaints and respiratory function parameters are likely to be associated with the duration of exposure, the use of personal protective equipment, other risk factors, and genetic characteristics. All these questions require further study.

This work has some limitations, which should be considered when planning future studies. First, this study was conducted on fire department workers in Almaty only, so the picture of the overall prevalence of obstructive syndrome, respiratory complaints, and COPD risk factors may not reflect the situation in other regions. Second, there is no comparative analysis of men’s and women’s exposure to workplace hazards because of the small number of women in the fire department. Third, this study did not include prospective observation of pulmonary function indicators in dynamics, and all the results and conclusions of this work are built on a one-stage, so-called cross-sectional section. It is necessary to conduct prospective studies of spirometry parameters to calculate the rate of annual change of the most significant indicators.

Conclusions

The conducted study of all personnel of the firefighting service of Almaty revealed a low prevalence of respiratory complaints, as well as bronchoobstructive syndrome, in some individuals verified by high-quality spirometry. Its rate was significantly lower than in the general population of Almaty, which may be explained by the effect of a healthy worker.

It is necessary to plan and conduct prospective observations on the indicators of the pulmonary function of firefighters for a dynamic assessment of respiratory health.

Authors’ contribution:

D.V. Vinnikov, L.A. Strizhakov, S.A. Babanov — research design development;

D.V. Vinnikov, Z.D. Tulekov — obtaining and analysis of the data;

D.V. Vinnikov, S.A. Babanov, N.E. Lavrentyeva — writing the text of the manuscript;

D.V. Vinnikov, Z.D. Tulekov, L.A. Strizhakov — review of publications on the topic of the article.

Conflict of interest. Authors declares no conflict of interest.