Respiratory Symptoms and Associated Factors among Cement Factory Workers and Civil Servants in North Shoa, Oromia Regional State, North West Ethiopia: Comparative Cross Sectional Study

Kebede Siyoum¹, Kassahun Alemu² and Manay Kifle^2*

¹North Shoa, Oromia Regional State, Labor and Social Affairs Office, Fitche, Ethiopia

²Department of Environmental and Occupational Health and Safety, Institute of Public Health, College of Medicine and Health Science, University of Gondar, P. O. Box. No. 196, Ethiopia

*Corresponding Author:

Manay Kifle
Department of Environmental and Occupational Health and Safety
Institute of Public Health, College of Medicine and Health Science
University of Gondar, P. O. Box. No. 196, Ethiopia
Tel: +251913372878
E-mail: manay2000@gmail.com

Received date: September 19, 2014; Accepted date: October 25, 2014; Published date: October 29, 2014

Citation: Siyoum K, Alemu K, Kifle M (2014) Respiratory Symptoms and Associated Factors among Cement Factory Workers and Civil Servants in North Shoa, Oromia Regional State, North West Ethiopia: Comparative Cross Sectional Study. Occup Med Health Aff 2:182. doi: 10.4172/2329-6879.1000182

Copyright: © 2014 Manay Kifle et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Background: In Ethiopia, workers are not well informed about the health effects of their work environment and occupational related respiratory symptoms are extensively high especially, in cement factories. Objective: This study was designed to determine prevalence of respiratory symptoms and associated factors among Cement Factories Workers and Civil Servants. Methods: An organization based comparative cross sectional study were done on 266 cement factories and 269 civil servant workers, using pre-tested questionnaire. Simple random sampling method was used to select participants from Civil Servants, while working section stratification with simple random was applied to select participant Cement Factories Workers. The data were entered to Epi-info version 7 and exported to SPSS version 20 for analysis. In the bivariate logistic regression variables with p≤0.2 were fitted to multivariate logistic regression and finally, variables with p<0.05 was considered as significantlly associated. Result: The prevalence of respiratory symptoms was 66.2% in cement factories workers and 31.2% in Civil Servants with a significant difference (p<0.001). The odds of developing respiratory symptoms were higher among exposed groups (AOR=7.60, 95% CI: 4.93-11.89). Respiratory symptoms were higher in ≥45years old workers (AOR=4.67, 95% CI: 1.16-18.74) than <25years old workers. Night shift workers were more likely to develop respiratory symptoms (AOR=2.07, 95% CI: 1.02-4.18) than their counterpart. Having trained in occupational health and safety (AOR=0.18, 95% CI: 0.09- 0.36) and education above secondary school (AOR= 0.15, 95% CI: 0.03-0.78) were protective for respiratory symptoms in the exposed groups. Smoking was positively associated with respiratory symptoms in both cement factories workers (AOR=11.7, 95% CI: 1.6- 85.76) and unexposed groups (AOR=3.4, 95% CI: 1.19-9.05). Conclusion: Respiratory symptoms were higher among cement factories workers than civil servants, so engineering and administrative control measures are needed to reduce the exposure of workers to cement dust.

Keywords

Cement dust, Ethiopia, Respiratory symptoms

Background

World health organization (WHO) 2010 reported that non-communicable diseases (NCD) were the leading cause of death resulting in loss of life of about 57 million people globally in 2008. From this, 36 million (63%) were due to cardiovascular diseases, cancer, respiratory diseases and diabetes [1]. From those non communicable diseases, respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD), contributed 4.2 million deaths. These problems always come after different respiratory symptoms. From those respiratory diseases occupation related respiratory diseases account 10 - 20%. Those occupational respiratory diseases accounts up to 30% of all registered work-related diseases with up to 50% prevalence among workers in high risk sectors such as mining, construction and dust generating works. Respiratory symptoms are preceding those occupational related respiratory disease and they are among the major causes of consultation at primary health care centers [1-4]. In low and middle income country, including Africa, occupational respiratory symptoms and diseases are huge burden due to the expansion of investments, high unemployment rate; workers are probably more likely to continue working even when having poor health status and outdated machine that are producing excessive dust to work environment are still used for production purpose [1,4]. Ethiopia is one of the low income countries, occupational related respiratory symptoms are extensively abundant and the expansion of investment, especially in cement product in Ethiopia exposes workers for dusty environment and workers are not well informed about health effect their work environment [1,4].

Cement is produced typically through a series of processes that includes quarrying, crushing, raw milling, blending, kiln burning to form clinker and homogenous blend of limestone and clay, which is then adjusted to a suitable content of Calcium, Silicon, Aluminum and Iron in a kiln [5,6]. During its heating clinker is formed, the clinker contains Calcium Silicates, Calcium Aluminates and Calcium Ferrites. Clinker is subsequently ground with gypsum and other additives, resulting in a fine particulate powder called Cement [2]. Substantial dust is emitted during these processes, exposing workers to dust [2,6]. In contact with water, clinker partly dissolves and forms an aqueous slurry of high alkalinity, giving clinker and cement strong irritant properties and cause respiratory symptoms and disease [2,7]. Dust with aero diameter of less 100µm is inhalable. In cement factories, dust is produced during crushing and grinding of raw materials, blending and kiln burning to form clinker, cement milling and packaging [7,8].

The main route of entry of cement dust particles in the body is the respiratory tract and/ or the gastrointestinal tract by inhalation or swallowing respectively. Both routes, especially the respiratory tract are exposed numerous to potentially harmful substances in the cement environment. Cement dust contains limestone, clay, calcium, silica-quartz, aluminum and iron. Some of those are irritants and fibrosis that can cause acute or chronic respiratory tract inflammation and scarring lung tissue, which is the overproduction of mucus, and lead to cough, dyspnea and others respiratory symptoms. Quartz (the common form of free crystalline silica) is highly insoluble compound, the toxicity of which is completely dependent on its penetration to the alveolar portion of the lungs that reach alveoli when enough small in size but most of time it deposited in the nose, throat, bronchi, or larger bronchiole to cause respiratory symptoms and disease Occupational lung diseases are preceded by different symptoms such as shortness of breath, cough, sputum, dyspnea, and wheeze. The existence of respiratory symptoms could indicate that there is a mild cold or a life threatening condition and show the chronic respiratory disorders [7,9,10].

Many researchers have found that the dust exposed workers in cement factory were significantly associated with high prevalence of cough, sputum, dyspnea and wheezing than the control group [6,8,11,12]. Several researchers from United Arab Emirate(UAE), Iran, Tanzania, and India show that chronic occupational exposure to dust in cement factories leads to a greater prevalence of respiratory symptoms such as Chest Tightness, Cough, Sputum, Wheezing and Dyspnea among exposed than unexposed [6,8,11,12]. However, there was a study that showed no significant difference of between exposed and unexposed workers on respiratory symptoms [13]. The expansions of labor intensive investments in developing country, especially in cement product create dusty work environment for workers and those workers are from low socioeconomic group and need special safety concern [1,4]. In Ethiopia even though the cement industry are extensively increasing, the study of respiratory symptoms and illness is limited. Studies from Dire Dawa and from two cement factories around Addis Ababa were the only existing study [5,14]. The aims of this study were to determine prevalence of respiratory symptoms in cement factories workers and civil servants and associated factors. The findings could help to policy makers and management of the organizations to develop appropriate workplace intervention measures to protect the health of their workforces.

Methods

Study area

The study was conducted in North Shoa Administrative Zone, Oromia Regional State which is one of the largest zones and well known for investment as there are rich natural resources and located 100km from Addis Ababa to Northwest of Ethiopia. Currently above 7,000 employees were employed in different private economic activities in this zone. Manufacturing contains a large percent, including three cement factories. The three cement factories have about 1011 workers and the Civil Service had 831 civil servants in the study area [15]. Currently there are three cement factories with two of them are functional and one has stopped production due to devastating accident at the workplace. Jema cement factory Share Company is one that found at Wucale district and has 437 workers out of which 77 are administrative, 112 raw material processing sections, 65 burner section, 87 clinker section and 96 cement mill and packing section. The other factory is an East Cement Share Company, which found in Degem district and has 574 workers out of which 93 are administrative, 153 raw material processing sections, 47 burner section, 103 clinker section and 178 are cement mill and packing section.The study was conducted on factory workers in two cement factories and civil servants from North Shoa Administrative Zone from March 22 to April 19, 2014.

Sample size determination

Stat Calc module of Epi Info™ 7 software was used to compute the sample size with an assumption of 95% level of confidence, 90% power, 1:1 ratio of exposed (cement factories workers) to unexposed (civil servant workers) and prevalence of cough among exposed 26.2% and among unexposed 14.1% from previous study [6]. A total of 544 (272 in each group) were the planned sample size, but during the actual data collection, a total of 535 participants (266 exposed and 269 unexposed) were included in the study.

Sampling procedure

Stratified sampling technique was used to select the study subjects in the exposed group. The workers in cement factories were stratified into Raw Mill Section, Burner Section, Clinker Section, Cement Mill and Packing Section and the sample size was proportionally allocated to these sections finally, using simple random sampling method workers were selected from each working section of the factories. The simple random sampling technique was used to select 272 participants for the unexposed group (civil servants) from 831 civil servants.

Operational definitions

Respiratory symptoms: Respiratory symptoms were defined workers who developed one or more symptom of cough, phlegm, wheezing, dyspnea, chest pain and chest tightness.

Cough: Cough was defined as cough as much as 4–6 times per day occurring for most days of the week (≥4days) for at least three months in a year and for at least two consecutive years.

Phlegm: Phlegm was classified as sputum expectoration as much as twice a day for most days of the week (≥4days) for at least three months in a year and for at least two consecutive years.

Wheeze: Chest sound whistling on expiration when have cold or occasionally apart from colds or most days or night for at least three months in a year.

Chest pain: In past two year’s chest pain that kept off work of the workers with phlegm.

Chest tightness: Tightness or constriction of the chest, occurring any time during the work shift and on any work day.

Dyspnea: Dyspnea was divided into 5 grades with the following definitions:- Grade 0: No breathlessness except with strenuous exercise; Grade 1: Breathlessness when hurrying on the level or walking up a slight hill; Grade 2: Walking slower than people of the same age on the level because of breathlessness or has to stop for breath when walking at own pace or level; Grade 3: Stopping for breath after walking about 100 yards (96 meter) or a few minutes on the level; Grade 4: Too breathless to leave the house or breathless when dressing or undressing. So, that the study was reported dyspnea grade 2 or more as an outcome American Thoracic Society [16].

Data collection tool

Interviewer administered modified standard questionnaire from American Thoracic Society [16] was used. The questionnaire was used with epidemiological studies of all respondent 13 or more age and have two parts that the first part was recommended as minimal question to be asked in every survey and followed by optional question that are left for discretion individual investigators to consider for inclusion at the end of the appropriate section of the questionnaire. The questionnaire was prepared in English then translated to Afaan Oromo (native language) and back to English to keep the consistence. Four trained nurses’ data collectors and two supervisors were assigned for data collection and practice of dust control mechanism and personal protective equipment (PPE) uses were observed in the workplace using an observational checklist.

Statistical analysis

The data were checked, coded and entered to Epi-info version 7 and exported to SPSS version 20 for analysis. Proportion, mean and standard deviation between parameters were analyzed. Pearson's X² test was used to compare both dependent and independent variable among exposed (cement factories workers) and unexposed group (civil servants). Variables that have p<0.02 in the bivariate logistic regression analysis were fitted to multivariate logistic regression analysis and finally, variables having p<0.05 was considered as significantly associated in the multivariate logistic regression analysis.

Ethical consideration

The research protocol was approved by the University of Gondar Ethical Review Board and permission letter was obtained from North Shoa Labor and Social Affairs. Verbal and written consent were obtained from all participants. Privacy and confidentiality of information given by each respondent was kept properly and personal identifiers were removed. Participants who had severe respiratory symptoms were referred to health centers for further treatment and health education was provided for other participants.

Results

Demographic characteristics

The study was conducted among 266 (49.7%) cement factories workers and 269 (50.3%) civil servants and, about 61.1% of respondents were male. The mean age of the study population was 35.6 ± 9.87 years, ranged from 19 to 68 years and the cement factories workers were significantly younger (33.5 ± 9.06years) than the civil servants (37.7 ± 10.21years) with p<0.001. Age, education, and service year were significantly different among the two groups (p<0.05) while, sex, smoking status and history of respiratory diseases were not (Table 2).

Table 2: Selected demographic characteristic of cement factory workers (exposed group) and civil servant workers (unexposed group) in North Shoa, Oromia Regional State, North West Ethiopia

Respiratory symptoms

The prevalence of respiratory symptoms in cement factories workers was 66.2% and 31.2% in civil servants with significant difference (p< 0.001). Cement factories workers reported high prevalence of cough, phlegm, dyspnea, wheezing chest pain and chest tightness than civil servants with significant difference in all symptoms (p < 0.05) (Table 1). About 12% of cement factories workers had grade III dyspnea when compared with 2.2% of civil servants similarly, 7.2% of cement factories workers had grade IV dyspnea unlike that of 1.1% civil servants and the difference is statistically significant for both grade III and IV dyspnea with p<0.05.

Table 1: Prevalence of respiratory symptoms in cement factories workers and civil servants in North Shoa, Oromia Regional State, North West Ethiopia

Factors associated with respiratory symptoms

Sex was significant in both cement factories workers and civil servant. In cement factories workers, males were more likely to develop respiratory symptoms (AOR= 5.46, 95% CI: 2.22-13.44) than females (Table 3) similarly, in civil servant workers, males were more likely to develop respiratory symptoms (AOR=3.65, 95% CI: 1.88-7.08) than females (Table 5). Cement factories workers aged 25-34years and ≥45years old were more likely to develop respiratory symptoms than <25years old workers with (AOR= 5.95, 95% CI: 1.94-18.23), (AOR= 4.67, 95% CI: 1.16-18.74) respectively (Table 3).

Table 3: Association of variable and respiratory symptoms among cement factory workers (Bivariate and Multivariate analysis) in North Shoa, Oromia Regional State, North West Ethiopia.

Higher education status was protective for respiratory symptoms among cement factory workers (AOR= 0.15, 95% CI: 0.03-0.78), compared to those had no education (Table 3). Both smokers in cement factories workers and civil servants smokers were more likely to develop respiratory symptoms. For cement factories workers, the odds of experiencing respiratory symptoms among smoker were almost 12 times compared with never smokers (AOR; 11.7, 95% CI: 1.6- 85.76) (Table 3) and among civil servant workers, smokers were 3.40 times to develop respiratory symptoms (AOR=3.40, 95% CI: 1.19-9.05) than never smokers (Table 5).

Table 5: Association of variable and respiratory symptoms among civil servant workers (Bivariate and Multivariate analysis) in North Shoa, Oromia Regional State, North West Ethiopia.

Shift work was another factor that was statically significant among cement factories workers. Those were working in night shift were two times more likely to develop respiratory symptoms (AOR=2.07, 95% CI: 1.02-4.18) than do not work the night shift. Dyspnea and chest pain were significantly associated with both evening and night shift work, while cough was more likely to develop among evening shift workers. Night shift workers were also more likely to develop wheezing than their counterpart. Among cement factories workers, training on occupational health and safety related to dust health effect was reduced respiratory symptoms by 82% (AOR=0.18, 95% CI: 0.09-0.36) (Table 3). Specially, those not trained workers were had Cough (39.4% versus 19.2%), Wheezing (47.7% versus 18.2%), Dyspnea (54.5% versus 22.7%), Phlegm (79% versus 21%), Chest Pain (81.5% versus18.5%) and Chest Tightness (81.2% versus 18.8%) than those trained. But the difference was significant only for Wheezing, Cough and Dyspnea. In case of working section of the cement factory workers, those working in Clinker Section (AOR= 8.46, 95% CI: 2.52-28.39), Burner Section (AOR= 4.59, 95% CI: 1.33-15.88) and Raw Mill section (AOR= 5.07, 95% CI: 1.77-14.48) were more likely to develop respiratory symptoms when compared with workers who work in Cement Mill and Packing Section (Table 3).

The work environment was the leading cause of difference for respiratory symptoms in the cement factories workers and civil servants. The odds of developing respiratory symptoms among cement factories workers were 7.60 times more (AOR=7.60, 95% CI: 4.93-11.89) than civil servants when adjusted for major confounders; age, smoking status, history of respiratory disease and home used energy source (Table 4).

Table 4: Association of variable and respiratory symptoms among cement factory workers and civil servant workers together (Bivariate and Multivariate analysis) in North Shoa, Oromia Regional State, North West Ethiopia.

Discussion

In this study, the prevalence of respiratory symptoms was 66.2% among cement factories workers and 31.2% among civil servant workers. Cough (32% versus 13.8%), Phlegm (30.5% versus 16.7%), Wheezing (38% versus 10.4), Dyspnea (44% versus 13.4%), Chest Pain (20.3% versus 1.5%) and Chest Tightness (42.1% versus 2.6%) among cement factories and civil servant workers respectively with significant differences.

Male, those age ≥45 years old, higher educational status, working section, history of respiratory disease, smoking, night shift work, and safety training on respiratory health were significant association with respiratory symptoms. The prevalence of respiratory symptoms, among the exposed group (cement factories workers) in the current study, (66.2%) is much higher than the study done in the United Kingdom with upper respiratory symptoms, 38.1% and lower respiratory symptoms 45.2% among organic dust exposed [17]. These differences might be due to the difference in level of concern given for workplace safety between the two countries, and the study in the United Kingdom was conducted among textile and agro-processing industries, that might not produce dust as cement factory.

The prevalence of Cough and Phlegm, both in the exposed and unexposed group in the current study, are lower than survey done on cleaners in other cement factory in Ethiopia, but almost similar, for Chest Tightness [5]. The difference of in the prevalence of Cough and Phlegm might be due to the cleaners in the former study were extremely exposed to dust. Both in the exposed and unexposed group the prevalence of Cough and Phlegm were in agreement with a study done in Tanzania [6]. But, the prevalence of Cough, Wheezing, and Chest pain in the exposed groups in the current study, were lower than the exposed workers in India [9]. The difference with Indian study, might be due to the difference in the definition of those symptoms. The Indian study, used only one year length period to said cough presence or absence while this study used minimum two years to say cough and wheezing. In the same way, for chest pain this study considered the presence of sputum with chest pain that kept off the workers from work, but in the case of the Indian study, only the presence of pain on chest.

I In the current study, there was a significant difference in all respiratory symptoms between the exposed and the unexposed group which is in agreement with studies other cement factories in Ethiopia and Iran [5,11]. In contrast with this study, in a study conducted in cement factory in United Arab Emirate (UAE) only Cough, Phlegm and Dyspnea were significantly varies among exposed and control group [8]. These differences might be due to the study in the UAE used administrative workers as a control group from the same organization and, these administrative workers had a chance of exposure to dust. Study finding from Ghean, Iran show the prevalence of respiratory symptoms among exposed and unexposed were not significantly different, which contrasts with the finging of current study [13].

The current study shows that, there were no significant difference of major confounding factors such as; sex, history of respiratory disease and smoking status between the exposed and unexposed groups so, the difference of respiratory symptom between them might be due to the exposure difference to cement dust. This is consistent with studies from Ethiopia, Tanzania, UAE, Iran, and India [6,8,11,12,14]. The result from work place observational show that neither of the two cement factories were was trying to apply the engineering dust control mechanism.

In this study there was a higher risk of respiratory symptoms among males than females, this might be due male were more smokers than female in both cement factories and civil servants, negligence was more observed in males and, females used their own cloth when personal protective equipment (PPE) was not available. Our finding was in agreement with WHO report 2006 on COPD that respiratory symptoms were main determinants of COPD [18].

The prevalence of respiratory symptoms among cement factories workers was increase with age and this was in line with study done in southern industry of Tehran, Iran and Pakistan [19,20]. As age increase the ability of immunity to compact the foreign body is decreased. In contrast to the current study, study in other cement factories of Ethiopia show that even though cleaners where younger than production workers, the prevalence of respiratory symptoms were higher among cleaners [14]. The difference with this study might be due to the cleaners were exposed to high concentrations of dust in the working environment due to their working activities of cleaning.

Working section was also the main factor that influences the prevalence of respiratory symptoms among exposed group. Raw Mill, Clinker and Burner Section were higher respiratory symptom than other. Findings from the workplace observation in one factory shows, Cement Mill and Packing Section were more automated and packing machinery were used and dust produced in these section was less. In one cement factory, the clinker drops from a height to the ground and workers were manually controlled the outlet valves and exposed to excessive dust, but, in the other factory clinker is transported with conveyer belts and workers were exposed only when they feed the Milling machine The high prevalence of respiratory symptoms, in the Raw Mill, Clinker and Burner Section may also probably due to open flow lines, leakages from machines, poor general mechanical ventilation and inefficient natural ventilation, lack of maintenance and local exhaust ventilation which was approved by workplace observation. Similarly, in other cement factory in Ethiopia, highest dust exposure among cleaners of cement dust was detected in Raw Mill department [5].

 

Cough, Phlegm, Chest Pain and Chest Tightness were higher among the smokers than nonsmokers in the exposed and unexposed groups in the current study, and this is in-line with studies from UAE, Tanzania, Pakistan and India [6,8,12,20] that smoking is an important contributing factor for the development of respiratory symptoms. The chemical compositions of Cigarette destroy the Cilia that the lungs use for the removal of particles and alter the ability of the lungs to clear themselves. The current study, shows that providing training on occupational health and safety related to dust significantly reduces respiratory symptoms which is consistent with a follow up study in Tanzania [21] Even though, proper utilization of PPE at work place reduce amount of dust inhaled per working time, only 21.8% of exposed group were used PPE which is almost similar with study from Ethiopia (21%) and UAE (19.5%)[4,8]. Proper utilization of PPE at work place reduce amount of dust inhaled per working time.

Conclusion

This finding concludes that the prevalence of respiratory symptoms was higher among cement factories workers than civil servants and this may be related to exposure to cement dust. In the cement factories workers, respiratory symptoms were found to be more common, among older ages, male, smokers, those with a previous history of respiratory diseases and, night shift workers. Whereas, in the civil servants, more respiratory symptoms were more among male, smokers and those had a history of respiratory diseases. In the cement factories workers providing of health and safety training on respiratory health effect of dust and being above secondary school were protective for the respiratory symptoms.

Authors’ contributions

KS contributed in the planning of the project, study design development, literature review, objective development, data collection, statistical analysis, and in the drafting of the manuscript. KA and MK contributed in the study design development, literature review, objective development, statistical analysis, and the drafting of the manuscript. All authors gave approval of the manuscript to be published.

Acknowledgements

We are grateful to our participants without whom we could not have done this study. We are thanking factories and Civil Servant management. We are grateful to University of Gondar and Oromia Labor and Social Affairs Agency for financial support of this study.

References

1. World health organization, Report on Global status of noncommunicable diseases, 2010.
2. Cementing respiratory research.
3. International Labour Organization, Action towards prevention of occupational non-communicable diseases Geneva, Switzerland. December 2011.
4. Zeleke ZK, Moen BE, Bråtveit M (2010) Cement dust exposure and acute lung function: a cross shift study.BMCPulm Med 10: 19.
5. Zeleke ZK, Moen BE, Bråtveit M (2011) Excessive exposure to dust among cleaners in the Ethiopian cement industry.JOccup Environ Hyg 8: 544-550.
6. Mwaiselage J, Bråtveit M, Moen BE, Mashalla Y (2005) Respiratory symptoms and chronic obstructive pulmonary disease among cement factory workers.Scand J Work Environ Health 31: 316-323.
7. Barbara A P, PJQ, Fundamental of industrials hygiene, (5 thedn.,)
8. Ahmed HO, Abdullah AA (2012) Dust exposure and respiratory symptoms among cement factory workers in the United Arab Emirates.Ind Health 50: 214-222.
9. Syed S, Bhat A, B h (2013) health risk associated with workers in cement factory. International Journal of Scientific and Research Publications 3: 1-5.
10. International Labor Organization, Encyclopedia of occupational health and safety (4th Edn) Geneva.
11. Mirzaee R, KA Hashemi R, Sadeghi M, Shahrakipour M (2008), effects of exposure to portland cement dust on lung function in portland cement factory workers in khash, iran J. Environ. Health. Sci. Eng5: 201-206.
12. Mandal A, MR (2013) Assessment of pulmonary function of cement industry workers from West Bengal, India. Prog Health Sci3: 66-77.
13. Kakooei H, Gholami A, Ghasemkhani M, Hosseini M, Panahi D, et al. (2012) Dust exposure and respiratory health effects in cement production.Acta Med Iran 50: 122-126.
14. Zeleke ZK, Moen BE, Bråtveit M (2011) Lung function reduction and chronic respiratory symptoms among workers in the cement industry: a follow up study.BMCPulm Med 11: 50.
15. North Shoa Labor and Social Affairs Office (2013), Annual report on human stastistic.
16. American thoracic society (1976) recommended respiratory disease questionnaires for use with adults and children in epidemiological research pp: 3-30.
17. Simpson JC, Niven RM, Pickering CA, Fletcher AM, Oldham LA, et al. (1998) Prevalence and predictors of work related respiratory symptoms in workers exposed to organic dusts.Occup Environ Med 55: 668-672.
18. World Health Organization (2006) global initiative for chronic obstructive lung disease, global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease.
19. Ghasemkhani M, Kumashiro M, Rezaei M, Anvari AR, Mazloumi A, et al. (2006) Prevalence of respiratory symptoms among workers in industries of south Tehran, Iran.Ind Health 44: 218-224.
20. Shaikh S, Nafees AA, Khetpal V, Jamali AA, Arain AM, et al. (2012) Respiratory symptoms and illnesses among brick kiln workers: a cross sectional study from rural districts of Pakistan.BMC Public Health 12: 999.
21. Tungu AM, Bråtveit M, Mamuya SH, Moen BE (2014) The impact of reduced dust exposure on respiratory health among cement workers: an ecological study.JOccup Environ Med 56: 101-110.

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