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Prevalence of coal workers’ pneumoconiosis in China: A systematic analysis of 2001–2011 studies
International Journal of Hygiene and Environmental Health 217 (2014) 46–51
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International Journal of Hygiene and Environmental Health journal homepage: www.elsevier.com/locate/ijheh
Mini-review
Prevalence of coal workers’ pneumoconiosis in China: A systematic analysis of 2001–2011 studies Jingfu Mo a,b , Lu Wang a,b , William Au b , Min Su a,b,∗ a b
Department of Pathology, Shantou University Medical College, Shantou 515041, Guangdong Province, China MPH Education Center, Shantou University Medical College, Shantou 515041, Guangdong Province, China
a r t i c l e
i n f o
Article history: Received 19 November 2012 Received in revised form 13 March 2013 Accepted 15 March 2013 Keywords: Coal workers’ pneumoconiosis Prevalence of pneumoconiosis Meta-analysis China
a b s t r a c t Nowadays, coal workers’ pneumoconiosis (CWP) is still believed to be the main occupational disease in China. However, information on the exact prevalence of the disease is not available. Therefore, the aims of our investigation were to provide the missing information in China by conducting a systematic evaluation of published data from 2001 to 2011 and to compare the prevalence of CWP with those in other countries. Published reports about the prevalence of CWP were searched from PudMed® (English language databases), Foreign Medical Journal Full-Text Service Database (FMJS, English language databases), Chinese Journal Full-Text Database (CJFD, Chinese language databases), Chongqing VIP Chinese Science and Technology Journals Database (VIP, Chinese language databases), Chinese Biomedical Literature Database (CBM, Chinese language databases) and Chinese Medical Association Journals Database (CMAJ, Chinese language databases). The quality of identified reports was strictly evaluated using predetermined inclusion and exclusion criteria. Based on these criteria, 11 reports were selected. Then, the content of these reports were reviewed and the needed information was extracted. Meta-analysis was performed on the extracted data. The R2.15.1 software was applied for statistical analysis. The total populations from these reports were 173,646 and 10,821 for dust-exposed coal workers and patients with CWP, respectively. The pooled prevalence of CWP was 6.02% (95%CI: 3.43–9.26%) and the pooled rate of CWP patients combined with tuberculosis was 10.82% (95%CI: 8.26–13.66%). The prevalence was analyzed according to the geographic areas of the study, years of the investigation, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories, etc. Among them, the prevalence of CWP in locally owned mines (9.86%; 95%CI: 1.25–25.17%) was significantly higher than that of stateowned mines (4.83%; 95%CI: 2.35-8.13%) (P < 0.05). Publication bias was assessed by the Egger’s test which showed insignificant results (P > 0.05). It was concluded that the prevalence of CWP were still high in China compared to UK (0.8%, during1998–2000) and USA (3.2% in 2000s). In addition, the conditions in locally owned mines had caused more CWP than that of state-owned mines. Our data clearly show that regulatory agencies in China need to step up their effort in implementing more rigorous policies to protect coal miners, especially those in locally owned mines. © 2013 Elsevier GmbH. All rights reserved.
Introduction The first case report on coal workers’ pneumoconiosis (CWP) was reported by Gregory in 1831 and then confirmed by others (Gregory, 1831; Castranova and Vallyathan, 2000; Ross and Murray, 2004). Initially CWP was thought to be a variant of silicosis due to their similarities in chest radiographs and coal dust was considered innocuous. However, such earlier belief was overturned since 1928 (Collins and Gilchrist, 1928; Castranova and Vallyathan,
∗ Corresponding author at: Department of Pathology, Shantou University Medical College, 22 Xinling Road, Shantou 515041, Guangdong Province, China. Tel.: +86 754 88900429; fax: +86 754 88900429. E-mail addresses: [email protected], [email protected] (M. Su). 1438-4639/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijheh.2013.03.006
2000), which led to better understanding of CWP as a unique disease for coal workers (Merchant et al., 1986). CWP is a chronic occupational lung disease which is caused by long-term inhalation of coal dust. The exposure can trigger inflammation of the alveoli, cause irreversible lung damage and subsequently CWP (CDC, 2012). Thus, CWP is a preventable but difficultly curable occupational lung disease. Without effective protection for workers, more and more of them are at risk for CWP because there is increased demand for coal around the world (Liu et al., 2009b). In China, CWP accounts for about 48% of the total number of cases of pneumoconiosis, the number of patients with CWP among patients with occupational disease remains the highest (Liu et al., 2009b; Ministry of Health of the People’s Republic of China, 2010. http://www.gov.cn/gzdt/2010-04/28/content 1594571.htm).
J. Mo et al. / International Journal of Hygiene and Environmental Health 217 (2014) 46–51
However, the national Chinese pneumoconiosis epidemiological survey (A total of 1,839,456 people were surveyed with crosssectional survey method in 1992; the overall prevalence of CWP mong Chinese Coal miners was 6. 49%) was conducted by the original Coal Industry Ministry of the People’s Republic of China was terminated since 1992 (Li et al., 2007). Therefore, with only individual regional studies, the national prevalence of CWP or the seriousness of this occupational disease is unknown, and can be under-estimated. We have conducted a systematic analysis of the 2001–2011 studies regarding the prevalence of CWP in China. From the pooled data, we analyzed the differences among the geographic areas of studies, years of the investigation, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories, etc. to provide a scientific basis for the prevalence and prevention of CWP.
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Chinese Medical Association Journals Database (CMAJ, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011), Foreign Medical Journal Full-Text Service Database (FMJS, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in English, time-span: 2001–2011), PudMed® (retrieval settings: all fields = “China” and all fields = “pneumoconiosis”, in English, time-span: January 1, 2001–December 31, 2011). Inclusion criteria were: 1 the study was about census or a sample survey in Chinese or English; 2 the study involved coal mine workers in China; 3 the investigation was on prevalence of CWP; 4 the time period of research was from 2001 to 2011. Exclusion criteria were: 1 the investigation was not on CWP; 2 the literature was duplicative; 3 the report was investigated before 2001; 4 the exact sample size and the prevalence of CWP cannot be calculated from the data (Fig. 1).
Materials and methods Background information of included studies Search and selection strategy Electronic search strategy was carried out using Chinese Journal Full-Text Database (CJFD, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011), Chongqing VIP Chinese Science and Technology Journals Database (VIP, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011), Chinese Biomedical Literature Database (CBM, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011),
The cases of CWP in the included 11 studies were screened and diagnosed by the professional doctor of occupational disease prevention and control institutions according to the China National Diagnostic Criteria for Pneumoconiosis (GBZ 70-2002) and the 1980 International Labor Organization (ILO) Classification of Pneumoconiosis or the corresponding standards, the above mentioned two standards are the same in the judgment of opacity profusion. The patients with CWP were classified into stage I–III according to the size, profusion, and distribution range of opacities on chest X-ray (Wang et al., 2011).
Fig. 1. Flow chart of the study search and selection process.
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Table 1 Relevant survey data of the adopted reports. Author and publication year
Studied areaa
Survey year
Nminers b
Fan (2007) Gao (2007) Ren (2008) Liu (2011) Wang et al. (2006) Zhu et al. (2011) Yang et al. (2005) Tian et al. (2009) Zhang et al. (2007) Zhang et al. (2008) Liu et al. (2009a)
Henan, Anhui, Beijing, Shandong, Hebei, Liaoning Henan Hebei Shanxi Anhui Sichuan Guangxi Liaoning Hunan Xinjiang Liaoning
2006 2006 2007 2009 2003 2009 2005 2004 2004–2006 2006 2007
21,675 13,986 3352 2,9887 34,130 5868 38,749 4807 5274 375 15,543
Npatients c
Prevalenced (%)
2912 548 293 1527 3140 228 859 60 1070 31 153
13.43 3.92 8.74 5.11 9.20 3.89 2.22 1.25 20.29 8.27 0.98
a The areas were analyzed according to the geographical classification method from the National Bureau of Statistics of China in 2011 (National Bureau of Statistics of China, 2011), a total of 16 studied areas in the 11 studies. b Number of dust exposed coal miners. c Number of patients with CWP. d Prevalence of CWP(%).
Literature screening and quality assessment
investigators. Disagreements between the two investigators were resolved through consulting a third reviewer.
The criteria of literature screening and quality assessment were: 1 assessing whether the designs are accurate and the practices
are strict. For example, inspecting whether the sampling and quality control methods are reasonable. 2 Evaluating whether the investigated objects are representative. 3 Inspecting whether the statistical analysis method are accurate. 4 Investigating whether the CWP Cases are diagnosed definitely by the professional doctor of occupational disease prevention and control institutions. The first screening was carried out by reading the titles and abstracts of the retrieved documents. The second step involved reading the full text of the qualified reports. The third step involved extraction of data and then cross-checked independently by two
Statistical analysis Meta-analysis of the collected data was carried out using the metaprop in R2.15.1 software. The pooled rates were calculated by using the Freeman-Tukey double arcsine transformation method (PFT). Random effects model or fixed effects model was employed according to statistical tests for homogeneity, if P < 0.05, using random effects model. Publication bias was assessed via funnel plots and the Egger’s test. The rates of two large samples were compared by using Z-test, the difference was considered statistically significant if P < 0.05. The pooled rates of subgroup were calculated on the
Table 2 The different subgroups of prevalence of CWP (%). Groups Total CWP combined with TBf
Nstudies b
Nminers c
Pooled rate (95% CId )
Q valuee
P value
11 6 7 3 6
173,646 9228a 39,091 44,992 89,563
6.02 (3.43, 9.26) 10.82 (8.26, 13.66) 7.19 (2.64, 13.73) 4.14 (2.37, 6.36) 10.89 (6.92, 15.63)
6310.38 68.13 2550.86 77.45 1956.58
<0.05 <0.05 <0.05 <0.05 <0.05
Studied area*
Eastern Western Central
Year of study* (years)
2001–2006 2007–2011
7 4
118,996 54,650
7.20 (3.39, 12.29) 4.20 (1.62, 7.89)
4884.28 845.17
<0.05 <0.05
Duration of dust exposure* (years)
<10 10–20 ≥20
4 4 4
9484 12,686 9933
2.27 (0.06, 9.20) 4.32 (0.29, 12.68) 13.46 (1.87, 33.12)
689.04 858.61 1138.02
<0.05 <0.05 <0.05
Coal rank*
Bituminous Anthracite Lignite
5 4 1
77,509 55,887 20,574
5.88 (2.21, 11.16) 5.38 (2.11, 10.04) 0.15
2630.23 1158.06 –
<0.05 <0.05 –
Stages of CWP*
Stage I Stage II Stage III
10 10 10
170,905 170,905 170,905
4.08 (2.28, 6.36) 1.21 (0.52, 2.16) 0.26 (0.08, 0.54)
3932.91 2035.91 698.79
<0.05 <0.05 <0.05
Types of work*
Mining Tunneling Auxiliary
3 3 3
7431 8617 8991
1.38 (0.15, 3.74) 3.72 (2.65, 4.96) 0.22 (0.95, 1.75)
80.55 11.94 28.13
<0.05 <0.05 <0.05
Coal-mining categories*
State-owned coal minesg Locally owned minesh
8 3
162,129 11,517
5113.08 803.69
<0.05 <0.05
*
4.83 (2.35, 8.13) 9.86 (1.25, 25.17)
Z-test p < 0.05. The number of patients with CWP. Number of studies. c Number of dust exposed coal miners. d 95% confidence interval. e Heterogeneity test (Q value). f Patients with CWP and tuberculosis concomitantly (patients with CWP and tuberculosis were diagnosed according to the bacteriology and radiographic inspection, which was reported in the 6 articles of our included 11 studies). g ≥300 employees. h <300 employees. a
b
J. Mo et al. / International Journal of Hygiene and Environmental Health 217 (2014) 46–51
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Fig. 2. Forest plot of prevalence of CWP for the meta-analysis.
extraction of data, which were available on these subgroups in all the included studies. Results Inclusion and exclusion of studies A total of 2416 reports were retrieved according to the mentioned search strategy. Among them 2071 reports were from Chinese journals, and 345 reports were from English journals. Based on our exclusion and inclusion criteria, 2405 reports were removed. Finally, 11 reports were accepted (Fig. 1). Among the adopted 11 reports, the maximum and minimum sample sizes of dust exposed coal miners were 38,749 and 375 workers, respectively (Table 1). Analysis of Data of CWP in China Analysis of the overall prevalence of CWP in China The eleven studies included 173,646 dust exposed coal miners and 10,821 patients with CWP from 11 provinces in China (Table 1). Test for heterogeneity of the adopted 11 studies was significant (P < 0.05). The pooled rate was calculated by using the random effects model. The pooled total prevalence of CWP was 6.02% (95%CI: 3.43–9.26%; Table 2). The forest diagram of metaanalysis on the 11 studies is shown in Fig. 2. The subgroup analysis of prevalence of CWP in China The prevalence of CWP was stratified by factors as the areas of study, research year, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories of the study. Test for heterogeneity of the each subgroup prevalence of CWP was significant (P < 0.05) and the pooled rate was calculated by using the random effects model. Among them, the pooled prevalence rates of CWP for Central, Eastern and Western areas of China were 10.89% (95%CI: 6.92–15.63%), 7.19% (95%CI: 2.64–13.73%) and 4.14% (95%CI: 2.37–6.36%), respectively. The rates were significantly different from each other (P < 0.05). The pooled prevalence rates of CWP were 7.20% (95%CI: 3.39–12.29%) in the study year of 2001–2006 and 4.20% (95%CI: 1.62–7.89%) in 2007–2011. The prevalence rates were significantly different from each other (P < 0.05). The pooled prevalence rates of CWP in the different duration of dust exposure were 13.46% (95%CI: 1.87–33.12%), 4.32% (95%CI: 0.29–12.68%) and 2.27% (95%CI: 0.06–9.20%) for ≥20 years, 10–20 years and <10 years, respectively. The prevalence rates were significantly different from each other (P < 0.05). The pooled prevalence rates of CWP for bituminous, anthracite
Fig. 3. Funnel plot for 11 studies included in meta-analysis.
and lignite coals were 5.88% (95%CI: 2.21–11.16%), 5.38% (95%CI: 2.11–10.04%) and 0.15%, respectively, (P < 0.05). The pooled prevalence rates of CWP for stage I–III pneumoconiosis were 4.08% (95%CI: 2.28–6.36%), 1.21% (95%CI: 0.52–2.16%) and 0.26% (95%CI: 0.08–0.54%), respectively, (P < 0.05). The pooled prevalence rates of CWP for tunneling workers, mining workers and auxiliary workers were 3.72% (95%CI: 2.65–4.96%), 1.38% (95%CI: 0.15–3.74%) and 0.22% (95%CI: 0.95–1.75%), respectively, (P < 0.05). The pooled prevalence rates of CWP were 4.83% (95%CI: 2.35–8.13%) in Stateowned coal mines and 9.86% (95%CI: 1.25–25.17%) in locally coal mines, (P < 0.05). In addition, the pooled total rate of CWP patients combined with tuberculosis was 10.82% (95%CI: 8.26–13.66%) (Table 2). Publication bias analysis Publication bias of the adopted 11 studies was assessed by the Egger’s test (P = 0.80>0.05). In addition, based on the funnel plot for 11 studies from the meta-analysis (Fig. 3), the publication bias is not obvious. Discussion The prevalence of CWP in China In this paper, the results of meta-analysis of the adopted 11 reports showed that the pooled prevalence (6.02%) of CWP was lower than that (6.49%) from the national Chinese survey in 1992 (Li et al., 1997), but higher than that (3.2%) in USA in the 2000s (Laney and Attfield, 2010). In addition, the pooled rate of CWP patients combined with tuberculosis (10.82%) was lower than the rate of 12.21% from national Chinese survey in 1992 (Li et al., 2007), but much higher than the prevalence (0.37%) of active
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J. Mo et al. / International Journal of Hygiene and Environmental Health 217 (2014) 46–51
Table 3 The comparison of CWP prevalence (%) in China and in other countries. Country
Yeas
Prevalence
Population and reference
China
1992 2001–2011 1970s 1980s 1990s 2000s 1959–1963 1969–1973 1978–1981 1986–1989 1990–1993 1994–1997 1998–2000 1986 1988 1985 1991 1999 2004 1988 1988 1986 1988 1949–1950 1951–1952 1953–1954 1956–1957 1957–1958 1959–1960
6.49 6.02 6.5 2.5 2.1 3.2 12.1 10.2 4.1 0.7 0.4 0.2 0.8 18.8 12 2.47 5.71 6.23 1.63 5.6 14.1 15 20 27.0 26.0 21.5 18.8 17.9 15.9
Coal miners; Li et al. (1997) Coal miners; our study Coal miners; Laney and Attfield (2010) Coal miners; Laney and Attfield (2010) Coal miners; Laney and Attfield (2010) Coal miners; Laney and Attfield (2010) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Van Sprundel (1990) Coal miners; Van Sprundel (1990) Underground coal miners; Tor et al. (2010) Underground coal miners; Tor et al. (2010) Underground coal miners; Tor et al. (2010) Underground coal miners; Tor et al. (2010) Coal miners; Van Sprundel (1990) Coal miners; Van Sprundel (1990) Coal miners;Van Sprundel (1990) Coal miners; Van Sprundel (1990) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963)
U.S.A.
UK
India Turkish
Brazil Chile Columbia Zimbabwe Dutch
tuberculosis from the Fourth National Chinese Tuberculosis survey in 2000 (Duanmu, 2002). The data indicate that the risk of complications from tuberculosis is very high in the coal miners with CWP. The analysis of the each subgroup with CWP showed that the prevalence of CWP was different among the different areas of the study, research year, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories. The prevalence of CWP in Central China was at a high level, which may be due to the presence of many small coal mines. For example, the prevalence of CWP in small coal mines was up to 20.29% in Hunan, China (Zhang et al., 2007). The pooled prevalence of CWP increased with the duration of dust exposure. The pooled prevalence among workers with ≥20 years dust exposure was as high as 13.46%. The pooled prevalence in the different coal ranks from high to low was bituminous, anthracite and lignite coal, respectively. However, these prevalences often differed greatly in the same coal rank, which may not only be related to the coal rank but also with the different coal dust exposure concentrations, toxicity, management and other factors. The pooled prevalence in the different stages of pneumoconiosis from high to low were stage I–III pneumoconiosis, respectively. This indicates that the number of CWP with stage I pneumoconiosis was at a high level, which should be dealt with efficiently to prevent further complications. The pooled prevalence from high to low for the different types of work was tunneling, mining and auxiliary work, respectively. Therefore, for prevention of health problems, mining companies should enhance the monitoring and reduction of dust in the tunneling and mining areas. The pooled prevalence in locally coal mines was higher than that of State-owned coal mines. Therefore, locally coal mines require stronger surveillance and management. Publication bias of the accepted 11 studies was assessed by the Egger’s test and the funnel plot showed that the publication bias is not obvious, and the cases of CWP in the included 11 studies were screened and diagnosed by occupational disease prevention and control institutions, so the results are credible. However, there are still some deficiencies due to the shortcomings of the meta-analysis
method itself. For example, the study may be impacted by the lack of sufficient data among some subgroups of CWP. Nevertheless, our meta-analysis data can be strengthened by conducting systematic national surveys. The comparison of CWP prevalence in China and in other countries In developing countries the prevalence of CWP was usually higher than those in developed countries and the rates for all countries may be increasing rather than decreasing (WHO, 1986; Van Sprundel, 1990). The prevalence of CWP in some developing countries of Asia, Africa and Latin America was still at a high level now, including China (Table 3). In developed countries the prevalence of CWP has been decreasing because many of these countries had developed better policy and management programs. For example, the prevalence declined from 12.1% during 1959–1963 to 0.2% during 1994–1997 in UK, and the prevalence was reduced from 6.5% in the 1970s to 2.1% in the 1990s for USA. However, it is disappointing that the reduction was not sustainable. For example, the prevalence in USA went up from 2.1% in 1990s to 3.2% in 2000s, and the prevalence in UK went up from 0.2% during 1994–1997 to 0.8% during 1998–2000 (Table 3). It is possible that the increase was caused by increased work hours, over-exposure to silica dust and the increase in work load (Nlandu et al., 2012; Laney and Attfield, 2010). Conclusion Our study highlights the high prevalence of CWP in China compared with those from some developed countries. In addition, our meta-analysis has identified specific factors such as duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories, which were significantly associated with the high risk for CWP. The information should be very useful to occupation regulatory agencies to design appropriate policies to reduce this highly preventable disease among coal workers. Specific examples include the proactive reduction of exposure to coal dust, the more stringent
J. Mo et al. / International Journal of Hygiene and Environmental Health 217 (2014) 46–51
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Contents lists available at ScienceDirect
International Journal of Hygiene and Environmental Health journal homepage: www.elsevier.com/locate/ijheh
Mini-review
Prevalence of coal workers’ pneumoconiosis in China: A systematic analysis of 2001–2011 studies Jingfu Mo a,b , Lu Wang a,b , William Au b , Min Su a,b,∗ a b
Department of Pathology, Shantou University Medical College, Shantou 515041, Guangdong Province, China MPH Education Center, Shantou University Medical College, Shantou 515041, Guangdong Province, China
a r t i c l e
i n f o
Article history: Received 19 November 2012 Received in revised form 13 March 2013 Accepted 15 March 2013 Keywords: Coal workers’ pneumoconiosis Prevalence of pneumoconiosis Meta-analysis China
a b s t r a c t Nowadays, coal workers’ pneumoconiosis (CWP) is still believed to be the main occupational disease in China. However, information on the exact prevalence of the disease is not available. Therefore, the aims of our investigation were to provide the missing information in China by conducting a systematic evaluation of published data from 2001 to 2011 and to compare the prevalence of CWP with those in other countries. Published reports about the prevalence of CWP were searched from PudMed® (English language databases), Foreign Medical Journal Full-Text Service Database (FMJS, English language databases), Chinese Journal Full-Text Database (CJFD, Chinese language databases), Chongqing VIP Chinese Science and Technology Journals Database (VIP, Chinese language databases), Chinese Biomedical Literature Database (CBM, Chinese language databases) and Chinese Medical Association Journals Database (CMAJ, Chinese language databases). The quality of identified reports was strictly evaluated using predetermined inclusion and exclusion criteria. Based on these criteria, 11 reports were selected. Then, the content of these reports were reviewed and the needed information was extracted. Meta-analysis was performed on the extracted data. The R2.15.1 software was applied for statistical analysis. The total populations from these reports were 173,646 and 10,821 for dust-exposed coal workers and patients with CWP, respectively. The pooled prevalence of CWP was 6.02% (95%CI: 3.43–9.26%) and the pooled rate of CWP patients combined with tuberculosis was 10.82% (95%CI: 8.26–13.66%). The prevalence was analyzed according to the geographic areas of the study, years of the investigation, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories, etc. Among them, the prevalence of CWP in locally owned mines (9.86%; 95%CI: 1.25–25.17%) was significantly higher than that of stateowned mines (4.83%; 95%CI: 2.35-8.13%) (P < 0.05). Publication bias was assessed by the Egger’s test which showed insignificant results (P > 0.05). It was concluded that the prevalence of CWP were still high in China compared to UK (0.8%, during1998–2000) and USA (3.2% in 2000s). In addition, the conditions in locally owned mines had caused more CWP than that of state-owned mines. Our data clearly show that regulatory agencies in China need to step up their effort in implementing more rigorous policies to protect coal miners, especially those in locally owned mines. © 2013 Elsevier GmbH. All rights reserved.
Introduction The first case report on coal workers’ pneumoconiosis (CWP) was reported by Gregory in 1831 and then confirmed by others (Gregory, 1831; Castranova and Vallyathan, 2000; Ross and Murray, 2004). Initially CWP was thought to be a variant of silicosis due to their similarities in chest radiographs and coal dust was considered innocuous. However, such earlier belief was overturned since 1928 (Collins and Gilchrist, 1928; Castranova and Vallyathan,
∗ Corresponding author at: Department of Pathology, Shantou University Medical College, 22 Xinling Road, Shantou 515041, Guangdong Province, China. Tel.: +86 754 88900429; fax: +86 754 88900429. E-mail addresses: [email protected], [email protected] (M. Su). 1438-4639/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijheh.2013.03.006
2000), which led to better understanding of CWP as a unique disease for coal workers (Merchant et al., 1986). CWP is a chronic occupational lung disease which is caused by long-term inhalation of coal dust. The exposure can trigger inflammation of the alveoli, cause irreversible lung damage and subsequently CWP (CDC, 2012). Thus, CWP is a preventable but difficultly curable occupational lung disease. Without effective protection for workers, more and more of them are at risk for CWP because there is increased demand for coal around the world (Liu et al., 2009b). In China, CWP accounts for about 48% of the total number of cases of pneumoconiosis, the number of patients with CWP among patients with occupational disease remains the highest (Liu et al., 2009b; Ministry of Health of the People’s Republic of China, 2010. http://www.gov.cn/gzdt/2010-04/28/content 1594571.htm).
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However, the national Chinese pneumoconiosis epidemiological survey (A total of 1,839,456 people were surveyed with crosssectional survey method in 1992; the overall prevalence of CWP mong Chinese Coal miners was 6. 49%) was conducted by the original Coal Industry Ministry of the People’s Republic of China was terminated since 1992 (Li et al., 2007). Therefore, with only individual regional studies, the national prevalence of CWP or the seriousness of this occupational disease is unknown, and can be under-estimated. We have conducted a systematic analysis of the 2001–2011 studies regarding the prevalence of CWP in China. From the pooled data, we analyzed the differences among the geographic areas of studies, years of the investigation, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories, etc. to provide a scientific basis for the prevalence and prevention of CWP.
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Chinese Medical Association Journals Database (CMAJ, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011), Foreign Medical Journal Full-Text Service Database (FMJS, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in English, time-span: 2001–2011), PudMed® (retrieval settings: all fields = “China” and all fields = “pneumoconiosis”, in English, time-span: January 1, 2001–December 31, 2011). Inclusion criteria were: 1 the study was about census or a sample survey in Chinese or English; 2 the study involved coal mine workers in China; 3 the investigation was on prevalence of CWP; 4 the time period of research was from 2001 to 2011. Exclusion criteria were: 1 the investigation was not on CWP; 2 the literature was duplicative; 3 the report was investigated before 2001; 4 the exact sample size and the prevalence of CWP cannot be calculated from the data (Fig. 1).
Materials and methods Background information of included studies Search and selection strategy Electronic search strategy was carried out using Chinese Journal Full-Text Database (CJFD, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011), Chongqing VIP Chinese Science and Technology Journals Database (VIP, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011), Chinese Biomedical Literature Database (CBM, retrieval settings: all fields = “prevalence” and all fields = “pneumoconiosis”, in Chinese, time-span: 2001–2011),
The cases of CWP in the included 11 studies were screened and diagnosed by the professional doctor of occupational disease prevention and control institutions according to the China National Diagnostic Criteria for Pneumoconiosis (GBZ 70-2002) and the 1980 International Labor Organization (ILO) Classification of Pneumoconiosis or the corresponding standards, the above mentioned two standards are the same in the judgment of opacity profusion. The patients with CWP were classified into stage I–III according to the size, profusion, and distribution range of opacities on chest X-ray (Wang et al., 2011).
Fig. 1. Flow chart of the study search and selection process.
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Table 1 Relevant survey data of the adopted reports. Author and publication year
Studied areaa
Survey year
Nminers b
Fan (2007) Gao (2007) Ren (2008) Liu (2011) Wang et al. (2006) Zhu et al. (2011) Yang et al. (2005) Tian et al. (2009) Zhang et al. (2007) Zhang et al. (2008) Liu et al. (2009a)
Henan, Anhui, Beijing, Shandong, Hebei, Liaoning Henan Hebei Shanxi Anhui Sichuan Guangxi Liaoning Hunan Xinjiang Liaoning
2006 2006 2007 2009 2003 2009 2005 2004 2004–2006 2006 2007
21,675 13,986 3352 2,9887 34,130 5868 38,749 4807 5274 375 15,543
Npatients c
Prevalenced (%)
2912 548 293 1527 3140 228 859 60 1070 31 153
13.43 3.92 8.74 5.11 9.20 3.89 2.22 1.25 20.29 8.27 0.98
a The areas were analyzed according to the geographical classification method from the National Bureau of Statistics of China in 2011 (National Bureau of Statistics of China, 2011), a total of 16 studied areas in the 11 studies. b Number of dust exposed coal miners. c Number of patients with CWP. d Prevalence of CWP(%).
Literature screening and quality assessment
investigators. Disagreements between the two investigators were resolved through consulting a third reviewer.
The criteria of literature screening and quality assessment were: 1 assessing whether the designs are accurate and the practices
are strict. For example, inspecting whether the sampling and quality control methods are reasonable. 2 Evaluating whether the investigated objects are representative. 3 Inspecting whether the statistical analysis method are accurate. 4 Investigating whether the CWP Cases are diagnosed definitely by the professional doctor of occupational disease prevention and control institutions. The first screening was carried out by reading the titles and abstracts of the retrieved documents. The second step involved reading the full text of the qualified reports. The third step involved extraction of data and then cross-checked independently by two
Statistical analysis Meta-analysis of the collected data was carried out using the metaprop in R2.15.1 software. The pooled rates were calculated by using the Freeman-Tukey double arcsine transformation method (PFT). Random effects model or fixed effects model was employed according to statistical tests for homogeneity, if P < 0.05, using random effects model. Publication bias was assessed via funnel plots and the Egger’s test. The rates of two large samples were compared by using Z-test, the difference was considered statistically significant if P < 0.05. The pooled rates of subgroup were calculated on the
Table 2 The different subgroups of prevalence of CWP (%). Groups Total CWP combined with TBf
Nstudies b
Nminers c
Pooled rate (95% CId )
Q valuee
P value
11 6 7 3 6
173,646 9228a 39,091 44,992 89,563
6.02 (3.43, 9.26) 10.82 (8.26, 13.66) 7.19 (2.64, 13.73) 4.14 (2.37, 6.36) 10.89 (6.92, 15.63)
6310.38 68.13 2550.86 77.45 1956.58
<0.05 <0.05 <0.05 <0.05 <0.05
Studied area*
Eastern Western Central
Year of study* (years)
2001–2006 2007–2011
7 4
118,996 54,650
7.20 (3.39, 12.29) 4.20 (1.62, 7.89)
4884.28 845.17
<0.05 <0.05
Duration of dust exposure* (years)
<10 10–20 ≥20
4 4 4
9484 12,686 9933
2.27 (0.06, 9.20) 4.32 (0.29, 12.68) 13.46 (1.87, 33.12)
689.04 858.61 1138.02
<0.05 <0.05 <0.05
Coal rank*
Bituminous Anthracite Lignite
5 4 1
77,509 55,887 20,574
5.88 (2.21, 11.16) 5.38 (2.11, 10.04) 0.15
2630.23 1158.06 –
<0.05 <0.05 –
Stages of CWP*
Stage I Stage II Stage III
10 10 10
170,905 170,905 170,905
4.08 (2.28, 6.36) 1.21 (0.52, 2.16) 0.26 (0.08, 0.54)
3932.91 2035.91 698.79
<0.05 <0.05 <0.05
Types of work*
Mining Tunneling Auxiliary
3 3 3
7431 8617 8991
1.38 (0.15, 3.74) 3.72 (2.65, 4.96) 0.22 (0.95, 1.75)
80.55 11.94 28.13
<0.05 <0.05 <0.05
Coal-mining categories*
State-owned coal minesg Locally owned minesh
8 3
162,129 11,517
5113.08 803.69
<0.05 <0.05
*
4.83 (2.35, 8.13) 9.86 (1.25, 25.17)
Z-test p < 0.05. The number of patients with CWP. Number of studies. c Number of dust exposed coal miners. d 95% confidence interval. e Heterogeneity test (Q value). f Patients with CWP and tuberculosis concomitantly (patients with CWP and tuberculosis were diagnosed according to the bacteriology and radiographic inspection, which was reported in the 6 articles of our included 11 studies). g ≥300 employees. h <300 employees. a
b
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Fig. 2. Forest plot of prevalence of CWP for the meta-analysis.
extraction of data, which were available on these subgroups in all the included studies. Results Inclusion and exclusion of studies A total of 2416 reports were retrieved according to the mentioned search strategy. Among them 2071 reports were from Chinese journals, and 345 reports were from English journals. Based on our exclusion and inclusion criteria, 2405 reports were removed. Finally, 11 reports were accepted (Fig. 1). Among the adopted 11 reports, the maximum and minimum sample sizes of dust exposed coal miners were 38,749 and 375 workers, respectively (Table 1). Analysis of Data of CWP in China Analysis of the overall prevalence of CWP in China The eleven studies included 173,646 dust exposed coal miners and 10,821 patients with CWP from 11 provinces in China (Table 1). Test for heterogeneity of the adopted 11 studies was significant (P < 0.05). The pooled rate was calculated by using the random effects model. The pooled total prevalence of CWP was 6.02% (95%CI: 3.43–9.26%; Table 2). The forest diagram of metaanalysis on the 11 studies is shown in Fig. 2. The subgroup analysis of prevalence of CWP in China The prevalence of CWP was stratified by factors as the areas of study, research year, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories of the study. Test for heterogeneity of the each subgroup prevalence of CWP was significant (P < 0.05) and the pooled rate was calculated by using the random effects model. Among them, the pooled prevalence rates of CWP for Central, Eastern and Western areas of China were 10.89% (95%CI: 6.92–15.63%), 7.19% (95%CI: 2.64–13.73%) and 4.14% (95%CI: 2.37–6.36%), respectively. The rates were significantly different from each other (P < 0.05). The pooled prevalence rates of CWP were 7.20% (95%CI: 3.39–12.29%) in the study year of 2001–2006 and 4.20% (95%CI: 1.62–7.89%) in 2007–2011. The prevalence rates were significantly different from each other (P < 0.05). The pooled prevalence rates of CWP in the different duration of dust exposure were 13.46% (95%CI: 1.87–33.12%), 4.32% (95%CI: 0.29–12.68%) and 2.27% (95%CI: 0.06–9.20%) for ≥20 years, 10–20 years and <10 years, respectively. The prevalence rates were significantly different from each other (P < 0.05). The pooled prevalence rates of CWP for bituminous, anthracite
Fig. 3. Funnel plot for 11 studies included in meta-analysis.
and lignite coals were 5.88% (95%CI: 2.21–11.16%), 5.38% (95%CI: 2.11–10.04%) and 0.15%, respectively, (P < 0.05). The pooled prevalence rates of CWP for stage I–III pneumoconiosis were 4.08% (95%CI: 2.28–6.36%), 1.21% (95%CI: 0.52–2.16%) and 0.26% (95%CI: 0.08–0.54%), respectively, (P < 0.05). The pooled prevalence rates of CWP for tunneling workers, mining workers and auxiliary workers were 3.72% (95%CI: 2.65–4.96%), 1.38% (95%CI: 0.15–3.74%) and 0.22% (95%CI: 0.95–1.75%), respectively, (P < 0.05). The pooled prevalence rates of CWP were 4.83% (95%CI: 2.35–8.13%) in Stateowned coal mines and 9.86% (95%CI: 1.25–25.17%) in locally coal mines, (P < 0.05). In addition, the pooled total rate of CWP patients combined with tuberculosis was 10.82% (95%CI: 8.26–13.66%) (Table 2). Publication bias analysis Publication bias of the adopted 11 studies was assessed by the Egger’s test (P = 0.80>0.05). In addition, based on the funnel plot for 11 studies from the meta-analysis (Fig. 3), the publication bias is not obvious. Discussion The prevalence of CWP in China In this paper, the results of meta-analysis of the adopted 11 reports showed that the pooled prevalence (6.02%) of CWP was lower than that (6.49%) from the national Chinese survey in 1992 (Li et al., 1997), but higher than that (3.2%) in USA in the 2000s (Laney and Attfield, 2010). In addition, the pooled rate of CWP patients combined with tuberculosis (10.82%) was lower than the rate of 12.21% from national Chinese survey in 1992 (Li et al., 2007), but much higher than the prevalence (0.37%) of active
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Table 3 The comparison of CWP prevalence (%) in China and in other countries. Country
Yeas
Prevalence
Population and reference
China
1992 2001–2011 1970s 1980s 1990s 2000s 1959–1963 1969–1973 1978–1981 1986–1989 1990–1993 1994–1997 1998–2000 1986 1988 1985 1991 1999 2004 1988 1988 1986 1988 1949–1950 1951–1952 1953–1954 1956–1957 1957–1958 1959–1960
6.49 6.02 6.5 2.5 2.1 3.2 12.1 10.2 4.1 0.7 0.4 0.2 0.8 18.8 12 2.47 5.71 6.23 1.63 5.6 14.1 15 20 27.0 26.0 21.5 18.8 17.9 15.9
Coal miners; Li et al. (1997) Coal miners; our study Coal miners; Laney and Attfield (2010) Coal miners; Laney and Attfield (2010) Coal miners; Laney and Attfield (2010) Coal miners; Laney and Attfield (2010) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Scarisbrick and Quinlan (2002) Coal miners; Van Sprundel (1990) Coal miners; Van Sprundel (1990) Underground coal miners; Tor et al. (2010) Underground coal miners; Tor et al. (2010) Underground coal miners; Tor et al. (2010) Underground coal miners; Tor et al. (2010) Coal miners; Van Sprundel (1990) Coal miners; Van Sprundel (1990) Coal miners;Van Sprundel (1990) Coal miners; Van Sprundel (1990) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963) Underground coal miners; Hendriks and Claus (1963)
U.S.A.
UK
India Turkish
Brazil Chile Columbia Zimbabwe Dutch
tuberculosis from the Fourth National Chinese Tuberculosis survey in 2000 (Duanmu, 2002). The data indicate that the risk of complications from tuberculosis is very high in the coal miners with CWP. The analysis of the each subgroup with CWP showed that the prevalence of CWP was different among the different areas of the study, research year, duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories. The prevalence of CWP in Central China was at a high level, which may be due to the presence of many small coal mines. For example, the prevalence of CWP in small coal mines was up to 20.29% in Hunan, China (Zhang et al., 2007). The pooled prevalence of CWP increased with the duration of dust exposure. The pooled prevalence among workers with ≥20 years dust exposure was as high as 13.46%. The pooled prevalence in the different coal ranks from high to low was bituminous, anthracite and lignite coal, respectively. However, these prevalences often differed greatly in the same coal rank, which may not only be related to the coal rank but also with the different coal dust exposure concentrations, toxicity, management and other factors. The pooled prevalence in the different stages of pneumoconiosis from high to low were stage I–III pneumoconiosis, respectively. This indicates that the number of CWP with stage I pneumoconiosis was at a high level, which should be dealt with efficiently to prevent further complications. The pooled prevalence from high to low for the different types of work was tunneling, mining and auxiliary work, respectively. Therefore, for prevention of health problems, mining companies should enhance the monitoring and reduction of dust in the tunneling and mining areas. The pooled prevalence in locally coal mines was higher than that of State-owned coal mines. Therefore, locally coal mines require stronger surveillance and management. Publication bias of the accepted 11 studies was assessed by the Egger’s test and the funnel plot showed that the publication bias is not obvious, and the cases of CWP in the included 11 studies were screened and diagnosed by occupational disease prevention and control institutions, so the results are credible. However, there are still some deficiencies due to the shortcomings of the meta-analysis
method itself. For example, the study may be impacted by the lack of sufficient data among some subgroups of CWP. Nevertheless, our meta-analysis data can be strengthened by conducting systematic national surveys. The comparison of CWP prevalence in China and in other countries In developing countries the prevalence of CWP was usually higher than those in developed countries and the rates for all countries may be increasing rather than decreasing (WHO, 1986; Van Sprundel, 1990). The prevalence of CWP in some developing countries of Asia, Africa and Latin America was still at a high level now, including China (Table 3). In developed countries the prevalence of CWP has been decreasing because many of these countries had developed better policy and management programs. For example, the prevalence declined from 12.1% during 1959–1963 to 0.2% during 1994–1997 in UK, and the prevalence was reduced from 6.5% in the 1970s to 2.1% in the 1990s for USA. However, it is disappointing that the reduction was not sustainable. For example, the prevalence in USA went up from 2.1% in 1990s to 3.2% in 2000s, and the prevalence in UK went up from 0.2% during 1994–1997 to 0.8% during 1998–2000 (Table 3). It is possible that the increase was caused by increased work hours, over-exposure to silica dust and the increase in work load (Nlandu et al., 2012; Laney and Attfield, 2010). Conclusion Our study highlights the high prevalence of CWP in China compared with those from some developed countries. In addition, our meta-analysis has identified specific factors such as duration of dust exposure, coal rank, stages of CWP, types of work and coal-mining categories, which were significantly associated with the high risk for CWP. The information should be very useful to occupation regulatory agencies to design appropriate policies to reduce this highly preventable disease among coal workers. Specific examples include the proactive reduction of exposure to coal dust, the more stringent
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regulation of non-state owned mines and the more stringent monitoring of mining activities in the Central areas of China. In addition, the policy should take into account the increased demand for coal which requires workers to work overtime and to work in less than desirable conditions. Acknowledgment This study was sponsored by China Ministry of Health standards amendments Funds (Certificates 20110701) and NSF Guangdong Province (Certificates S2011020002393) and Guangdong International Cooperative Technical Innovation Platform(Certificates gihz1106). References CDC (Centers for Disease Control and Prevention), 2012. Pneumoconiosis and advanced occupational lung disease among surface coal miners – 16 states, 2010–2011. MMWR. Morb. Mortal. Wkly. Rep. 61, 431–434. Castranova, V., Vallyathan, V., 2000. Silicosis and coal workers’ pneumoconiosis. Environ. Health Perspect. 108, 675–684. Collins, E.L., Gilchrist, J.C., 1928. Effects of dust upon coal trimmers. J. lnd. Hyg. Toxicol. 10, 101–109. Duanmu, H.J., 2002. Report on fourth national epidemiological sampling survey of tuberculosis in China. Chin. J. Tuberc. Respir. Dis. 25, 3–7. Fan, H.M., 2007. A study on epidemiology and control measures of tuberculosis between coal worker’s pneumoconiosis in the national coal mines [PhD Dissertation]. Peking Union Medical College, Beijing, CN. Gao, Q., 2007. The investigation and study on occupational disease hazard in stateowned mining enterprises of Henan province [Master Dissertation], Tianjin University, Tianjin, CN. Gregory, J.C., 1831. Case of particular black infiltration of the whole lungs resembling melanosis. Edinburgh. Med. Surg. 36, 389–394. Hendriks, C.A.M., Claus, H., 1963. Effect of dust suppression measures on the prevalence of coal workers’ pneumoconiosis in the dutch coal mines. Brit. J. Ind. Med. 20, 288–292. Liu, F.Y., 2011. The analysis of pneumoconiosis prevalence in Jincheng anthracite mining group based on ARIMA model [Master Dissertation], Shanxi Medical University, Shanxi, CN. Laney, A.S., Attfield, M.D., 2010. Coal workers’ pneumoconiosis and progressive massive fibrosis are increasingly more prevalent among workers in small underground coal mines in the United States. Occup. Environ. Med. 67, 428–431. Liu, H.B., Tang, Z.F., Weng, D., Yang, Y.L., Tian, L.J., Duan, Z.W., Chen, J., 2009a. Prevalence characteristics and prediction of coal workers’ pneumoconiosis in the Tiefa Colliery in China. Ind. Health 47, 369–375. Liu, H., Tang, Z., Yang, Y., Weng, D., Sun, G., Duan, Z., Chen, J., 2009b. Identification and classification of high risk groups for coal workers’ pneumoconiosis using an artificial neural network based on occupational histories: a retrospective cohort study. BMC Public. Health 9, 366. Li, B.Q., Zhou, Y.Z., Yang, D.C., Zeng, Q.Y., 2007. The epidemiology of pneumoconiosis [in Chinese]. Occup. and Health 23, 549–552.
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