| China is one of the most severe countries affected by productive dust in the world since it has the largest number of pneumoconiosis and dust exposed population. In recent years, over 20000 new cases were reported annually, which accounted for 85% of all reported cases of occupational diseases. Coal Workers’ Pneumoconiosis (CWP) accounted for about 50% of total reported cases of pneumoconiosis. CWP is a kind of chronic systemic diseases characterized by diffuse lung fibrosis, resulting from long-term inhalation and deposition of respirable dust in professional activities. CWP is the most serious occupational disease and has the highest incidence rate in coal enterprises.Coal production base of China National Coal Group Corp. in Jiangsu has a mining history of nearly 50 years. The base experienced the establishment of occupational disease prevention laws and regulations as well as the development of dust-proof technologies, measures and equipment from scratch. The replacement of coal mining equipment, the implementation of dust control measures, dust exposure of miners and incidence of CWP of this base can be a good representative one of Chinese state-owned coal mines.ObjectiveThe present study was aimed to analyze the trend of dust pollution, the characteristics of CWP, as well as the relationship between exposure and incidence of CWP to comprehend the occurrence regularity of CWP and forecast the incidence trend of CWP in the future. Furthermore, this study will provide scientific basis for prevention and control measures, preventing or delaying the development of CWP preventing or declining the occurrence of complications, and therefore prolonging the survival time and improving the life quality of CWP patients.Subjects and MethodsThe dust data was from the dust monitoring data of this mine from 1975 to 2014, including dust concentrations of different types of dust in major work areas.This study consisted of 8928 underground workers whose dust exposed years in this mine account for more than 50% of all the length of dust exposure. There were 495 CWP patients among all of the subjects. The subjects’information was collected, which included the dust exposure history and demographic characteristics, such as date of birth, job titles, the start date of dust exposure, the end date of dust exposure and the date of retirement. We also collected the spectific information of CWP patients, including the date of first diagnosis, stage, the duration of CWP progress, complication of pulmonary tuberculosis and so on. In addition, the date and causes of death were also collected for the death cases of CWP.Data were analyzed by χ2-test for the categorical variables and two-sample t-test, ANOVA or Kruskal-Wallis rank test for continuous data. Survival analysis of CWP patients with Kaplan-Meier method and Cox proportional hazards regression model based on partial maximum likelihood estimation method forward (Forward:LR). CDE (cumulative dust exposure) of each miner was calculated. And cumulative incidences were calculated using life table. Peto Log-rank Test was used to compare the cumulative incidences of different cohorts. In order to predict the incidence of future, incidence density was calculated by adding time factor observed-years.ResultsThe range of free silica content in the coal dust varied from 0.9% to 9.9% in different sampling sites from 1975 to 2014, and the average was 5.2%. And the range of concentration of free silica in the silica dust was from 10.9% to 52.4%, and the average was 22.7%. The underground dust concentration was declining as a whole after 1990, especially for the average dust concentration of coal dust and silica dust. The exceeded standard rates of total dust concentration were decreased before 2000. However, it was increased in tunneling and mining work faces after 2000. Compared with those from 2000 to 2005, the dust pollution was improved after 2006.From 1977 to 2014, the rates of occupational health surveillance(OHS) of underground miners varied from 62.9% to 98.78%, which were fluctuated significantly. It was more than 85% in 2004,2008,2010,2012 and 2014. However, it was only 62.91% in 2009, the lowest in these years. There were 414 CWP patients were diagnosed from 1977 to 2014.Among these CWP cases,90.71% was tunneling and mining workers and 71.11% was at the stage I. With the increase of the stage,the mean ages at the first diagnosis, the average exposure durations and latent period decreased. The average age of diagnosis, exposure duration and latent period of the tunneling and mining workers were less than those of the transporting and helping workers. The average ages of diagnosis, exposure duration and latent period were gradually extended with the diagnostic era pass. Among the total CWP cases,39.60% was diagnosed after ending dust exposure, and the average interphase was 9.5 years. The ratios of CWP cases who were diagnosed after ending dust exposure increased remarkably with the time pass. Additionally,7.27% of CWP cases were complicated with pulmonary tuberculosis. Furthermore, the incidence of tuberculosis increased significantly with the CWP progress.Among the 95 death cases of CWP, the main causes included pneumoconiosis, other tumors, tuberculosis, lung cancer and heart disease. If excluded the death causes of CWP, tuberculosis, lung cancer and pulmonary heart disease, the life span could be prolonged 4.3,1.4,1.2,1.4 years, respectively. The average survival time of CWP patients without complication of pulmonary tuberculosis was longer than those with the pulmonary tuberculosis. The main risk factors which could affect the survival of CWP patients were the start eras of dust exposure, the age and stage of first diagnosis. The stage of first diagnosis topped the list of RR, followed by the age of first diagnosis and the start eras of dust exposure.Among the workers whose CDE were more than 2000 mg each years,40.44% developed to CWP. Cumulative incidences of the tunneling and mining workers were higher than those of the transporting and helping workers in 40-year observation period. The cumulative incidence rate of those miners whose CDE were between 100 to 2000 mg each years was lower than whose CDE more than 2000mg each years in 40-year observation period. We assumed that the future dust concentration was the same as the level in 2014, there will be 304.5 cases in the tunneling and mining workers and 29.3 cases in the transporting and helping workers for these exposure miners.Conclusions(1) The underground dust concentration of the mine were decreased significantly from 1975 to 2014. However, the exceeded standard rates of dust concentration were still more than 40%.(2) Among the total CWP cases,90.71% was tunneling and mining workers and 39.60% was diagnosed after ending dust exposure.(3) If excluded the death causes of CWP, tuberculosis, lung cancer and pulmonary heart disease, the life span could be prolonged 4.3,1.4,1.2,1.4 years respectively.(4) The cumulative incidences of CWP were increased with the CDE, and 40.44% of the workers whose CDE were more than 2000 mg each year developed into CWP cases. It suggested that there was a dose-response relationship between CDE and cumulative incidence.(5) There will be 334 cases in this mine if the dust concentration was same as the level in 2014. |
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