Cases Of Silicosis Research Articles

Six cases of silicosis: implications for health surveillance of stonemasons.

Silicosis is one of the oldest occupational lung diseases, but it continues to cause significant morbidity and mortality worldwide. To report cases of silicosis presenting to two specialist respiratory clinics. A retrospective analysis of prospectively collected data of cases of silicosis in workers referred to specialist respiratory clinics. Over the course of 6 years, six cases were identified. The patients were all male with an age range between 24 and 39 years. The duration of silica exposure ranged between 7 and 20 years (mean 13 years). Four cases were entirely asymptomatic at presentation, and two cases described minimal shortness of breath on exertion. Pulmonary function tests were normal in three cases, and a mild restrictive ventilatory defect was documented in the other cases. All had a low apparent predicted probability of pneumoconiosis based on health questionnaires, spirometry and duration of silica exposure. The initial chest X-ray was abnormal in all six cases with radiological evidence of silicosis (International Labour Office profusion category ≥1/1) on imaging, and all had evidence of silicosis on high-resolution computed tomography (HRCT). Three patients had already progressed to progressive massive fibrosis on HRCT scanning at the time of referral to specialist respiratory services. The appearances of these six cases of silicosis in young, asymptomatic construction workers emphasizes the importance of enforcing effective exposure control and comprehensive surveillance programmes. Our observations highlight the importance of having a low threshold for early radiological screening to promote early and effective detection of this disease.

Silico-tuberculosis and associated risk factors in central province of Iran.

IntroductionCo-existence of silicosis and tuberculosis is known as silico-tuberculosis. This article review the frequency of silicosis and tuberculosis in workers who exposed to silica and evaluate influencing factors that may increase the risk of silico-tuberculosis.MethodsAn analytical cross-sectional study was performed in silica exposed workers in central province of Iran during 2011-2012. Sampling method was un-randomized and considering all workers who at least 6 months exposed to silica. The study was done via questionnaire, clinical examination, spirometry, chest x-ray and tuberculosis investigations.ResultsA total of 3121 workers were included in the study, the mean age of participants was 43.1±12.4 years, and mean employment duration 14.9±6.8 years. Prevalence of TB in silica-exposed workers without silicosis was 172 cases per 100 000 people and prevalence in silicosis cases was 917 cases per 100 000 people. Incidence of TB in silica-exposed workers without silicosis was 69 cases per 100 000 people and incidence in silicosis cases was 459 cases per 100 000 people. The frequency of LTBI/TB was higher in age over thirty years old (P = 0.02), in workers with employment duration over 10 years (P = 0.004), in workers with exposure duration over 5 years (P = 0.03) and smokers with over 5 pack-years (P = 0.01).ConclusionExposure to silica causes a renewed multiplication of bacilli in the healing TB lesions. Prevalence of pulmonary tuberculosis in Silicosis is more common when compared to prevalence in general population, hence all should use prophylactic measures Intensification of work place.

Pulmonary Silicosis Presents with Pleural Effusion.

Silica and silicate mineral dust inhalation can cause a variety of histopathological changes in the lungs and pleura. These include pulmonary silicotic nodules, interstitial infiltrate, fibrosis, and pleural thickening. Pleural effusion is an extremely rare presentation of silicosis. To our best knowledge, there have been only 2 cases of silicosis with pleural effusion reported in medical literature. Herein, we describe a case of a 77-year-old male with almost 50 years' history of occupational silica exposure. He presented with a 4-week history of exertional shortness of breath. He is a lifetime nonsmoker, with no known other significant pulmonary disease. He had chest X-ray which showed a right lung infiltrate and bilateral pleural thickening and effusion. Chest CT showed moderate-sized bilateral pleural effusion and thickening with multiple bilateral intrapulmonary nodules seen. He had undergone extensive workup and was diagnosed with silicosis.

Epidemiological analysis of pneumoconiosis in the Xinjiang Uygur Autonomous Region and cases reported by the Urumqi Railway Bureau.

This study investigated the incidence and development of pneumoconiosis in the Xinjiang Uygur Autonomous Region and cases reported by the Urumqi Railway Bureau to provide a scientific basis for developing prevention and control measures against pneumoconiosis. Data from pneumoconiosis cases were input into Excel and analyzed by SPSS version 17.0. There were 13,165 cases of pneumoconiosis through 2010. Coal workers accounted for the largest proportion of cases. From July 2006 through 2010, a total of 1233 new cases of pneumoconiosis were reported in the Xinjiang Uygur Autonomous Region; most cases were reported in Urumqi. From 1981 to 2012, 3332 new cases of pneumoconiosis had been confirmed by the Urumqi Railway Bureau, including 77.73, 16.96, and 5.31% stage I, II, and III cases, respectively. In the last 30 years, the number of new pneumoconiosis cases peaked in 1986; most of them were silicosis cases. In addition, there were more than 200 cases of pneumoconiosis combined with pulmonary tuberculosis reported by the Urumqi Railway Bureau. The coal industry in Urumqi is the main industry in which occupational pneumoconiosis occurs in Xinjiang. Thus, substantial effort is still required to eliminate pneumoconiosis by 2030.

Study on tissue Doppler imaging in diagnosis of right ventricular hypertrophy in patients with silicosis complicated by chronic pulmonary heart disease

To investigate the value of tissue Doppler imaging (TDI) in the diagnosis of right ventricular hypertrophy in patients with silicosis complicated by chronic pulmonary heart disease. A total of 50 cases of silicosis complicated by chronic pulmonary heart disease in our hospital underwent conventional electrocardiography (ECG) and TDI. The detection rates for right ventricular hypertrophy by two methods were compared. Of 50 cases of silicosis complicated by chronic pulmonary heart disease, 19 were diagnosed with right ventricular hypertrophy by ECG, with a detection rate of 38.0%; 29 were diagnosed with right ventricular hypertrophy by TDI, with a detection rate off 58.0%. Statistical analysis suggested that TDI leads to a significantly higher detection rate for right ventricular hypertrophy in patients with silicosis complicated by chronic pulmonary heart disease (χ² = 4.006, P = 0.036). Both TDI and ECG can be used for detecting right ventricular hypertrophy in patients with silicosis complicated by chronic pulmonary heart disease, but the detection rate is higher when TDI is employed. In addition, ECG cannot directly reflect the increase in pulmonary artery pressure. Therefore, TDI is more suitable for the diagnosis of right ventricular hypertrophy in patients with silicosis complicated by chronic pulmonary heart disease and provides a strong diagnostic basis for the clinical treatment of silicosis complicated by pulmonary heart disease.

Estimación de la incapacidad causada por la neumoconiosis

El término Neumoconiosis incluye todas las enfermedades pulmonares causadas por inhalación de polvo. Entre estas la Silicosis, debida a la acción de polvo de silica (SiO2) inhalado, es la más importante y la qur constituye en el mundo un problema médico-sanitario de grandes proporciones. Nuestro país no es ajeno a este problema. En los últimos años se ha comprobado, y se sigue comprobando, la existencia de numerosos casos de Silicosis en las zonas mineras, donde el trabajo requiere, urgentemente, la adopción de medidas preventivas, plenamente justificadas por los resultados satisfactorios que han proporcionado en otros lugares, y porque es necesario conservar un capital humano, irremplazable, si se toma en cuenta las condiciones ambientales de esas zonas.

Relationship between genetic polymorphisms of matrix metalloproteinase-2 and -3 and susceptibility to silicosis

To investigate the relationship between the genetic polymorphisms of matrix metalloproteinase-2 (MMP-2) (-735) and matrix metalloproteinase-3 (MMP-3) (-1171) and the susceptibility to silicosis. A case-control study was conducted in 113 patients diagnosed with stage I silicosis (case group) and 115 dust-exposed workers without silicosis (control group); the two groups had the same sex, ethnic group, and type of dust and similar age and cumulative exposure time. Polymerase chain reaction-restriction fragment length polymorphism was used to determine the genotypes of MMP-2 (-735) and MMP-3 (-1171). No significant difference was observed in age, cumulative exposure time, or smoking rate between cases and controls (P > 0.05). The frequencies of genotypes C/C, C/T, and T/T at MMP-2 C-735T in the case group were 57.5% (65/113), 31.0% (35/113), and 11.5% (13/113), respectively, which were significantly different from those of the control group (69.6% (80/115), 26.9% (31/115), and 3.5% (4/115)), χ² = 6.542, P < 0.05). The frequencies of T allele in cases and controls were 27.0% and 17.0%, respectively, which were significantly different from each other χ² = 6.704, P < 0.05). Carriage of T allele at MMP-2 C-735T increased the risk of silicosis (OR = 1.811, 95% CI: 1.151-2.847). The frequencies of genotypes 6A/6A, 5A/6A, and 5A/5A at MMP-3 A-1171A were 67.2% (76/113), 24.8% (28/113), and 8.0% (9/113), respectively, in the case group, versus 59.1% (68/115), 37.4% (43/115), and 3.5% (4/115) in the control group (χ² = 5.519, P > 0.05). Genetic polymorphism at MMP-2 C-735T is significantly associated with the development of silicosis. Carriage of T allele increases the risk of silicosis among workers exposed to dust. No significant association was found between MMP-3 A-1171A polymorphism and silicosis in this study.

0225 Cancer, mortality and acute myocardial infarction in workers exposed to respirable crystalline silica dust at a Swedish porcelain factory

ObjectivesExposure to silica dust is a health hazard in the ceramic industry. We studied cancer, mortality and acute myocardial infarction (AMI) among workers at a Swedish porcelain factory.MethodAnnual average of...

Threshold Value Estimation for Respirable Quartz Dust Exposure and Silicosis Incidence Among Workers in the German Porcelain Industry

Threshold Value Estimation for Respirable Quartz Dust Exposure and Silicosis Incidence Among Workers in the German Porcelain Industry

Impact of occupational carcinogens on lung cancer risk in a general population

We wish to comment upon the article ‘Impact of occupational carcinogens on lung cancer risk in a general population’ by De Matteis et al., published in your journal in June 2012. In the conclusion of their population-based study, the authors state that there is a causal relationship between lung cancer and ‘low-dose’ exposure to certain carcinogens and/or to other agents for which the aetiological role is still under debate. Based on a jobexposure matrix (JEM), the authors used three different exposure categories: no exposure; low exposure; and high exposure. The difficulty in defining ‘past exposure’ in occupationally exposed subjects, even those for whom data on exposure level are available, is well known. This difficulty is much more pronounced when dealing with estimating the exposure levels in the general population. Indeed, this is one of the main problems in population-based studies. Since the authors stated that their conclusions are evidence-based, it goes without saying that it is crucial to know what they mean by ‘exposure’ and what is the weight of the exposure to ubiquitous agents (e.g. silica, asbestos) in causing cancer (i.e. the causal relationship). In fact, when dividing exposure into categories, there was no clear definition of the range values for low and high exposure. We can only presume from the data that they may refer to levels based on ‘higher’ and ‘lower’ general concepts without any strong, documented data that allow, at least, for a distinction between the no exposure category and the low exposure category. We found no analytical data supporting the JEM range, without which it is impossible to prove the validity of the results. We asked for the authors opinion on the cases of silicosis reported in the group of subjects without exposure. In fact, we were more than surprised when noting that there were a total of eight cases of silicosis, four of which were included in the group considered as having had no exposure (according to the JEM the authors used). The authors stated that they made a mistake in data analysis and the sentence reported in the original article was incorrect: the number of people with silicosis classified as ‘not exposed’ was two instead of four. In our opinion a relevant exposure to silica is the basic condition to compensate silicosis cases. The reduction of the percentage in the error (25% vs 50%) in identifying the silica exposure in people with silicosis is not a sufficient condition to confirm the validity of the JEM. So the correction of the sentence does not change our evaluation of the limitations of the adopted methodology to assess the exposure to carcinogenic agents in a general population, and on this basis our opinion continues to be that the JEM the authors adopted may not be able to distinguish between the categories ‘no exposure’, ‘low exposure’ and ‘high exposure’. Therefore the authors’ conclusion, that ‘past occupational exposure to asbestos, silica and Ni-Cr even at low levels contributes substantially with PAHs to the current lung cancer burden of 18.1% 5.7% and 7%, respectively’, should be further discussed.

Authors' Response to: Comment upon the article: Impact of occupational carcinogens on lung cancer risk in a general population

We thank Pira and Coggiola for their comments1 on our paper.2 We agree that to estimate lifetime exposure to occupational carcinogens in a general population setting is a difficult task and requires valid assessment tools. It is for this reason that we chose as our job exposure matrix (JEM) the DOM-JEM that was developed specifically to be applied in studies of this kind.3 Pira and Coggiola express concern that the DOM-JEM is unable to distinguish between ‘no’, ‘low’ and ‘high’ exposed jobs/subjects. Their reasoning comes from the fact that among the 2529 men in our study classified as non-exposed to crystalline silica, two subjects reported at interview having been diagnosed with silicosis. We believe that our method is sound. First, with a JEM approach in a population-based study (as this lung cancer case-control is) the JEM constructors would have to aim for a more specific than sensitive JEM3 in order to prevent serious misclassification of non-exposed individuals and consequent attenuation of risk estimates.4 By creating a very specific JEM, like DOM-JEM, only jobs with relatively high intensity and high prevalence of exposed individuals performing these jobs will be assigned (high) exposure. So for instance, within DOM-JEM the job titles shown in Table 1, coded using the five-digit International Standard Classification for Occupations (ISCO) 1968 codes,5 are assigned a ‘high’ exposure to crystalline silica. Table 1 International Standard Classification for Occupations (ISCO) 1968 codes Also, to take into account the small actual difference in silica exposures between the ‘no’ and ‘low’ categories we decided to use the intensity weights of 0, 1 and 4 when estimating cumulative years of silica exposure. Second, as stated in our paper, the DOM-JEM has been compared with other JEMs and individual expert assessments in previous international studies.6,7 Notably, in the study of Peters et al.,6 the odds ratio for the association between lung cancer and silica obtained by applying the DOM-JEM was 1.26, almost identical to those obtained using case-by-case expert assessment (1.26) and a population-specific JEM (1.24). Similar results were obtained for exposure to diesel motor exhaust, whereas for asbestos DOM-JEM showed more consistent results as compared with the other two methods. Third, it is of course possible on rare occasions for a worker performing a theoretically non-exposed job to be exposed (e.g. a schoolteacher exposed to asbestos from a ceiling), but any resultant occurrence of cases of silicosis in the ‘no’ exposure group does not intrinsically invalidate the JEM. This misclassification can only be addressed (if at all) when the exposure can be assigned at the individual level, but it requires a much more detailed job history. Assigning all schoolteachers an exposure to asbestos based on an anecdotal example would be wrong and would create an enormous amount of falsepositively assigned exposures resulting in risk estimates attenuated towards the null. Fourth, the two cases of silicosis that we classified as non-exposed maybe incorrect due to reporting or diagnosis error. In fact, silicosis was only reported at interview in our study. Also, silicosis diagnosis is far from straightforward; radiographic evaluation even by qualified and experienced chest radiographers8 has a poor sensitivity and, whereas specificity is very good, false-positives may occur.9 In summary, we believe that the critique made by Pira and Coggiola of the DOM-JEM, based on a couple of (supposedly) misclassified subjects, without consideration of the whole study, is unfounded. DOM-JEM is a job-exposure matrix specifically developed for population-based studies, with only job-title information in the job histories and with the explicit philosophy of being rather more specific than sensitive in the assignment of exposures so as to avoid misclassification of non-exposed subjects as much as possible. The assigned levels are an informative relative ranking of ‘no’, ‘low’ and ‘high’ exposure and without calibration will have no absolute meaning on a ratio scale (e.g. mg/m3-years of silica exposure). Therefore, we stand by our conclusion that past occupational exposure to asbestos, silica and nickel-chromium, even at low levels, contributes substantially to the current lung cancer burden. Our estimates of population-attributable fractions of 18.1%, 5.7% and 7.0%, respectively, are necessarily imperfect but state-of-the-art and reasonable measures of the impact of these occupational carcinogens on lung cancer risk in this study population.2

12 Mortality and acute myocardial infarction in RCS exposed workers at a Swedish porcelain factory

ObjectivesExposure to silica dust is a health hazard in the ceramic industry. The Swedish porcelain factory Gustavsberg started production in 1827, and have since 1971 performed occupational measurements of respirable...

364 Smoking cessation and lung cancer mortality in a historical cohort of workers with silicosis in Hong Kong, 1981–2006

ObjectivesTo evaluate the impact of smoking cessation on the risk of lung cancer mortality among workers with silicosis.MethodsWe recruited all 3202 incident cases of silicosis in Hong Kong from 1981...

Analyses on the characteristics and the trends of pneumoconiosis notified between 1997 and 2009, in China

To describe the incidence of pneumoconiosis reported in China from 1997 to 2009 and investigate the epidemiological trends and characteristics of pneumoconiosis, and to provide basic data for formulating the guidelines and policies for control of pneumoconiosis, research on pneumoconiosis, and establishing the time series model for monitoring and early warning of pneumoconiosis. The national database of new cases of pneumoconiosis reported from 1997 to 2009 was subjected to systematic arrangement, descriptive analysis, and trend test using SPSS 15.0. The statistical indices included number of new pneumoconiosis cases in each year, types of pneumoconiosis, regional and industrial distributions of pneumoconiosis cases, work types of pneumoconiosis cases, and the annual changes in mean length of service and mean age at the onset of pneumoconiosis. From 1997 to 2009, a total of 122 333 new cases of pneumoconiosis were reported; the number of new cases increased since 1998, but fell to 7620 in 2003, and then it increased again to a maximum of 12 492 in 2009. Of all patients, 87.5% were cases of coal-workers' pneumoconiosis and silicosis; 54 068 (44.2%) were coal-workers' pneumoconiosis cases, and 52 930 (43.3%) were silicosis cases. The pneumoconiosis cases were distributed mainly in Hunan Province (12 995 cases, 10.6%), Shandong Province (8952 cases, 7.3%), and Sichuan Province (8417 cases, 6.9%). Most cases were distributed in coal industry (61270 cases, 50.1%), architectural, material industry (9754 cases, 8.0%), nonferrous metals industry (9380 cases, 7.7%), and metallurgical industry (8773 cases, 7.2%). The work types of these cases mainly included tunneling as the main work (15 659 cases, 12.8%), mining as the main work (15 009 cases, 12.3%), drilling (14 010 cases, 11.5%), tunneling (12 122 cases, 9.9%), and hybrid coalmine work (10 612 cases, 8.7%). The mean length of service at the onset of pneumoconiosis in new cases of pneumoconiosis was shortened from 1997 to 2009, with a median length of service of 20.00 years; the median lengths of service at the onsets of coal-workers' pneumoconiosis, silicosis, and asbestosis were 21.58, 17.00, and 20.00 years, respectively. The median age at the onset of pneumoconiosis was 51.00 years, and the mean age of onset in new cases of pneumoconiosis increased over the 13 years. The incidence of pneumoconiosis is still high, with a marked concentrated trend in several industries, work types, and pneumoconiosis types, a marked rising trend in number of new cases, and a marked shortening trend in length of service at the onset of pneumoconiosis. The prevention and control of pneumoconiosis should be enhanced in key industries and for people engaging in key types of work according to the epidemiological characteristics of pneumoconiosis. In addition, the demonstration project of comprehensive prevention and control of occupational dust hazards should be carried out, and the monitoring and early warning system for pneumoconiosis should be established.

The influence of the functional capacity on subjective well-being and quality of life of patients with silicosis

Objectives: Silicosis is a fibrosing and irreversible lung disease. In China, 9870 new silicosis cases were reported in 2010. The physical and mental status of patients with silicosis should be paid attention to. The aims of this study were to evaluate the influence of the patients’ functional capacity on subjective well-being (SWB) and quality of life (QOL), provide the scientific basis for further intervention measures, and improve their health status. Methods: We investigated 324 inpatients with silicosis during April 2011 to September 2011. The 6-minute walk test (6MWT) was the major methodology used to evaluate the functional capacity, the SF-12 (Short Form-12) to evaluate the QOL, and the MUNSH (Memorial University of Newfoundland Scale of Happiness) scale to evaluate the SWB. Results: The distance of 6MWT suggested a significant and positive correlation with SWB and QOL of patients with silicosis (P < 0.01). In China, patients with silicosis had low SWB and QOL. Conclusions: The SWB and QOL of patients with silicosis are still relatively low and their health status needs improvement. At the same time, longer distances walked by patients suggest more positive influences on their SWB and QOL. It indicates that when the 6MWT cooperates with SWB and QOL, it may be able to get more accurate evaluation results of patients’ survival status.

English

The clinical and imaging characteristics of cryptococcal meningitis (CM) with concurrent pulmonary cryptococcosis&nbsp;(PC) were presented in the present study. Retrospective clinical data analysis of 20 histopathologically confirmed cases of CM with concurrent PC. The patients included eight males and four females, with four 62-year olds and an average age of 33.3&nbsp;years&nbsp;&plusmn;&nbsp;23.8&nbsp;years. The course was from 14&nbsp;days to 120&nbsp;days (41.0&nbsp;&plusmn;&nbsp;39.9). The first symptom in ten cases was fever, eight cases had headache, three cases had productive cough and one case had chest pain. Ten cases have underlying diseases, which include six cases of chronic viral hepatitis B, three cases of silicosis with concurrent tuberculosis, one case of malnutrition, one case of systemic lupus erythematosus and one case of sinusitis. Ten of the cases were misdiagnosed as pulmonary tuberculosis, and one case was misdiagnosed as lung cancer. The chest X-rays revealed patchy, nodular shadows scattered in both lungs, with blurred edges and irregular low density areas. The computed tomography (CT) showed highly dense, patchy and speckled shadows widespread in both lungs, cavities of varying sizes, and elliptical, smooth-edged high density nodules. The cases were treated with intravenous amphotericin B (AMB) combined with fluconazole and intrathecal AMB. Eight cases were cured, whereas four cases improved. The clinical symptoms and imaging of CM with concurrent PC lack specificity. The increasing the understanding of CM imaging is beneficial to early diagnosis. &nbsp; Key words:&nbsp;Cryptococcus neoformans meningitis, pulmonary cryptococosis, imaging.

Silicosis in Coimbatore district of Tamil Nadu: A passive surveillance study

Introduction:Silicosis in Coimbatore district of Tamil Nadu: A passive surveillance study.Aim:This study was done to describe the level of preventive measures and level of awareness among the patients diagnosed with silicosis during a one-year period.Settings and Design:Coimbatore Medical College Hospital.Materials and Methods:This is a passive surveillance study based on patients diagnosed with silicosis in our outpatient facility for a one-year period between January 1, 2012 and December 31, 2012.Results:Seventeen cases of silicosis were diagnosed based on history of exposure to silica and radiological features. The mean age was 55 years with 16 males and one female. The average duration of exposure was 22 years. A protective mask was used by 29% of the patients and one patient had awareness about the risks of exposure to silica. Active tuberculosis was found in 12% and old tuberculosis in 47% of patients; 59% of the patients were smokers. Spirometry showed a restrictive pattern in 59% of the patients. Radiologically nodular opacities with upper-zone predominance was found in majority of the cases.Conclusion:Most patients are exposed to silica in unorganized industries. Majority of the patients lack awareness about the disease and there is a low implementation of preventive and control measures. As this study was a passive surveillance, it represents only the tip of iceberg and an active field-level surveillance could reveal the true prevalence of this disease.

P112 Therapeutic Whole Lung Lavage For Silicosis – First Application in the UK

Silica is a highly fibrogenic dust and this is reflected in the low amounts of dust found in the lungs of those with fatal silicosis – approximately 3g in total....

Statistics on notification of pneumoconiosis in China in 2010

To describe the reported incidence of pneumoconiosis in China in 2010, and to investigate the reasons for increase in the number of new cases. Descriptive analysis was performed on the new cases of pneumoconiosis reported by the "Monitoring System of Health Hazard Factors" under "China Information System for Disease Control and Prevention" in China in 2010. A total of 23812 new cases of pneumoconiosis were reported in all provinces, autonomous regions, and municipalities except Tibet, Hong Kong, Macao, and Taiwan, as well as Production and Construction Corps of Xinjiang, increased by 64.28% compared with the number in 2009. There were 12 564 cases of coal-workers' pneumoconiosis and 9870 cases of silicosis, accounting for 94.21% of all new cases. The cases of silicosis were distributed mainly in Sichuan, Liaoning, and Jiangsu, from which 52.21% of all new silicosis cases were reported; most of the cases were in railway, nonferrous metal, and coal industries, and the majority of them were drillers. The cases of coal-workers' pneumoconiosis were distributed mainly in Hunan, Chongqing, Sichuan, Shanxi, and Beijing; most of the cases were in coal industry, and the majority of them were coal-getters. The main reasons for increase in the number of new cases were as follows: increased numbers of reporting agencies and diagnosis agencies, expanded coverage of occupational health surveillance and occupational insurance, closing down and integration of small coal mines, solution of untreated problems, enhanced legal awareness of employers and employees, and investigation into omission of pneumoconiosis case reporting. Coal-workers' pneumoconiosis and silicosis are the most serious occupational diseases in China, and specific measurements for prevention and control should be taken according to the geographic, industrial, and occupational distributions.

Silicosis exposure–response in a cohort of tin miners comparing alternate exposure metrics

BACKGROUND.: The detailed lung radiographic response to silica exposure has not been described. In estimating the exposure-response relationship in silicosis with statistical models, the absence of baseline (unattributable) risk can disable relative-rate estimation or produce widely varying estimates. This obstructs identification of optimum exposure metrics and invalidates comparisons and meta-analyses, which assume a common background rate. METHODS.: A cohort of 3,000 Chinese tin miners with more than 1,000 cases of silicosis was analyzed for the period 1961-1994. Regular surveillance documented three stages of silicosis. To examine the exposure-response relationship, the intercept in relative-rate models was fixed to correspond to 1% of the observed silicosis rate. Exposure metrics for contributions in different time-windows were simultaneously evaluated, as were burden and cumulative burden metrics. RESULTS.: Silica exposures that most contributed to silicosis onset occurred in the period 5-10 years prior (excess annual rate per 10 mg-year/m(3) , ER = 0.158, 95% CI = 0.125-0.192, or 16% per year). During 10-20 year prior, the excess rate contribution was much smaller (ER = 0.048, 95% CI = 0.037-0.060) but larger again during 20-30 year prior to onset (ER = 0.112, 95% CI = 0.098-0.126). For advanced silicosis, all time periods contributed about equally to the rate of onset. CONCLUSIONS.: Reliable estimates of parameters were observed, demonstrating exposure contributions over time. Burden metrics with different half-lives suggested some reversibility for silicosis onset with a half-life of 20 years. Advanced silicosis was best predicted with a cumulative burden metric which was consistent with prior observations that previously deposited silica continues to cause pulmonary damage.