Exposure to respirable coalmine dust and incidence of progressive massive fibrosis.

Data gathered since 1953 concerning more than 30,000 coalminers while employed at 24 collieries in England, Scotland, and Wales have been used to study the incidence of progressive massive fibrosis (PMF) in working coalminers. Results refer to 52,264 approximately five year intervals when the miners were at risk of an attack of PMF. One objective of the present study was to describe how the five year attack rate of PMF was related to miners' age, colliery, and simple pneumoconiosis category at the start of the periods at risk. The main objective was to estimate the relation between exposure to dust and incidence of PMF and to examine how this relation changes in the presence of coalworkers' simple pneumoconiosis (CWSP). Film readings, in some cases based on clinical assessments only, showed 462 attacks of PMF over the five year risk periods. The men concerned had experienced higher cumulative exposures to dust than their colleagues of similar age at the same collieries, a result found at 65 of the 68 age colliery groups where an attack had occurred. The association was highly significant statistically. Simple pneumoconiosis clearly predisposed to PMF, with five year attack rates of 13.9%, 12.5%, 4.4%, and 0.2% among men with categories 3, 2, 1, and 0 respectively at the start of the risk periods. Once simple pneumoconiosis category 1 or more had been attained, those with higher cumulative exposure to dust were not at greater risk of an attack of PMF than other men with the same CWSP category. Among most miners, those with category 0, however, the risks of an attack of PMF increased clearly with exposure. Risks of an attack were higher among older men irrespective of CWSP category. In addition, there were large colliery specific variations in incidence related to variations in the carbon content of the coal though not fully explained by them. It is concluded that cumulative exposure to respirable dust is the decisive central factor in the development of PMF. Its effect is primarily in causing simple pneumoconiosis category 1 or higher which predisposes to PMF, though the dust related incidence among men with category 0 is not negligible in view of the large numbers at risk. Continuation of the policy to minimise dust concentrations underground therefore seems the only secure strategy to limit, and eventually eliminate, PMF.     

Dust exposure, pneumoconiosis, and mortality of coalminers

General mortality in approximately 25 000 British coalminers over 22 year periods ending in 1980 was 13% lower on average than in English and Welsh men in the same regions of Britain. There were significant within region variations between collieries, and standardised mortality ratios increased during the later years of the follow up, approaching or slightly exceeding 100 in most of the 20 coalmines studied. Age specific comparisons of 22 year survival rates were made in subgroups. Relative risks of death from all non-violent causes for men with the earliest stage of progressive massive fibrosis (PMF category A), compared with risks in miners with no pneumoconiosis (category O), ranged from 1.2 in those aged 55-64 initially to 3.5 for those aged 25-34. Mortality in miners with higher categories of PMF (B or C) was even more severe. Survival rates in men with category 1 simple pneumoconiosis were about 2% to 3% lower than in miners with radiographs classified as category O, but there was no consistent evidence of an increase in mortality with increasing category of simple pneumoconiosis. Mortality from all non-violent causes increased systematically with increases in estimates of exposure to dust before the start of the follow up. That gradient was attributable primarily to deaths certified as due to pneumoconiosis and those recorded as due to bronchitis and emphysema (p less than 0.001). There was some evidence of a dust related increase in deaths from cancers of the digestive system (p approximately equal to 0.05), but none of an association between exposure to coalmine dust and lung cancer. Lung cancer mortality, assessed over 17 year periods, was about 5.5 times higher in smokers than in life long non-smokers. Smokers with no pneumoconiosis had slightly higher lung cancer death rates than smokers with pneumoconiosis. We conclude that miners exposed to excessive amounts of respirable coalmine dust are at increased risk of premature death, either from progressive massive fibrosis or from chronic bronchitis or emphysema.     

Dust exposure, pneumoconiosis, and mortality of coalminers.

General mortality in approximately 25 000 British coalminers over 22 year periods ending in 1980 was 13% lower on average than in English and Welsh men in the same regions of Britain. There were significant within region variations between collieries, and standardised mortality ratios increased during the later years of the follow up, approaching or slightly exceeding 100 in most of the 20 coalmines studied. Age specific comparisons of 22 year survival rates were made in subgroups. Relative risks of death from all non-violent causes for men with the earliest stage of progressive massive fibrosis (PMF category A), compared with risks in miners with no pneumoconiosis (category O), ranged from 1.2 in those aged 55-64 initially to 3.5 for those aged 25-34. Mortality in miners with higher categories of PMF (B or C) was even more severe. Survival rates in men with category 1 simple pneumoconiosis were about 2% to 3% lower than in miners with radiographs classified as category O, but there was no consistent evidence of an increase in mortality with increasing category of simple pneumoconiosis. Mortality from all non-violent causes increased systematically with increases in estimates of exposure to dust before the start of the follow up. That gradient was attributable primarily to deaths certified as due to pneumoconiosis and those recorded as due to bronchitis and emphysema (p less than 0.001). There was some evidence of a dust related increase in deaths from cancers of the digestive system (p approximately equal to 0.05), but none of an association between exposure to coalmine dust and lung cancer. Lung cancer mortality, assessed over 17 year periods, was about 5.5 times higher in smokers than in life long non-smokers. Smokers with no pneumoconiosis had slightly higher lung cancer death rates than smokers with pneumoconiosis. We conclude that miners exposed to excessive amounts of respirable coalmine dust are at increased risk of premature death, either from progressive massive fibrosis or from chronic bronchitis or emphysema.     

Factors associated with the development of progressive massive fibrosis in British coalminers: a case-control study.

Possible associations between the incidence of progressive massive fibrosis (PMF) over periods of average length 11 years during 1963-80 and a range of explanatory variables, both environmental and medical, were examined in a study group of 4772 miners and ex-miners using case-control methods. Cases were members of the study group who developed PMF during the study period; controls were men who remained free of the disease. Cases and controls were matched on cumulative dust exposure to the start of the study period, colliery of employment, and whether or not employment before and during the study period had been at a single colliery only. Of 257 cases of PMF, 142 were matched to four controls each, 39 to three controls, 33 to two controls, and 31 to a single control only. Twelve cases could not be matched. Age and category of simple pneumoconiosis were each found to be associated with the incidence of PMF, confirming the results of many previous studies. Quetelet's index of body mass (a measure of weight, normalised for height) was found to differ considerably between cases and controls, cases tending to be lighter for their height. The difference did not vary significantly between three groups of collieries, defined by coal rank. Regression analysis confirmed the high level of statistical significance of the difference (p less than 0.001), allowing for the effects of age and prior category of simple pneumoconiosis. Of the environmental factors considered, an index of residence time of dust in the lungs was found to have the most statistically significant association with the incidence of PMF. The crudeness of the measure used, however, together with unreliability in estimates of early exposure to dust for some of the men studied, means that further work is necessary to investigate the magnitude and significance of this apparent association. In low and medium rank collieries there were large differences between the proportion of cases and controls showing a range of respiratory symptoms, cases consistently displaying a higher prevalence. In the high rank collieries of south Wales, however, symptoms occurred with equal frequency in cases and controls, the prevalence at these collieries being the same as among cases generally. Regression analysis (low and medium rank collieries only) showed that the presence of breathlessness was the symptom most strongly associated with the risk of attack of PMF, allowing for the effects of age and Quetelet's index.     

Coalworkers' simple pneumoconiosis and exposure to dust at 10 British coalmines.

Five physicians' radiological assessments of coalworkers' simple pneumoconiosis (CWP) in 2600 coalminers at 10 British collieries have been studied in relation to the individuals' estimated lifetime (mean 33 years) exposure to respirable coalmine dust. Estimates of exposure were based on 20 years of observations at each colliery. Radiographic classifications were clearly associated with the measures of dust exposure. Important unexplained differences between some of the collieries were disclosed. Among men with similar cumulative dust exposures those with longer exposure time had higher prevalence of CWP. In general there was no evidence that the quartz concentrations experienced (average 5% of mixed dust) affected the probability of developing coalworkers' simple pneumoconiosis. Some men reacted unfavourably (two or more steps of change on the 12-point radiological scale) over a 10-year period to coalmine dust with a relatively high quartz content.     

Progressive massive fibrosis and simple pneumoconiosis in ex-miners.

A group of 17 738 working miners, medically examined during 1953-8, were followed up from 1974 to 1980. Of the 7118 men re-examined, 2547 were still working miners and 4526 had left the industry (45 were of unrecorded status). The incidence of progressive massive fibrosis (PMF) over an average follow up period of 22 years among men who had remained in the industry was 27 per 1000, but 94 per 1000 among men who had left. This difference was only partly related to the difference in age between the groups; for men without simple pneumoconiosis at the start of the period, and for similar age groups (45-64), the attack rate in miners was 20 per 1000 and in the ex-miners 41 per 1000. In a group of 1902 leavers who did not have PMF at a medical examination conducted at most four years before leaving, 172 had developed PMF by the time of the follow up examination. Of these, 116 had had simple pneumoconiosis at the earlier examination. Cumulative exposure to respirable dust, category of simple pneumoconiosis, and age were each found to influence the probability of developing PMF in a subgroup of the 1902 men. Among the 1902 leavers, there was no overall progression or regression of simple pneumoconiosis.     

Progressive massive fibrosis and simple pneumoconiosis in ex-miners

A group of 17 738 working miners, medically examined during 1953-8, were followed up from 1974 to 1980. Of the 7118 men re-examined, 2547 were still working miners and 4526 had left the industry (45 were of unrecorded status). The incidence of progressive massive fibrosis (PMF) over an average follow up period of 22 years among men who had remained in the industry was 27 per 1000, but 94 per 1000 among men who had left. This difference was only partly related to the difference in age between the groups; for men without simple pneumoconiosis at the start of the period, and for similar age groups (45-64), the attack rate in miners was 20 per 1000 and in the ex-miners 41 per 1000. In a group of 1902 leavers who did not have PMF at a medical examination conducted at most four years before leaving, 172 had developed PMF by the time of the follow up examination. Of these, 116 had had simple pneumoconiosis at the earlier examination. Cumulative exposure to respirable dust, category of simple pneumoconiosis, and age were each found to influence the probability of developing PMF in a subgroup of the 1902 men. Among the 1902 leavers, there was no overall progression or regression of simple pneumoconiosis.     

Factors predisposing to the development of progressive massive fibrosis in coal miners.

Altogether 238 759 miners employed by the National Coal Board were examined in the third of the Board's radiological surveys from 1969 to 1973 inclusive. Excluding those diagnosed as having progressive massive fibrosis (PMF) on that occasion, 210 847 were in collieries still operating at the time of the fourth survey four to five years later 132 728 attended for radiography at the same colliery on the second occasion, and were used to study the attack rate of PMF. In all groups in the age range 35-54 and having category 2 simple pneumoconiosis (SPN) or less, 80% or more had a second radiograph. It was found that the probability of developing PMF increased sharply with rising category of SPN; however, half the cases occurred in men having SPN categories 0 or 1, who were in the majority. Current coalface work had no significant effect on the attack rate. Age increased the attack rate of PMF within each major SPN category (0, 1, 2, and 3), especially the higher categories. All or part of this effect may have been due to the fact that SPN in younger men with categories 1 and 2 tends to lie in the lower range within these categories. Similarly, a lower distribution of SPN within each category associated with a low overall local prevalence may account wholly or in part for the great difference between the attack rates of PMF supervening on each category of SPN in Scotland and South Wales. The rank (quality) of coal mined had no effect on the attack rate.     

Quantitative relations between exposure to respirable coalmine dust and coalworkers'' simple pneumoconiosis in men who have worked as miners but have left the coal industry.

Present estimates of the quantitative relations between exposure to mixed respirable coalmine dust and risk of developing coalworkes' simple pneumoconiosis are based on studies of working miners. These studies did not include men who had been miners but had left the coal industry, and it was not known whether the estimates of risk were also appropriate for these men. The results are reported of a study in which the dust/disease relations in men who have been miners but have left the industry have been compared with those in men who have remained in it. A sample of 17738 men who were first examined when working in 24 British collieries in the 1950s has been followed up about 22 years later. It was possible to examine 61% of the survivors, 44% of the original sample. Simple pneumoconiosis was more frequent among men (particularly older men) who had left the industry than among those who had stayed in it. A detailed analysis did not show any systematic or statistically significant difference between men who stayed and men who left in the quantitative relations between dust exposure and simple pneumoconiosis. Present estimates of risk of simple pneumoconiosis in relation to exposure to mixed respirable dust in working miners adequately describe the relation found in men who have been miners but have left the industry.     

Quantitative relations between exposure to respirable coalmine dust and coalworkers' simple pneumoconiosis in men who have worked as miners but have left the coal industry

Present estimates of the quantitative relations between exposure to mixed respirable coalmine dust and risk of developing coalworkes' simple pneumoconiosis are based on studies of working miners. These studies did not include men who had been miners but had left the coal industry, and it was not known whether the estimates of risk were also appropriate for these men. The results are reported of a study in which the dust/disease relations in men who have been miners but have left the industry have been compared with those in men who have remained in it. A sample of 17738 men who were first examined when working in 24 British collieries in the 1950s has been followed up about 22 years later. It was possible to examine 61% of the survivors, 44% of the original sample. Simple pneumoconiosis was more frequent among men (particularly older men) who had left the industry than among those who had stayed in it. A detailed analysis did not show any systematic or statistically significant difference between men who stayed and men who left in the quantitative relations between dust exposure and simple pneumoconiosis. Present estimates of risk of simple pneumoconiosis in relation to exposure to mixed respirable dust in working miners adequately describe the relation found in men who have been miners but have left the industry.     

Classification of progressive massive fibrosis of coalminers by type of radiographic appearance.

In a pilot study the chest radiographic appearances of 112 coalminers who developed progressive massive fibrosis (PMF) over an 11 year period have been classified into six types based on the appearances of the large radiographic opacities. The most common type of PMF was one or more large shadows of homogeneous radiodensity. Less common types included markedly rounded shadows usually less than 3 cm in diameter, non-homogeneous shadows appearing to consist of conglomerations of small rounded opacities, and condensations of linear or streaky shadows. Good reproducibility by one reader between two readings were obtained. The lifetime exposures to mixed respirable coal mine dust, and to its quartz component, of these 112 men were compared with those of control subjects matched for age and starting category of simple pneumoconiosis but without PMF. Overall, the men with PMF had been exposed to more mixed dust than controls, confirming that one of the reasons some men with simple pneumoconiosis develop PMF is that they have inhaled more dust than others. Eleven of the 112 cases had large opacities that were not homogeneous and appeared to consist of conglomerations of "r" type small rounded opacities. The average quartz exposures of these men were much higher than in control subjects, suggesting that in this type of PMF quartz was an important causative factor.     

煤矿工人实际接尘工龄及脱尘率变动趋势分析

研究煤矿井下工人实际接尘工龄及脱尘率对评价粉尘危险度，进行尘肺发病预测具有重要意义，笔者采用回顾性队列研究方法，对某煤矿１９５８～１９８８年入矿工人实际接尘工龄及脱尘情况进行分析，结果表明：（１）工种对接尘工龄有影响，例如接尘１０年时，采煤工累积脱尘概率为３２．３６％，掘进工为２１．９４％，辅助工为２１．６５％，判别非常显著；（２）接尘工龄与工人进行矿年代有关，累积脱尘率达３０％时，１９５８～１９     

煤工尘肺预期发病工龄寿命表法研究

目的 研究煤工尘肺预期发病工龄。方法 收集整理某局1960－1995年期间的8291份接尘工人健康检查资料,分别计算不同时间的尘肺累积发病数,队列寿命表法求得矿工预期发病工龄。结果 煤矿工人的接尘工龄与累积患病率的概率单位之间呈正相关（r=0.98,P=0.0001),煤工尘肺的发病率随工龄的增加而增高,预期发病工龄随工龄的增加而缩短。结论 煤矿工人的尘肺发病工龄约为15年左右,在目前煤矿粉尘浓度水平的条件下,若想把尘肺患病率控制在1％左右,各工种的工人接尘期限以不超过6年为宜。     

Dust exposure, dust recovered from the lung, and associated pathology in a group of British coalminers

The relation between dust exposure, retained lung dust, and pneumoconiosis have been examined in 430 dead coalminers who had participated in a large scale epidemiological survey of respiratory health. The men were divided into three groups depending on the presence of particular lesions in their lungs. Lungs containing no fibrotic lesions in excess of 1 mm were included in the "M" group, those with fibrotic lesions of between 1 mm and 9 mm in diameter were included in the "F" group, and those with any lesion 10 mm or more were categorised as having progressive massive fibrosis (PMF). The men were further divided into four groups according to the rank of coal mined at the colliery of employment. The mean weight of lung dust increased over the pathological range (M----F----PMF) regardless of the rank of coal mined. The men with PMF had not received unusually high exposures to dust in life but were found to have accumulated more dust in their lungs per unit of dust exposure than men without PMF, providing further evidence for differences in the patterns of deposition or clearance, or both, of dust in these men compared with those who do not develop PMF. For men who had mined the higher rank coals there was no difference in the composition of the lung dust between the pathological groups. Lungs from men mining low rank coal, however, showed a striking increase in the proportion of ash over the pathological groups (M, F, and PMF). In men who had mined low rank coal the proportion of ash in the airborne dust to which they had been exposed and in the dust retained in their lungs was, as expected, greater than in men who had worked with higher rank coals. For the same men, and particularly associated with the presence of some dust related fibrosis, the proportion of ash in retained dust was higher than that in the dust to which the men were exposed suggesting the occurrence of selective deposition or retention of the mineral components of dust in this group.     

Dust exposure, dust recovered from the lung, and associated pathology in a group of British coalminers.

The relation between dust exposure, retained lung dust, and pneumoconiosis have been examined in 430 dead coalminers who had participated in a large scale epidemiological survey of respiratory health. The men were divided into three groups depending on the presence of particular lesions in their lungs. Lungs containing no fibrotic lesions in excess of 1 mm were included in the "M" group, those with fibrotic lesions of between 1 mm and 9 mm in diameter were included in the "F" group, and those with any lesion 10 mm or more were categorised as having progressive massive fibrosis (PMF). The men were further divided into four groups according to the rank of coal mined at the colliery of employment. The mean weight of lung dust increased over the pathological range (M----F----PMF) regardless of the rank of coal mined. The men with PMF had not received unusually high exposures to dust in life but were found to have accumulated more dust in their lungs per unit of dust exposure than men without PMF, providing further evidence for differences in the patterns of deposition or clearance, or both, of dust in these men compared with those who do not develop PMF. For men who had mined the higher rank coals there was no difference in the composition of the lung dust between the pathological groups. Lungs from men mining low rank coal, however, showed a striking increase in the proportion of ash over the pathological groups (M, F, and PMF). In men who had mined low rank coal the proportion of ash in the airborne dust to which they had been exposed and in the dust retained in their lungs was, as expected, greater than in men who had worked with higher rank coals. For the same men, and particularly associated with the presence of some dust related fibrosis, the proportion of ash in retained dust was higher than that in the dust to which the men were exposed suggesting the occurrence of selective deposition or retention of the mineral components of dust in this group.     

Pneumoconiosis and advanced occupational lung disease among surface coal miners--16 states, 2010-2011

Coal workers' pneumoconiosis (CWP) is a chronic occupational lung disease caused by long-term inhalation of dust, which triggers inflammation of the alveoli, eventually resulting in irreversible lung damage. CWP ranges in severity from simple to advanced; the most severe form is progressive massive fibrosis (PMF). Advanced CWP is debilitating and often fatal. To prevent CWP, the Coal Mine Health and Safety Act of 1969 established the current federal exposure limit for respirable dust in underground and surface coal mines. The Act also established a surveillance system for assessing prevalence of pneumoconiosis among underground coal miners, but this surveillance does not extend to surface coal miners. With enforcement of the exposure limit, the prevalence of CWP among underground coal miners declined from 11.2% during 1970-1974 to 2.0% during 1995-1999, before increasing unexpectedly in the last decade, particularly in Central Appalachia. Exposure to respirable dust is thought to be less in surface than underground coal miners. Although they comprise 48% of the coal mining workforce, surface coal miners have not been studied since 2002. To assess the prevalence, severity, and geographic distribution of pneumoconiosis among current surface coal miners, CDC obtained chest radiographs of 2,328 miners during 2010-2011 through the Coal Workers' Health Surveillance Program of the National Institute for Occupational Safety and Health (NIOSH). Forty-six (2.0%) of 2,257 miners with >1 year of surface mining experience had CWP, including 37 who had never worked underground. Twelve (0.5%) had PMF, including nine who had never worked underground. A high proportion of the radiographs suggested silicosis, a disease caused by inhalation of crystalline silica. Surface coal mine operators should monitor worker exposures closely to ensure that both respirable dust and silica are below recommended levels to prevent CWP. Clinicians should be aware of the risk for advanced pneumoconiosis among surface coal miners, in addition to underground coal miners, to facilitate prompt disease identification and intervention.     

2003至2008年某矿务集团煤工尘肺发病情况分析

目的 分析某煤矿2003至2008年尘肺病检出情况,探讨该矿尘肺发病特点,为尘肺病的防治提供科学依据.方法 收集1949年以来井下粉尘监测数据及2003至2008年的健康监护资料和尘肺诊断资料,分析尘肺发病情况,根据不同年代的粉尘接触水平结合工种和工龄推算安全总粉尘累积剂量.结果 2003至2008年该矿务集团在岗工人职业性健康监护率呈逐年提高趋势,共新检出煤工尘肺病例296例,总检出率为0.57%,平均年检出率为0.32%;Ⅰ期煤工尘肺268例,占全部病例的90.59%,87.20%(258例)的煤工尘肺患者为采掘工;新发病例的接尘工龄最短为3年,最长38年;每年总粉尘累积剂量为86.1～4926.0mg/m3.用百分位数法(第99%百分位数)推算煤矿井下工人每年安全总粉尘累积剂量为120.6 mg/m3.结论 尘肺病防治的重点工种是采掘工,在现有工作条件下井下采掘作业工龄不应超过13年.

Abstract：

Objective Analyzed associations among the incidence of coal workers' pneumoconiosis from 2003 to 2008, jobs, exposure years and cumulative total dust exposure levels(CTE ) and found the current characteristics of the mine incidence of pneumoconiosis disease. Methods collected the health care information of the new diagnosed pneumoconiosis of underground mine workers from 2003 to 2008 and the dust monitoring data of underground mine from 1949 and estimated the personnel cumulative total dust exposure levels (CTE); analyzed the incidence features of the new diagnosed pneumoconiosis. Results The rates of health surveillance of workers were gradually improved from 2003 to 2008 and 296 new coal workers pneumoconiosis were diagnosed. The total incidence was 0.57%, and the average annual rate was 0.32%. Among the new diagnosed cases, phase I accounted for 90.5% and the 87.2% from coal mine drillers. The shortest exposure period was 3 years and the longest was 38 years, and the cumulative total dose of dust was varied between 86. 1 and 4926 mg/m3 per year. The total dust accumulated limited dose was calculated by the percentile method to prevent 99% of miners from pneumoconiosis, which was 120.6 mg/m3 per year, so we suggested that the exposure years should be shorter than 13 years under the current working conditions. Conclusions Preventive coal workers' pneumoconiosis should be focused on mine drillers and their limited exposure years should be within 13 years.     

Histocompatibility antigens in coal miners with pneumoconiosis.

Twenty-five histocompatibility antigens have been measured in 100 coal miners with pneumoconiosis attending a pneumoconiosis medical panel and the results compared with a panel of 200 normal volunteers not exposed to dust. Chest radiographs were read independently by three readers according to the ILO U/C classification. On a combined score, 40 men were thought to have simple pneumoconiosis and 60 men complicated pneumoconiosis. The number of antigens tested and associations between antigens caused difficulties in assessing the statistical significance of differences in prevalence of antigens between groups of men. Using stringent criteria for statistical significance, no significant differences were found in antigen prevalences between miners and controls, or miners with simple or complicated pneumoconiosis. When a less stringent statistical approach was applied, three antigens appeared to have abnormal prevalences in these 100 miners by comparison with the normal volunteers. More detailed examination of these antigen prevalences in relation to radiographic category of pneumoconiosis did not provide any supportive evidence that these slight associations were of statistical or clinical significance. Reports on histocompatibility antigens in miners with pneumoconiosis are reviewed briefly and the results compared. There is no good evidence that any of the histocompatibility antigens so far tested are associated with a clinically important altered risk of simple or complicated pneumoconiosis when dust is inhaled.     

Histocompatibility antigens in coal miners with pneumoconiosis

Twenty-five histocompatibility antigens have been measured in 100 coal miners with pneumoconiosis attending a pneumoconiosis medical panel and the results compared with a panel of 200 normal volunteers not exposed to dust. Chest radiographs were read independently by three readers according to the ILO U/C classification. On a combined score, 40 men were thought to have simple pneumoconiosis and 60 men complicated pneumoconiosis. The number of antigens tested and associations between antigens caused difficulties in assessing the statistical significance of differences in prevalence of antigens between groups of men. Using stringent criteria for statistical significance, no significant differences were found in antigen prevalences between miners and controls, or miners with simple or complicated pneumoconiosis. When a less stringent statistical approach was applied, three antigens appeared to have abnormal prevalences in these 100 miners by comparison with the normal volunteers. More detailed examination of these antigen prevalences in relation to radiographic category of pneumoconiosis did not provide any supportive evidence that these slight associations were of statistical or clinical significance. Reports on histocompatibility antigens in miners with pneumoconiosis are reviewed briefly and the results compared. There is no good evidence that any of the histocompatibility antigens so far tested are associated with a clinically important altered risk of simple or complicated pneumoconiosis when dust is inhaled.     

The Attack Rate of Progressive Massive Fibrosis

A radiological follow-up of the miners and ex-miners in two Welsh mining valleys whose chest radiographs showed simple pneumoconiosis in 1950/51 has been carried out to study the factors associated with the attack rate of progressive massive fibrosis. The radiographs were read in pairs, and also with the pairs separated, the radiographs being randomized and identifying features concealed. The relative value of these two types of reading is discussed.

An attempt to investigate the importance of exogenous tuberculous infection by comparing the attack rate in the two mining valleys, in one of which great efforts had been made to eradicate tuberculosis, failed. The reasons for the failure are discussed.

No evidence was found of any association between the attack rate of progressive massive fibrosis and age, energy expenditure at work, smoking habits, body type, exogenous tuberculous infection, or endogenous infection as measured by the presence of primary complexes in the first radiographs. The only factor related to the attack rate was the average category of simple pneumoconiosis. The attack rate is zero at category ½ and rises to 30 or more per 100 in eight years for category 3. It is argued from this that the logical way to control the appearance of progressive massive fibrosis is to concentrate on preventing miners reaching category 2 of simple pneumoconiosis. Evidence is also presented that considerable progression of simple pneumoconiosis has been occurring during the past eight years amongst coal-face workers at the collieries in this area.