pneumoconiosis coal-miners · moshkovsky, 1941; hartandaslett, 1942). during recent years there...

BrilJ. industr. Med., 1948, 5, 120

- PNEUMOCONIOSIS OF COAL-MINERSA STUDY OF THE DISEASE AFTER EXPOSURE TO DUST HAS CEASED

BY

ALICE STEWARTWrr nTH ASSISTANCE OF

IDRIS DAVIES, LYNETrE DOWSETT, F. H. MORRELL, AND J. W. PIERCE

From the Medical Research Council pneumoconiosis Unitand Emergency Public Health Laboratory, Cardiff

(RECERva FOR PUBLICATION, APRIL 22, 1948)

Introduction

Throughout the nineteenth century the coal-miningindustry of Great Britain steadily expanded and thenumber of workers increased over twenty-fold. By1831 it was recognized that colliers were liable todevelop " miner's asthma" (Thackrah), and in1857 Cox referred to this disease as "the scourge ofthe mines." Working conditions at this time werenotoriously bad, but in 1842 the first Mines Act waspassed,. and eight years later a Mines Inspectoratewas established. Thereafter ventilation steadilyimproved, and by the end of the century it wasconfidently stated that coal-mining was no longeran unhealthy occupation (Arlidge, 1892). Lungdiseases such as- bronchitis and emphysema werestill prevalent among older miners; but, as colliersappeared to be relatively immune to tuberculosis, itwas assumed that inhalation of coal dust did notproduce silicosis (Oliver, 1902; Colfis, 1915;

- Haldane, 1931).Thus, when legislation was introduced to enable

workmen to obtain compensation for silicosis(Workmen's Compensation Act, 1925-, coal-miningwas not scheduled as a dangerous occupation, andit -was not until 1931 that workers at the coal facewere allowed to apply to the Silicosis Medical Board(Various Industries (Silicosis) Scheme, 1931). Sincethen the numbers of colliers certified by the Medical'Board have rapidly increased, and "coal-minerspneumocomosis is now recognized as the common-est variant of silicosis in this country.

The tardy recognition of this disease has a three-fold explanation. In the first place the true natureof the so-called bronchitis and emphysema was notrealized vntil radiological examination came intogeneral use. Secondly, since coal-miners with dustdisease were not particularly prone to developclinically recognizable tuberculosis, the relationship

between " miner's asthma " and silicosis was notappreciated. Finally it was not until the' 1880'sthat there was any large scale development of " hardcoal" mining, and it is chiefly in these mines thatpneumocomosis occurs.

In this country anthracite and steam coal (bothtypes of hard'coal) are mined in South Wales; andhere, according to the only available statistics, therisk of contracting pneumoconiosis is nearly fortytines as great as in the bituminous mines of Englandand Scotland (Table 1). Similar differences -havebeen observed in other parts of the world, and,although the explanation is obscure it is nowgenerally believed that there is a close relationshipbetween incidence of pneumoconiosis and rank ofcoal, as measured by the non-volatile content of themineral (Sayers, 1938; Flinn and others, 1941;Moshkovsky, 1941; Hart and Aslett, 1942).During recent years there have been several

changes in legislation relating to industrial lungdiseases, which have affected both the numbersentitled to claim compensation and the legaldefinition of dust disease*. The result of these hasbeen a remarkable increase in the number of coal-miners applying to, and certified by, the SilicosisMedical Board. Undoubtedly this is largely dueto increased awareness of the dust hazard, but it ispossible that there has also been some deteriorationin underground working conditions since theintroduction of mechanized mining (Fletcher, 1948.)

Before 1943 the disease contracted by workers incoal-mines was officially known as silicosis, but when

* From 1929 to 1931 miners employed on "special processesconcemed with the mining of certain types of silica rock" wereentitled to claim compensation for silicosis. In 1931 the Workme'sCompensation Act was amended so that some other undergroundoccupations were scheduled under the Silicosis Schemes, and in 1934all underground workers were included (Various Industries (Silicosis)Scheme). In 1943 the Act was completely revised, and the Coal-wining Industry (Pneumoconiosis) Compensation Scheme wasintroduced. -Since then surface workers handling coal and coaltrimmers have become eligible for compensation.

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PNEUMOCONIOSIS OF COAL-MINERS 1

the Workmen's Compensation Act was revised thelegal definition of dust disease was altered and theterm " pneumoconiosis of coal-miners " was sub-stituted for silicosis. Under the old ruling threestages of the disease, defined in accordance with thescheme drafted by the International Conference onSilicosis (International Labour Office, 1930) wererecognized. After July, 1943, men with a slightlyearlier stage of the disease-corresponding toreticulation as defined by Hart and Aslett-becameeligible for compensation*.While it is customary for examining panels of the

Silicosis Medical Board to record the stage of thedisease as revealed by radiological findings, this isnot compulsory. In every case, however, thedegree of pulmonary disability is stated, for on thisdepends the amount of compensation payable bythe employer. In practice there is a close relation-ship between disability award and radiologicalfindings; men with "partial disability" beingfound in the reticulation and first-stage silicosiscategories, and men with " total disability " in thesecond- and third-stage silicosis categories.

Since no provision has been made for periodicexamination of workers in the coal-mining industry,the only official statistics relating to incidence ofpneumoconiosis are those compiled by the SilicosisMedical Board, which has, since 1931, handled allapplications for compensation from workmenemployed in occupations recognized by the Work-men's Compensation Act (Silicosis and AsbestosisMedical Arrangements Scheme, 1931). The Boardusually bases its decisions on a single clinical andradiological examination and, if a man is found tobe " suffering from the disease to such an extent asto make it dangerous for him to continue in theprocess," it has the power to suspend him fromwork. In practice no coal-miner who is certifiedas suffering from silicosis or pneumoconiosis isallowed to work underground, and once he has leftthe industry he is unlikely to be examined again.However, if a relative claims further compensationon death, the Board is informed and an autopsy ismade.

The Present InvestigationIn 1945, when the present investigation was

planned, the Silicosis Medical Board was suspending* Reticulation is defined by Hart and Aslett as " a fine network

shadow, sometimes sharp and lacelike in appearance but more oftenblurred, which occupies from half of one lung field to the whole ofboth fields, and is as marked at the periphery as at the hila."The radiological counterpart offirst-stage silicosis is " appearances

not less than the presence ofnodular shadows together with an increaseof hilar shadows, linear shadows, and pulmonary reticulation."Three sub-groups are recognized: (a) nodules present but localized;(b) nodules more numerous; (c) nodules generally distributedthroughout the films but still discrete.

Second-stage silicosis is described as " nodulation with larger areasofcoalescence."; and third-stage silicosis as " massive consolidation."

men from the South Wales coalfield at the rate ofover one hundred a week. More than 10,000 casesof pneumoconiosis had been reported, and thecountry was faced with the problem of providingalternative work for these disabled men. TheGovernment were anxious to implement a re-habilitation scheme (Ministry of Fuel and Power,1944), but were hampered by not knowing what typeof work was most suitable, or whether men withpneumoconiosis suffered from a latent form oftuberculosis which might endanger other workers.Although several writers had described the diseaseas it occurs in South Wales (Cummins and Sladden,1930; Welsh National Memorial Association,1931; Williams, 1933; Harper, 1934; Amor andEvans, 1934; Sen, 1937; Gough, 1940; Hart andAslett, 1942; Belt and Ferris, 1942; etc.) only onesmall follow-up study had been reported (Aslettand others, 1943), and it was not known whether thedisease continued to progress after exposure to dusthad ceased.

It was decided, therefore, to design a socio-medicalsurvey which-in addition to revealing the overallmortality in the certified population, the incidenceof open tuberculosis, and any clinical or radiologicalchanges that might have occurred after leaving themines-would also show what proportion of menin early and late stages of the disease were able todo full-time work, and whether there were anyindications that the disease had been affected bysubsequent occupations. The survey was begunin November, 1945, and was completed in December,1946, and only men certified by the Silicosis MedicalBoard between 1931 and 1944 were included. Noneof these men had worked underground or handledcoal on the surface after being examined, so that itcould be safely assumed that there had been noexposure to dust between the two examinations.The incidence of the disease in different pits in

South Wales had been computed by the Ministry ofFuel and Power, and copies of the certificates issuedby the Silicosis Medical Board on behalf of menemployed in every mine were available from thatdepartment. Since miners necessarily live withintravelling distance of the pit where they work, theserecords provided a convenient starting point for thepresent investigation; and, before a preliminarysurvey was instituted to discover the present where-abouts of the certified men, a series of " MinesLists" was obtained from the Ministry. On thesewere recorded the names of the men from each pit,together with the address, age, date of certification,and disability award. By consulting the recordskept by the Cardiff and Swansea panels of theSilicosis Medical Board it was possible in mostcases to add the x-ray category, and the date and

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BRITISH JOURNAL OF INDUSTRIAL MEDICINE

TABLE ICOAL-MINERS CERTIFIED (DURING LIFE) BY THE SILICOSISMEDICAL BOARD: SOUTH WALES AND OTHER REGIONS,

1931-1945

South Wales England andScotlandPeriod _

Total Included in TotalSurvey

1931-2 143 100 161933-4 364 254 381935-6 477 324 661937-8 632 391 721939-40 823 580 831941-2 1,218 695 941943-4 2,699 1,431 6121945 4,180 _ 574

Total.. 10,536 3,775 1,555

"Incidence " ofpneumoconiosis * 86%* Men certified 1931-1945 expressed as a percentage of the under-

ground working population in 1931.

cause of death in the fatal cases. In addition, allthe original films were available for inspection.By the end of 1944 over 6,000 miners employed

in South Wales had been certified by the SilicosisMedical Board, and between seven and eighthundred deaths had been recorded. These mencame from pits in all parts of the coalfield, but thenumber of cases varied from none to over threehundred in different pits. The " high incidence "pits were mainly in the western part of the coalfieldwhere anthracite is mined, but some steam coal pitsin the central part of the coalfield had been respon-sible for more than a hundred certifications.

In view of geographical difficulties, and theelaborate transport arrangements required to bringpatients to Cardiff to be examined, random samplingwas not attempted. Instead two regions, one in theanthracite area and one in the steam coal area, weredefined, and a preliminary survey was made todiscover the whereabouts of certified men from thepits situated in these regions.

Colliery officials had records of men who hadremained in receipt of weekly compensation, but alarge number had settled their claims and were nolonger on the colliery books. Fortunately themajority had remained in touch with the Miners'Federation, so that no great difficulty was exper-ienced in tracing men who had changed theiraddress since certification. Surprisingly few hadleft the district, and during the survey 3,435 of the3,775 men from the two regions were traced.

In view of misunderstandings which may arisewhen men in receipt of compensation are asked to

undergo examination, meetings were arranged inorder to explain the disinterested object of theenquiry. These were remarkably well attended,and the opportunity was taken to circulate a briefquestionnaire relating to employment since leavingthe mine. The men showed themselves keen toco-operate and this questionnaire was later circulatedto all the men who were traced. In this way answerswere obtained from most of the survivors, whichwere found to be substantially correct when checkedby cross-questioning men who afterwards receiveda medical examination. In addition a large numberof deaths which had never been reported to theSilicosis Medical Board was discovered, and in mostcases the date and cause of death ascertained.

Statistical Analysis of Findings.-In the followingaccount no attempt has been made to distinguishbetween men from the anthracite and steam coalpits unless the findings revealed a statistically

TABLE 21946 SURVEY: RESULTS OF PRELIMINARY INVESTIGATION *

Results of SurveyTotal

Date of Un- Sur- Deadcertification traced viving

% % % % No.

1931-6 9 49 42 100 215

0~n 1937-42 7 74 19 100 692O 1943-4 10 89 1 100 1,003

) Total % 9 80 11 100Total

No. 169 1,533 208 1,910

z Mean age atcertification 46-4 45-9 51-8 46-3in years

1931-6 13 16 71 100 463o 1937-42 7 53 40 100 974

l4 1943-4 9 79 12 100 428

% 9 50 41 100Total - _ _ _ _

No. 171 926 768 1,865

> Mean age at73 certification 49 5 4941 51 0 49.9

in years

* The data cover the certified men from the anthracite and steamcoal regions included in the preliminary survey. The early diseasegroup consists of the men certified as having reticulation or first-stagesilicosis, and the advanced disease group those certified as havingsecond- or third-stage silicosis.

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PNEUMOCONIOSIS OF COAL-MINERS

significant* difference between the cases from thetwo regions. Since, however, the investigationrevealed a considerable difference between men withearly and advanced x-ray changes, both in' mortalityrates and clinical findings, the cases have beendivided into two main disease groups. The " early "disease group includes all men certified as havingreticulation orflrst-stage silicosis, and the "advanced"disease group all those in the second- and third-stagesilicosis categories. In the few cases (less than10 per cent. of the total) where the x-ray findingswere not recorded by the Silicosis Medical Board,the disability award was used to decide the diseasegroup, " partially disabled " men being included inthe first group, and " totally disabled " men in thesecond.

Early Disease Group (1,533 survivors, 208 deaths,169 untraced).-The early disease group includedjust over half the total number of men, the majorityof whom had been certified for less than four yearsand only 10 per cent. for more than ten. Over threequarters of the men were between 30 and 60 yearsof age when certified, and the average agevof thegroup at certification was 46-6 years. Overallmortality among those who were traced was 12 percent., but there was a close relation between theproportion surviving and the interval since certifica-tion, so that although nearly half the men certifiedbefore 1937 were dead, nearly all those certifiedafter 1942 were still alive. The death rate washigher among older men, and there was a differenceof nearly six years between the average age ofsurvivors and of men who died ( Table 2).Advanced Disease Group (926 survivors, 768

deaths, 171 untraced).-The advanced disease grouporiginally included nearly as many men as the earlygroup, but by the time of the follow-up there werefar fewer survivors. This was due partly to thefact that the former contained the bulk of thelong-standing cases, and the latter most of the mencertified since 1942: But the contrast was duemainly- to a real difference between the mortalityrates. For instance, 12 per cent. of men withadvanced disease who had been certified since 1942were known to be dead, compared with only1 per cent. in the early group.Men with advanced disease tended to be slightly

older than those with early disease, and the averageage at certification was 49 9 years. There was,however, a difference of only two years in the meanages of survivors and those who died.

Answers to Employment Questionnaire.-A moredetailed analysis of the answers to the employment

* Where the odds against a difference in the data being due tochance are 95 per cent. or more (that is, not less than 19 to 1) thisdifference is described as significant.

TABLE 3LIFE TABLES FOR MEN IN EARLY AND ADVANCED DISEASEGROUPS FROM THE DATE OF CERTIFICATION BY THE

SILICOSIS MEDICAL BOARD, 1931-1944

Disease GroupIntervalsince Early Advanced

certifica-tion in 1 d p 1 d Pyears x x x x x x

0* 1,000 15 0-985 1,000 71 0-9291 985 17 0-983 929 89 0 904II 968 21 0-978 840 84 0 9002j 947 18 0-981 756 82 0-8923j 929 51 0-945 674 71 0-8954j 878 46 0-948 603 73 0-8795j 832 51 0-939 530 82 0-8456j 781 62 0-920 448 53 0-8827j 719 53 0-927 395 70 0-82481 666 46 0-930 325 48 0-85391 620 34 0-945 277 48 10827

Totalnumber 1,741 1,694of cases

Number 208 768of deathslx= Number of men per 1,000 certifications alive at the

beginning of each interval. dx = Deaths per 1,000 certificationsduring next interval. px = Probability of surviving until beginningof next interval.

* The death rates shown in the first line are for a six monthsperiod and require to be doubled to make them comparable withthose for subsequent periods.

questionnaire will appear in a separate report. Hereit need only be said that certain differences were foundbetween men who lived in the western part of the coal-field, which is a rural area, and those who lived in themore densely populated region in the centre. Forinstance, there was a higher rate of unemploymentamong anthracite miners, and those who did find workwere often employed out of doors, whereas many steamcoal miners worked in factories. More men from theanthracite mines had remained in receipt of weeklycompensation, and when they settled their claims theyreceived more money than the steam coal miners.Until 1939 the rate of certifications was higher in theanthracite region, but during 1943 and 1944 a majorityof cases came from the steam coal region. Finally theproportion of totally disabled men was higher in thesteam coal region.

Judging by the men's own account of their fitness forwork, and their difficulty in obtaining jobs, the employ-ment situation was far from satisfactory, although itimproved during the war years. Older men evidentlyexperienced greater difficulty in obtaining work thanyounger men, but a surprisingly large number of menin the advanced disease group felt fit for full-timeemployment and worked whenever jobs were available.

Mortality Rates.-Mortality rates in the twodisease groups have already been mentioned, andthe proportions of dead and surviving are shown in

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Table 2. The total number of deaths discoveredduring the survey was 976. In 123 cases the causeof death was not ascertained, in 804 it was ascribedto the disease, and in 49 to other causes. Only 451of the deaths- had been reported to the SilicosisMedical Board.To show more precisely the probability of survival

in the two disease groups, life tables were constructed-for the men traced during the preliminary survey.These- are shown in Table 3. Each table coversthe first ten years after certification, but since only11 per cent. of the men in the early disease groupand 25 per cent. in the advanced group had beencertified for as long as ten years, the survival ratesfor the second quinquenium are based on fewercases and are less reliable than those for the firstfive years. In addition, as the tables are basedonly. on the traced men, they necessarily ignore9 per cent. of the population. Since, however,the percentage of untraced cases in the two diseasegroups was identical, whereas the advanced diseasegroup had -a much higher mortality than the early

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PERCENTAGE MALES SURVIVING FROM SO YEARSOF AGE ONWARDS ( ENGLISH LIFE TABLE, 1931, N.0).

PERCENTAGE SURVIVING IN EARLY DISEASE GROUPPNEUMOCONIOSIS).

PERCENTAGE SURVIVING IN ADVANCED DISEASE GP(PNEUMOCONIOSIS).

ItJ 2) 3.I . 4J 5'23 6½ 74 8s½ 9YEARS.

it is inlikely that it is correlated withlity. Therefore the omission of the 'untracedis unlikely to have upset the comparisonen the two disease groups.ough interpolAtion in these tables shows that85 per cent. ofmen in the early disease group,7 per cent. in the advanced disease group, areto survive five years after leaving the mines.e time ten years have elapsed, about 60 perof men in the early and 25 per cent. in theced group, may still be alive.Chart 1 the survival rates are compared withfor males aged 50 years given in the 1931;h Life Table No. 10 (Registrar Generalmial Supplement). The comparison is notfair, because the latter is derived from malesry social class whereas all men with pneumo-is are included in Social Classes III and IV.theless the survival rate in the case of thewith pneumoconiosis is so much lower than- other group that it is most unlikely -thatIcing age and the normal hazards of life-were1%

the only factors determining thenumber of deaths.

Separate study of the anthraciteand steam coal workers revealedcertain differences in the survival

-85° rates in these two groups which atfirst sight suggested that the disease

- acquired by the anthracite minersfollowed the more benign course.Since this finding was at variancewith the observations of Pancoast

2%; and Pendergrass (1931) and withother findings in this survey (see page128) a more detailed investigationof the men from the two regions wasmade. This showed that the 'differ-ence was confined to men withadvanced disease, and when thisgroup was separated into its twocomponents it was found that the

°b proportion of third-stage silicosiscases was higher in the steam coalsample. Since these men tended todie sooner than those classified ashaving second-stage silicosis (seeChart 2), the difference in mortalityrates in the-wo regions need not beascribed to any fundamental differ-ence in the disease in the two partsof the coalfield.

CHART 1.-Mortality after certification by Silicosis Medical Board: mentraced in 1946 Survey. The early disease group comprises mencertified as having reticulation or first-stage silicosis, the advanceddisease group those with second- and third-stage silicosis.

Examinaton of Survivors.-It was-originally intended to examine fourhundred men in the early, and four

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TABLE 41946 SURVEY: SURVIVORS TRACED AND SAMPLE EXAMIN: ANALYSIS BY DISEASE GROUP, AGE, AND DATE OF CERTIFCATION

(SAMPLE FIGURES IN BRACKETS)

Age at certification 20-48 49 and overinyears20449adoeI__________________ Total

Date of certification .. .. 1931-9 1940-4 1931-9 1940-4

Early disease group .. .. 187 (88) 671 (91) 149 (83) 526 (87) 1,533 (349)

Advanced disease group .. 158 (76) 257 (77) 197 (74) 314 (78) 926 (305)

Total .. .. .. 345 (164) 928 (168) 346 (157) 840 (165) 2,459 (654)Method of sampling: one hundred cases were chosen at random

The figures in brackets are the numbers actually examined.

hundred in the advanced disease group, andto choose the two samples so that the timefactor and the age distribution were the same inboth. This was done by dividing the availablecases into eight groups (see Table 4), and taking arandom sample of one hundred cases from each.However, owing to- a considerable lapse rate, only654 men were examined, of whom 349 were in theearly, and 305 in the advanced disease group. Theformer included 171 men certified before 1940,

35 I- SECOND STAGE SILICOSIS----- -. ( 250 CASES)

THIRD STAGE SILICOSIS

(518 CASES )

2 4 6 8 10

YEARS SINCE CERTIFICATION

CHART 2.-Intervals between certification and death inadvanced disease group: contrast between second-and third-stage silicosis. (1946 Survey.) Theadvanced disease group comprises men certified ashaving second- and third-stage silicosis.

i from each of the third-order classes (i.e., the cells shown in the table).

and 178 certified between 1940 and 1944; thelatter 150 and- 155 respectively. The mean age atcertification in the early group was 48-2 years, andin the advanced group 49 8 years.Most of the men were examined as out patients, but

a few were admitted to hospital. In every case a detailedhistory was taken, and this was followed by a clinicalexamination, which included a standard exercise test,measurement of the vital capacity and blood pressure,and' urine examination. Special investigations includedx-ray examination of the chest, and examination of thesputum and blood (hiamatocrit, erythrocyte sedimenta-tion rate, and Wassermann reaction).Employment History.-Before certification all the

men had been employed underground, and overTABLE 5

1946 SURVEY: EMPLOYMENT SINCE CERTICATION (BYDISEASE GROUP AND AGE AT CERTICATION)

Employment sincecertification Total

Age at __Disease certifica- GOod2 Fair3 Nilgroup" tion in

years % % % % Num-Iber

.Under 50 65 29 6 100 223

Early 50 and 29 29 42 100 126over

Total 52 29 19 100 349

Under 50 56 22 22 100 167

Ad- Over 50 17 27 56 100 138vanced

Total 38 24 38 100 305

%°MO 45 27 28 100Total

Number 299 174 181 654(1). The early disease group consists of men certified as having either

reticulation or first-stage silicosis,.and the advanced disease groupthose certified as having second- or third-stage silicosis.

(2). Good employment = in work for over half the period betweencertification and follow-up.

(3). Fair employment = in work but for less than half the periodbetween certification and follow-up.

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95 per cent. had spent tIhe greater part of the timeat the coal face. About half the colliers had spentperiods in hard ground (rock drilling) and a fewhad worked exclusively in rock. The shortest timespent underground was ten years, the longest overfifty years, but there was only a slight differencebetween the duration of dust exposure in the earlyafid advanced disease groups; the average periodbeing 29i6 years in the former and 30 9 years in thelatter*.

After leaving the mines the employment rate washigher among younger men; and men under 50years with advanced disease found employmentmore often than men over 50 years with earlydisease. Approximately one third of the men whoobtained employment worked out of doors, onethird indoors, and one third in mixed occupations.The proportion of men in the early and advanceddisease groups was the same in all types of employ-ment, but whilst 37 per cent. of outdoor workerswere over 50 years of age at the time of certification,only 26 per cent. of indoor workers were in thisage group.

Symptomatology.-According to the £linical his-tories obtained at the time of the follow-up, thedisease appeared to be relatively benign and topursue a slow courset, but there did not seemto be much permanent improvement after leavingthe mine. Occasionally disease had been discoveredbefore the patient was aware of symptoms, and ityvas clear that gross radiological changes werecompatible with remarkably little disturbance ofgeneral health. However, most of the men com-plained of dyspncea and cough, and both thesesymptoms persisted and frequently increased inseverity after certification.Dyspnoea usually preceded cough by several

years, but as it was often slight in degree its presencewas frequently ignored until some intercurrentinfection or " breakdown" occurred. By the timeof the follow-up several men who had continuedto do a full day's work up to the time of certification,were unable to walk more than a few yards withoutbecoming short of breath. The commonest causesof an aggravation of this symptom were: particulartypes of exertion to which the man was notaccustomed, work which involved heavy lifting, andintercurrent illnesses.

* This close approximation corresponds to the similar age distribu-tiod of the men tn the two disease groups. Had a random sample ofmen in the two groups been examined it is likely that there would havebeen a shorter length of exposure in men with early disease and alonger period in men with advanced disease, corresponding with thedifference in average age at certification of the two disease groups(see Table 2).

t This may be an understatement, as the disease was probably lessbenign and had pursued a more rapid course in some of the menincluded in the original sample (for example, those who had diedshortly after leaving the mines).

TABLE 61946 SURVEY: PERCENTAGE INCIDENCE AND SEVERITY OFSYMPTOMS IN 654 MEN WHOW MEDICALLY ExAmED

Incidence- SeverityWorse Im-

Symptom Before After after provedcertifi- certifi- certifi- aftercation cation cation certifi-

cation% % % %

Dyspncea .. 90 98 54 13

Cough .. .. 79 87 30 24

Asthenia .. 54 63 43 30

Loss of weight.. 33 27 28 23

Acute respiratory 24 26illnesses

Chest pain 17 34 39 20

Hemoptysis. . 6 8 -

Melanoptysis .. 1 14 -

Other' .. 10 33 24 10(1). Other symptoms included giddiness, palpitations, vomiting, and

headache.

Cough, though common, was not as a rule adistressing feature until the' disease was welladvanced. During the late stages, however, it wasoften associated with a particularly tenacious typeof sputum, and efforts to expectorate this led tosevere paroxysms of coughing and intense exhaus-tion. Htemoptysis was recorded in 103 cases. Thisusually accompanied an acute respiratory illness butoccasionally occurred without warning. Blacksputum was the rule before certification, and thisdiscoloration tended to persist for several monthsafter leaving the mine. A particular type-of blackspit*, resembling an haemoptysis both in the abrupt-ness of its onset and in the copious amount of fluidexpectorated, was recorded in 101 cases. Thisso-called " melanoptysis" usually occurred for thefirst time several years after leaving the mine, andwas evidently a feature of the late stage of thedisease. In two cases a melanoptysis occurredwhile the patient was in hospital, and serial radio-graphs showed a large cavity developing in thecentre of an area of consolidation. In one of thesepatients the sputum was found after the event tocontain tubercle bacilli, but in the other sputumtests remained persistently negative.Most of the men who continued to work under-

ground after dyspncea had become severe experienced* Copious black sputum is such a characteristic feature of coal-

miners' pneumoconiosis that in early accounts the disease is oftenreferred to as " black spit, or miners' melanosis " (Thomson, 1858).

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TABLE 71946 SURVEY: RADIOLOGICAL PROGRESSION SINCE CERTIFICATION RELATED TO OTHER DATA

Radiological progression 1 Total

Nil Slight Marked | Number

Disease group 2 Early 47 23 30 100 349Advanced 26 24 50 100 305

Age when certified in years .. Under 50 32 20 48 100 36250 and over 43 30 27 100 292

Interval since certification in years Under 5 53 27 20 100 2885 and over 23 22 55 100 366

Tt...% 37 24 39 100Total _ _ _ _ _ _ _ _ _ _ _ _

Number 241 156 257 654(1) In no case was any evidence of regression of the disease observed.(2) The early disease group consists of men certified as having reticulation or first-stage silicosis, and the advanced disease group those certified

with second- and third-stage silicosis.

either asthenia, loss of weight, or pain in the chest;-and in several cases one or other of these symptomsfirst drew the patient's attention to his condition.Although leaving the mine often caused temporaryrelief of these symptoms, later they frequentlybecame prominent features of the disease.Acute respiratory illnesses, variously described

as pneumonia, pleurisy, or acute bronchitis, wererecorded in 272 cases. These usually occurred afterthe onset of other symptoms of pneumoconiosis,and recurrences after certification were common.The illness was sometimes accompanied by hemo-ptysis, and several patients had been intensivelyinvestigated for tuberculosis, but with negativeresults. Occasionally symptoms suggested a spon-taneous pneumothorax and in five cases radiologicalevidence of this was found.A variety of other symptoms such as giddiness,

palpitations, and vomiting was described, whichbecame increasingly frequent after certification,and by the time five years had elapsed most of themen had noticed an appreciable deterioration intheir general health. This downward trend wasmore conspicuous among men with advanced diseasebut was also common in the early disease group.

Radiological Findings.-When the Silicosis Medi-cal Board x-ray films were compared with the onestaken at the time of the follow-up, changes werefound to have occurred in the majority of cases.These invariably suggested further progression ofthe disease and, although a third of the cases showedno appreciable difference between the two radio-graphs, no instance of spontaneous resolution of thedisease after removal from the dust hazard was

observed. The commonest findings were an exten-sion of shadows in both lung fields with an associatedincrease in emphysema, but either of these changessometimes occurred alone, and sometimes only onelung was involved. Occasionally a large shadowseen in the first film was no longer visible in thesecond, but it was clear from the context- that the" disappearance" was due to cavitation and notto resolution (see illustrations).

These apparently irreversible changes evidentlyoccurred slowly, and only 47 per cent. of cases inwhich the interval was less than five years showeddefinite evidence of radiological progression, where-as 77 per cent. of those in which the interval wasover five years showed increase of shadows in thesecond film. The frequency with which changesoccurred was also intimately related to the stageof the disease at the time of certification, evidenceof radiological progression being nearly half ascommon again in the advanced disease group as inthe early group. Nevertheless 12 per cent. of casesof reticulation (a category first recognized in July,1943) had developed new shadows in less than threeyears. Finally more younger men showed evidenceof progression of the disease after exposure to dusthad ceased.The earliest stage of the disease included in the

present series was represented by radiographs inwhich fine mottling was visible throughout bothlung fields. This tended to obscure normal lungmarkings, and produced instead a characteristiccircle-and-dot pattern which extended right out tothe periphery. Accompanying this diffuse shadow,which closely resembles the annular and punctatemottling described by Caplan (1946) there was

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128 BRITIS-H JOURNAL OF

almost always increase in the hilar. shadows, andstrbi radiating from the hila. appeared to incorporateseveral small areas-of coalescence.At the other end of the scale were films in which

there was such gross distortion of both lung fieldsthat it was difficult to recognize familiar landmarks.Either the major part of both lug fields wasobliterated by ill-defined shadows resemblingbunches of cotton wool, or well-defined "cricketball" or "angel wing" shadows alternated withareas of increased translucency. In the latter,elongated strii were seen stretching from the largeshadows to the diaphragm, mediastinum, and peri-phery of the lung fields, causing these to assume amost bizarre appearance. Frequently the hilaappeared to be displaced or incorporated in largershadows, and the trachea sharply kinked immedi-ately above the clavicle.- A central area of trans-lucency 'within a massive shadow' sometimessuggested the presence of a cavity, but unless thisshowed evidence of a fluid level it was difficult todistinguish from other translucent areas which werealmost certainly due to emphysematous bulle.Every intermediate 'stage between these two

extremes was represented, and there appeared tobe little doubt that, after the diffuse shadow patternwas established, the disease progressed by the slowdevelopment of new areas of consolidation, whichgradually coalesced and produced emphysematouschanges in the surrounding lung tissue. Theseconglomerate shadows appeared in both lung fields,but the right lung was usually more heavily infil--trated than the left, and upper and mid zones morethan lower zones; the right upper zone immediatelybelow the clavicle appeared to be the site of electionfor the first "local" shadow, whilst the apices ofboth lungs often remained quite clear.Ineachx-ray category and each sub-group (seefoot-

note, page 121) there were cases in which progres-sion of-the disease had occurred within three yearsof certification, but even in the " third-stagesilicosis" group there were cases in which theradiological appearances had remained unalteredfor more than ten years. The findings as a wholesuggested that the disease might become temporarilyarre4ted at any stage; and evidently furtherextension of the shadows in one region could gohand -in hand with compaction' of 'pre-existingshadows and development of emphysema in anotherpart of the lung. Although more cases in theadvanced disease group showed signs of progression,it was impossible to decide from the appearance ofthe original film whether or-not changes would befound in the follow-up plate.

Careful scrutiny of the films fjiled to reveal anydifference between anthracite and steam coal miners,

INDUSTRIAL MEDICINE

and the rate of progression was the same in bothgroups of workers. Neither the length of tirmespent underground nor the type of work done-before certification appeared to influence the courseof the disease after leaving the mine; but in eachage group men who obtained outdoor work after-certification did rather better than those who-worked in factories CiTable 8).

Tests of significance on the data given in Table 8showed that when the two age groups were con-sidered separately they did not provide undoubtedevidence that the course of the disease had beenaffected by the type of employment. But when thejoint probability was calculated, a statisticallysignificant relationship was established between-incidence of radiological progression and type ofwork done since leaving the mines; the diseaseshowing less tendency to progress in outdoorworkers than in factory operatives.

Clinical Findings.-By the time of the follow-upthere were 145 men whose radiographs showedevidence of "mild" disease, -175 with " well-estab-lished" disease, 188 with " severe " disease, and146 with "gross " disease*.Most of the men in the mild disease group were

found to have a normal physique, and although 90per cent. of them complained of breathlessness onexertion, nearly halfcompleted the exercise tolerancetest without showing signs of distress, and one thirdhad a vital capacity within normal limitst. Apart

* To obtain an indication of the stage of the disease at the time ofthe follow-up, the radiographs taken at this time were arranged infour groups. To avoid confusion with the x-ray classification usedby the Silicosis Medical Board, and with the two disease groups usedfor selecting cases for examination, these four groups have beennamed as follows:

Category 1 (representing mild disease).-Not more than generalizedreticulation with small areas of coalescence confined to one or twozones.

Category 2 (representing well-established disease).-Not less thanthe maximal appearances found in category 1 and not more thangeneralized reticulation with early emphysema and either widelyscattered but small areas of coalescence, or larger areas confined toone or two zones.

Category 3 (representing severe disease).-Not less than the maximalappearances found in category 2 and not more thanpartial obliterationof the original reticulation by multiple areas of coalescence andemphysema.

Category 4 (representing gross disease).-Not less than the maximalappearances found in category 3 and including films in which thereticulation was completely obliterated by large areas of coalescenceand emphysema.When the films from the Silicosis Medical Board were also cata-

logued in this way it was found that 35 per cent. of the certificationfilms and 22 per cent. of the follow-up films were in the mild diseasegroup * while 6 per cent. of the certification films and 22 per cent.of the follow-up films were in the gross-disease group.

t For the exercise tolerance test a step 18 inches high was used.The subject placed, and kept, one foot on the step and raised his bodyto the erect position on the step twenty times in sixty seconds. 'Menwho were too breathless to attempt or failed to complete thistest were recorded as " severely dyspnceic," those who were still out,of breath one minute after completing the test were recorded as" moderately dyspnaeic," and those who did the test without unduedistress were recorded as normal.The vital capacity was measured on a simple spirometer and the

best of three readings was taken. The result in each case was com-pared with the " expected " value from men of the same age and samesitting height (McMichael, 1945) and expressed as a percentage of theexpected value.


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PNEUMOCONIOSIS OF COAL-MINERSI TABLE 8

1946 SURVEY: EAMPLOYMENT SINCE CERTICATION RELATE TO RADIOLOGICAL PROGRESSIONWORK OWING TO SICKNESS

129

AND ABSENCE FROM

Age at certification in years Under 50 50 and over Total

Employment since certification Outdoor Indoor Outdoor Indoor L Number

Radiological ~~~Marked 39 49 16 29 37 il1Radiologicl progression 7i3ght20920 1241sinceertlflatiofl Nil 41 31 57 32 39 114

Sickness absence Long spells 16 28' 13 33 23 68from work Short spells 36 37 38 39 37 109Nil 48 35 49 28 ~ 40 119

% 100 100 100 100 100Total _____.._____

Number 87 117 51 41 296l(1) A further 167 men obtained employment after leaving the mines, but as they had worked partly indoors and partly out of doors they have

not been included. The interval since certification and the proportion of men in the early and advanced disease groups was the same in allthree types of employment. Tests of significance: when the marked progressors " and " non-progressors " were compared separately inthe two age groups a gross chi squared (with two degrees of freedom) of 5-788 was obtained. Since both age groups showed deviations in thesame direction the value of i p is 0 03.

from a tendency to poor expansion and ratherdistant breath sounds, very few showed abnormalphysical signs in the chest, but slight clubbing of thefingers was recorded in 12 per cent. of cases, andpale mucous membranes in 5 per cent.The gross disease group included 43 per cent. of

men in whom the physique was recorded as good;and 18 per cent. in which it was poor. Over 80per cent. were observed to be unduly dyspnceic on

attempting the, exercise tolerance test, and nearly100 per cent. had a sub-normal vital capacity. Thetendency to poor chest expansion was not muchmore marked than in the mild disease group, butmany more cases showed other physical signs inthe chest. Compared with the radiological findingsthese were slight and indefinite, but either markedflattening of the chest below the clavicles, hyper-resonance over the bases, or an unusual variation

TABLE 91946 SURvEY: CLINICAL AND RADIOLOGICAL FINDINGS AT TIME OF FOLLOW-UP

Radiological findings1 TotalClinical findings Well-

Mild established Severe Gross % Number____ _ _ _ _ % % . % __

Good 85 78 64 43 68 442General condition Fair 14 20 29 39 25 168

Poor 1 2 7 18 7 44

Nil 47 38 32 15 33 219Objective dyspnoea 2 Moderate 30 32 31 25 30 -193

Severe 23 30 37 60 37 242

Over 90% 36 19 15 2 18 117Vital capacity3 70-90% 43 50 41 23 40 259

Under 70% 21 31 44 75 42 278

2-3 in. 22 22 18 7 17 112Chest expansion 1-2 in. 70 68 -70 73 72 470

Under 1 in. 8 10 12 20 11 .72

% 100 100 100 100Total .. .. 100 654Numnber 145 175 188 146

(1) For the definition of the x-ray categories shown in this table (see footnote on . 128).(2) Objective dyspnxa was classified as nfl, moderate, or severe, on the results of standard exercise tolerance test (see footnote on p 128)(3) The vital capacity is expressed as a percentage of normal (see footnote on p. 128).


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TABLE 101946 SURVEY: RESULTS OF SPUTUM TESTS RELATED TO

OTHER FINDINGS

Sputum1

Number of cases .. .. Positive Negative

17 472

Interval since Under 5 11 245certification 5 and over 6 227in years

General con- Worse 14 290dition No.change or 3 182

improved

Dyspncea (sub- Worse 9 255jective) No change or 8 217

improved

Change m Less 12 147weight Stationary or 5 325

gaIRadiological None 2 179

progression Progression 15 293

E.S.R. mm. 0-9 2 203per hr. 10-60 15 269(Wintrobe)(1) Sputa from 489 men were examined for tubercle bacilli 89 men

had no sputum and 42 men with sputum were not tested.

in intensity of the breath sounds over adjacent areasof the-lung, were recorded in nearly 100 per cent.of cases and in over 70 per cent. adventitious soundswere heard. Clubbing of the fingers was observedin one third of the cases, and pale mucous mem-branes in 15 per cent. Albuminuria was recordedin twenty cases, but peripheral cedema (one case)and cyanosis (two) were extremely rare.

A'majority of cases (56 per cent.) bridged the gapbetween mild and gross disease. Two thirds ofthese men were found to be dyspnoeic on exertionand over 80 per cent. had a subnormal vital capacity.On the other hand the physique was good in about70 per cent. of cases and fair in 25 per cent. Despitethis higher level of general physique, abnormal chestsigns, clubbing of the fingers, and albuminuria werealmost as common as in the gross disease group.

Incidence of " Open "Tuberculosis.-Examinationof the sputum is not part of the routine procedureof the Silicosis Medical Board, but most men whohave #,productive cough are investigated elsewherefor tuberculosis. The present series included 401men who had had their sputum tested after leavingthe mines; but in only two cases were tuberclebacilli detected. One of these patients had apleural effusion, and although this had resolved bythe time of the follow-up (nearly four years later),

other shadows in the radiograph had increased,and he was a very ill man. There appeared to bea large cavity in the left lung and the sputum wasfound to be still heavily infected with tuberclebacilli. In the second case the original film showedgeneralized reticulatibn with a small area of coal-escence in the right upper zone. This patient'sonly symptom was cough, which ceased after heleft the mine, and when he was seen three yearslater he- declared that he was feeling quite well.Clinical examination revealed no abnormal physicalsigns, the sputum was negative, and there was noappreciable difference between the findings in thetwo radiographs.During the follow-up it was found that 89 men

had no cough, 34 had cough but no sputum, and531 had a productive cough. Only 42 men failedto return the sputum outfit supplied at,the time ofthe medical examination, and in 489 cases.a specimenwas examined for tubercle bacilli. Nineteen ofthese men were admitted to hospital within sixmonths of being examined, and in these cases thesputum tests were repeated -on several occasions.Method.-In every case at least 10 ml. of sputum was

concentrated by Jungmann's Method (Jungmann, 1938;Nassau, 1942) and a direct smear was made from thedeposit. Heavy inocula were seeded on to eight slopesof Lowenstein-Jensen's medium and eight of Dorset'segg (unglycerinated), and the residue from every fourthspecimen was inoculated into a guinea-pig. If eitherdirect smear or culture suggested the presence of tuberclebacilli, the finding was confirmed by guinea-pig inocula-tion.

Results.-Tubercle b,acilli were isolated fromseventeen cases. This represents 2-6 per cent. ofall cases, 3-2 per cent. of cases with sputum, and3*5 per cent. of the specimens examined. In twocases a suspicious finding on culture was notconfirmed on animal inoculation, and one specimenwhich yielded a negative culture produced apositive result when injected into a guinea-pig.In only one of the nineteen patients admitted tohospital was the original finding reversed. Thisman had a negative sputum at the time of thefollow-up and again when admitted to hospitalfour months later. While in the ward he had amelanoptysis and a cavity developed in the rightlung; on four subsequent examinations his sputumwas found to contain tubercle bacilli.One patient with positive sputum was found to

have a pleural effusion in addition to evidence ofadvanced pneumoconiosis, butin the remainder theradiological findings were indistinguishable fromthose found in negative cases. The group as awhole, however, contained -a disproportionatelylarge number of " ill" men, most of whom had

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developed new shadows after certification and werein an advanced stage of pneumoconiosis. Theerythrocyte sedimentation rate (E.S.R.) was usuallyraised, and the general impression was that thesemen were suffering from a more rapidly progressivetype of disease than men with no bacteriologicalevidence of tuberculosis (see Table 10).To this rule, however, there were a few interesting

exceptions. *For instance one patient with tuber-culosis was practically symptomless and showedno signs of radiological progression over a periodof four years, and three had " held their own " formore than eight years before their health began tofail. Finally two patients, in spite of being veryill men and showing signs of rapid progression ofthe disease, had erythrocyte sedimentation ratesof less than 7 mm. per hour (Wintrobe).

Hsematology.-in 641 cases' the erythrocyte sedi-mentation rate and corpuscular volume (hzemato-crit) were estimated by methods described byWintrobe and Landsberg (1935). The formerranged from less than one to over 60 mm. per hour,with an average value of 15-7 mm. per hour*.At first there appeared to be little in common

between radiological findings and erythrocytesedimentation rate, as several men with grosslyabnormal radiographs showed normal values, andvice versa. When, however, the results were finallyanalysed, it was found that there was a definitetendency for the sedimentation rate to be higherin men with gross than in those with mild disease,while the distribution of sedimentation rate valuesin the intermediate x-ray categories lay betweenthese two extremes.More striking, however, was the association

between " radiological progression " and raise4erythrocyte sedimentation rate (Table 13). Wherethe interval between certification and follow-up wasless than five years, the sedimentation rate was10 mm. or over per hour in 86 per cent. of cases inwhich marked progression had occurred, in 81 percent. of those showing slight progression, and in42 per cent. in whom no radiological changes wereobserved. Where the interval was over five yearsthe rate was-10 mm. or over per hour in 67 per cent.of the cases showing marked progression, in 64 percent. with slight progression, and in 15 per cent.with no radiological changes.

In both long- and short-interval groups thedifference between " progressors " and " non-progressors" was statistically significant; the twoextremes being represented on the one hand bycases in which marked radiological changes had

* According to Wintrobe and Landsberg the average erythrocytesedimentation rate for healthy adult males is 3-7 mm. per hour(standard error, ±0-16).

TABLE 111946 SURVEY: ERYTHROCYTE SEDIMENTATION RATES

Interval Radio- Meansince logical Number E.S.R. in Standard

certifica- progres- of mm. per deviationtion in sion cases hr.years (Wintrobe)

Nil 150 12-0 11.1Under 5 Slight 75 20-6 12-4

Marked 58 27-3 14-1

Nil 84 6-7 6-45 and over Slight 77 13-5 10.5

Marked 197 17-9 13-2

Total 6411 15-7 13-1

Cases with tubercle 17 29-5 14-9bacilli in the spu-tum2(1) In thirteen cases the erythrocyte sedimentation rates were not

estimated.(2) These cases are included in the main body of the table.

occurred within five years of the erythrocytesedimentation rate being estimated, and on the otherby cases in which the disease had remainedstationary for over five years.The corpuscular volume, as determined from

hvmatocrit readings, ranged from 23 to 55 per cent.,with an average value of 39 5 per cent. Since thenormal range for healthy adult males is 41 to 52 5per cent., with an average of 46 8 per cent. (Price-Jones and others, 1935), the findings showed thatthe group as a whole was animic.

This tendency to anmmia was fairly closely relatedto stage of the disease as shown by radiologicalfindings (Table 12). This being so, there was alsoan association between low hematocrit readingsand raised sedimentation rates, but further investiga-tion of this relationship indicated that this couldnot explain the general increase in the sedimentationrate.

DiscussionIt is abundantly clear from the foregoing account

that pneumoconiosis of coal-miners frequentlycontinues to progress after exposure to dust ceases,but since no comparable survey of men whocontinued to work underground has yet been made,it is impossible to say how much the course of thedisease was affected by change in environment.To judge from the general sequence of events andthe clinical histories-which suggested that men withadvanced disease may continue working under-ground for long periods without - experiencingdisabling symptoms-it is unlikely that leaving themine was more than slightly beneficial.The apparent absence of any relationship between

time spent underground and progression of the

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BRTISH- JOURNAL OF INDUSTRIAL MEDICINETABLE 12

1946 SuRvEY: ERYYTOCYTE SEDIMENTATION RATE AND HIEMATOCRIT READINGS RE3LATED TO RADIOLOGICALTI!!A mm ro rmArn. qrn E7-T T v1XZ_v.FIINGS AT TBk TIME OF TiE FOLLOW-UPRadiological findings Total

Well-Mild established Severe Gross % Number

E.S.R. mm. per hr. 0-9 66 44 37 27 43 275(Wintrobe) 10-19 27 30 28 27 28 179

20-61 7 26 35 46 29 187

41-55 57 -42 30 -37 40 259Ieematocrit (%) 36-40 37 46 50 47 46 291

23-35 6 12 20 16 14 91

100 100 100 100 100Total ____.

Number 139 171 185 146 641 2

(1) For the definition of the x-ray categories shown in this table see footnote on p. 128.(2) In thirteen cases the erythrocyte sedimentation rate and hematocrit were not estimated.

disease after leaving the mine suggests that somefactor other than dust is necessary, if the diseaseis to run its full course. The radiological appear-ances, raised sedimentation rates, and tendency toanemia* all point to infection superimposed on awidespread pulmonary fibrosis; while the fact thatareas of coalescence frequently originated in theupper lobe of the right lung, and that the radio-logical findings in cases with open tuberculosis wereindistinguishable from the others, suggest that,despite the low incidence of open tuberculosis, theinfective agent.may be the tubercle bacillus.Autopsy studies have produced convincing

evidence that tuberculosis plays a major role in the* See also Tortori-Donati (1947), who found a tendency to anmnia

and a raised erythrocyte sedimentation rate in coal-miners withadvanced pneumoconiosis.

late stages of coal-miners' pneumoconiosis. Butjust as in the present study of living men there wasa gross disparity between incidence of open tuber-culosis (2 5 per cent.) and radiological evidence ofprogression -of the disease (63 per cent.), so alsohas it often proved impossible to obtain bacterio-logical confirmation of tuberculosis in fatal caseswith gross pathological changes in the lungs (Rogers,1946: Gough, 1946). Nevertheless, despite theabsence of this final piece of evidence, pathologistsbelieve that the late lesions are frequently those ofa'curiously modified form of tuberculosis (Cumminsand Sladden, 1930; Belt and Ferris, 1942).The disparity between bacteriological findings

and clinical and pathological manifestations suggestseither that the tuberculous infection has been so

TABLE 131946 SURvEY: ERYTIROCYTE SEDIMENTATION RATE RELATED TO RADIOLOGICAL PROGRESSION SINCE CERTIFICATION

lE.S.R. | Radiological progression Totalmm./hr. Nil Slight Marked | Number

-0-9 58 19 14 39 110Interval since certification 10-19 25 35 21 26 75

less than 5 years 20-61 17 46 65 35 98

% 100 100 100 100Total _ _ ______-_I-

Njmber 150 75 58 2830-9 85 36 33 46 165

Interval since certification 10-19 11 38 33 29 104oVer 5 years 20-61 4 26 34 25 89

% 100 100 100 100Total ' l-_-_

Number 84 77 197 358

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profoundly modified by the co-existent pulmonaryfibrosis that the infecting organism is no longeridentifiable, or that other infective agents mayproduce chronic lesions which are morphologicallyindistinguishable from silico-tuberculosis. It isoutside the scope of the present enquiry to determinewhich of these alternatives is correct, but the lowincidence of open tuberculosis and the fact that bythe time this develops patients are usually unfit forwork, indicate that it is fairly safe for men withpneumoconiosis to be employed alongside otherworkers. An even greater degree of safety wouldbe achieved if all men with pneumoconiosis under-went regular medical examination.

Nearly all the men who were examined during thefollow-up were more breathless than ill, and itwould appear that, in the absence of clinicalyrecognizable tuberculosis, pneumoconiosis not onlycauses remarkably little disturbance of the generalhealth but also often pursues a very slow course.It is likely, therefore, that a majority of men certifiedby the Silicosis Medical Board will remain fit forfull-time employment for several years after leavingthe mines, only the type of work that they can dois likely to be limited by the amount of exertionrequired.The observation that men who obtained outdoor

employment after certification did better than thosewho worked indoors may be due to selectiverecruitment. But the even distribution of men inthe early and advanced disease groups in the twotypes of employment is an argument against suchan hypothesis, and the possibility that the workingenvironment had some effect on the course of thedisease must be considered.Inasmuch as the late effects of pneumoconiosis

may be due to infection superimposed on the originaldust disease, the difference between indoor and out-door workers may be due to the fact that the latterwere less prone to contract respiratory infectionsfrom fellow workers. On the other hand it isequally possible that either the need to take morestrenuous exercise, or the absence of excessivehumidity or dust in the working environment, orless exposure to abrupt changes of temperature,may have had a relatively favourable effect on theoutdoor workers. Clearly more work must bedone before attempting to define optimal conditionsof employment but, crude as it is, the observeddifference between the indoor and outdoor workerssuggests that the successful application of certainmeasures designed to reduce the incidence ofrespiratory infections might reduce the tendency toprogression. As they exist at present most outdoorjobs are too heavy for men with pneumoconiosisto tackle, so that our findings should not be taken

to suggest that these are always suitable. Rather,attention should be directed to improving factoryconditions so that the risk of cross infection isreduced to a minimum.

Since the survey necessarily covered only twodates in each case, it is possible to draw onlytentative conclusions regarding the erythrocytesedimentation rate findings. The comparativelylarge number of normal values observed in menwho had left the pits for more than five yearssupports the general impression gained fromexamination of the radiographs; namely that thedisease may become temporarily arrested at anystage. On the other hand the high proportion ofraised sedimentation rates among men who wereobserved after a short interval and showed noradiological evidence of progression of the disease,suggests that a rise in sedimentation rate mayprecede detectable changes in serial radiographs,and may thus provide a valuable indication of theimmediate prognosis.

It is generally thought that emphysema causes anincrease in the&number of erythrocytes circulatingin the blood stream, but none of the men examinedhad polycythaemia and many were definitely anemic.As already suggested, this tendency to anemia maybe due to intercurrent infection; but it is possiblethat the whole subject of emphysema and poly-cythlumia needs reinvestigation.

I Summary1. Nearly 3,500 miners who contracted pneumo-

coniosis while working in the anthracite and steamcoal pits of South Wales were followed up after theyhad been away from the mines from two to fifteenyears.

2. The subsequent mortality rates of men wholeft the mines during the " early " stage of pneumo-coniosis were higher than normal. Those who didnot leave underground work until the disease hadreached an " advanced " stage had even highermortality rates after leaving the pit.

3. Findings in respect of 654 men who. wereexamined are described. These show that thedisease frequently continues to progress afterremoval from the dust hazard, and suggest that thelate results are due to infection superimposed ongeneralized pulmonary fibrosis. This progressionof the disease after leaving the mine was rathermore frequent in younger men, and somewhat lessfrequent among men who worked entirely out ofdoors during this period.

4. The disease in its early stages is often symptom-less and even in late stages dyspneea on exertion maybe the sole manifestation. In men with advanceddisease a particular type of black spit may occur

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which is associated with breakdown of large areasof diseased lung tissue.

5. The overall incidence of open tuberculosis wasless than 3 per cent., but although these men wereusually much less fit than the others, the investigationrevealed no specific criteria other than sputumexamination whereby " tuberculous " and " non-tuberculous " cases may be distinguished.

6. In the absence of tuberculosis the diseasefrequently pursues a slow course and, apart fromdyspncea, produces remarkably little disturbance ingeneral health despite gross radiological changes.

7. Progression of the disease is often accompaniedby raised erythrocyte sedimentation rate and periodsof arrest by normal sedimentation rate.

8. Early stages of the disease are not associatedwith any conspicuous alteration in corpuscularvolume, but in more advanced stages anaemia iscommon.

A survey of this magnitude could not have beenundertaken without the help of numerous people, manyofwhom it is impossible to mention by name. We wouldlike particularly to thank Dr. Charles Sutherland, ChiefMedical Officer of the Silicosis Medical Board, and hiscolleagues Dr. Keating and Dr. McVittie, who kindly'allowed us access to all the records of this departmentand gave us much helpful advice. We are also indebtedto the Ministry of Fuel and Power for compiling all the" Mines Lists," to the South Wales Miners Federationfor organizing a large part of the preliminary. survey,to the Oxford Bureau of Health and Sickness Recordsfor sorting all the records, and to Miss Clarke of Ilfords'for providing the illustrations. The Cardiff RoyalInfirmary should also be thanked for the radiographs.A large amount of statistical Work was involved both inplanning the experiment and checking the results, andwithout the assistance of Professor Bradford Hill, Dr.Russell, and Mr. Ian Sutherland the survey could not havebeen made. Finally we would like to thank Dr. CharlesFletcher, Director of the Pneumoconiosis Research Unit,who was responsible for initiating the investigation andprovided us with invaluable help and criticism at everystage.

REFERENCESArlidge, J. T. (1892). " Hygiene, Diseases and Mortality of Occupa-

tions." London.Amor, A. J., and Evans, R. G. Prosser (1934). Practitioner, 132, 700.

Aslett, E. A., Davies, T. W., and Jenkins, T. I. (1943). Brit. J. Radiol.,16, 308.

Belt, T. H., and Ferris, A. A. (1942). Spec. Rep. Ser. med. Res.Coun., Lond., No. 243.

Caplan, A. (i947). Proc. Inst. Min. Engrs. and Inst. Metall. SilicosisConference. London. p. 33.

Coalmining Industry (Pneumoconiosis) Scheme. S.R. and 0.(1943). No. 885.

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