The Australian Mesothelioma Surveillance Program

Transcription

1 166 August 17, 1987 Vol. 147 THE MEDICAL JOURNAL OF AUSTRALIA The Australian Mesothelioma Surveillance Program David A. Ferguson, Geoffrey Berry, Tatiana )elihovsky, Sally B. Andreas, Alan ). Rogers, S. Chung Fung, Ashraf Grimwood and Rebecca Thompson ABSTRAO The Australian Mesothelioma Surveillance Program was planned in 1977 in order to improve diagnostic criteria, to monitor the incidence of the disease, to develop methods of counting lung fibres, and to explore occupational and other associations of mesothelioma. This paper presents a preliminary analysis of data that were collected between January 1, 1980 and December 31, 1985 on the pathological findings and the work and environmental history of 858 cases of mesothelioma. The annual incidence rate of mesothelioma in Australia was 15 per million population who were aged 20 years and over. This is more than the incidence rate of mesothelioma in any other country for which data are available. However, uncertainty over diagnostic criteria and the degree of ascertainment of cases places doubt on the validity of such comparisons. In 69% of cases, a history of work with or other exposure to asbestos was obtained. Due to the long interval between the first exposure to asbestos and the provisional diagnosis of a mesothelioma (up to 60 years), more than three-quarters of the 456 exposed cases first contacted asbestos in the years of its heavy use between 1930 and This article analyses cases by the industry and the occupation in which exposure to asbestos first occurred. (Med J Aust 1987; 147: ) exposure to asbestos gave impetus to the recording of cases. 1.2 In1960, Many ofthe these reported series have association been personal of malignant cases that mesothelioma were collected and by pathologists,3 or applied to specific industrial cohorts4-6 and geographical areas. 7 In 1964, the Union Internationale Contre Ie Cancer recommended that regional and international collections be made. In the following years national collections were initiated in England,' The Netherlands, France! Denmark,lO the United Statesll and other National Occupational Health and Safety Commission, level 30, 31 Market Street, Sydney, NSW David A. Ferguson, MD, FRACP, FFOM, FACOM, Consultant; Program Convenor; and Professor Emeritus, The University of Sydney. Sally B. Andreas, SRN, formerly Program Coordinator. Alan J. Rogers, MSc, CIH, MAIOH, lecturer in Occupational Hygiene. Ashraf Grimwood, MB ChB, Consultant. Rebecca Thompson, Program Coordinator. Department of Public Health, The University of Sydney, NSW Geoffrey Berry, MA, FIS, Associate Professor of Biostatistics. S. Chung Fung, SSe, CPH, MPhil, Research Officer. Fairfax Institute of Pathology Department, Royal Prince Alfred Hospital, Missenden Road, Camperdown, NSW Tatiana Jelihovsky, MB BS, DCP, FRCPA, FRCPath, Staff Specialist in Anatomical Pathology. Reprints: Ms R. Thompson. countries.12 Some of these collections have taken the form of statutory mesothelioma registers;' 9 others of mesothelioma panels in national cancer registers or tumour reference centres;13others again of extraction from national cancer registers;l4 and at least one collection was obtained by extraction from a central register of asbestos workers. 15All these forms of collection suffer from various drawbacks, which include underreporting of cases, uncertain diagnoses due to lack of necropsy and histological diagnoses,and poor elucidation of the role of occupational and environmental exposure to asbestos. The sources and types of data collection and their pitfalls have been reviewed extensively, 16particularly the use of the collections in the identification of asbestos and other potential hazards, and thus their use in the prevention of disease.'7 A collection of cases is of more value if additional data from sources other than those of the case notifications are included. Australia has had a special need to undertake such a task because crocidolite (blue asbestos), the most potent commercial agent that is able to induce mesothelioma, has been mined to a significant extent only in South Africa and in Western Australia (at Wittenoom between 1943 and 1966). The Wittenoom fibres are a particular cause of concern, as they are of a finer diameter than those in South Africa.' Accordingly, in 1977, the Australian Mesothelioma Register was planned'9 and was inaugurated formally in In 1981, its name was changed to The Australian Mesothelioma Surveillance Program (the Program) in order to differentiate it from a statutory register and to identify the wider concept of a surveillance programme. This paper presents our findings on the epidemiology of mesothelioma in Australia and the role of occupational and environmental exposure to asbestos. Methods The Program operated between January I, 1980 and December 31, 1985, by voluntary formal notification from clinicians and pathologists, as soon as a patient was suspected clinically of having a mesothelioma. As a crosscheck th~ Program relied on state cancer registries, which also advised on the death of patients whose cases had been notified previously.

2 THE MEDICAL JOURNAL OF AUSTRALIA Vol. 147 August 17, On formal notification of a case, a letter to the patient's general practitioner was sent. It sought permission to approach the patient or their next-of-kin for the administration of a questionary by an interviewer who had been trained specially. Subsequent enquiry was often made in regard to particular industries and occupations. The occupational and environmental details that were obtained were reviewed for exposure to asbestos and were coded by occupational hygienists. Occupational exposure to asbestos was classed as definite, where exposure was undoubted; probable, where exposure was highly likely; and possible, where experience suggested that exposure might have occurred. Lack of any evidence of occupational exposure led to the consideration of environmental exposure, which could include cohabitation with an asbestos worker; residence next to an asbestos factory or mine; or household exposure, such as the machining of asbestos-cement sheeting. The coding of the occupation and industry in which asbestos exposure first occurred was based on the Australian Bureau of Statistics' Industry and Occupation codes and the classification of Malker et al. 2. The year of presumptive diagnosis was the year in which a mesothelioma was suspected clinically. The definitive diagnosis, which was made by the Pathology Panel of the Program (members of which are appointed by The Royal College of Pathologists of Australasia), occurs some time after notification and combines the opinions of all five Panel members. The Panel then reports the diagnosis as being "definite", "probable", "possible" or "not mesothelioma". The level of consensus among the Panel pathologists for the first 202 cases was good, with exact agreement or a disagreement of only one category in of assessments. Therefore, an average score was used, which was calculated from scores of I (definite); 0.75 (probable); 0.5 (possible); and 0 (not mesothelioma). The definitive diagnosis is the category with a score that is nearest to the mean score. Post-mortem examinations were sought in all cases that were notified, in order to obtain lung tissue for analysis by means of the methods that were outlined by the Lung Fibre Counting Panel," and to correlate the counts with exposure data from the occupational and environmental histories. Results The Program began to collect cases in New South Wales in 1979 as a pilot study but did not attempt to cover all Australia until May 1, 1981, when the Secretariat was established. The Program had received notifications of 903 patients (796 men and 107 women) to December 31, Thirty-two cases were withdrawn on later advice from the notifier that the diagnosis was not that of mesothelioma, and on confirmation of this by checking of the clinical records. The omission of these cases leaves 871 cases for further study. Initially, over half the notifications carne from New'South Wales; this disproportion is indicative of the unequal ascertainment in the early years (Table 1). Thus, while all except one of the notifications in 1979 and 1980 carne from New South Wales, the proportion dropped to 60% (164/274) of notifications in 1981 and 1982, to 39llfo (80/206) of notifications in The first source was counted in instances of the multiple notifications of cases. Clinicians contributed 40llfo (348/871) of the notifications, cancer registries 36llfo (314/871) of notifications and pathologists 20llfo(174/871) of notifications; only a few notifications carne from other sources, such as the NSW Dust Diseases Board. Of the 355 cases on which the Pathology Panel has reached a definitive diagnosis to date, 68llfo (240/355) of cases were classed as "definite", 21llfo (74/355) of cases were classed as "probable" and 7llfo(23/355) of cases were classed as "possible" mesotheliomas. In five other cases, the histological material was insufficient to enable TABLE ' t Total : 110 Notified patients by state of residence and year of notification +Includes one case from the Northern Territory. Year of notification a definitive diagnosis to be reached, although mesothelioma was likely on clinical grounds. Thirteen cases were assessed as "not mesothelioma". The 516 cases that remained have yet to be reviewed by the Panel. However, on the basis of the above findings, only 20 of these cases would be rejected. Therefore, only the 13rejected cases are excluded from the discussion that follows; this leaves 858 cases of mesothelioma for consideration, if it is accepted that the great majority of diagnoses will be confirmed. Of the 342 cases with a definitive diagnosis, 309 cases had pleural (including pericardia!) involvement and 37 cases had peritoneal (including tunica vaginalis) involvement (eight patients were affected in both sites). In four cases the site was not reported. At the time of notification, 61llfo of the 903 patients were living. However, 77llfo of notifications from clinicians were of living patients, whereas 42llfo of the notifications from pathologists and 55llfo of the notifications from cancer registries were made after death, as might be expected. The proportion of living patients who were notified has increased over the years from 28llfo (3l/1IO) of patients in 1981 to 70llfo (144/206) of patients in This is indicative of the earlier ascertainment of cases, which was due presumably to the awareness campaign that was mounted by the Program. The number of notifications in the year of presumptive diagnosis have increased steadily over the years of study, reaching a total of 174 notifications in By 1982, 49llfo (64/131) of the cases were notified in the year of the diagnosis; in 1983, 65llfo(89/137) of cases and in 1984,750/0 (130/174) of cases were so notified. This indicates again, that reporting is taking place progressively earlier. However, in the two years after 1983 the numbers of presumptive diagnoses are likely to be incomplete. As 75% of the cases with a presumptive diagnosis of mesothelioma in 1984 were notified in 1984, and if it is assumed that a similar rate will also apply for 1985, the incidence rates per million population who are aged 20 years and over, can be calculated for cases with a presumptive diagnosis of mesothelioma in (Table 2). This represents a period of three years and nine months. On average, about 150 cases occurred a year over these four years. Although the great majority were in men, 12llfo (18) of cases a year occurred in women, which is over twice the expected number of incidental (nonoccupational) cases.22 All states had excess cases of mesothelioma; the highest rates were in Western Australia. TABLE 2: National incidence rate from patients notified with a presumptive diagnosis of mesothelioma in State New South Walest Victoria Queensland South Australia' Western Australia Tasmania Total Australia Number of cases Men Women Rate per year per million population aged 20 years and over' Men Women *Assuming casesoccurred within a period of three years nine months (see text). tjncludes five cases from the Australian Capital Territory. *Includes one case from the Northern Territory which was diagnosed in Western Australia. The assessment of occupational and environmental exposure to asbestos has been completed for 726 of the 858 patients with mesothelioma. Definite occupational exposure had occurred in 45llfo (324/726) of these patients, probable exposure in 7llfo (49/726) of patients and possible exposure in 11llfo(83/726) of patients. Of the 6llfo(43/726) of subjects with environmental exposure, without work exposure, 14 subjects had used asbestos cement for domestic construction; 13 subjects lived next to an asbestos-cement factory and/or with an asbestos product-worker; five subjects worked in a rubber factory which was located next to an asbestos-cement factory; six subjects came from Wittenoom and were either

3 THE MEDICAL JOURNAL OF AUSTRALIA Vol. 147 August 17, cohabiting with a miner or had received environmental exposure (two childhood exposures); and five subjects had worked in the vicinity of asbestos-lagging or spraying,' or with asbestos-contaminated products (for example, hessian bags). In 26070(191/726) of cases no history of exposure was elicited. The information that was gained in 5% (36/726) of cases was insufficient. New South Wales was the most common state in Australia in which a first occupational exposure to asbestos was recorded. Characteristics Number (n =456j Place of first exposure New South Wales Victoria 192 (42"70) 67 (15"70) 38 (8"70) 26 (6"70) 62 (14"70) 3 «1"70) 62 (14"70) 6 (I "70) Queensland South Australia and Northern Territory Western Australia Tasmania Overseas Unknown Year of first exposure Before (1 "70) Unknown (8"70) (24"70) (29"70) (26"70) (9"70) (I "70) (2"70) Length of exposure Less than three months 14 (3"70) Three to less than six months 10 (2"70) Six to less than 12 months II (2"70) One to less than two years 20 (4"70) Two to less than five years 70 (15"70) Five to less than 10 years 69 (15 "70) 10 to less than 20 years 95 (21 "70) 20 years and over 140 (31"70) Unknown 27 (6"70) However, the proportion (42%) is little more than expected in accordance with the industrial and population distribution at the time. Victoria is underrepresented on that basis, and Western Australia is overrepresented (the latter presumably because of the crocidolite mine at Wittenoom). Many (14%) patients were first exposed to asbestos overseas. Seventy-nine per cent of the 456 occupationallyexposed subjects experienced their first contact with asbestos between 1930 and 1959; the onset of exposure to asbestos occurred fairly evenly over this 30-year period, which is in keeping with the heavy use of asbestos under adverse conditions. In 52% of cases, exposure had extended for a period of over more than 10 years; only 7% of subjects had experienced exposures of less than 12months' duration. TABLE3: Age distribution at presumptive diagnosis of mesothelioma by exposure to asbestos Not 23(12%) 66(35%) 33(17%) 15 (n= ( Environmentallyexposed «1%) 3«1%) (11%) (33%) (20%) (32%) years (3%) (1%)62.6 (n=43) exposed (8%) 19(44%) 8(19%) 3 Occupationally 191) 9(21%) (2%) years (7%) years (n=456) (4%) Whether the exposure to asbestos was occupational, environmental or was not apparent, made little difference to the mean age or to the range of ages at the presumptive diagnosis of mesothelioma (Table 3). In about 65% of subjects who had either a history of occupational or of environmental exposure to asbestos, and in 56% of subjects who did not experience such exposure, the age at diagnosis fell within the 55 to 74 years' range. Similarly, whether the exposure was occupational or environmental did not affect materially the mean time-lag (about 37 years) between the first exposure to asbestos and the diagnosis of mesothelioma, or the time range. Occupationally- Environmentally- Time-lag (years) exposed (n = 456) exposed (n = 43j Less than 10 3 «I "70) I (2"70) (5"70) 2 (5"70) (20"70) 10 (23"70) (32"70) 15 (35"70) (25"70) 6 (14"70) 50 and over 71 (16"70) 7 (16"70) Unknown 9 (2"70) 2 (5"70) Mean time-lag 37.4 years 36.8 years Range 4-66 years 8-75 years The time-lag was 30 years or longer in 73% of the subjects who were exposed occupationally to asbestos. In 41% of cases that involved occupational exposure to asbestos, the time-lag was 40 years or longer, which included periods of up to 60 years. As expected, the time-lag between the first exposure to asbestos and the diagnosis of mesothelioma was rarely less than 10 years. Of the cases with occupational exposure to asbestos, 49% (225/456) of subjects had been employed in primary asbestos production or manufacturing, and in shipping. Industry Primary asbestos production or manufacture Asbestos mining and milling Asbestos-cement (A/C) production Asbestos-cement transport Asbestos-insulation manufacture/installation Asbestos-product manufacture Shipping Construction/demolition/maintenance (on shore) Reconstruction/repairs (at sea) Ship service (cook, steward, and so on) Stevedoring Building Construction/ maintenance/demolition (general) Construction/maintenance/demolition (A/C usage) Railways Rolling-stock fabrication/repair/maintenance Metal fabrication Steel/non-ferrous smelting Boiler fabrication. Engineering fabrication/repairs Occupation Labourer Carpenter/woodworker Boilermaker Fitter /turner /maintenance engineer Lagger /insulator T echnical/ clerical/ manager Semi-skilled/process worker Electrician Wharf labourer Asbestos miner/miller Welder/structural metalworker Plumber Transport/driver (all modes) Automotive mechanic Stoker Painter Storeman Bricklayer Service/ sport/recreation Blacksmith/metal treatment Able-seaman/ships officer Cases in industry (n=456j ) 7~ 19 I } 13 II 15 } 119 (26.1"70) 106 (23.2"70) 60 (13.2"70) 42 (9.2"70) 39 (8.6"70) Power stations (coal-fired) Construction/maintenance 19 (4.2"70) Chemical/paint 8 (1.8"70) Motor-vehicle repair (including brake/clutch repair) 7 (1.5"70) Textile/fur/leather 6 (1.3"70) Sugar production (maintenance/repair or equipment).7 (1.5"70) Miscellaneous industries (fewer than five cases in each) 36 (7.9"70) Inadequate information to assess asbestos exposure 7 (1.5"70) In addition, many cases occurred in workers in the building, railway, metal-fabrication and power industries. Labourers, carpenters, boilermakers and fitters/turners/maintenance engineers constituted 49% (222/456) of the occupations with a history of exposure to asbestos. Cases in occupation (n=456j 78 (17.1"70) 56 (12.3"70) 45 (9.9"70) 43 (9.4"70) 27 (5.6"70) 26 (5.7"70) 26 (5.7%) 23 (5.0'70) 19 (4.2"70) 16 (3.5"70) 16 (3.5"70) 12 (2.6"70) II (2.4"70) 8 (1.8%) 7 (1.5%) 6 (1.3%) 5 (l.l %) 3 (0.7"70) 2 (0.4%) 2 (0.4"70) 2 (0.4%)

4 170 August 17, 1987 Vol. 147 THE MEDICAL JOURNAL OF AUSTRALIA Furnace worker I (0.2"70) Plasterer I (0.2"70) Marine engineer 1 (0.2"70) Miscellaneous occupations (fewer than five cases in each) 12 (2.6070) Inadequate information to assess asbestos exposure 8 (1.8"70) Most subjects other than those who had worked in the primary asbestos production industry had worked with amphiboles (crocidolite, amosite [brown asbestos]), often during repair and maintenance work that involved thermal insulation. Local asbestoscement products were used extensively in home building. These sheets contained crocidolite until the mid 1960s, which may account for the relatively large number of carpenters with mesothelioma that was reported. Membership of certain occupations that would be expected to be associated with cases of mesothelioma as a result of exposure to asbestos, indeed contributed many cases: these included workers such as laggers/insulators, electricians. and wharf labourers. Discussion The analyses indicate that all states in Australia have a special problem with mesothelioma in comparison with the estimates of the incidence rates of mesothelioma in other countries. 12International comparisons are complicated by differences in the methods of notification and recording and in the diagnostic criteria. Private collections of cases by clinicians and pathologists provide no idea of incidence rates. Statutory notifications can be incomplete, and can exclude non-occupational and peritoneal cases of mesothelioma. In addition, notifications from Workers' Compensation boards and pneumoconiosis panels can prove to be incomplete. The diagnoses that the cancer registries receive may change according to the time of the diagnosis. Diagnoses that are made while patients are alive may alter when a post-mortem examination is held. The International Classification of Diseases (ICD) classification (before the ninth revision) had coded mesothelioma in an unreliable manner. 23 Great regional differences in diagnostic practices by pathologists have been observed in notifications to cancer registries, for ~xample, an underascertainment of notifications of mesothelioma of occurred in one estimate.'6 The use of death certificates alone, even since the ninth ICD revision, has led to serious inaccuracies - only about half the known cases of mesothelioma have proved acceptable as pathological diagnoses, and those which were accepted represented about half the known cases only.'6 In Australia, in 1982 to 1985, there were 296 deaths (256 men, 40 women) that were certified as having been caused by malignant pleural mesothelioma (ICD number, 163), that is, an average of 74 deaths a year (Australian Bureau of Statistics, personal communication).24 The number of presumptive diagnoses that were notified to the Program was about 150 per year, of which about 85070would be confirmed as cases of pleural mesothelioma. Thus, if the inaccuracies of death certificates are accepted, experience in Australia suggests that this source of ascertainment underestimates the incidence rate of mesothelioma by about Even then, the Program's data cannot be regarded as representative of the true incidence rate of mesothelioma over this period. Clearly none of the above modes of ascertainment gives complete data. Cancer registries require the combination of sources and checks that are afforded by our Program in order for their data to be useful in the monitoring and control of mesothelioma. The Program also provides the extra dimension on the accuracy of diagnoses, the development of methodology and the recognition of hazards that is necessary for scientific study. The Program's experience to the end of 1985 shows that it takes several years to establish a reliable notification system from a wide network of authorities and professional persons. The notification rate and the year of the presumptive diagnosis suggest that the Program had achieved high notification rates by Notification rates are now more uniform by region and notifications are occurring sooner after a diagnosis of mesothelioma is made. Clinicians, pathologists and the cancer registries have all been important sources of notifications in New South Wales and Queensland. In Victoria, South Australia and Tasmania, the majority of notifications have been from clinicians. In Western Australia, the Cancer Registry notified of cases from that State, due to the fact that the W A Government had established a statutory Mesothelioma Register in their Department of Public Health, which was later subsumed into the State's Cancer Registry.23 In Australia the annual incidence rate of mesothelioma per million population who were aged 20 or more years, was far in excess of that in any other country for which data are available, except for recent data from the United Kingdom (Table 4).2S However, the reported studies have all used different systems of data collection, some with a tendency to bias in certain areas. For example, in the French study, cases with known exposure to asbestos were reported mainly,9 and in the French, Canadian and UK studies, abdominal cases of mesothelioma were underreported The data from other countries in some instances relate to persons of all ages, which would, in effect, reduce the incidence rate of mesothelioma. In addition, the published data are not as recent as are those for Australia, and reported national incidences are increasing generally For example, the rate for England, Scotland and Wales among persons who are aged 20 years and over, is now 13.9 per million population, according to the data of Jones and Thomas.25 However, the rates of increase in these countries (if these were projected into the 1980s) would still not account for Australia's TABLE 4: International incidence of cases of mesothelioma as calculated from available information 1984,n, :C!:67% NA 45% 68% 67% 70% Exposure 54% 72% 85% Annual confirmation NA :C!: asbestos (women)*(men)* 100% t 90% Annual NA 7.0t Histological incidence* NA , Years Annual incidence ~Per million of population (applies to all ages where not qualified). tone per cent of cases excluded which were pericardia!. +Pleural mesothelioma casesonly. 90ccupational exposure only. IIJ. Bignon, French Mesothelioma Register, personal communication. 'H. Otto, Pathologisches Institut der Stadt, personal communication. *-A. Donna, Italian representative of CEC Mesothelioma Panel, personal communication. NA== not available.

5 THE MEDICAL JOURNAL OF AUSTRALIA Vol. 147 August 17, unenviable pre-eminence. It is still unclear whether it is better reporting or an increasing occurrence rate of mesotheliomas that contributes more to the increased rates of notification. The data that have been presented confirm the very strong association of mesothelioma with exposure to asbestos. Exposure to asbestos usually occurred over a long period and started in years of poor dust control. Crocidolite mining and milling at Wittenoom accounted for 33 cases of mesothelioma that \\ue notified between 1980 and 1985 in a population of some 6000 persons (about 65 cases in the Program were associated with the mine and its environs, but complete exposure histories currently are not available). A similar occurrence of cases that was reported from the mine before the Program started23 and an expected continuing occurrence of cases (mining finished in 1966), confirm the particularly hazardous nature of the Wittenoom fibre that was noted by Timbrell et al. 30 Two subjects in the Program were exposed to asbestos at Baryulgil, a chrysotile (white asbestos) mine in northern New South Wales. One subject was a maintenance engineer who had worked in the mine for 25 years and the other subject was a woman who lived in the town. Both had experienced exposure to chrysotile. However, this was not the only asbestos fibre that was associated with their cancers. Hessian bags that were used by.the townspeople and the miners were recycled, after they had been used to transport chrysotile, amosite and crocidolite. Therefore, this does not strengthen any possible association of chrysotile with mesothelioma, although the amount of asbestos that was mined at Baryulgil was only about onetenth of that which was mined at Wittenoom and the population that was exposed directly was much smaller. The Wittenoom fibre has been distributed widely and persists throughout Australia. However, before 1940 workers would have been exposed to imported amphiboles. In about 10% of cases, occupational exposure to asbestos occurred in multiple industries or occupations. In this article, analysis by industries and occupations in which the exposure to asbestos first occurred, does not imply that such exposure is most important in inducing mesothelioma, but it still permits an overview of industrial exposure in Australia. On this basis, the analysis reveals the expected associations but not the relative risks that are involved, which are to be the subject of further study. Presumably, small populations that had a high rate of exposure to asbestos, such as insulation engineers, contributed a disproportionately greater number of cases, as was noted also by Hodgson and Jones.31 Nevertheless, in agreement with Zoloth and Michaels' findings in sheet-metal workers,'2 we noted that larger occupational groups, with intermittent exposure to asbestos, contributed more cases of mesothelioma than did smaller-sized occupational groups with more constant, heavy exposure to asbestos. Because of the smaller scale of production in Australia, no history of occupational exposure in an asbestos-textile industry worker has been elicited as yet. This is in contrast with the experience in other countries such as England. 33Many of the cases among welders and metal fabricators may reflect, in part, the historical use of crocidolite strands to coat welding rods between 1920 and Although the occupational association was very strong, the absence of a history of exposure to asbestos in 191 of 726 cases of mesothelioma invites enquiry into other environmental causes of the disease that have yet to be explored by the Program. However, the oncogenic potential of the burden of lung fibres in those who are not occupationally-exposed to asbestos, remains to be addressed.21 Are some cases of mesothelioma wrongly not being attributed to asbestos? Conversely, are other cases with a history of intermittent or low exposure to asbestos being so attributed incorrectly? It is difficult to be accurate about an exposure that was incurred in the past (short of awaiting the lung-fibre analysis after death), even in industries where such measurements have been made.33 The Program constitutes a non-statutory reference collection, which is complementary to those of the cancer registries. The high level of public and professional concern in regard to the incidence and diagnosis of mesothelioma in Australia is evidence of the need for such measures. It is crucial to resolve uncertainty at the lower end of the dose-relationship curve between exposure to asbestos and the development of mesothelioma, which is best described by a linear non-threshold model. 34The risk that was inherent in exposure to asbestos at Wittenoom and other high industrial sites of the past is clear. However, the risks that are involved in the present rates of industrial exposure are less well defined. It is imperative to resolve the risks from the following types of exposure to asbestos: indirect occupational; bystander; incidental neighbourhood; domestic; and recreational. In addition, questions that concern the differential risk from fibre types and the possibility of other presently unknown aetiological agents of mesothelioma must be resolved. The Program proposes to address some of these questions in further detailed analyses of its data. Trends in the occurrence of mesotheliomas will also be analysed progressively from notifications to the continuing Australian Mesothelioma Register. Acknowledgements \Ve wish to thank Dr Thea Constance, Dr Phillip \\' Allen, Professor A. Harold Attwood, Dr Douglas W. Henderson, Dr Keith B. Shilkin, and Dr Richard H. Steele of the Pathology Panel; Dr Thomas Ng, World Health Organization, Geneva, and Mr Gersh Major, Consulting Occupational Hygienist, both of whom were instrumental in the development of the Program; Dr Joyce Ford of the NSW Cancer Registry; Dr Julian Lee, The Thoracic Society of Australia's representative; Ms Gay Summers and Ms Margaret Ackad of the Lung Fibre Counting Panel; Dr Bery! Edye; and all the colleagues throughout Australia who participated in the Australian Mesothelioma Surveillance Program, particularly the state occupational health division medical officers, the state Department of Health community nurses, and the pathologists for their invaluable assistance. The Program has received support from the National Health and ~'1edical Research Council, the NSW Workers' Compensation (Dust Diseases) Board, and various other donors, and has been fully funded by the National Occupational Health and Safety Commission since References 1. \Vagner JC, Sleggs CA, Marchand P. 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6 172 August 17, 1987 Vol. 147 THE MEDICAL JOURNAL OF AUSTRALIA Perth, September Hodgson JT, Jones RD. Mortality of asbestos workers in England and Wales Br J Ind Med 1986; 43: Zoloth S, Michaels D. Asbestos disease in sheet metal workers: the results of a proportional mortality analysis. Am J Ind Med 1985; 7: 315~ Peto J, Doll R, Herman C, et al. Relationship of mortality to measures of environmental asbestos pollution in an asbestos textile factory. Am J Occup Hyg 1985; 29: Royal Commission on Matters of Health and Safety Arising from the Use of Asbestos in Ontario. Report. 'loll Toronto: Queen's Printer for Ontario, (Received A1arch 22, 1985,' accepted April 10, 1987) AUSTRALASIAN MEDICAL PUBLISHING COMPANY LIMITED Arundel Street, Glebe, N.S.w. 2037