Part 1: Review of Asbestos-Related Disease Notifications

1.1 Summary

This report reviews 1125 cases that were notified to the National Asbestos Medical Panel between March 1992 and July 2008. They include:

• 212 cases of mesothelioma
• 107 cases of lung cancer
• 253 cases of asbestosis
• 553 cases of pleural abnormalities.

The number of lung cancer cases reported is roughly half of the number of mesothelioma cases. This suggests that the taking of a lung cancer history is still dominated by the smoking factor, and that occupational factors are downplayed.

The transfer of asbestos from workers to the home is another emerging feature of asbestos-related disease in New Zealand. Family members are presenting with pleural changes or, rarely and tragically, mesothelioma.

Mesothelioma notifications continue to rise, reflecting exposure in the 1960s and 1970s, and this trend is likely to continue for some years to come.

Three Department of Labour publications have arisen from the registers. They are:

• Respiratory Symptoms and Asbestos Dust Exposure (1997)
• Mesothelioma in New Zealand (2000)
• Lung Function Changes in Asbestos Exposed Workers with Pleural Abnormalities (2000).

In addition, two special reports have been published:

• Recent Advances in Asbestos-Related Disease
  (Dr M Becklake, 1994)
• The Epidemiology of Mesothelioma in Historical Context
  (Doctors J C and A D McDonald, 1998)

1.2 Results

Figure 1 shows the distribution of the four main diagnostic categories:

• Lung Cancer
• Pleural Disease
• Asbestosis
• Mesothelioma.

Figure 1: Categories of Disease 1992-2008
View data table for Figure 1

What is noticeable is that pleural disease is the main category with lung cancer clearly under-represented when compared with mesothelioma.

Figure 2 looks at occupations for the total number of notified asbestos disease cases during the period.

Figure 2: Notified Asbestos Disease by Occupation 1992-2008
View data table for Figure 2

It is clear that carpenters, plumbers and electricians are together responsible for 67 percent of all cases. These 'all purpose' construction workers are an occupational category at risk particularly because, unlike asbestos cement workers, they are not always seen as being at obvious risk.

The non-occupational category refers to cases where an individual's exposure was not work-related. This includes all cases resulting from secondary or environmental exposure, such as children brought up in the home of an asbestos worker, and people who washed asbestos-contaminated clothes. The 'no known exposure' category refers predominantly to mesothelioma cases where conclusive exposure histories were not available. (Note: the time delay is often 40-50 years from exposure and has either been forgotten, never recognised, or not known by the surviving family member).

1.3 Mesothelioma

Mesothelioma - a rare cancer of the pleural membranes on the surface of the lungs - is strongly related to asbestos exposure. The panel reviewed 212 cases of mesothelioma, of which:

• 204 were Caucasian
• 6 were Maori
• 2 were identified as "Other"
• 199 were males, 13 were females
• The mean age at diagnosis was 67 years (range 35-85)
• The mean number of years since first exposure was 45 (range 12-74)
• The mean exposure index was 178 (range 1-780)
• There were 19 current smokers, 116 ex-smokers and 59 never-smokers (information for 10 cases was unavailable).

The three occupations: asbestos processors, plumbers/fitters/laggers, and carpenters/builders, accounted for over 60 percent of all registered cases.

It has been noted that an asbestos exposure history may be lacking with mesothelioma cases. Our experience suggests that with patience and recognition of the range of likely exposures, it is often possible to obtain evidence of asbestos exposure. In one case the disease developed in a middle-aged woman living in a small rural town. It was revealed that as a teenager she had washed the clothes of an older brother who had been a railway workshop apprentice. Asbestos lagging was used in the repair and maintenance of the boilers, and apprentices were known to use asbestos in 'snowball fights'.

Figure 3: Distribution of Mesothelioma by Occupation
View data table for Figure 3

1.4 National Cancer Figures on Mesothelioma

Figure 4: Number of Cases of Mesothelioma in New Zealand 1954 to 2005
View data table for Figure 4

Over the period 1954-2005 a total of 797 cases of mesothelioma have been registered. Figure 4 shows that the total number of cases continues to rise up to 2005 (the latest figures) and exceeds 100 for the first time.

Mesothelioma is very much a disease of old age as Table 1 illustrates, with over 50% of cases occurring to people aged 70 or over.

Age Group	Gender		Total
	Male	Female
Under 20	0	0	0
20 to 44	6	10	16
45 to 69	335	42	377
70+	346	58	404
Total	687	110	797

The male:female ratio is about 7:1 except in those under 45, where this gender ratio is reversed at 1:1.6. Of the 797 cases, 110 occurred to women and 687 to men. As women are seldom employed directly in the asbestos-exposed workplaces, their exposure could be as a result of "secondary" exposure to dust brought home from work on the hair and clothes of family members.

1.5 Lung Cancer

Lung cancer is a cancer of some of the cells in parts of the lung, usually beginning in the lining of the airway.

The panel reviewed a total of 107 cases of lung cancer, of which:

• 101 were Caucasian
• 4 were Maori
• 1 was from a Pacific Island
• 1 was identified as "Other"
• 105 were males, 2 were females
• The mean age at diagnosis was 69 (range 42-86)
• The mean number of years since first exposure was 46 (range 17-63)
• The mean exposure index was 165 (range 12-565)
• There were 25 current smokers, 72 ex-smokers, 7 never smokers and 3 unknown.

Lung cancers are classified according to the type of cell affected. Histological classification revealed 52 cases of squamous cell carcinoma, 27 adeno, 12 small cell, 4 undifferentiated, 1 bronchiolar-alveolar, 3 large cell and 8 cases where classification was not stated. In addition, the tumour sites were as follows: 43 upper lobe, 39 lower lobe, 11 middle lobe, and 14 not stated.

The occupational distribution of lung cancer follows a similar pattern to both pleural plaques and asbestosis, in that plumbers, fitters, carpenters and asbestos processors account for most of the cases. See Figure 5: Distribution of Lung Cancer by Occupation.

Figure 5: Distribution of Lung Cancer by Occupation
View data table for Figure 5

1.6 Asbestosis

Asbestosis is a fibrotic or scarring disease of the lung tissue. The disease develops slowly over many years from initial exposure. It can continue to develop after exposure to asbestos has ceased.

The panel reviewed a total of 253 cases of asbestosis, of which:

• 249were Caucasian
• 2 were Maori
• 2 were from a Pacific Island
• 237were males, 16 were females
• The mean age at diagnosis was 68 (range 37-86)
• The mean number of years since first exposure was 43 (range 15-71)
• The mean exposure index was 180 (range 10-720)
• There were 20 current smokers, 183 ex-smokers and 43 never smokers (accurate smoking histories were not available in 7 cases)
• Radiological changes showed 142 cases with pleural plaques and/or pleural thickening.

Figure 6: Distribution of Asbestosis Notifications by Occupation
View data table for Figure 6

Figure 7: ILO Grading of Asbestosis Cases (n = 150)
View data table for Figure 7

Of the 253 asbestosis cases, 148 were categorised by ILO classification, and others were categorised on the basis of CT, HRCT or pathology, where available. With the recent trend to use HRCT, categorisation by ILO classification is less frequently done.

1.6.1 Definition of Asbestosis Used in the Register

An important issue with this disease is 'what criteria constitute a diagnosis of asbestosis?' The main point of discussion is the difference between a clinical diagnosis of asbestosis, and a diagnosis suitable for use in a national database where the inclusion of patients with early disease is desirable.

The definition of Gilson^[a] in his review of asbestosis-related lung conditions in the ILO encyclopaedia has been chosen by the panel and is as follows:

1. A history of significant exposure to asbestos dust rarely starting less than 10 years before examination
2. Radiological features consistent with basal fibrosis (1/0 and above, ILO 1980)
3. Characteristic bilateral crepitations
4. Lung function changes consistent with at least some features of the restrictive syndrome.

Gilson notes not all criteria need to be met in all cases, but that (a) is essential, and (b) should be given greater weight than (c) or (d). However, occasionally (c) may be the sole sign. Further, he notes that although the restrictive syndrome is the most common pattern (about 40%), in about 10% of cases airway obstruction is the main feature, while in the remainder a mixed pattern is seen.

Of the 253 asbestosis cases:

• All had a significant exposure history, with a mean exposure index of 180 (range 10-720)
• Mean latency was 42 years, with a range of 15-71 years
• Most cases had an ILO rating 1/1 or greater where this rating was used, although this criterion is now seldom used
• Detailed clinical examination results were not always available from the records, thus the presence of crackles was not measurable
• Lung function changes are recorded in the register based on the availability of data either from respiratory laboratories, respiratory physicians, or occupational health nurses
• Additional information from HRCT scanning has led to the recognition of some cases of asbestosis not covered by the Gilson criteria. As noted, HRCT diagnosis is now the norm.

The lung function test numbers in the report confirm the classical restrictive lung function pattern picture does not dominate, with obstructive, mixed, and normal patterns occurring.

1.7 Pleural Abnormalities

Pleural abnormalities include pleural plaques, diffuse pleural thickening, chronic fibrosing pleuritis and pleural effusions. It does not include pleural disease occurring together with mesothelioma, lung cancer or asbestosis.

Figure 8: Distribution of Pleural Abnormality Notifications by Occupation
View data table for Figure 8

Of the 553 cases reviewed:

• 542 were Caucasian
• 7 were Maori
• 4 were from Pacific Islands
• All but 10 were males
• The mean exposure index was 162 (range 6-708)
• There were 52 smokers, 328 ex-smokers and 138 never smokers
  (accurate smoking histories were not available in 35 cases).

1.8 Discussion

Information recorded in the Disease Register under-estimates the total burden of asbestos-related disease in NewZealand. This is a consequence of the voluntary nature of the Register, lack of understanding of work as a factor in disease causation by the medical profession, and failure by the Cancer Registry to code occupation in their database. However, the Register continues to serve a useful purpose. There is now greater awareness of the work factor in disease than in 1992 when the Register was established. The Department of Labour now has greater commitment to the importance of occupational illnesses; the Accident Compensation Corporation employs a greater number of occupational doctors, and there are increasing numbers of occupational nurses and safety officers in the private sector.

The Registers, part of the wider Notifiable Occupational Disease System (NODS) operated by the Department of Labour have, in the view of the medical panel, played an important part in encouraging these developments.

1.8.1 Pleural Plaques

One of the aims of the medical panel was to confirm the view that pleural plaques were not just a marker of exposure, but represented a disease state. The Department of Labour publication Lung Function Changes in Asbestos Exposed Workers with Pleural Abnormalities in 2000 indicated a clear dose response pattern, including a reduction of FVC and FEV1 with increasing asbestos exposure, independent of smoking habit.

Reference was made earlier to the impact of an asbestos-related occupation on the health of a worker's partner and children. Two cases of pleural plaques notified in the last few years illustrate two women developing widespread plaques in their early 70s. Their only exposure was to asbestos dust brought home on their husbands' clothes which they washed. In one case the husband was an asbestos sprayer; the other, a carpenter.

1.8.2 Asbestosis

The increasing use of HRCT has resulted in the identification of minor degrees of asbestosis often with few, if any, symptoms and no disability. It is possible that these individuals will have a better long-term outlook, although this is not yet established.

1.8.3 Lung Cancer

The contribution of occupational asbestos exposure to the causation of lung cancer is well recognised as being underestimated, and over-attributed to smoking among workers exposed to asbestos. One approach to this issue is to determine the ratio between mesothelioma and lung cancer on the grounds that most mesotheliomas are diagnosed and the majority are regarded as being caused by asbestos exposure at work. Various estimates of such a ratio have been suggested and, as noted by Kjellstrom^[b] can range from 1 to 10. Even if the lower ratio of 1:2 is taken - based on the mesothelioma cases diagnosed over 1994-2005, for example - some 1,594 cases of lung cancer due to asbestos exposure would have occurred, or approximately 145 a year. It is likely that this figure could be even higher.

1.8.4 Mesothelioma

Reported cases of mesothelioma have continued to rise in New Zealand over the past decade as was shown in Figure 4, and based on the New Zealand Cancer Registry. It is of interest to note the mean exposure index for mesothelioma of 152 - as recorded by the panel - is not dissimilar to exposure indices for pleural plaques (162), lung cancer (162) and asbestosis (180). In other words, mesothelioma, like other asbestos-related conditions, is in general dose dependent.

1.8.5 Chronic Obstruction Pulmonary Diseases (COPD) and Asbestos Exposure

These conditions are now being recorded if present in individuals with an asbestos-related disease, as well as in those asbestos-exposed workers who have no confirmed asbestos-related lung or pleural disease. Over the past year 33% of the 85 cases of asbestos-related disease also had COPD, 40% among cases of pleural plaques, 45% among asbestosis cases, 80% among lung cancer cases and 0% among cases of mesothelioma. In addition, eight cases that were referred to the Panel because of asbestos exposure but without classical asbestos-related conditions, had COPD.

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Footnotes

^[a] Gilson JC: Asbestosis, Encyclopaedia of Occupational Health and Safety, 1983 3^rd edition, vol 1 pp 187-191

^[b] Kjellstrom T: The Epidemic of Asbestos-Related Diseases in New Zealand. International Journal Occupational - Environmental Health 2004, 102 June