Occupational malignant mesothelioma in Singapore

INTRODUCTION Malignant mesothelioma (MM) is linked to asbestos exposure. The global estimate for occupation-attributable MM deaths was 27,600 in 2016.1 Although asbestos had been banned in 55 countries as of 2014, this corresponds to only 16% of the world population (about 1,110,000,000).2 Asbestos is a silicate mineral composed of fibres that are heat resistant. These properties make it ideal for fire-retardant coatings, and it was used widely in the construction and shipping industry. Exposure to asbestos causes asbestos-related diseases such as asbestosis, lung cancer and MM. Despite the ban on asbestos, cases of MM continue to rise, owing to the long latency period between asbestos exposure and the development of MM. Therefore, clinicians need to have a strong index of suspicion, as MM is a notifiable and compensable occupational disease in Singapore under the Workplace Safety and Health (WSH) Act and the Work Injury Compensation Act (WICA), respectively. There is also a need to pay special attention to particular industries, which this paper will discuss. Information on the historical use of asbestos, the types of industries as well as the legislative requirements for asbestos control in Singapore and other preventive measures are described in the country report in 20023 and more recently in 2011.4 Singapore had introduced the Factories (Asbestos) Regulations in 1980 to regulate asbestos exposure in factories and manufacturing plants. Since 1989, Singapore has banned the import and use of asbestos in construction materials. From 1980 to 2000, the number of brake and gasket manufacturers using raw asbestos was further reduced, and since 2001, there have been no known users of raw asbestos. However, MM remains relevant today owing to the long latency from first asbestos exposure and the continued presence of asbestos in old buildings and ships. Ho et al. described the occupational profile of six cases of MM in 1987.5 This was followed by other reports of MM cases in Singapore in 1996,6 2002,3 20037 and 2011.8 We conducted a population-based observational study that aimed to present an epidemiological profile and industry analysis of occupational MM (OMM) cases in Singapore. METHODS Data on OMM were obtained from the Occupational Safety and Health Division, Ministry of Manpower (MOM), Singapore. The sources of data included notifications of occupational diseases from doctors and employers, claims from Work Injury Compensation Department and referrals to the joint occupational lung clinic in Singapore General Hospital. The cases were investigated by MOM occupational physicians to determine if MM was a result of exposure to asbestos at work. The cases were subsequently screened for eligibility for compensation under WICA. The Singapore Cancer Registry (SCR), managed by the National Registry of Diseases Office under the Singapore Ministry of Health, tracks all cancer data (including MM), as reported by clinicians nationwide for Singapore citizens and permanent residents. We estimated the crude incidence rates (CIR) for the overall and working population. The number of cases in the 5-year periods from 1980 till 2019 was divided by Singapore's average total population and average labour force population during that same period, respectively.9,10 The population of the labour force used to calculate CIR for the working population was only available from 1991 onwards. Data relating to latency were extracted from the individual case reports. The occupational history was taken from interviews with patients or the next of kin at the time of investigation of each case. Photos, salary statements and other supporting documents, where available, were referred to as evidence. Latency was estimated by subtracting the year of first estimated exposure to asbestos from the year of diagnosis of OMM. A limitation of grouping the cases by occupation was that some job titles were generic and might not reflect where the patients were exposed to asbestos. Hence, an industry classification was used based on the actual location of exposure to asbestos. For example, a general worker or welder exposed to asbestos in a ship or shipyard was classified as working in the marine industry. The cases were grouped according to the Singapore Standard Industrial Classification 2015 (version 2018), after verifying that the industry matched their actual place of exposure. RESULTS A total of 94 cases of OMM were confirmed from 1984 to 2019. The majority (95.7%) were males. Eighty-two (87.2%) had pleural mesothelioma, while 12 (12.8%) had peritoneal mesothelioma. The mean age at diagnosis was 66.9 (range 46–84) years, and the mean latency period was 43.4 (range 24–65) years. During the same period, 394 MM cases were reported to the SCR, of which only 94 were confirmed as OMM by MOM. From 1980 to 2019, the number of MM cases increased from five in 1980–1984 to 110 in 2015–2019 Figure 1. The OMM cases made up 23.9% of all MM cases from 1980 to 2019. Occupational MM comprised 40% of all MM cases from 1980 to 1984 and 26.4% of all cases from 2015 to 2019.Figure 1: Graph shows the number of malignant mesothelioma (MM) cases in Singapore every 5 years from 1980 to 2019.The CIR for all MM cases increased from 0.2 per 100,000 (1980–1984) to 2.1 per 100,000 (2015–2019) of the total population and from 0.8 per 100,000 (1990–1994) to 3.0 per 100,000 (2015–2019) of the employed population Figure 2. The CIR for OMM cases also showed increasing trends.Figure 2: Graph shows the 5-year crude incidence rate (CIR) of malignant mesothelioma (MM) in Singapore (per 100,000).Both the latency and age at diagnosis of MM had been steadily increasing over the 40-year period. The mean latency increased from 33.0 years (1980–1984) to 48.1 years (2015–2019). The mean age at diagnosis increased from 51.5 years (1980–1984) to 71.9 years (2015–2019). The mean latency of 44.1 years for pleural mesothelioma (n = 82) was significantly longer than the mean of 37.9 years for peritoneal mesothelioma (n = 12) (P = 0.021). There was no significant difference in the mean latency between genders (male 43.29 years vs. female 43.75 years; P = 0.92). The mean latency was shorter for cases from the asbestos manufacturing industry than those from the marine industry (n = 21, 40.8 years vs. n = 45, 45 years; P = 0.053). Overall, the majority of the 94 OMM cases came from three industries: marine (48%), asbestos manufacturing (22%) and construction (10%). Of the 28 cases confirmed in the first 20 years, 13 (46%) were from asbestos manufacturing and 10 (36%) were from marine industries. The construction industry had only one case Figure 3. Of the 66 cases confirmed in the next 20 years, cases from the asbestos manufacturing industry declined sharply to eight (12%), while cases from the marine industry increased to 35 (53%). Cases from the construction industry increased from one (3%) to eight (12%) Figure 3. Further analysis of the cases within the marine and construction industries revealed a diversity of occupations. In the marine industry, the cases were involved in occupations such as pipe fitter, labourer, electrician, welder, technician, cleaner, boiler worker, painter and air-conditioning technician, while in the construction industry, the occupations were site supervisor, labourer, demolition worker, roofer, painter and lorry driver.Figure 3: Graph shows the industry distribution of occupational malignant mesothelioma (MM) cases over time.DISCUSSION Mesothelioma is rare in Singapore. Therefore, this study analysed 5-year trends instead of annual trends. The cases and CIR have been increasing even 30 years after the asbestos ban, owing to the long latency and exposures to existing asbestos in old buildings. While there was a slight dip in the number of cases and CIR in the most recent period from 2015 to 2019, it is premature to confirm if this is a reversal of the increasing trends. Cases of MM have been observed to peak and then decline in many developed countries. Cases and age-standardised incidence rates for malignant pleural mesothelioma in males have peaked and started to decline in the four Nordic countries.11 In the 1970s, the Nordic countries limited certain uses of asbestos, with a resulting drop in its imports. Denmark and Norway banned the use of asbestos in the early 1980s, Sweden in 1986 and Finland in 1992. There has been a year-on-year increase in annual MM deaths in Great Britain over the last 50 years, with nearly 10 times as many deaths in the most recent decade, 2010–2019, as compared to 1970–1979. The number of male deaths was 9% lower in 2019 as compared to the average for 2012–2018 and was consistent with earlier predictions that annual MM deaths would start to reduce around 2020.12 Crocidolite and amosite were banned in the UK in 1985 and chrysotile in 1999. Based on these observations, a significant reduction in the use and exposure to asbestos would eventually lead to a decline in cases of MM. We can expect to see a similar trend in Singapore, where there have been significant preventive efforts to limit and reduce such exposures. These include banning of the import and use of asbestos in all construction materials in 1989, phasing out of all asbestos manufacturing industries and enforcement of WSH (Asbestos) Regulations 2014 for any work involving the removal of existing asbestos from buildings, ships, machinery, etc., It is possible that cases of MM in Singapore could peak in the coming decade, given that banning of the import and use of asbestos in all construction materials and gradual phasing out of the use of asbestos started more than three decades ago. The difference in the number of OMM and total MM cases is not unexpected. Such differences have also been observed in other countries when comparing compensated cases of MM to total MM cases reported. In the UK, about 20% of all MM cases were assessed for Industrial Injuries Disablement Benefit in the 1980s. This improved to about 80% in the last 5 years.12 In Canada, 35% and 33% of all MM cases were compensated in the states of Alberta13 and British Columbia,14 respectively. In France, 42% of all malignant pleural mesothelioma cases were compensated.15 For Singapore, the proportion of OMM was 24% (1980–2019) and 26% (2015–2019) of all MM cases. There could be many reasons for these observed differences between the total number of MM cases and the MM cases that were assessed for or received compensation for an industrial injury or an occupational disease. These include awareness that the disease could be work related and that it is a reportable occupational disease, the eligibility criteria (e.g. the self-employed are excluded), and the confirmation of work-relatedness, which is largely dependent on the ability to obtain an accurate occupational history of relevant past exposures to asbestos. Although OMM is listed as a compensable occupational disease in WICA, the eligibility or limitation period for making a claim under WICA is 12 months from the date the worker ceased to be employed in the hazardous occupation for most occupational, diseases including OMM. Given the long latency for MM, most workers who develop OMM would have left their jobs for many years by the time they developed MM. The Work Injury Compensation (Workers' Fund) Regulations 2020 provides for ex-gratia payments for injured workers, including those that suffer from an occupational disease after the limitation period. One of the occupational diseases listed in the schedule of occupational diseases contracted after the limitation period in the regulations is MM. Workers who develop OMM can apply for financial assistance from the Workers' Fund through the Work Injury Compensation Department of MOM. In a newspaper article,16 it was reported that there were 26 OMM cases confirmed between 2000 and 2011 (12 years), of which two received compensation of SGD 111,000 and SGD 140,000 under WICA and six received ex-gratia payments ranging from SGD 16,300 to SGD 60,000 from the Workers' Fund. As expected, compensation under WICA was higher than ex-gratia payments from the Workers' Fund. Overall, 6/26 (30.7%) received some form of compensation for OMM during the period 2000–2012. In an internal review of 46 confirmed OMM cases between 2013 and 2021 (9 years), four received compensation under WICA and 17 received payments from the Workers' Fund. The range of compensation under WICA was SGD 54,736 to SGD 272,500. The ex-gratia payments from the Workers' Fund ranged from SGD 1812 to SGD 219,282. All these payments are related to the permanent incapacity awards. The workers are also entitled to claims for medical expenses up to the prevailing limit under WICA. The payment amounts are higher in recent years due to the increase in compensation limits for death, permanent incapacity and medical expenses under WICA. Overall, 21/46 (45.6%) received some form of compensation for OMM in 2013–2021. This is a significant improvement over the previous period of 2000–2012. The reasons for non-compensation in the remaining cases included decisions of some workers to withdraw their application or not apply for Workers' Fund. In Singapore, only 94/394 (23.9%) total MM cases were confirmed to be OMM. This figure is low, as MM almost always develops from past asbestos exposure in workplaces. An Italian study found that about 70% of all MM cases investigated had occupational exposure to asbestos.17 Although MM has been a notifiable and compensable occupational disease in Singapore since 1985, there is still an underdetection of occupational cases. The reasons include a lack of awareness that MM is a notifiable occupational disease, as well as difficulties faced in obtaining an accurate and complete occupational history. Medical practitioners may lack awareness of the relevant at-risk industries when interviewing patients. Patients are often not aware that they were exposed to asbestos in their work many decades ago. They often have difficulties in recalling and providing evidence for such exposures. Medical practitioners need to actively ask every patient with MM for all possible past exposures to asbestos (whether occupational, para-occupational or environmental) and notify these cases to both SCR and MOM. There has been a shift in the distribution of OMM cases across industries over time. While asbestos manufacturing contributed many cases in the first 20 years, there was a subsequent decline. This can be explained by the closure of the only asbestos cement manufacturing plant in the early 1980s. Recently, the marine and construction industries have become a growing concern. The marine industry is the dominant source of asbestos exposure owing to Singapore's heavy reliance on shipbuilding and ship repair as a significant driver of economic development in its earlier years. Asbestos-containing materials continue to remain in old ships and buildings. Exposure to asbestos in Singapore today is from asbestos that is already present in existing buildings, ships, pipes, equipment, etc. Preventive efforts must focus on identifying the presence of asbestos and the safe management of such asbestos, such as strict measures to prevent exposure during removal or any work involving such asbestos. The enactment of WSH (Asbestos) Regulations 2014 has imposed further requirements, including an asbestos survey by a competent person for the identification of asbestos materials before carrying out any building works, which include demolition, alteration, addition or repair of building. In addition, all asbestos removal work must be done by an approved asbestos removal contractor licensed by MOM, and measures must be taken to prevent the spread or release of asbestos during such work.18 Enforcement and preventive efforts should continue, especially in the shipbuilding and construction industries, to prevent future MM cases. Both the latency and age at diagnosis of MM have been steadily increasing over the 40-year period. This trend has also been observed in other countries. Comparison of latency across industries did not show any clear trends, as there were numerous types of occupations within each industry, each with varying levels of asbestos exposure. There were also limitations in quantifying the intensities of asbestos exposure from the occupational histories alone. Differences in mesothelioma latencies observed in different occupations have often been attributed to an inverse relationship between the intensity of asbestos exposure and the length of the latency period.19 This contrasts, however, with the study of a cohort of British asbestos workers, which did not find any association between latency and occupation, although a shorter latency was found among females and those who died from asbestosis.20 In conclusion, the incidence rates of MM continue to increase, consistent with the long latency period of MM. Physicians should ask every patient with MM for possible past exposures to asbestos and notify cases to the relevant agencies. Workers who have OMM can receive compensation under WICA or the Workers' Fund. This includes payment for both medical expenses and permanent incapacity up to the prevailing limits. The ban on asbestos use and enactment of WSH (Asbestos) Regulations 2014 were steps taken in the right direction. Preventive and enforcement efforts should continue, especially for the marine and construction sectors. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.