Disease Background

 

What is mesothelioma?

Mesothelioma is a cancer of the tissue lining the lungs and other organs. Mesothelioma is the most well-known modern occupational cancer dating back to the 1950s when asbestos miners experienced high rates of this highly fatal disease. It is characterized by a long latency, upwards of 40 years, after exposure to asbestos fibers. There is no cure and survival is extremely poor with only 10% of cases living five years after being diagnosed. Men are more likely to be diagnosed than women, but second-hand exposure to asbestos through clothing washing is a historic risk factor for mesothelioma in women. The diagnostic difference in sex is due to more men working in environments with asbestos than men being more susceptible to women.

Risk factors

  • Asbestos fibers
  • Ionizing radiation

Approximately 80% of mesothelioma cases are attributable to occupational asbestos exposures.  There are several types of asbestos fiber, including chrysotile asbestos, which is the most widely used fiber. All fiber types are known to cause mesothelioma. Asbestos was heavily mined in the early and mid 20th century and used across a variety of applications due to its favourable thermal and tensile properties.

Why are we interested?

There are multiple occupations and industries that have consistently shown increased risks of mesothelioma. The recent national asbestos ban (link) is a positive step to reduce the health burden of mesothelioma, but exposure to asbestos is an ongoing concern. Using the occupational disease surveillance system (ODSS), we sought to identify workplace trends for mesothelioma in Ontario.

Key Findings

Within the construction industry, ODSS results indicate that insulating occupations, pipefitters and plumbers, electricians and repairmen and carpenters are all at elevated risks of mesothelioma. Insulating occupations require workers to handle asbestos materials when either installing or removing insulation materials from homes. Pipefitters and plumbers as well as electricians and repairmen are required to work within wall spaces in buildings, which potentially exposes them to insulating materials, such as asbestos. Disturbing these materials can lead to the inhalation of asbestos fibers.

Workers within the education and related services sector include teachers and administrative staff. These workers are possibly exposed to asbestos that was installed as pipe insulation in older school and university buildings. The degradation of these buildings can lead to water damage, which can volatilize asbestos and pose a health risk to staff. ODSS results indicate that university and college staff as well as elementary and secondary school staff are at increased risks of mesothelioma. While these findings may not appear obvious given the clerical and teaching tasks of education workers, these associations have been previously observed and are supported in the scientific literature.

Unlike Quebec, Ontario’s asbestos mining was not a large industry. Nevertheless, ODSS results indicate that asbestos miners in Ontario are at a dramatically increased risk of mesothelioma relative to other Ontario workers. This is expected given the known etiology of mesothelioma and the extraordinarily high levels of exposure asbestos miners would incur.

Iron and steel mill workers are required to operate machinery, including boilerplates, furnaces, and other heating apparatuses.  Asbestos was commonly used as an insulating material in metalworking machinery. When these materials are disturbed or degrade asbestos fibers are released into the air. ODSS results demonstrate that iron and steel workers are at an increased risk of mesothelioma relative to other Ontario workers.

Risk by Industry and Occupation

FIG1. Incidence of Mesothelioma diagnoses among workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater incidence of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).

FIG2. Incidence of Mesothelioma diagnoses among workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016 

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater incidence of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).

Table of Results

Table1. Surveillance of Mesothelioma: Number of cases, workers employed, and hazard ratios in each industry (SIC)

SIC Code * Industry Group Number of cases Number of workers employed Hazard Ratio (95% CI) †
1 Agriculture 11 35,119 0.81 (0.45, 1.47)
2/3 Forestry, Fishing and
Trapping
<5 10,722
4 Mines, Quarries and
Oil Wells
21 23,230 1.63 (1.06, 2.52)
5 Manufacturing 340 694,923 1.10 (0.95, 1.26)
6 Construction 170 211,572 1.87 (1.58, 2.22)
7 Transportation, Communication
and Other Utilities
83 197,583 1.00 (0.80, 1.26)
8 Trade 93 429,967 0.55 (0.44, 0.68)
9 Finance, Insurance and
Real Estate
6 24,021 0.76 (0.34, 1.70)
10 Community, Business and
Personal Service
126 600,448 0.89 (0.74, 1.09)
11 Public Administration and
Defense
82 191,139 1.24 (0.99, 1.56)
         
         
* SIC: Standard Industrial Classification (1970)    
† Hazard rate in each group relative to all others    

Table2. Surveillance of Mesothelioma: Number of cases, workers employed, and hazard ratios in each occupation (CCDO) group

CCDO Code * Occupation Group Number of cases Number of workers employed Hazard Ratio (95% CI) †
11 Managerial, administrative
and related
15 31,037 2.73 (1.64, 4.56)
21 Natural sciences, engineering
and mathematics
12 26,369 1.28 (0.73, 2.27)
23 Social sciences and
related fields
<5 30,728
25 Religion 0 129
27 Teaching and related 9 48,524 1.43 (0.74, 2.77)
31 Medicine and health 17 135,475 1.04 (0.63, 1.71)
33 Artistic, literary,
recreational and related
<5 15,009
41 Clerical and related 35 197,593 0.62 (0.44, 0.87)
51 Sales 20 148,272 0.59 (0.38, 0.93)
61 Service 77 371,368 0.74 (0.58, 0.94)
71 Farming, horticultural
and animal husbandry
12 50,269 0.62 (0.35, 1.09)
73 Fishing, hunting,
trapping and related
0 558
75 Forestry and logging <5 10,710
77 Mining and quarrying,
including oil and gas field
7 13,046 0.97 (0.46, 2.04)
81 Processing
(mineral, metal, chemical)
33 79,386 0.97 (0.68, 1.37)
82 Processing
(food, wood, textile)
19 99,382 0.50 (0.32, 0.79)
83 Machining and related 109 189,800 1.20 (0.98, 1.47)
85 Product fabricating,
assembling and repairing
157 328,825 1.05 (0.89, 1.26)
87 Construction trades 223 216,117 2.55 (2.18, 2.98)
91 Transport equipment
operating
54 168,487 0.69 (0.53, 0.92)
93 Materials handling and related,
not elsewhere classified
55 153,323 0.80 (0.61, 1.06)
95 Other crafts and
equipment operating
20 28,360 1.61 (1.03, 2.51)
99 Other occupations not elsewhere classified 85 215,629 0.90 (0.72, 1.13)
         
         
* CCDO: Canadian Classification Dictionary of Occupations (1971)  
† Hazard rate in each group relative to all others