Acute Myocardial Infarction 

Background
What is acute myocardial infarction (AMI)?

Acute myocardial infarction (AMI) is the medical term for a heart attack and occurs when a blood clot forms around plaque in the arteries, blocking supply of blood to the heart [1]. Approximately 200 heart attacks per 100,000 adults over the age of 20 occur in Canada each year [2]. AMI risk is primarily attributed to lifestyle factors including smoking, poor diet, alcohol consumption, obesity, physical inactivity, and recreational drug use [3]. Evidence for occupational risk factors for AMI are inconsistent, but certain occupations have been associated with higher cardiovascular risk [4].

Possible occupational risk factors [5–10]

• Noise
• Vibrations
• Temperature extremes
• Secondhand smoke
• Shift work
• Occupational physical activity
• Chemical and particulate hazards
• Psychosocial stress

Key Findings

Almost 25,000 cases of AMI were diagnosed among workers in the ODSS between 2007 and 2016. Increased AMI risk was associated with employment in a large variety of occupation groups in the ODSS. This reflects the variety of possible occupational risk factors. Future studies are necessary to examine which work-related hazards might be contributing to these excess risks.

In general, AMI risk was higher among blue-collar workers compared to white-collar workers, and the most consistently elevated risks were observed for workers in industry and occupation groups related to logging and wood production and mining with increased risks observed for some construction sector and textile processing groups.

Despite exposure to psychosocial stress and shiftwork, employment in some protective services occupations including firefighting and police was associated with reduced risk of AMI. The reduced risk observed for these workers may reflect the stringent health-related requirements enforced across these occupations. Another factor may be that workers with an accepted claim for compensation related to AMI were excluded from this analysis, so the association estimated by our approach may underestimate the true risk.

 
Wood-related industries and occupations

The most consistent excess risks for AMI in the ODSS cohort were for workers in industry and occupations groups related to wood and wood processing. These workers may be exposed to a variety of AMI risk factors including noise, stress and vibrations. Inhalation of wood dusts may cause irritation and inflammatory responses that could contribute to cardiovascular disease [11]. An increased risk of AMI associated with high noise exposure has been seen in BC sawmill workers [9]. An increased risk of AMI has also been observed among a cohort of Swedish pulp and paper mill workers [12], and attributed to a combination of workplace exposures including dust, sulfur compounds, shiftwork and noise.

Forestry and logging
  • Forestry industry: 1.38 times the risk
    • Logging industry: 1.37 times the risk
    • Forestry services: 1.55 times the risk
  • Forestry and logging occupations: 1.35 times the risk
    • Log hoisting, sorting, moving and related occupations: 1.75 times the risk
    • Timber cutting and related occupations: 1.28 times the risk
Wood products manufacturing
  • Wood manufacturing industries: 1.27 times the risk
    • Wooden box factories: 1.56 times the risk
    • Veneer and plywood mills: 1.41 times the risk
    • Sawmills, planning mills and shingle mills: 1.32 times the risk
    • Sash, door and other millwork plans: 1.26 times the risk
  • Wood processing occupations: 1.49 times the risk
    • Inspecting, testing, grading and sampling occupations: 1.81 times the risk
    • Occupations in labouring and other elemental work: 1.73 times the risk
    • Other wood processing occupations, nec: 1.50 times the risk
Pulp and paper
  • Pulp and papermaking and related occupations: 1.30 times the risk
    • Cellulose pulp preparing occupations: 2.25 times the risk

 

Mining and quarrying

Increased risks for acute myocardial infarction and other cardiovascular disease have been previously observed for mining industry workers, with potential links to exposure to high levels of noise [13,14], vibration [15] and radon gas, particularly for uranium mining workers [16]. Diesel engine exhaust, a common exposure in mining, is also a potential cause of acute cardiovascular events [17]. While elevated risks were observed for some mining industry workers, risks among mining and quarrying occupations groups were generally only slightly increased.

  • Quarries and sand pits industry: 1.40 times the risk
    • Sand pits and quarries: 1.57 times the risk
  • Metal mine industry: 1.12 times the risk
    • Gold quartz mines: 1.53 times the risk
    • Uranium mines: 1.39 times the risk

 

Construction

Construction workers are exposed to loud noise [18] and vibrations in their work. Construction workers can also be exposed to crystalline silica dust and diesel engine exhaust. In the ODSS, increased risk of AMI was greatest among workers involved in excavating, grading and paving, who are exposure to a variety of occupational risk factors for AMI.

  • Occupations in labouring and other elemental work: excavating, grading and paving: 1.41 times the risk
  • Excavating, grading and related occupations: 1.31 times the risk

 

Textile manufacturing and processing

Increased risk of AMI was observed for workers employed in the leather and textile manufacturing industries and related occupations. Evidence regarding AMI risk factors for these workers is limited, but textile dust exposures [19] and exposure to bacterial endotoxin [20] have been previously suggested.

  • Textile fibre preparing occupations: 2.65 times the risk
  • Shoemaking and repairing occupations: 1.74 times the risk
  • Occupations in labouring and other elemental work, fabricating, assembling and repairing, textile, fur and leather products: 1.44 times the risk
  • Fabricating, assembling and repairing occupations, textile, fur and leather products: 1.44 times the risk
  • Leather industries: 1.48 times the risk
    • Luggage, handbag and small leather goods manufacturers: 1.55 times the risk
    • Shoe factories: 1.48 times the risk
    • Leather tanneries: 1.44 times the risk
  • Textile industries: 1.16 times the risk
    • Automobile fabric accessories industry: 1.46 times the risk
    • Man-made fibre, yarn and cloth mills: 1.43 times the risk

 

Rubber and plastics manufacturing

Increased AMI risk was observed among workers in the ODSS employed in rubber and plastic products fabrication. Plastic stabilizers frequently include cadmium, which has been posited to increase AMI risk through atherosclerosis [21]. A cohort study of British rubber factory workers found increased risk of cardiovascular deaths associated with exposure to N-nitrosomorpholine, rubber dust, rubber fumes and N-nitrosamines sum [22].

  • Occupations in labouring and other elemental work: fabricating, assembling and repairing, rubber, plastic and related products: 1.91 times the risk
  • Bonding and cementing occupations, rubber, plastic and related products: 1.40 times the risk

 

Other groups:

Excess AMI risk was detected in the ODSS for a variety of occupation groups, which likely reflects the numerous risk factors for cardiovascular disease including both workplace and lifestyle factors.

  • Receptionists and information clerks: 1.62 times the risk
  • Fish canning, curing and packing occupations: 1.52 times the risk
  • Truck drivers: 1.32 times the risk

For more details: Troke, N, Logar‐Henderson, C, DeBono, N, et al. Incidence of acute myocardial infarction in the workforce: findings from the Occupational Disease Surveillance System. Am J Ind Med. 2021; 1– 20.

Relative Risk by Industry and Occupation

Figure 1. Risk of acute myocardial infarction diagnosis 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 risk 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).

 

Figure 2. Risk of acute myocardial infarction diagnosis 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 risk 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
Table 1. Surveillance of Acute Myocardial Infarction: 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 339 24904 0.93 (0.84-1.04)
2/3 Forestry, Fishing and Trapping 190 6468 1.38 (1.20-1.60)***
4 Mines, Quarries and Oil Wells 376 13707 1.15 (1.04-1.27)**
5 Manufacturing 9589 473168 1.11 (1.09-1.14)***
6 Construction 2781 151153 1.01 (0.97-1.05)
7 Transportation, Communication and Other Utilities 3044 143012 1.11 (1.07-1.16)***
8 Trade 5045 317800 1.09 (1.05-1.12)***
9 Finance, Insurance and Real Estate 256 15688 0.99 (0.88-1.12)
10 Community, Business and Personal Service 4928 421561 1.01 (0.98-1.05)
11 Public Administration and Defense 2112 132668 0.93 (0.89-0.97)***
* SIC: Standard Industrial Classification (1970)
† Hazard rate in each group relative to all others

Table 2. Surveillance of Acute Myocardial Infarction: 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 275 23568 0.84 (0.74-0.94)**
21 Natural sciences, engineering and mathematics 329 20218 0.89 (0.79-0.99)*
23 Social sciences and related fields 192 23146 0.86 (0.75-1.00)*
25 Religion <5 83
27 Teaching and related 237 36802 0.60 (0.53-0.68)***
31 Medicine and health 837 95161 0.94 (0.87-1.01)
33 Artistic, literary, recreational and related 111 11744 0.79 (0.65-0.95)*
41 Clerical and related 2073 141042 1.03 (0.98-1.08)
51 Sales 1265 110656 1.03 (0.97-1.09)
61 Service 3395 253769 1.03 (0.99-1.07)
71 Farming, horticultural and animal husbandry 489 36677 0.92 (0.84-1.00)
73 Fishing, hunting, trapping and related 10 373 1.38 (0.74-2.57)
75 Forestry and logging 181 6474 1.35 (1.17-1.56)***
77 Mining and quarrying, including oil and gas field 211 7722 1.15 (1.01-1.32)*
81 Processing (mineral, metal, chemical) 1263 58540 1.16 (1.09-1.22)***
82 Processing (food, wood, textile) 1247 70950 1.09 (1.03-1.15)**
83 Machining and related 3123 137820 1.11 (1.07-1.15)***
85 Product fabricating, assembling and repairing 4930 233837 1.09 (1.05-1.12)***
87 Construction trades 3108 152813 1.02 (0.98-1.06)
91 Transport equipment operating 3116 122651 1.26 (1.21-1.30)***
93 Materials handling and related, not elsewhere classified 2158 111390 1.11 (1.06-1.16)***
95 Other crafts and equipment operating 416 19357 1.05 (0.95-1.15)
99 Other occupations not elsewhere classified 2954 157206 1.12 (1.08-1.17)***
* CCDO: Canadian Classification Dictionary of Occupations (1971)
† Hazard rate in each group relative to all others
Please note that ODSS results shown here may differ from those previously published or presented. This may occur due to changes in case definitions, methodological approaches, and the ongoing nature of the surveillance cohort.

 

References

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