The following results show the percent increase in risk among groups of workers by industry or occupation compared to all other workers followed in the ODSS. Industry and occupation results are shown in the same tables for each group of workers. Results shown are for diagnoses of COPD prior to age 65, which are more likely to be related to exposures at work than COPD diagnoses among older individuals. It is important to note that COPD diagnoses may not be based on lung function criteria, which can lead to misclassification of COPD with other respiratory conditions such as asthma.

No data were available for cigarette smoking in the ODSS, so some observed occupational risks may be due to smoking patterns. On the other hand, studies of respiratory disease among workers in dusty, often physically demanding workplaces may under-estimate occupational risks because people with chronic lung disease may avoid these occupations and workers experiencing respiratory symptoms are more likely to transfer to less exposed occupations or leave the workforce [14]. This is called the “healthy worker effect.” The ODSS attempts to address these issues by comparing each occupation and industry to all others workers in the system, rather than to the general population [14]. The over 2 million workers in the ODSS are people who received workers’ compensation in the past and the great majority were employed in hazardous jobs where smoking rates and physical demands may be similar.

Farming

Residence and employment in agricultural and rural environments are often associated with a lower risk of disease. However, farming exposures have been linked to some adverse health outcomes including respiratory diseases such as COPD. Although farmers commonly have lower smoking rates than other workers and the general population, increased risk of respiratory diseases had been previously observed which may be related to occupational exposures [15-17].

An increased risk for COPD was observed for several farming industries and occupations in the ODSS. Workers in farming may be exposed to a variety of dusts, pesticides, and diesel engine exhaust, which may increase their risk of COPD. Livestock farm workers are exposed to dusts including animal dander, hair, animal feed, and other microbiological components [18-20] including ammonia, methane and hydrogen sulphide from animal manure [21-22]. Workers cultivating crops have previously been reported to have lower COPD risk than those who also had livestock exposure [23-24]. This was consistent with findings in the ODSS cohort, where the highest risk was observed for crop and livestock combination farms workers. Compared to other workers, increased risk of COPD was also observed among crop farmers and workers in the feed industry, where exposure to grain dusts and molds can be common [23]. Farm workers that use diesel-powered equipment (i.e. tractors) may be exposed to diesel engine exhaust, which has also been associated with increased risk of COPD [6].

Flour and grain milling and baking

In addition to the increased risk observed among grain producers and handlers in the agricultural sector, previous studies have also indicated increased risks among workers that process grains into flours, as well as among bakers working with those flours [21,25-26]. Workers in flour and grain milling and baking jobs have shown increased risks of COPD in the ODSS. Flour dusts from various cereals can contain contaminants including fungi, endotoxins, chemical additives, and insects and mites [27]. Several studies have identified an increased prevalence of respiratory symptoms and lung function decline among mill and bakery workers [21,28-30], with the highest risk among workers with sensitization to allergens, particularly fungal amylase present in flour improvers [21,31].

Textile

Workers in textile processing can be exposed to a variety of organic and synthetic dusts, with reported pulmonary function declines differing across materials. The strongest evidence exists for exposure to cotton dust, contaminated with endotoxins, which has been linked to acute airway responses (e.g. coughing, narrowing of airway) with short-term exposure and loss of pulmonary functions and inflammation with longer exposure [14, 32-33]. The highest risk of COPD observed among textile workers in the ODSS was for those employed in the cotton yarn and cloth mills industry. Large variations in exposure to inhalable dust and airborne endotoxin have been observed across different textile processing sectors [34].

Wood processing, pulp and paper, and forestry

In the ODSS worker cohort, increased risk was observed for several wood related occupations, and in the wooden box factory industry, but no excess risk was observed for the broader logging or forestry industries. Previous studies have observed increased risks of respiratory symptoms and conditions among workers exposed to wood dust [35-36], but evidence regarding COPD and specific causal agents remains mixed [37-39]. Fresh wood dust may contain fungi, endotoxin, and gram-negative bacteria [40-41]. In addition to dusts from wood, workers in wood products fabrication may be exposed to a variety of respiratory irritants including waxes, resins, glues, and formaldehyde in the production and use of MDF (medium-density fiberboard) [42]. Bleaching workers in wood pulp mills are also exposed to ozone, a known respiratory irritant, and chlorine dioxide/sulphur dioxide gassings which have also been shown to have obstructive effects on airflow and pulmonary function [43]. Timber cutting and related forestry work can result in pesticide exposure which has been shown to accelerate lung function decline and increase risk of COPD [12].

Construction

Workers in construction trades occupations showed increased risks of COPD. These workers are exposed to a number of possible risk factors for COPD, including many different dusts (e.g. silica, cement, concrete, wood, metal), fibres (e.g. asbestos), and irritant fumes (e.g. asphalt, engine exhausts, metal welding) [3,37,44]. This makes it challenging to identify particular causative agents, but increased risk of COPD has been observed for construction workers in previous studies [3,8,45-46].

Mining

Workers in mining have historically been exposed to high levels of dusts and fine particles, including silica, as well as diesel engine exhaust from heavy machinery. These exposures have been linked to increased risk of COPD among miners [37,44,47-48]. The greatest COPD risk observed among ODSS mining industry workers was for workers in quarries and sand pits, which may be due to their exposure to silica [49-51]. There may be less monitoring of workplace dust exposure in quarry and sand pit workers, who are likely to be working in open spaces, compared to other mining workers.

Metal processing and welding
A consistent excess risk of COPD was observed for workers in metal processing and welding related industries and occupations. These workers may be exposed to heavy metals (e.g. cadmium, arsenic, chromium), welding fumes, crystalline silica and dusts, solvents and other agents that may increase the risk for COPD in these workers [22]. Exposure to heavy metals and welding fumes can cause oxidative damage, among other mechanisms, which can increase susceptibility to lung infection and worsen lung function [51-53].

Understanding your risk and recognizing the symptoms of COPD allows for early detection and treatment. Symptoms of COPD include shortness of breath (especially during physical activity), tiredness, persistent cough, cough with phlegm, wheezing, and multiple diagnoses of cold, flu, or pneumonia that are slow to recover. If you have any of these symptoms, you should visit your health care provider and tell them about the work you do [54]. Diagnosis of COPD should include lung function tests and early detection of COPD can help to reduce problems with lung function and breathing that often lead to damage of the lungs [54,55].

Public health, employer and occupational health, as well as regulatory efforts to reduce the population burden of COPD need to address workplace exposures in addition to the cumulative exposure with smoking. Medical professionals should be aware of risks among high-risk occupational groups in order to identify early stage disease. Workplace health promotion and workers should recognize the benefits of smoking cessation programs in preventing and managing work related respiratory disease.

Workers diagnosed with or who suspect they have COPD can also submit a claim through the Workplace Safety and Insurance Board (WSIB). Recent changes have been made where benefits will no longer be offset for most workers who have a history of smoking and submit a claim for COPD [56].

There is also the National Lung Health Framework action plan that was developed to improve lung health in Canada and help to coordinate prevention and management approaches of respiratory conditions [57]. These efforts can enhance prevention and management of respiratory diseases like COPD and improve health outcomes and economic benefits.

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