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Occupational asthma is generally defined as a respiratory disorder directly related to inhaling fumes, gases, or dust while “on the job.” Asthma may develop for the first time in a previously healthy worker, or pre-existing asthma may be aggravated by exposures within the work place. Symptoms of asthma include wheezing, chest tightness and cough. Other associated symptoms may include runny nose, nasal congestion and eye irritation. The cause may be allergic or non-allergic in nature. Of particular importance is the fact that the disease may persist for a lengthy period in some workers, even if they are no longer exposed to the irritants that caused it. Many workers with persistent asthma symptoms have been incorrectly diagnosed as having bronchitis.
It is important to remember that persons living in residential areas near these factories may also be exposed to these fumes and may suffer symptoms as well. In many cases, a previous family history of allergies will make a person more likely to suffer from occupational asthma. However, many individuals who have no such history can still develop this disease if exposed to conditions that trigger it. Workers who smoke are at greater risk for developing asthma following some occupational exposures. The length of occupational exposure that triggers asthma varies and can range from months to years before symptoms occur.
Occupational asthma has become the most prevalent work-related lung disease in developed countries. However, the exact proportion of newly diagnosed cases of asthma in adults due to occupational exposure is unknown. Researchers estimate that 15% of all male cases of asthma in Japan result from exposure to industrial vapors, dust, gases, or fumes, and 5 – 15% of asthma cases in the U.S. may have job-related origins.
The incidence of occupational asthma varies within individual industries. For example, in the detergent industry, inhalation of a particular enzyme used to produce washing powders has lead to the development of respiratory symptoms in approximately 25% of exposed employees. In the printing profession, 20 – 50% of employees experience respiratory symptoms due to gum acacia, which is used in color printing to separate printed sheets and prevent smearing. Isocyanates are chemicals that are widely used in many industries, including spray painting, insulation installation, and in manufacturing plastics, rubber and foam. These chemicals can lead to asthma in 10% of exposed workers.
Occupational asthma may be caused by one of three mechanisms, including direct irritants, allergic triggers or pharmacological factors. Irritants that provoke cases of occupational asthma include exposure to hydrochloric acid, sulfur dioxide or ammonia found in the petroleum or chemical industries. These asthmatic episodes will frequently occur immediately after exposure occurs to the irritant substance, and allergic sensitization is not involved. Workers who already have asthma or some other respiratory disorder are particularly affected by this type of exposure.
Allergic factors play a role in many cases of occupational asthma. This type of asthma frequently requires long term exposure to a work related substance before allergic sensitization occurs. Examples of this allergic-type of occupational asthma include exposure to the enzymes of the bacteria Bacillus subtilis in the washing powder industry, and exposure to castor beans, green coffee beans and papain in the food processing industry. Other allergic forms of occupational asthma can occur in workers in the plastic, rubber or resin industries following exposure to small chemical molecules in the air. Furthermore, veterinarians, fishermen and animal handlers in laboratories can develop allergic reactions to animal proteins. Health care workers can develop asthma from aerosolized proteins from latex gloves or from the mixing of powdered medications.
Pharmacological factors include the inhalation of dust or liquid. These substances do not lead to allergic sensitization, but instead directly lead to the release of naturally occurring substances such as histamine within the lung, which then in turn lead to asthma.
Once the cause is identified, exposure levels should be reduced (a worker could be moved to another job within the plant, for example).
Employers might consider prescreening potential employees with lung function tests and then continue to test for symptoms after certain periods on the job once the worker has been hired. Work areas should be closely monitored so that exposure to asthma-causing substances is kept at the lowest possible levels. Under an allergist’s care, pre-treatment with specific medications to counteract the effects of these substance may be helpful in some cases.