Occupational Asthma

Occupational lung disease results from the inhalation of dusts, gases, fumes, or vapors encountered in the work place. The effects of inhaled substances depend on many factors including particle size, physical characteristics, toxicity, the person’s susceptibility and the duration of exposure. Are you exposed to occupational asthma?

Inhaled substances can affect the airways of the lung and lung tissue in several different ways. Some substances cause a nonspecific irritant effect that is characterized by coughing, e.g. dusty rooms. Some substances are toxic to the airways such as ammonia or chlorine and affect anyone who inhales it. Other substances can induce a hypersensitivity or allergic reaction in people who are susceptible and cause asthma. Some inhaled substances can cause fibrosis (hardening) of lung tissue and cancer.

Asthma is the most common type of occupational lung disease. Occupational asthma is defined as variable airway obstruction caused by sensitizing agents inhaled at work. The number of agents that can cause occupational asthma is great. New and harmful agents are discovered everyday. The incidence of occupational asthma is the greatest in production and service professionals, e.g. spray painters, bakers, hairdressers and workers in the plastic and chemical industries.

Causes of Occupational Asthma Agents             Occupational Exposure
Animals (rats, mice)                                                   Laboratory workers
Azodicarbonamide                                                      Polyvinyl plastic manufacture
Colophony                                                                       Electronic soldering flux
Drugs (penicillin)                                                          Pharmaceutical industry
Epoxy resins                                                                   Hardening agents & adhesives
Flour                                                                                  Bakers
Grain dust                                                                        Farmers, millers, bakers
Persulphate salts                                                            Hairdressers
Wood dust                                                                         Sawmill workers, joiners

The diagnosis of occupational asthma is two-fold. First, the presence of asthma must be confirmed. Then a causal relationship between the asthma and the work environment must be proven. This is often difficult to do, since a pulmonary function test may be normal during a medical visit because they the person is away from the work environment. Primary care providers can usually diagnosis occupational asthma from an individual’s history. It is important to identify the causative agent whenever possible to improve the management of the asthma, avoid further exposure, and reduce the risk to other workers.

The amount of time a person is exposed to the causative agent and before symptoms develop vary from a few weeks to several years. The sensitizing agent can also cause rhinitis and dermatitis. Often it is difficult to diagnose occupational asthma because an individual may have an early asthmatic response (within 30 minutes of exposure), a late asthmatic response (4-12 hours later), or both. If an early response occurs, the relationship between the symptoms and the work environment is easily notable. This is not true with late responses. Late response symptoms typically develop in the evening after the exposure, making it difficult to sleep, causing wheezing and coughing the next morning.

In the initial stages of occupational asthma, the symptoms improve away from work, during the weekend, or while on vacation and deteriorate on return to work. Once an individual’s exposure is long enough to develop the full-blown disease of asthma, the symptoms persist even away from the work environment and are also triggered by factors such as cold air and exercise. Occupational asthma may develop in workers who have pre-existing asthma. The relationship between the work environment and symptoms can easily go undiagnosed.

Peak expiratory flow or spirometry done several days at work and away from work can usually show the relationship between asthma and the work environment. A workplace challenge study can also be performed in which the person is removed from the work environment for about 2 weeks and then returned to work and tested with spirometry, peak expiratory flow, and airway responsiveness to methacholine or histamine. Once possible causative agents are identified, laboratory challenge studies can be done to identify the agent and measure the intensity of the sensitivity.

Treatment involves management of the affected individual and the work environment. The key intervention in the treatment of occupational asthma is not medication, but avoidance of exposure to the causative agent. Early cessation of exposure to the causative agent can result in complete resolution of the asthma. In incidences where there has been a long delay in recognizing occupational asthma, ceasing exposure prevents further progression of the disease, but long-term inhaled steroid and bronchodilator drugs usually are required.

The management of occupational asthma can be very difficult. Some individuals are reluctant to admit symptoms or may deny they have asthma for fear of losing employment. Other people are not diagnosis for many years and may be close to retirement, fear facing job retraining, or are unable to make a change in employment because of financial obligations.

Treatment of the work environment involves the cooperation of the factory safety manager, management, OSHA, and an industrial exposure expert. Substitution of an alternative to the causative agent is the best solution. It decreases the exposure risk for all workers. This isn’t always possible and can be very expensive. Often the industry will build an enclosure for the process with exhaust ventilation to control employee exposure. Segregation of the hazardous process may be done to limit exposure to a small group of employees who are then provided appropriate protective devices such as respirator masks.

Surveillance of all employees should be undertaken in any work environment that has been shown to cause asthma. This should include a pre-employment medical examination, periodic assessment for asthma symptoms, and a spirometry test. It has been only within the last twenty years that we have learned the relationship and health risks of many chemicals we use every day. It is important to be aware the chronic exposure to chemicals can cause hypersensitivity of the airways and airway obstruction. If gone unrecognized chronic exposure can cause asthma. If you or someone you know are experiencing respiratory symptoms that may be caused by exposure to chemicals or from the workplace, discuss it with your primary care provider. It could be a bigger problem then you know.

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