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Occupational asthma is a work related type of respiratory disorder. It is characterized by irreversible, intermittent and recurrent breathing difficulty including tightness of the chest, coughing, shortness of breath as well as wheezing as a result of exposure to some agents at work place.
This condition is the most prevalent occupational lung disease in developed countries. It is estimated that up to 15% of asthmatic cases reported in US are occupational related. Many are not aware that certain agents at work place could lead to hyper-responsiveness of airway or aggravating the pre-exisiting asthmatic symptoms. In view of that, it is quite likely that the cases of occupational related asthma are under reported.
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While the clinical presentations of asthma are similar to non occupational asthma such as coughing, wheezing, chest tightness and shortness of breath, it is crucial to have a detailed work history when one is suspected to have the occupational condition. Specific questions must be asked on type of work/ industry involved, frequency of asthma attack, the onset of the asthmatic symptoms in relation to work, possible exposure for asthma causing agents, provision and correct usage of personal protective equipment at work place, duration of work, previous asthma episodes prior to current work and severity of asthma during holiday or seasonal change.
A classical case of work related asthma would be someone who is free of symptoms during weekends and vacation, with recurrence of symptoms on returning to work. In addition, symptoms may be more severe at the end of the week as compared to the beginning of the week. Such symptoms could be clearly work-related in workers who have no known asthma prior to the current employment.
A good clinical history would help in identifying the possibility of work related asthma. Another important criteria is to identify the known asthma-causing agents at work place. Occupational physician would carry out a walk through survey in the work place to identify the possible agents that cause asthmatic attack. A look at the list of chemicals in Material Safety Data Sheets (MSDS) would give a clue to that.
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Asthma Inducing Agents at the Workplace
Asthma inducing agents can be of 2 types: agents with sensitisation (immunological) or without sensitisation (non immunological). Organophosphate pesticides used in agriculture is one of the common asthma inducing agents without sensitisation. Textile workers are also at risk of exposure to cotton dust while workers in paper manufacturing are exposed to chemicals like acids, ammonia and chlorine which are known to trigger asthmatic attack.
Asthma inducing agents with sensitisation involve the immune response which may be antibody-mediated (IgE) or cell-mediated which would sensitizes the person such a way that subsequent exposure to the same antigen elicits an allergic response. Common agents that stimulate the immunological response are animal and plant proteins (bakeries and food processing industries), antibiotics (pharmaceutical manufacturing and packaging) as well as chemicals like diisocyanates, acid anhydrides ( plastics and paints manufacturing).
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However, not all individuals exposed to these conditions will develop asthma given the different level of susceptibility to asthma than others. Risk factors for occupational asthma include frequent exposure to the agents, allergies, family history of allergies or asthma and smoking.
Once diagnosis is made, asthma must be treated well to avoid the airways developing a pattern of overreacting.
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1) United States Department of Labour, Occupational Safety & Health Administration
2) Health and Safety Executive, HSE
3) American Academy of Allergy, Asthma & Immunology
4) Centre for Occupational and Environmental Health, University of Manchester