Research studies on occupational diseases have shown that mortality due to occupational diseases is higher than mortality due to accidents (1). Asthma is a chronic disease of the lower respiratory tract that is defined by its clinical and pathophysiological characteristics, where chronic inflammation is associated with the hyperresponsiveness of the airway, which generates episodes of cough, dyspnea, tightness in the chest and wheezing, particularly at night, early in the morning or due to the causes such as viral and bacterial infections, allergens and chemical compounds (2,3).
Developed countries has shown that occupational asthma has become the most common work-related respiratory disease. There is a proportion of 10–15% of individuals who present new cases of asthma in whose major target is related to exposure at work. Asthma has a 7% prevalence within the world population as one of the most frequent diseases. Becoming a serious public health problem (4,5). A proper diagnosis and early management are key points for the prognosis of the disease and its socio-economic consequences. The cost of asthma treatment is very high for health systems, but it is even higher when prevention is not carried out immediately and treated effectively (6).
Epidemiological studies of occupational asthma are responsible for up to 25% of cases of asthma in adults becoming the lung disease of occupational origin more common in industrialized countries and the second most common in developing countries (7,8). It contributes significantly to the mortality and disability of the economically active population. The literature defines asthma related to work as asthma that is induced or exacerbated by exposure to inhalants in the workplace. The definition of occupational asthma is referred to de novo asthma or the recurrence of quiescent asthma and asthma exacerbated by work which is defined as the pre-existing or concurrent asthma that is initiated by related factors with work (9).
Occupational asthma can be divided into two forms of work-related exposure: Irritant-Induced OA and Allergic OA. Irritant Induces OA occurs usually after a very high exposure (single) to any irritant chemical. Ammonia, acids, and smoke are the causes of direct burns which affect the airway. Symptomatic effects are presented within 24 hours of being exposed with no latent period. Symptoms might disappear over time but if symptoms persist for more than 6 months then major problems can be arising (10). Allergic OA is caused by respiratory sensitization or can be an allergic exposure to a specific chemical in the workplace. The sensitization process is a process that can only be developed over time, not after one exposure. Latency periods can vary from being a short period but as well as reaching 30 years (11).
During the past years, occupational respiratory has become the most frequently developed disease within most industrialized countries. As shown, pathologies such as pneumoconiosis have been decreasing periodically and on the other hand, we have occupational asthma which has been increasing rapidly (12). In different studies, it has been found that the proportion of new cases of asthma attributable to occupational exposure is high and reaches up to 10-15% in patients (7). Studies have been carried out in specific companies along with certain working groups and for the population. The estimated prevalence varies according to the definition given to OA along with the diagnostic standards. Those carried out with a questionnaire of symptoms in the general population tend to overestimate the prevalence, which is very sensitive but not very specific (13). Prevalence studies are useful for analyzing populations exposed to new agents and in countries where the OA is not well recognized, nevertheless it is necessary to unify criteria of definition and diagnostic tools that allow comparing results (14).
Clear clinical diagnostic criteria have not been yet developed for this disease, there are no complete records that determine if the incidence and the actual frequency of the disease are unknown. However, it is believed that the proportion of asthma in adults due to occupational causes can be as high as 25%, making it a search on how adults are presenting airway obstruction due to occupational asthma (15,16).
Even though the respiratory symptoms appeared about the third year for those workers exposed to any kind of chemical, enzyme, and laboratory workers the incidence of probably obtaining OA was of 2.7% (17). In this case, medical records are not a reliable source therefore many of the patients do not declare the illness because of the bad compensatory system and fear of dismissal from their workplace (17,18).
Interventions have allowed the modification of the incidence in various workplaces, an example made was the detergent industry that demonstrated the drastic reduction of new cases and how excluding atopic workers performed a better control of the environment. The two most significant sentinels’ registries that initiated standard measures for voluntary purposes were (Surveillance of Work-Related and Occupational Respiratory Disease) SWORD made in the United Kingdom and in the United States (17,19,20).
The symptoms of occupational asthma vary depending on the type of asthma a worker presents. Whether it is occupational asthma with exacerbated previous asthma which may present severe symptoms compared to real occupational asthma. Patients are known to have (work-related) OA because they are patients who present or report symptoms during work hours and/or exacerbation which symptoms improve during weekends or vacation periods (21).
Occupational asthma naturally deals with the classic symptoms of asthma in general. The classic indicators are cough, wheezing, and dyspnea (2). The cough is usually not unique but followed by several accesses which makes it a dry cough can evolve to a more humid aspect with sputum production. The wheezing is noticeable among patients even without using a stethoscope if noticed on an early stage it will do no harm. The dyspnea described is dyspnea of small exertions exacerbated by the need for air that causes anxiety and high-intensity movements in the patient. The asthmatic patient may present mild to severe dyspnea with associated respiratory failure. Sometimes the indications become chest pain commonly described as oppression (22,23).
Among other symptoms and less common signs are vomiting, syncope, fatigue, abdominal pain, myalgia, headache, loss of visual acuity and others (24).
Patients diagnosed with OA should be revised periodically even though they have changed their previous jobs. Approximately 25% of them have a complete recovery of lung function but there are still chances of developing bronchial hyperactivity within diagnosed patients (25). Occupational asthma can lead to serious health consequences, loss of employment and financial losses for employers. Early diagnosis is important for the removal of the precipitating agent during the first year of the onset of symptoms and can lead to a better prognosis (26).
A well-performed diagnosis and a complete medical history should be performed as mentioned in the guidelines of the American chest association, which suggests that a well-structured questionnaire should be asked to all patients to identify a proper diagnostic of their OA history (9). Nevertheless, a patient’s occupational asthma clinical history should include the following type of questions: previous work-related jobs, exposure to chemical compounds, the use of specific equipment and any medical respiratory diseases among colleagues. The patient’s work history should also be investigated to determine if there was prior exposure and if there are other factors affecting those still at the workplace (27).
Whenever you think about the diagnosis of occupational asthma you should first analyze the affected chemical products with which the patient has worked with (28). There are many biochemical reagent cases of patients who work with high molecular weight compounds whose symptoms improve over days as well as long periods of time, which in cases like this would be enough to determine the diagnosis of the patient (29). Within these risk factors nasal symptoms, wheezing and cough in the workplace should be investigated and verified to perform the exact diagnosis.
When medical professionals have the correct diagnosis of an OA patient the Peak Expiratory Flow (PEF) measurements should be taken during work days and the following days (30, 31). This method should be the first line for the diagnosis of occupational asthma because it is cheap, non-invasive and can be implemented in low-complexity medical services (30).
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Through the analysis of spirometry tests, there are three different patterns can be recognized (32). The first pattern is the daytime worsening of the PEF, this pattern is observed during the workday which it does not progressively get worse during the week but improves within the days off. The second pattern is the worsening of progressive PEF during the work week. Intermittent falls in the PEF during workdays will mark improvement in the holidays (32).
The methacholine challenge test (MCT) is another diagnostic aid if a negative response is detected the MCT should not be even considered for a patient with OA (33). However, in other situations the response might be positive and if so other conditions such as a recent respiratory infection, heavy smoking, and chronic bronchitis are detected. Inclusions have even been reported of negative responses to MCT in occupational asthma due to isocyanates (9). It is suggested to perform the airway responsiveness test with methacholine or histamine at the end of a week of work with a repeated test after ten to fourteen days of absence of exposure to the agent. Performing MCT on patients after work has shown a decrease of about 20% during work (8,30).
Among other less common tests we can find the increase of eosinophils in the induced sputum, this test is associated with the measurement of exhaled nitric oxide but there is still limited evidence of its usefulness (34). However, there are differential diagnoses that can imitate occupational asthma among them: Dysfunction of the vocal cords, irritation of the upper respiratory tract, pneumonitis, rhinosinusitis, psychogenic factors, byssinosis, bronchiolitis obliterans and eosinophilic bronchitis (9).
Patients who present a diagnosis of occupational asthma should be considered for observation following any related work-related asthma, de novo asthma and/or worsening asthmatic symptoms (35). Following this, the diagnosis of asthma and its onset must be confirmed, as well as: medical history probably asthma in childhood or any kind of allergies, symptoms, spirometry, and medications which depends on the result of the diagnosis on previous asthmatic patient or patient without a history of the asthmatic disease (9,36).
In some cases, the non-asthmatic patient is presented leading to other clinical pictures like asthma are evaluated such as vocal cord dysfunction, irritation of the upper respiratory tract, hypersensitive pneumonitis, eosinophilic bronchitis, other occupational lung diseases (byssinosis, bronchiolitis obliterans), rhinosinusitis and psychogenic factors (9).
It must be considered that all these conditions can coexist with asthma. When diagnosing asthma, exposures will be sought by factors that cause or exacerbate asthma-like: occupational history, allergens, irritants at work, exercise, cold, infections, type of work process, ventilation, use of respiratory protection, symptoms of co-workers, magnitude and exposure time, environmental history, atopy, allergies, rhinitis, gastroesophageal reflux and smoking (37).
After considering everything previously mentioned, a relationship between asthma and work must be verified: the onset of symptoms and their severity during work hours, spirometry and airway hypersensitivity tests must be performed as well as immunological tests if available (9,15). The greater the number of positive results, the greater the relationship between symptoms and work-related issues which in this case occupational asthma or asthma exacerbated can be diagnosed effectively (15).
If work-related asthma is diagnosed, it should be classified as primary occupational asthma (sensitizer or irritant) or asthma exacerbated by work (9,15,38). When asthma is intensified by work-related medical issues it should be optimized, the triggers should be reduced at work and at home. If a diagnosis of occupational asthma is obtained, the management in OA should be divided by irritants, sensitizers or both (37,38).
The best way to treat occupational asthma is to avoid the trigger or allergen because the prognosis is better in those patients who leave the job than those who continue in it. Optimizing medical management, and implementing employment with compensation are to be considered for preventing measures for exposing workers (39).
In patients who do not want or cannot give up their work, the implementation of high hygiene in the work area or the use of protective respiratory measures should be mandatory as an alternative. These actions have only shown good results in some types of occupations, in the case of asthma triggered by Toluene Diisocyanate TDI-asthma and some sensitizers of low molecular weight but unfortunately, no promising results have been found (40,41). Patients who continue to be in contact with their sensitizer in the workplace should be kept under medical supervision.
Treatment measures for the patient can have a negative impact on their economy because they must leave their place of work and have lower-paying jobs or become unemployed. The pharmacological treatment is essentially the same as for non-occupational asthma patients. One of the first steps for the management of occupational asthma is to determine the severity of the disease to select the medications necessary to intervene immediately for a patient.
The prevention of occupational asthma can be divided into primary, secondary and tertiary phases. The first phase involves environmental control measurements and industrial hygiene to help reduce any exposure. The second phase essentially focuses on the early detection of asthma, this, however, is obtained by information needed through questionnaires and clinical records among workers. The third phase involves therapeutic measures and environmental resources on how to control the evolution of a diagnosed patient (43,47).
A most important fact for the prevention of occupational asthma is to eliminate any type of sensitized agent at the workplace (42). The use of protective respiratory equipment lowers the incidence and lowers the intensity of exposure but does not completely prevent the development of occupational asthma. Continuous monitoring and surveillance by medical and well-trained personnel could identify which agent is harming the patient’s health and thus come up with a plan to remove or avoid the exposure (42,43).
There is a low predictive level between atopy and the development of occupational asthma. It is estimated that about 50% of young adults are atopic and these should not be excluded from high-risk workplaces (44). However atopic individuals who work in a high-risk place and are exposed to agents that can provoke occupational asthma should be followed for early detection of respiratory sensitizers and bronchial hyperresponsiveness (45).
Advises To quit completely the consumption of cigarettes is a useful tip for health in general, especially in patients presenting OA. It has shown that the decrease of nicotine can lower the levels of the aerial routes of the antigens because it diminishes the chronic inflammation that causes the toxic agents of tobacco (46).
In conclusion, occupational asthma is a quite common disease in developing countries, despite this, it is underdiagnosed, therapeutically poorly managed and compensated. A greater number of surveillance systems and the application of international definitions are required for an accurate medical diagnosis and proper management of the disease. The use of internationally validated questionnaires, immunological tests, and serial PEF measurements used uniformly and standardized, will increase the detection of the disease in developing countries.
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