Dr Paul Nicholson examines the latest evidence in relation to occupational asthma, which practitioners should be aware of if they are to have a positive influence on helping prevent future cases.
At the start of the last decade, the Health and Safety Commission set the HSE some demanding targets in terms of occupational health, including a goal to reduce the number of new cases of occupational asthma by 30 per cent by 2010.
Data from the HSE suggests that, in regard to asthma at least, this target was achieved.1 However, during this last decade, we also witnessed the largest ever single outbreak of occupational asthma, which also amounted to the world’s largest outbreak of respiratory disease related to metal-working fluids.2 This, and the fact that one third of workers who develop occupational asthma remain unemployed several years after diagnosis,3 underlines that there is no room for complacency.
Since only about one in eight workers in the UK has access to an occupational physician many workers may depend on their safety and health practitioner for advice and help in relation to their health and work. Furthermore, occupational asthma is the most frequently reported work-related lung disease, so it is important that safety and health practitioners understand what occupational asthma is, as well as the evidence in relation to risk factors, prevention, surveillance and management of the affected worker.
As part of its strategic programme, the HSE asked the British Occupational Health Research Foundation (BOHRF) to undertake a systematic review of the evidence related to the prevention, identification and management of occupational asthma. This review has recently been updated to include the latest evidence.3
During an attack of asthma the lining of the small airways in the lungs become swollen and the muscles around them contract to narrow the airways. This makes it difficult to breathe and causes wheezing, coughing and chest tightness. Most people with asthma have intermittent symptoms, which are usually worse at night, or in the early morning. About two-thirds of asthma sufferers also suffer from hayfever-type symptoms, e.g. rhinitis (sneezing, runny nose) and/or conjunctivitis (itchy red eyes).
Occupational factors account for about one in six cases of asthma in adults of working age. There are two types of work-related asthma: firstly, work-aggravated asthma, where someone’s pre-existing asthma is aggravated by exposure at work to non-specific agents, e.g. dust, cold air, etc; and occupational asthma, i.e. asthma that is caused by workplace exposure and not by factors outside of the workplace.
Occupational asthma is sub-divided into two types: irritant-induced occupational asthma, which develops, typically, within a few hours of a high-concentration exposure to an irritant gas, fume, or vapour at work, e.g. chlorine, ammonia, etc; and allergic occupational asthma where, after a latent period of some months or years following first exposure, someone develops asthma mediated by an immune mechanism. About 90 per cent of cases of occupational asthma are of the allergic type.
The risk factors for occupational asthma are:
The major risk associated with the development of occupational asthma is the level of exposure to inhalable substances at work. Personal factors only influence the development of occupational asthma to some agents. For example, people with a history of hayfever are at increased risk of developing asthma from high molecular-weight agents, especially proteins, whereas cigarette smokers are at increased risk from isocyanates and complex platinum salts.
Personal factors are poor predictors of future disease and should not be used to screen out job applicants, unless a person has asthma caused by a particular substance, to which further exposure could not be avoided in their new job. Additionally, hayfever and asthma are very common, and many good job candidates would be rejected inappropriately because of very small additional risk. People with no such history may also develop occupational asthma, so the focus should be to make the workplace safe for all.
In the case of allergic occupational asthma, there may be a “progressive march” through stages of increasing severity, characterised by the development of specific antibodies without symptoms, followed by eye and/or nasal symptoms, and then asthma. However, asthma can also develop without, or at the same time as, other preceding symptoms. As the severity of symptoms increases, the effectiveness of interventions decreases. In the case of irritant occupational asthma, a sudden exposure leads to the immediate onset of asthma, without intervening stages. Provided further irritant-level exposures are avoided, this will be followed by gradual improvement and return to health.
In about two-thirds of cases asthma may be accompanied by rhinitis and/or conjunctivitis, symptoms very much associated with hayfever. These may develop at the same time as the onset of asthma, or they may precede it, typically by up to a year, especially in the case of high molecular-weight agents. Likewise, where there is an allergic mechanism symptoms may be preceded by the development of allergic antibodies – a process known as sensitisation.
Monitoring for sensitisation, and rhinitis or conjunctivitis, can act as an early-warning system. However, asthma is not an inevitable consequence of sensitisation or occupational rhinitis, since many people will not progress beyond those stages. Prospective surveillance for the development of antibodies acts more as a means of monitoring the effectiveness of control of exposure. Antibody tests are not widely performed and require access to trained health staff and availability of standardised test agents.
It is more practical to ensure that periodic respiratory questionnaires are used for people who work with asthmagens and include questions that ask about eye and nasal symptoms.
The BOHRF systematic review made recommendations for practice based on evidence statements derived from more than 300 primary pieces of research. The evidence statements and recommendations that are relevant to the safety and health practitioner are shown in table 1 overleaf as what you need to know and what you need to ensure.
While asthma is most likely to develop in the first years of exposure to substances such as enzymes, complex platinum salts, isocyanates and laboratory animal allergens, for substances such as bakery allergens and persulfate salts, the latent period can be much longer. It is also important to remember that changes in exposure level at work, e.g. through loss of control or increased manufacturing volume, can cause occupational asthma in later years.
Health surveillance should include a questionnaire inquiring about wheeze, cough, shortness of breath, chest tightness, runny nose, sneezing, itchy eyes, use of any medications for such symptoms, and smoking. Where a suitable and sufficient risk assessment indicates that there is higher risk, lung-function tests should also be undertaken.
While there is no evidence base to inform us how often health surveillance should be performed, it would make sense to conduct this annually, and more frequently where there are individual indicators of increased risk, e.g. in the first two years of exposure and within one year of a worker developing rhinitis, or conjunctivitis.
An employee who is suspected of having occupational asthma should have an early medical referral. Making a diagnosis of occupational asthma is not straightforward and requires objective testing by a doctor with expertise in occupational asthma. Furthermore, the management of asthma differs, depending on whether it is non-occupational, work-aggravated, or occupational asthma (see table 2).
The level of exposure needed to trigger an asthma attack in the case of allergic occupational asthma is exceptionally low and is thought to be some orders of magnitude lower than the level needed to cause someone to develop asthma. This is why complete avoidance of exposure is the preferred management option. Where this is not possible, employees should be redeployed to low, or occasional-exposure areas, and be monitored through increased health surveillance. In the case of latex allergy, and where clinical considerations permit, reduction of exposure may be a useful alternative – associated with fewer socio-economic consequences – to complete removal from exposure.4
Where continued but reduced exposure of an employee diagnosed with occupational asthma is associated with ongoing symptoms, they must be advised that continuing this work will lead to the condition becoming permanent.
Occupational asthma is a preventable condition. However, once a worker has developed asthma, there is a relatively narrow window of opportunity, probably about a year, in which to investigate symptoms, make a full diagnosis, and institute suitable medical and workplace measures to reduce the impact of the disease.
The most important action is to prevent cases of occupational asthma by reducing exposure at source. Thereafter, carrying out surveillance should help identify, at an early stage, symptoms of asthma, rhinitis and conjunctivitis. Effective management of workers suspected to have occupational asthma involves the identification and investigation of symptoms suggestive of asthma immediately they occur. Early diagnosis and early avoidance of further exposure, either by relocation of the worker or substitution of the hazard, offer the best chance of improvement, or recovery.
Table 1: Summary of the BOHRF review evidence statements and recommendations
You need to know that:
Exposure
Health surveillance
Health surveillance can detect occupational asthma at an early stage of disease
Management of a worker who develops occupational asthma
You need to ensure that:
Exposure
Health surveillance
Management of a worker who develops occupational asthma
Table 2: Management of different types of asthma
Type of asthma
Not work-related
Work-aggravated
Irritant occupational asthma
Allergic occupational asthma
Focus of management
Adjust medication
Avoid triggers in the workplace
Avoid high exposures to irritant gases
Avoid further exposure completely and early in the course of the disease
1 www.hse.gov.uk/statistics/causdis/asthma/index.htm
2 www.hse.gov.uk/press/2006/e06049.htm
3 Nicholson P J, Cullinan P, Burge P S and Boyle C (2008): Occupational asthma: ‘Prevention, identification & management: Systematic review & recommendations’, British Occupational Health Research Foundation, London – www.bohrf.org.uk/
4 NHS Plus/Royal College of Physicians (2008): ‘Latex allergy: occupational health aspects of management: a national guideline’, Royal College of Physicians, London – www.rcplondon.ac.uk/pubs/contents/f0ba0178-f790-48e8-a764-b319357f974a.pdf
Paul J Nicholson OBE FRCP FFOM MRCGP is associate medical director for Procter & Gamble in Europe, Middle East & Africa.
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