Guidance on occupational asthma

In the first part of this special report, Diane Romano-Woodward explores the 2010 BOHRF Occupational Asthma Guidance on sensitiser-induced occupational asthma.

The second part of the research looks at how serial peak respitory flow can be used to identify occupational asthma.

In 2004 the British Occupational Health Research Foundation (BOHRF) published evidence-based guidelines on occupational asthma (OA). A systematic review was undertaken in 2010 by an occupational health physician, two respiratory physicians and a scientific secretary from the Health and Safety Executive. The guidance was updated using information from an additional 90 studies.

The scope was expanded to include two newer diagnostic tests: sputum eosinophilia and exhaled nitric oxide. Genetic factors were removed from the scope of the review as risk information as a result of a genetic test was perceived to be poorly understood, and the use of genetic testing in OH is unlikely to be ethically justifiable.

The stated intention of the guidelines is to reduce the incidence of OA. The review has resulted in a series of three guidance leaflets, available to download from the

BOHRF website and as hard copy, for: OH and safety professionals and safety representatives; GP and practice nurses; and employers, workers and their representatives.

Occupational factors account for about one in six cases of asthma in adults of working age, with almost 90% of these attributed to an allergic response. The substances responsible for this are known as sensitising agents. OA is readily preventable by controlling exposure to sensitising agents. The most frequently reported agents are:

  • isocyanates;
  • flour and grain dust;
  • latex;
  • aldehydes;
  • colophony and fluxes;
  • animals; and
  • wood dust.

These and other sensitisers affect a range of occupations including:

  • bakery workers;
  • pastry makers;
  • paint sprayers;
  • cleaners;
  • nursing and care staff;
  • catering workers;
  • lab technicians;
  • chemical workers;
  • animal handlers;
  • woodworkers;
  • welders; and
  • timber workers.

The risk of developing OA has a direct relationship with the level of exposure, so the chance of developing an allergy to the substance increases at higher exposures and reducing or removing exposure will reduce the risk and incidence of the disease. This is a simple concept, which needs to be reinforced to workers and employers.

Key recommendations

Responsibilities of employers and their health and safety personnel

The level of exposure to an asthmagen is the major determinant of risk of development of OA, and programmes should be implemented to remove or reduce exposures.

Respiratory protective equipment (RPE) does not completely prevent OA. When worn as a control measure employees should be instructed in its use. This should include how to wear, remove and replace it. It is important that the RPE is an appropriate type for the hazard encountered, that fit testing is performed and that the RPE is properly maintained.

Information and training about the causes of asthma should be given to workers, and they should be encouraged to report symptoms as soon as they develop.

Health surveillance should be provided regularly and more frequently in the first years of exposure to those who are at risk of developing OA.

Health practitioner responsibilities

A variety of health practitioners will be involved in a suspected case of OA. This might be nurses and doctors in primary care, occupational health practitioners and respiratory specialists.

At the pre-placement stage there is no reason to exclude applicants on the basis of poorly discriminating factors, such as atopy, cigarette smoking or a family or personal history of asthma.

If a prospective worker has pre-existing asthma, and it is caused by an agent they are likely to be exposed to, then they should not undertake this work if exposure cannot adequately be controlled.

Health surveillance

There is an association between OA and occupational rhinitis (OR), and the risk of developing OA is highest in the year after the onset of OR. Therefore, the recommendation is that more frequent health surveillance should be provided to workers with rhinitis who are exposed to substances known to cause OA.

A careful occupational history and details of current work, including the materials with which they work, should be taken for any person who has new, recurrent or deteriorating symptoms of rhinitis or asthma. This will be particularly important for primary care practitioners, who may be the first health professional that the worker contacts.

On the strength of the 2004 BOHRF guidance, the Department of Health introduced two new Read Codes – the standard medical diagnosis coding system used in general practice in the UK – prompting GPs with patients of working age presenting with either rhinitis or conjunctivitis (precursors of OA) to ask what job they do, to give the opportunity to break the cycle of early-stage OA (Health Protection Report, 19 March 2010).

The guidance then prompts the GP with a screen of the jobs most associated with OA and prompts the GP to refer the patient for serial peak flow measurement. The peak flow measurements should be recorded at least four times a day for at least three weeks. If fewer than this number of readings are taken, the diagnostic performance of peak flow readings falls.

The diagnosis should be confirmed by objective criteria, (functional, immuno-logical or both) and not on the basis of a compatible history alone, as a diagnosis of OA may impact upon future employability.

Once diagnosed, measures should be taken to protect the worker from further exposure in the workplace. This will prevent deterioration, and increases the likelihood of the improvement or resolution of the symptom. Redeployment to low exposure areas sometimes leads to an improvement. This may not always be effective but it may be preferable for socioeconomic reasons, for example the impact on the employee’s future employability. Early diagnosis and avoidance of further exposure, by relocation or substitution of the hazard, offers the best chance of complete recovery.

Good practice points

In addition to the key recommendations, which are evidence-based, a number of good practice points were highlighted. These were formulated where there is no research evidence and none is likely to be produced. They are based on the clinical experience of the research working group, legal requirement or other consensus.

These included:

  • The suggestion that health surveillance should be more frequent in workers with pre-existing asthma in order to detect any deterioration at an early stage.
  • Assessing whether skin-prick or serological tests would add value as part of health surveillance in assessing the effectiveness of control measures, when the worker is exposed to agents that cause immunoglobulin E-associated OA.
  • If any one worker develops OA or OR, the control measure in place should be examined to assess exposure and identify remedial measures to protect other workers. These other workers should also be asked about any relevant symptoms.
  • Any worker suspected of having OA should be referred at an early stage for assessment by a physician with expertise in OA. This is likely to be an OH physician or respiratory physician.
  • The treatment of OA by physicians should follow published clinical guidelines in terms of drug therapy, as well as recommending avoidance of the agent that has caused the OA.

Newer tests

Eosinophils are a type of white blood cell that constitute between 1% and 3% of the total white cell count. When foreign substances or infectious cells enter the body, lymphocytes and neutrophils attract eosinophils which release toxic substances that can destroy abnormal cells. Eosinophils function in allergic responses and in helping resist some infections. They are often found in the sputum of those with asthma.

One potentially interesting role for induced sputum is the early diagnosis of OA, before the occurrence of respiratory symptoms and pulmonary function changes. In asthma, changes in induced sputum may precede functional changes (Lemière, 2004). Sputum eosinophilia is a test done on sputum from deep in the lungs, which has been produced by induction. This means that a strong (hypertonic) saline solution is nebulised, and because of an irritant effect, a productive cough is encouraged.

The BOHRF guidance suggests that the measurement of sputum eosinophils may be helpful in the diagnosis of OA, however in the clinical setting, the absence of sputum eosinophilia does not exclude a diagnosis of OA.

Exhaled nitric oxide

Nitric oxide (NO) is made from the amino acid arginine by enzymes called nitric oxide synthases that are found in the lungs and it is found in the exhaled air. NO functions to regulate vascular tone, response to vascular injury, and haemostasis. It acts as a neurotransmitter for the nonadrenergic noncholinergic nerves and has antimicrobial, immunologic and proinflammatory activities. Measuring exhaled NO (eNO) is being recognised as a non-invasive test for the evaluation of lung inflammation in patients with asthma. An increase in eNO has been shown to accompany eosinophilic inflammation and to correlate with other indicators of inflammation in asthma. During exacerbations of asthma, eNO increases and it decreases with recovery.

The BOHRF guidance points out that the measurement of eNO has not been validated as an effective diagnostic test for OA as it is also increased in other inflammatory lung disorders. A normal eNO does not exclude OA.

Putting the guidance into practice – a summary

Pre-employment

The prospective worker should be asked about pre-existing asthma caused by the substance that they might be exposed to. Only if they have asthma caused by the substance they will be exposed to should they be advised that they are unsuitable to undertake the work. Do not exclude those with a history of atopy, personal or family history of asthma, or cigarette smoking.

BOHRF will be funding the dissemination phase of a study into “pre-employment guidelines re:asthmatics for use in screening”, a project being led by Dr Paul Cullinan of the National Heart and Lung Institute. The hope is to produce an evidence base for further removing discrimination against asthmatics at work (Ashutosh, 2000).

Prevention

As with other hazards, preventive measures should include risk assessment and application of the hierarchy of control. If RPE is used, it should be fit tested by a competent person.

The British Safety Industry Federation (BSIF), together with industry stakeholders, has developed accreditation under the “Fit2Fit RPE Fit Test Providers Accreditation Scheme”, a presentation that explains the accreditation and the reason a company would wish to use an accredited tester.

Information and instruction to workers is essential on the substances, risks and the preventative measures taken by the employer. They should also be encouraged to report symptoms as soon as they develop. This may include wheezing, coughing, chest tightness or shortness of breath, and may not develop immediately after exposure so a connection with work may not be obvious. Rhinitis with sneezing and runny nose or conjunctivitis with itchy inflamed red eyes may be associated. Occupation- or trade-specific leaflets about OA are available from the HSE website covering:

  • bakers;
  • vehicle spray painters;
  • solderers/electronics;
  • woodworkers;
  • healthcare workers;
  • laboratory animal workers;
  • agricultural workers; and
  • engineering workers.

Health surveillance

While there is no evidence to guide the frequency of health surveillance, common practice and most studies report as a minimum an annual questionnaire enquiring about upper and lower respiratory symptoms. Further testing of lung function and immunological blood testing or skin-prick testing, which detects sensitisation, may be appropriate depending on the substances concerned, the control measures in place and the likelihood of exposure.

More frequent surveillance is recommended:

  • in the first few years of exposure;
  • if there is pre-existing asthma from any cause; and
  • if rhinitis develops (and exposure should be reduced).

If OA is suspected, the individual should be asked if the symptoms improve regularly when away from work. They should be referred without delay to a physician with expertise on OA. If this is via the GP as primary carer, it may be useful to provide a copy of the BOHRF guidance for GPs. Although BOHRF sent the summary of the 2004 evidence to every GP and practice-based nurse in the UK via their local medical committees, a study has shown that nearly half of respondents professed never to have heard of the BOHRF evidence.

While awaiting specialist advice, the worker should be asked to complete serial peak flow readings at least four times a day for three to four weeks. Guidance on this can be found on the Occupational Asthma website, as well as a suitable record form 13.

Management

Early identification and early avoidance of further exposure to its cause improves the prognosis of OA. Workers diagnosed as having OA should avoid further exposure in the workplace. Workers who remain in the same job and continue to be exposed to the same agent after diagnosis are unlikely to improve and may worsen. RPE may not be effective in preventing exposure and air-fed helmets may improve or prevent symptoms in some but not all workers who continue to work with the causative agent.

Take action and consider these points:

  • Are your pre-employment activities evidence-based, and are they discriminatory?
  • What training is given to the employees in the prevention of OA, and by whom?
  • Who is responsible for RPE and fit testing in your organisation?
  • Is your current health surveillance programme effective? Is it adequate or excessive for the known risks?
  • If OA is suspected, do you visit the workplace to see if control measures are being properly applied?
  • Have you identified and set up links with appropriate physicians for onward referral, as well as facilities for immunological blood or skin-prick testing if appropriate?
  • Could you improve your communication with primary care practitioners on this issue?

Occupational asthma is preventable and the OH practitioner can make a real difference in preventing ill health.

Case studies

HSE Asthma case studies.

SIGN Case study: Bob.

SIGN Case study: Nigel.

Asthma patient group information

Asthma UK Asthma at work.

Asthma UK People with asthma at work.

Asthma at work charter

Asthma UK Occupational hazard.

Advice to employers on health surveillance at work under COSHH.

Industrial Diseases Disablement Benefits – prescribed industrial diseases.

CPD module including case studies.

References

Nicholson PJ, Cullinan P, Burge PS & Boyle C. Occupational asthma: Prevention, identification & management: Systematic review & recommendations. BOHRF. London. 2010.

Romano-Woodward D. Take a Fresh Breath Occupational Health 2004 OCT 57 (10): 16-18.

BOHRF Occupational Asthma: A Guide for Occupational Health Professionals, Safety Professionals and Safety Representatives.

BOHRF Occupational Asthma: A Guide for Employers, workers and their representatives.

BOHRF Occupational Asthma: A Guide for General Practitioners and Practice Nurses.

Health Protection Report News Archives 19 March 2010.

Lemière C. 2004. The Use of Sputum Eosinophils in the Evaluation of Occupational Asthma: Use of Sputum Eosinophils as Early Markers for Occupational Asthma or as Prognostic Factors in Subjects with Occupational Asthma Removed From Exposure Curr Opin Allergy Clin Immunol. 2004;4(2).

Ashutosh K. Nitric Oxide and Asthma: a review Curr Opin Pulm Med. 2000 Jan; 6(1): 21-5.

British Occupational Health Research Foundation Occupational Asthma.

Fit2Fit Presentation on fit testing.

HSE Fit testing of respiratory protective equipment facepieces.

HSE Your trade.

Occupational Asthma Asking a patient for a serial peak flow record.

Occupational Asthma Peak Flow Form.

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