How to diagnose and support patients with occupational asthma

In the next in our series on complex asthma presentations, consultant in respiratory medicine Dr Jennifer Hoyle explains how GPs can help diagnose occupational asthma and provide ongoing care and support

What is occupational asthma?

‘Work related asthma’ describes asthma which is made worse by workplace factors. It encompasses work aggravated asthma (WAA), irritant induced asthma (IIA) and occupational asthma due to a sensitiser (OA).¹

Work aggravated asthma (WAA) describes patients with pre-existing asthma (or those who coincidentally develop late onset asthma) whose symptoms are worse at work, but the workplace exposure ha[1]s not caused the onset of asthma or contributed to an increase in its severity.¹

Typical environmental factors which cause WAA include extreme temperature changes or non-specific dust and fume exposure. The management of these patients focuses on improving asthma control with medication and adjusting workplace factors to reduce symptom burden.²

Irritant induced asthma (IAA) is caused by an acute inhalation of dusts/vapours, gases or fumes followed by a rapid onset of respiratory symptoms and airway inflammation, which results in persistent asthma symptoms and increased bronchial hyper reactivity. There is no lag period or sensitisation, rather a direct airway injury. Most events are due to accidental exposures and management is the same as national asthma guidance. The patient should be able to continue at work once symptoms are controlled and the cause of the high-level exposure has been dealt with.³

Occupational asthma (OA) is the commonest work related asthma and it is caused by an airborne workplace sensitiser.⁴ Following diagnosis there are serious consequences for the patient, their workplace colleagues and the employer. The prognosis of occupational asthma caused by sensitisation relies on removal from exposure; the sooner a person is removed from the exposure the more likely their asthma is to improve, and continued exposure increases the likelihood of severe asthma.²

When should we suspect occupational asthma?

Occupational asthma should be suspected with any new diagnosis of asthma where the patient is of working age, or where asthma control is deteriorating despite good compliance with medications. There is no single diagnostic test for OA and no substitute for taking a careful history of asthma symptom onset, frequency and its relationship to work.

A quick and effective approach is to ask all patients with a diagnosis of asthma and who work:

• Are you the same, better or worse on days away from work and when on holiday?¹

If a high-risk job for occupational asthma is identified and symptoms are better away from work a direct and early referral for specialist assessment is recommended (see Table 1).¹

Table 1. Standardised rate ratios – the standardised rate in the reference versus control population – for medically reported occupational asthma compared with all other employment sectors combined (1999-2019).⁵

Further enquiry as to work related upper airway symptoms of rhinitis or eye itching prior the onset of chest symptoms should be documented as this is a feature of occupational asthma due to high molecular weight sensitisers such as wheat flour.⁴

There are hundreds of substances which are described to cause occupational asthma, a useful source of information can be found on the HSE website.

In addition, look out for the risk phrase R42 ‘may cause sensitisation by inhalation’ on product labels or safety data sheets. A patient can ask for copies of these for the substances they are exposed to at work.

How can the diagnosis be proved, and should this be the remit of primary or secondary care?

According to national guidance objective tests should confirm OA before removal from exposure. Serial peak flow measurement offers a cheap and simple first line approach to OA diagnosis. They are only helpful if the patient is still exposed to the potential agent when performed at work and require recordings to be taken at times both at and when away from work. This testing can be done by a GP or workplace health practitioner, but the patient should not be removed from exposure until the evidence is gathered unless there is clinical concern about leaving the person exposed.¹

Patients should be taught how to take PEF recordings (a you tube video is available) and copies of the chart should be kept by the patient. Ideally these should be recorded on a proforma which allows easy entry into software which is available online as a step-by-step guide.⁶

The evidence-based minimum for a serial PEF recording is:

• At least 4 readings per day (pre- bronchodilator), the ideal is every 2 hours
• For at least 3 weeks with at least 3 consecutive workdays and at least 3 periods at work and away from work, with work tasks and times noted
• The dose of medications should remain constant when taking records and should document when these are taken.⁷

Do not wait for the results from a peak flow series where OA is suspected. National guidance recommends early a referral to a specialist centre because management can be complex and time consuming. Non-specific bronchial reactivity testing and specific inhalation challenges are useful adjuncts to diagnosis. Specific inhalation challenges should only be performed in specialist centres with experience of the test.¹

Is the best approach to avoid the precipitant or manage the situation? Does continued exposure even if apparently well controlled adversely affect prognosis?

In the case of WAA and IIA, continued controlled exposure in the workplace should not affect symptoms or prognosis.  This is not the case for OA due to a sensitiser, because even low dose exposure will precipitate asthma, and it is detrimental to prognosis. If a patient continues exposure and is apparently well controlled, then it is most likely that they have WAA rather than sensitisation. It can be challenging to tell the difference between WAA and OA. It is for this reason that the national recommendations advise than anyone who continues to be exposed to a sensitiser should be under the care of an expert who can monitor them closely. National recommendations for managing OA include:¹

• Early referral to a physician with expertise in the condition. A list of centres of expertise is found on the HSE website.
• Advise the patient that stopping exposure to the sensitiser as soon as possible gives the best outcome in occupational asthma.
• Work collaboratively with patients to balance employment issues and long-term health outcomes.
• Management of asthma is the same as national guidance, but de-escalation of treatment should be remembered for those recovering.
• Co-existing conditions such as rhinitis, breathing pattern disorder, inducible laryngeal obstruction (ILO) anxiety and depression should be assessed and treated.

One in six patients with OA meet severe asthma definitions, but about 25-30% will recover completely and another 30-35% will have improved asthma symptoms and treatment once removed¹.

Earlier removal after symptom onset increases the likelihood of recovery, but there is a risk of unemployment, with one in three remaining out of work 3-5 five years after diagnosis. Anxiety and depression affect up to half of all patients.¹

If a patient is apparently well controlled but exposed, they may have WAA and they can remain at work. If unclear refer to an expert for advice. National recommendations state that sensitised patients with potential exposure should be monitored by an expert.¹

What are the workplace and legal implications of the diagnosis?

Work has an important benefit for long term health; thus, current guidance advises removal from exposure to a sensitiser but protection of employment where possible to avoid wage loss. To achieve this experience in recognising workplace sensitisers, a close working relationship with the occupational health department and/ or employer is necessary to explore where sensitisers can be substituted or contained.

The employer has legal obligations, such as submitting reports through RIDDOR, which is an HSE reporting system. This is not the responsibility of the diagnosing clinician.

National guidance advises that a patient should be given a letter from the diagnosing physician confirming the diagnosis. In addition, written advice in the form of a letter or leaflet should be given to the patient explaining industrial injuries benefits (IIDB which can be applied for via the department of work and pensions) and the three year civil compensation rule (which means civil claims have to be submitted within 3 years of knowledge of the cause of injury).¹

If a patient is a union member the clinician can signpost them to speak to their union. Most areas do not have charities which specialise in occupational asthma; however, the clinician can signpost to local citizens advice for help with applications for IIDB and most local asbestos support charities are happy to provide help with the claims process.

Liaison with workplace occupational health providers needs written patient consent but gives the best opportunity for workplace intervention and helps co-workers stay safe. Ask the patient to contact their occupational health department or nurse if they have one.

Dr Jennifer Hoyle is Consultant Respiratory Physician and Occupational Lung Disease Lead at Pennine Acute NHS Trust, based at North Manchester General Hospital

References

1. Barber C et al. British Thoracic Society Clinical Statement on occupational asthma. Thorax 2022;77(5):433-42
2. Baur X et al. Guidelines for the management of work-related asthma. Eur Respir J 2012;39(3):529-45
3. Vandenplas O et al. EAACI position paper: irritant-induced asthma. Allergy 2014;69(9):1141-53
4. Newman Taylor A et al. BOHRF guidelines for occupational asthma. Thorax 2005;60(5):364-66
5. Barradas A et al. Trends in occupational respiratory conditions with short latency from 1999 to 2019 in the UK – evidence from the Surveillance of Work-related and Occupational Respiratory Disease (SWORD) reporting scheme. medRxiv 2023: 2023.05.19.23290195
6. OASYS website. Available at: https://www.occupationalasthma.com/oasys.aspx
7. Moore V et al. A Systematic review of serial peak expiratory flow measurements in the diagnosis of occupational asthma. Ann Respir Med 2010; 1