Last month the British Occupational Health Research Foundation (BOHRF) published Guidelines for the prevention, identification and management of occupational asthma. The publication provides a timely opportunity to review your organisation’s approach to the prevention of respiratory sensitisation and considerations that can be taken into account when developing policies and procedures.
Definition of occupational asthma
Asthma is a condition of chronic inflammation of the airways, characterised by widespread airflow limitation that is reversible, either spontaneously or with treatment over short periods of time. The inflammation results in hyper-responsiveness of the airways to many stimuli, for example, cold air, cigarette smoke, exercise, etc and in the clinical setting, to methacholine and histamine. Symptoms include wheezing, coughing, shortness of breath and chest tightness and are often worse at night or early in the morning.
Asthma is common, affecting adults and children of all ages. It is especially prevalent in the UK, where 4 per cent of adults report symptoms. Adult asthma may be a continuation of childhood asthma, reactivation of quiescent childhood asthma or new-onset asthma. Between a third and two-thirds of adult asthmatic patients develop asthma for the first time during working years.
Asthma is work-related when there is an association between symptoms and work. The different types of work-related asthma should be distinguished, since the implications to the worker and the occupational health management of the disease differ. Work-related asthma includes two distinct categories:
– Work-aggravated asthma, ie pre-existing or coincidental new onset adult asthma that is made worse by non-specific factors in the workplace, and
– occupational asthma, ie adult asthma caused by workplace exposure and not by factors outside the workplace. Occupational asthma can occur in workers with or without prior asthma.
Occupational asthma can be subdivided into: allergic occupational asthma characterised by a latency period between exposure to a respiratory sensitiser at work and the development of symptoms, and irritant-induced occupational asthma that occurs typically within a few hours of a high concentration exposure to an irritant gas, fume or vapour at work.
Workplace agents that induce asthma through an allergic mechanism can be broadly divided into those of high and low molecular weight. The former are usually proteins and appear to act through a type I, IgE-associated hypersensitivity. While some low-molecular weight chemicals are associated with the development of specific IgE antibodies, this is not the case for the majority. The most frequently reported agents include isocyanates, flour and grain dust, colophony and fluxes, latex, animals, aldehydes and wood dust.
There are many recognised sensitisers. Occupational factors account for between 9 per cent and 15 per cent of cases of asthma in adults of working age, thus at least 1 in 10 cases of new or recurrent asthma are attributable to occupation. Almost 90 per cent of cases of occupational asthma are of the allergic type and this is the focus of the evidence review. The term occupational asthma is used throughout the guidelines to mean allergic occupational asthma unless specified otherwise.
The workers most commonly reported to surveillance schemes of occupational asthma include paint sprayers, bakers and pastry makers, nurses, chemical workers, animal handlers, welders, food processing workers and timber workers.
There are obligations under the Health and Safety at Work Act 1974, the Management of Health and Safety at Work Regulations 1999, and the Control of Substances Hazardous to Health Regulations 2002. Under The Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995, occupational asthma is a reportable disease for many substances and in similar circumstances the Industrial Injuries Advisory Council IIAC has prescribed Allergic Rhinitis (D4) and OA (D7) as industrial diseases.1 The Safety Representatives and Safety Committees Regs give safety representatives powers of investigation should a reportable disease occur in the workplace.2
How can it be prevented?
Primary prevention: aims to prevent the onset of disease often by reducing or eliminating exposure to the agent in the workplace.
Secondary prevention: aims to detect disease at an early or pre-symptomatic stage, for example by health surveillance.
Tertiary prevention: aims to prevent worsening symptoms by early recognition and early removal from exposure.
Employers should assess their workplace for known agents and the risk of exposure, which depends on how the substance is being handled. Exposure should be reduced by elimination or substitution. Where this is not possible, then effective control of exposure at source should be implemented.
Personal respiratory protective equipment reduces the incidence of, but does not completely prevent, occupational asthma. When respiratory protective equipment is worn, employers must ensure the appropriate type is used and maintained, fit testing is performed and workers understand how to wear, remove, and replace it.
The guidelines put a strong emphasis on communication with workers. This should include information about the causes of asthma in the workplace and the need to report symptoms as soon as they develop.
Robust, auditable health surveillance programmes should be devised, following the identification by management of workers for whom exposure cannot be adequately controlled.3
As a minimum, a respiratory questionnaire enquiring about work-related upper and lower respiratory symptoms should be completed annually. OH professionals should assess the requirement for further health surveillance on the employer’s risk assessment, which will depend on the nature of the substance handled and the likelihood of exposure. Further testing of lung function and referral for immunological blood tests or skin prick testing, which detect sensitisation, may be appropriate.
For many substances, the risk of developing occupational asthma is greatest during the early years of exposure. Therefore, more frequent surveillance is indicated for the first two years of exposure. Individual vulnerability may indicate a requirement for increased levels of surveillance or increased frequency for pre-existing asthma, and those who develop rhinitis in the course of their work. When an employee develops occupational asthma or rhinitis, the exposure and the presence of symptoms of other workers should be investigated.
It is important that there is an agreed outcome if an employee becomes sensitised to the extent that they are considered unsuitable to continue working with the substance. If this outcome can be negotiated in advance with interested parties, such as workers’ representatives, then the surveillance programme is more likely to be supported and be effective.
When spirometry is considered to be appropriate, procedures should be specific and the responsibilities of the spirometry technician, occupational health advisor and occupational health physician defined and understood by all participants.
Equipment will need to be calibrated and maintained according to manufacturers’ instructions, including the calibration syringes used to verify the accuracy of volumetric machines. It is prudent to keep a log of the daily calibration, which may consist of a collection of the print-out slips or a hand-written record (if spirometers that rely on heat-sensitive paper are used, the print may fade over time). A photocopy of the results will provide a permanent record and a copy of the calibration slip on the same page proves that quality assurance is being taken into account. The moving parts of spirometers, which use a flow rate mechanism, may need to be washed in distilled water to prevent excessively high readings caused by the accumulation of debris.
It is essential for the criteria for referral to an OHP or GP to be clear to those undertaking spirometry. Sample respiratory questionnaires are provided by Nicholson et al.4 It is important to compare individuals’ new and previous result to see if there has been a relative deterioration in lung function.
It is important to feedback information to the individual and managers on whether the individual is suitable to continue in the work environment. The COSHH regulations require a record of health surveillance to be available for inspection. Anonymous group results can be produced for different work areas, which will provide managers with an overview that can be compared year-on-year to detect any increase in problems. They can be made available to workers’ representatives and safety committees through appropriate channels.
Any worker with symptoms of asthma or rhinitis that are new, recurrent or getting worse should be asked about their job, the materials with which they work and whether their symptoms improve regularly when away from work. The nature of the job or work processes may change with the possibility of increased exposure.
If a worker is suspected of having occupational asthma they should be referred without delay to a physician with relevant expertise. This is likely to be an occupational health or respiratory physician. The diagnosis is likely to be confirmed in approximately half of these individuals.
Evidence shows that the prognosis of occupational asthma is improved by early identification and avoidance of further exposure to its cause. This requires prompt reporting of symptoms by workers who may fear losing their job if they are found to be affected.
To assist in diagnosis, the worker should be provided with a peak flow meter and asked to note the best of three readings at least four times a day for two to three weeks. Pre- and post-shift spirometry is not recommended as it is unlikely to be sufficiently sensitive or specific in detecting asthma.
New scales for peak flow meters were introduced in September 2004 and meters supplied after this date will need to conform to EU standard 13826. It is important to use a single meter throughout an individual’s record and to record which scale is being used. It will be feasible for many OH departments to perform venepuncture to collect blood for serological tests for antibodies to a specific substance. However, it is important to understand that it is possible for a worker to become sensitised and not have occupational asthma. Skin prick testing is likely to be considered viable – either in-house or by third party OH providers – only if they have had specific training.
Occupational asthma diagnosis should be supported by objective criteria, such as lung function or blood test and not on the basis of compatible history alone. It is hoped that by involving and informing GPs about the condition, potential cases will be identified earlier, referred and investigated objectively before confirming a diagnosis.
Occupational asthma is preventable and it is hoped that these guidelines will produce a greater awareness among employers, workers and health practitioners to reduce the incidence of this condition.
Diane Romano-Woodward is an independent occupational health practitioner and professional development director of the Association of Occupational Health Nurse Practitioner
The guidelines can be accessed at www.bohrf.org.uk. Three leaflets have been devised for managers, workers and representatives, OH professionals and primary care practitioners and can be downloaded from the site.
For information on sensitisers go to: www.hse.gov.uk/asthma/causes.htm#causes
For more information on peak flows, go to: www.peakflow.com/portal_nav/nurse-doctor/index.html
1. Industrial Injuries Advisory Council. www.iiac.org.uk/papers/main.shtml
2. Safety Representatives and Safety Committees Regulations 1988. HSE.ISBN: 0 1188 3959 4
3. Medical Aspects of Occupational Asthma MS25 Second edition 1998. ISBN 0 7176 1547 2
4. PJ Nicholson, AJ Newman Taylor, P Oliver, M Cathcart. Current Best Practice for the health surveillance of enzyme workers in the soap and detergent industry. Occup. Med. Vol. 51 No2, pp81-92, 2001.