Key institutes have expanded the principles of health screening and introduced new ethical guidelines, while companies around the world have agreed guidelines on occupational allergens. Important new guidance on spirometry has also been published by leading medical bodies in the UK and the US, and a range of evidence reviews have appeared, including one on occupational asthma carried out by the British Occupational Health Research Foundation (BOHRF).
In light of this new knowledge and changed opinion, we need to challenge the status quo and examine the factors that influence clinical practice which, as well as law and custom, include principles, current best practice, consensus and evidence.
Principles
With regard to the principles of health surveillance, the UK National Screening Committee has expanded the accepted principles of health screening.1 These include:
You should know the normal range of results in a healthy population
There should be effective treatment or intervention for patients identified through early detection, with evidence of early treatment leading to better outcomes than late treatment
There should be evidence from high quality randomised controlled trials that the screening programme is effective in reducing mortality or morbidity
The benefit from the screening programme should outweigh physical and psychological harm
There should be a plan for managing and monitoring the screening programme and an agreed set of quality assurance standards.
Ethical considerations for health surveillance are defined in updated guidance from the Faculty of Occupational Medicine2. There must be consultation with employers, staff and their representatives, and a programme of communication of individual and anonymised group data agreed. The programme must incorporate a physician who is competent to interpret results, make arrangements for further care and, with consent, notify the individualÕs GP.
Current best practice
More guidelines on health screening have emerged from an agreement in the detergent industry between US and European trade associations on the safe handling of occupational allergens. This was possible because health did not affect competition between the companies.
All potentially exposed workers are given a questionnaire, spirometry is performed according to the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines, health surveillance is performed and interpreted by competent, qualified occupational health professionals, and immunological tests (skin-prick test or serology) are undertaken to detect specific IgE (Immunoglobulin E) antibodies.
Surveillance is performed annually in a stable environment and every six months in the first year of work, or when there is a new enzyme or process change.
The questionnaire is validated for the detection of asthma and includes questions on asthma symptoms. These include chest tightness, breathing difficulty, wheezing, shortness of breath, night-time or early morning symptoms, being diagnosed as having asthma by a doctor, sneezing, a runny or blocked nose, itchy or watering eyes, and use of medication for any of these symptoms.4
The programme is now available for free for other industries to use. Factories that follow industry guidelines and survey employees for the development of specific IgE before the onset of symptoms experience a very low number of asthma cases, or none at all.3
Spirometry guidance
The ATS/ERS published guidance for spirometry in 2005, which defines criteria for quality assurance, infection control and other issues, advises as follows:
Activities to be avoided prior to spirometry include:5
Smoking (for at least one hour before)
Alcohol (for at least four hours before)
A large meal (for at least two hours before)
Vigorous exercise (for at least 30 minutes before)
Criteria for assessing whether spirograms are acceptable:
For acceptable spirograms, the test should be free of the following:
Coughing during the first second of exhalation
Glottis closure affecting measurement
Early termination or cut-off
Leakage
Obstructed mouthpiece
With breathing at maximum effort
Extrapolated volume <5% of forced vital capacity (FVC) or 0.15L, whichever is greater
With tests that show satisfactory exhalation:
Duration of >6s or a plateau in the volume-time curve or if the subject can/should not continue to exhale
After obtaining three acceptable spirograms:
The two largest values of FVC must be within 0.15L of each other
The two largest values of FEV1 (forced expiratory capacity) must be within 0.15L of each other.
If both criteria are met, testing may be concluded. If not, continue testing until both criteria are met, or eight tests have been performed, or the subject cannot or should not continue. Save the data from at least three satisfactory tests.
Late and mid-maximal expiratory flows are of limited clinical significance, meaning that you cannot draw clinical conclusions about them, when FEV1 and FVC are normal. They may indicate airway obstruction when FEV1 and FVC are borderline, but their wide variability in healthy subjects (see table above) must be remembered when interpreting the results. 7
The more occasions you collect data over a period of time, the more likely you are to interpret a real trend, rather than chance results. It is important not only to look at the results of the test findings, but also to take effective clinical histories and examine the employee.7
Evidence reviews
Systematic evidence reviews rank the credibility of evidence depending on the likelihood of bias influencing data collection and interpretation. Recent evidence reviews include screening for lung cancer in at-risk groups and occupational asthma.
The US Preventive Services Task Force 8 concluded that there is:
insufficient evidence to recommend for or against screening asymptomatic persons for lung cancer with low-dose computerised tomography (CT), chest x-ray, sputum cytology, or a combination of these tests
fair evidence that screening can detect lung cancer at an earlier stage
poor evidence that any screening decreases mortality.
A Cochrane Review found that chest x-ray, sputum testing or CT scans do not appear to have much impact on either treatment or the number of deaths from lung cancer. 9 Frequent chest x-rays might be more harmful, being associated with an 11% relative increase in mortality from lung cancer compared with less frequent screening, although more research is needed. 9
A BOHRF systematic review found few studies of the efficacy of health surveillance for occupational asthma. The only study offering valid conclusions is of employees exposed to di-isocyanate, such as paint sprayers for motor vehicle repairs. This found evidence, although limited, that health surveillance can detect occupational asthma at an earlier stage of disease and improved the outcomes for workers who are included in a health surveillance programme.
The results might be partly attributable to simultaneous reduction in exposure to di-isocyanate. Very few studies have evaluated the separate components of health surveillance. For example, there is limited evidence that questionnaires may underestimate the prevalence of asthmatic symptoms, and that spirometry detects few cases of occupational asthma that would not otherwise be detected by a respiratory questionnaire. This will depend on the sensitivity and specificity of individual questionnaires, and whether there is quality assurance of the spirometry programme.
Skin prick and serological tests can detect specific IgE in workers who have become sensitised to high molecular weight agents (such as di-isocyanate) and a few low molecular weight agents. There is moderate evidence that skin prick and serological tests can be used to measure reaction to di-isocyanate in the workplace, and also that the surveillance for the development of specific IgE antibodies can be used as part of a broader risk management programme to reduce the incidence of occupational asthma.
There is moderate evidence that occupational rhinitis/rhino-conjunctivitis frequently precedes and occurs together with IgE-associated occupational asthma, and limited evidence that the risk of developing occupational asthma is highest in the year after the onset of rhinitis.
There is moderate evidence that occupational asthma caused by azodicarbonamide, enzymes, complex platinum salts, isocyanates and laboratory animal allergens are most likely to develop in the first years of exposure.
Based on these facts, there is moderate evidence to recommend that where a risk of occupational asthma is identified, occupational health practitioners should provide health surveillance at least annually, and more frequently in the first two years of exposure and to workers who develop rhinitis. This should include a questionnaire enquiring about work-related upper and lower respiratory symptoms, with additional functional and immunological tests, where appropriate.
In the absence of evidence, BOHRF recommends that, as good practice, occupational health practitioners should:
provide more frequent health surveillance to staff with pre-existing asthma to detect any evidence of deterioration
consider the use of skin-prick or serological tests as part of the health surveillance of workers exposed to agents that cause IgE-associated occupational asthma to assess the effectiveness of the control of exposure and the risk of occupational asthma among workers.
Paul J Nicholson is associate medical director, P&G Beauty Care in Europe, Middle East & Africa, and the Faculty of Occupational Medicine and Society of Occupational Medicine joint representative on the Health and Safety ExecutiveÕs Asthma Project Board. He was deputy chairman of the BOHRF research working group on occupational asthma.
References
1 The UK National Screening Committee (2003) Criteria for appraising the viability, effectiveness and appropriateness of a screening programme http://www.nsc.nhs.uk/pdfs/criteria.pdf
2 Faculty of Occupational Medicine (2006) Guidance on ethics for occupational physicians, sixth edition, London
3 Sarlo K, Kirchner D B (2002) Occupational asthma and allergy in the detergent industry: new developments. Current Opinion in Allergy and Clinical Immunology, April 2:97-101
4 Nicholson P J, Newman Taylor A J, Oliver P, Cathcart M (2001) Current Best Practice for the Health Surveillance of Enzyme Workers in the Soap and Detergent Industry, Occupational Medicine 51: 81-92. London
5 Miller M R, Crapo R, Hankinson J, et al (2005) ATS/ERS Task Force. General Considerations for Lung Function Testing, European Respitory Journal J. 26: 153-61
6 Miller M R, Hankinson J, Brusasco V, et al (2005) Standardisation of spirometry.
European Respitory Journal 26: 319-38
7 Pellegrino R, Viegi G, Brusasco V, et al. (2005) Interpretative strategies for lung function tests, European Respitory Journal 26: p948-68
8 US Preventive Services Task Force (2004) Lung Cancer Screening: Recommendation Statement, Annals of Internal Medicine 140: p738-9
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9 Manser R L, Irving L B, Stone C, Byrnes G, Abramson M, Campbell D (2003) Screening for lung cancer, The Cochrane Database of Systematic Reviews, Issue 3
10 Newman Taylor A J, Nicholson P J (Editors) (2004) Guidelines for the Prevention, Identification and Management of Occupational Asthma, Evidence review and recommendations, British Occupational Health Research Foundation, London http://www.bohrf.org.uk/content/asthma.htm
