Preface to the British Occupational Health Research Foundation (BOHRF) Occupational asthma guidelines.
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 e.g. cold air, cigarette smoke, exercise, etc and in the
clinical setting to methacholine and histamine. Symptoms include
wheeze, cough, shortness of breath and chest tightness and are often
worse at night or in the early morning.
Asthma is common, affecting adults and children of all ages. It is
especially prevalent in the UK, where 4% of adults report asthma1.
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 2,3,4.
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, i.e. pre-existing or coincidental new onset adult asthma which is made worse by non-specific factors in the workplace, and
- occupational asthma i.e. adult asthma caused by workplace
exposure and not by factors outside of 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 first 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. Whilst some low molecular weight chemicals
are associated with the development of specific IgE antibodies, this is
not the case for the majority.
Occupational factors account for 9-15% of cases of asthma in adults of working age 5. Almost 90% of cases of occupational asthma are of the allergic type 2,6,7,8,9,10 and therefore this is the focus of this evidence review. The term occupational asthma is used throughout the guidelines to mean allergic occupational asthma unless specified otherwise.
Occupational asthma is the most frequently reported work-related respiratory disease in many countries, including the UK 8.
The Health and Safety Executive (HSE) estimate that 1,500 to 3,000
people develop occupational asthma each year. This rises to 7,000 cases
a year if work-aggravated asthma is included. The disease may leave
people severely disabled having to take early retirement, while many
others have to change jobs to avoid contact with the substance, which
caused their asthma. HSE estimates that the costs to society of new
cases of occupational asthma are up to £1.1bn over 10 years.
Occupational asthma is unique in that it is the only type of asthma
that is readily preventable. Prevention depends on the effective
control of exposure to respiratory sensitisers in the workplace.
Occupational asthma has important long-term adverse health and economic
consequences. Although symptoms may resolve completely with early
diagnosis and early removal from exposure, many patients fail to
recover even when completely removed from exposure. In rare cases,
occupational asthma has been fatal. Thus prevention is the most
important factor in reducing the impact of occupational asthma on
individual workers and on society at large.
Evidence-based guidelines are becoming the benchmarks for practice in
many areas of health care and the process used to prepare such
guidelines is well established. This evidence review and the
recommendations derived from it concentrate on interventions and
outcomes. The aim is to provide a robust approach to the prevention,
identification and management of occupational asthma, based on and
using the best available medical evidence.
Anthony Newman Taylor and Paul Nicholson
Chairman and Deputy Chairman of the Research Working Group
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Book. The first comprehensive survey on respiratory health in Europe.
European Respiratory Society. 2003. pp 16-25.
- Milton DK, Solomon GM, Rosiello RA, et al. Risk and incidence of
asthma attributable to occupational exposure among HMO members. Am J
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- Tarlo SM, Leung K, Broder I, et al. Asthmatic subjects symptomatically worse at work. Chest, 2000; 118: 1309-1314.
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- Chatkin JM, Tarlo SM, Liss G, et al. The outcome of asthma related
to irritant exposures: a comparison of irritant-induced asthma and
irritant aggravation of asthma. Chest, 1999;116: 1780-1785.
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work-related and occupational respiratory disease in the UK. Occup Med
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- Hnizdo E, Esterhuizen TM, Rees D, et al. Occupational asthma as
identified by the Surveillance of Work-related and Occupational
Respiratory Diseases programme in South Africa. Clin Exp Allergy, 2001;
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