Letter from Professor Anthony Newman Taylor
CBE, Head of National Heart and Lung Institute, Faculty of Medicine,
Imperial College, London
Thank you for inviting me to submit evidence
to your committee's inquiry into Allergy.
I will focus on occupational asthma because
it is the most important of the occupational allergic respiratory
disease and the one in which I have most experience.
Occupational asthma, is asthma induced by an
agent inhaled at work. This may occur in one of two ways:
1. The inhalation of an irritant chemical,
such as chlorine or sulphur dioxide, in concentrations toxic to
the lining cells of the bronchial airways. This causes an acute
inflammatory reaction with local injury in the airways, which
in a minority of cases is followed by the development of chronic
asthma.
2. The development of a hypersensitivity
reaction (allergy) to an inhaled protein or low molecular weight
chemical. Proteins which may be inhaled at work and cause asthma
include enzymes used in the detergent and baking industries, proteins
excreted in the urine of laboratory animals—rats, mice,
guinea pigs—and proteins in flour encountered in bakeries.
Low molecular weight chemicals, so called "chemical sensitisers",
inhaled at work include isocyanates, used in the manufacture of
polyurethane plastics and polyurethane spray paints, acid anhydride
used in the manufacture of epoxy resin, plastics and paints and
complex platinum salts, essential intermediates in platinum refining.
Of these two, hypersensitivity induced (or allergic)
asthma occurs considerably more frequently than irritant induced
asthma. Occupational asthma is the most frequent category of occupational
lung disease reported by chest physicians and occupational physicians
to the voluntary reporting scheme, SWORD (Surveillance of Work
and Occupational Respiratory Disease). The total number of cases
of occupational asthma reported by SWORD has fallen during the
past decade, primarily due to a reduction in the number of cases
reported by chest physicians between 1999 and 2000. The number
of cases attributable to isocyanates is now less and the increase
in the number of cases caused by latex allergy has decreased since
the widespread use of low protein non-powdered rubber gloves.
However, a similar decline has not occurred in the number of cases
attributed to flour in bakery workers.
It has been estimated by a panel of the American
Thoracic Society about 15 per cent of asthma in adult life
(ie one in seven) is attributable to an occupational cause.
Occupational asthma is distinguished as a type
of asthma by being potentially preventable and, in many cases,
curable. Several studies, undertaken by different groups in the
1990s, showed that the major risk factor for developing occupational
asthma, caused by allergy to an agent inhaled at work, was the
level (concentration) in air of the specific agent in the place
of work. This was demonstrated in studies of enzymes in the detergent
industry, animal urinary proteins in the pharmaceutical industry,
flour and enzymes in the baking industry and acid anhydrides in
the chemical industry. Prior to this, allergic occupational asthma
had been considered as a consequence primarily of individual susceptibility.
The important implication of evidence for an exposure—response
relationship is that the incidence of occupational asthma should
be decreased by reducing the level of exposure to its causes in
the workplace. This has now been demonstrated in studies of enzymes
in the detergent industry, of latex in health care workers and
of isocyanates in Ontario, Canada. Comparable interventions now
need to be extended into other industries in order to make further
impact on the overall incidence of the disease.
Because occupational asthma in the majority
of cases is due to the development of an allergy to an agent inhaled
at work, to provide the best opportunity for asthma to improve
and in some cases resolve it is, in general, important to avoid
further exposure to the responsible agent. There is consistent
evidence to indicate that early diagnosis and avoidance of exposure
to the cause of allergic occupational asthma provides the best
opportunity to prevent the development of chronic asthma. It is
therefore important to provide services which enable an early
and accurate diagnosis of occupational asthma. Of similar importance
mis-diagnosis of a case of occupational asthma, ie attributing
asthma incorrectly to an occupational cause, can lead to inappropriate
advice to leave work often it is difficult for individuals to
get back into the labour market, with important financial and
social consequences.
There is therefore an important need to provide
specialist services within the United Kingdom, to which possible
cases occupational asthma can be referred, in order that an accurate
diagnosis and informed advice about future employment can be provided.
The number of such specialist centres does not need to be great,
probably no more than half a dozen throughout the United Kingdom.
They are an important resource for the specialist management of
a disease which requires understanding of respiratory illness
and the hazards of work as well as the provision of well-informed
advice about future management.
Unfortunately in many cases the only way to
avoid expose to an allergic cause of asthma is a change of job,
which can mean the loss of employment. There is evidence from
a number of studies that those who leave their job because of
occupational asthma can remain out of work for several years;
they seem less likely than other asthmatics of a similar age to
obtain new employment. There is a real need to provide the means
to support re-training for individuals with occupational asthma,
with facilitation into new jobs. This could be a function of the
Industrial Injuries Scheme, which provides compensation for occupational
asthma as a prescribed disease. Unfortunately, since the withdrawal
of Reduced Earnings Allowance in 1990, this opportunity is no
longer available under the scheme. Review of the Industrial Injuries
Scheme, with a view to reforming it, is currently under way. The
introduction of a benefit which could support and enable re-training
of individuals unable to continue in their current job because
of a prescribed disease, such as those with occupational asthma,
to enable them to remain in or return to work should be an important
function of a reformed scheme.
20 November 2006
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