What is asthma?
Before discussing work-related asthma I will briefly define asthma
in general. Asthma is a pulmonary condition characterized by episodic
airflow obstruction that is at least partially reversible. Obstruction
to flow of air occurs in the bronchial tubes within the lungs. In
asthmatics these air passages become inflamed when affected by various
triggers; the inflammation in turn leads to narrowing (bronchoconstriction)
and resultant respiratory symptoms. Asthma symptoms typically manifest
as wheezing, chest tightness, cough and shortness of breath. Wheezing
is a high pitched sound generated by air going through the constricted
passages. Shortness of breath is typically felt with exertion, but
in severe cases can be at rest. Symptoms are highly variable, from
mild and non-limiting, to disabling and, rarely, fatal. Overall,
asthma is a common condition, affecting in some fashion an estimated
5-10 percent of the general population.
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What is the cause of asthma?
At a basic level the cause of asthma is unknown. Given an individual's
predisposition to asthma, a variety of factors can trigger symptoms
(Table 1). Perhaps the most common trigger in adults is respiratory
viral infections, including the common cold. Less common, but very
important, are allergens, substances that when inhaled can react
with the host's antibodies to generate an allergic response. Allergens
include various plant pollens, animal furs, excreta from house mites,
proteins in shellfish, and some metals. Allergens play a major role
in many cases of occupational asthma. Irritants can also trigger
an asthma attack through a non-allergic mechanism, by directly injuring
cells within the lungs. Other triggers of an asthma attack include
climate changes; exercise, particularly in cold weather; certain
medications such as aspirin; and acid-reflux from the stomach. Although
everyone is subjected to the types of triggers listed in Table 1,
only the 5-10 percent of the population with asthma are prone to
develop symptoms when so exposed.
Table 1
Some common triggers of symptoms (the asthma attack) in patients
with asthma
- Respiratory viral infections
- Allergies (e.g., to pollen, animal fur, grain
dust, dust mites, shell fish, diisocyanates, etc.)
- Irritants (smoke, fumes, gases, other pollutants)
- Climate changes
- Exercise (particularly in cold air)
- Sinus infections
- Drug reactions, e.g., aspirin
- Stomach acid reflux
What is work-related asthma?
There are two basic types of work-related asthma.
1. Occupational asthma
With latency period - allergic
Without latency period - irritant
(RADS)
Occupational asthma is when the asthma
first begins on the job, and is directly related to the job. Two
types of occupational asthma are distinguished by whether symptoms
appear after a latency period, i.e., a period of time (weeks to
years) between the very first exposure and first development of
symptoms.
With latency period
This is allergic or immunologic asthma. With repeated exposure over
time to an allergen, such as latex in hospital gloves, the worker
becomes sensitized to the allergen. The next exposure after sensitization
might lead to symptoms diagnosed as asthma.
Without a latency period
This is non-allergic or non-immunologic asthma, and is better known
as irritant-induced asthma. It is also sometimes called reactive
airways dysfunction syndrome, or RADS. The irritant - typically
a chemical fume - inflames the airways and the worker has symptoms
immediately.
In both types of occupational asthma symptoms can range from mild
to life-threatening, and leave the worker chronically disabled.
Generally, once a worker is sensitized he or she must no longer
be exposed to the allergen, as even tiny amounts can trigger renewed
symptoms.
2. Work-aggravated asthma
The second type of work-related asthma is called work-aggravated
asthma. This is when pre-existing asthma (such as childhood or teenage
asthma) flares up because of exposure to some allergen or irritant
on the job. Distinction between true occupational asthma and work-related
asthma is often important because workers' compensation agencies
may handle them differently; to the individual patient, though,
asthma is asthma, and overall management should be no different.
How common is work-related asthma?
It is estimated that one out of 10 adult asthmatics have a work-related
connection, i.e., asthma either caused directly by their occupation
or with preexisting asthma reactivated by the job. There are approximately
200 million people in the U.S. age 18 or older (source: www.census.gov).
Given a 5-10 percent prevalence rate of asthma, an estimated 1-2
million US adults have asthma in some way related to work place
exposures. (These are prevalence estimates, and do not mean 1-2
million new cases each year.)
What are some allergens that can cause work-related asthma?
Many people mistakenly equate all asthma with allergy, but in fact
allergy is only one of the potential triggers of an asthma reaction
(Table 1), including work-related asthma. However, on the job, allergy
is an important cause of asthma. Over 250 substances have been identified
in the workplace that can elicit an antigen-antibody response and
cause occupational asthma. These allergens are typically categorized
as high or low molecular weight compounds, but the two groups cannot
be distinguished on clinical grounds. Generally, high molecular
weight compounds are mostly proteins from animals and plants; low
molecular weight compounds include numerous chemicals. Examples
of these compounds and the occupations at risk are given in Table
3.
Table 3
Some Antigens Responsible for Work-related Asthma
- High MW antigens
Occupation animal danders animal handlers insect scales entomologists,
lab workers egg white proteins egg producers grain dusts farmers,
grain store workers wood dusts saw mill workers, carpenters latex
health care workers.
- Low MW antigens
Diisocyantes workers in printing and painting industry anhydrides
workers in plastics and drug industries metallic salts tool and
dye workers antibiotics pharmaceutical workers.
- Low molecular weight diisocyanates
are the leading causes of occupational asthma; they are used in
many different manufacturing processes and their fumes can sensitize
the worker. Occupational asthma can also occur in clean environments,
such as in the pharmaceutical industry, where workers may develop
sensitization after repeated exposed to low molecular weight antibiotics;
an example is latex allergy.
How does asthma arise from latex allergy?
Latex allergy is an example of occupational asthma in a clean environment.
Latex allergy in health care workers appears to be increasing in
incidence. Latex, or natural rubber, is found in many medical products,
particularly gloves. Latex allergy is also seen in patients repeatedly
exposed to health care workers' gloves and other latex-containing
products. Allergic reactions range from contact hives (skin reaction
only) to asthma and in some extreme cases, shock (anaphylaxis).
For this reason many hospitals and dental offices have switched
to non-latex gloves and other products. (Note that latex is not
just confined to gloves, but is a component of numerous other hospital
products, including intravenous lines and ventilation bags.) Factors
predisposing to latex allergy include a history of other allergies
(such as hives or hay fever) and frequent exposure to latex products.
Sensitization to latex doesn't happen after a single exposure; instead,
the worker becomes sensitized to the latex after repeated exposures,
over time. Antibodies gradually build up until there is sufficient
amount to produce an antigen (latex)-antibody reaction that produces
bronchial inflammation and symptoms. Asthma from latex allergy is
thought to arise from repeated inhalation of airborne latex particles
that adhere to the cornstarch used to powder gloves. (Cornstarch
is placed in gloves to make them easy to slip on and off.)
What is RADS?
RADS, or reactive airways dysfunction syndrome, was first described
in the 1985, is now a well-recognized form of occupational asthma.
It is non-immunologic, i.e., unrelated to allergy. The exposure
is obvious and the symptoms are usually immediate, although they
may gradually worsen over the first 24 hours (see Table 4). The
inhaled irritant (e.g., fumes from a chemical spill), causes direct
irritation of the lining of the bronchial tubes, leading to asthma
symptoms. Symptoms can persist long after exposure, and indeed become
chronic and disabling.
Table 4
Reactive Airways Dysfunction Syndrome (RADS)
- Exposure to a high concentration of irritant gas,
smoke, fume, or vapor
- Immediate onset of symptoms after single exposure
to the irritant, although symptoms may not peak for several hours
- Documented absence of preceding respiratory complaints
- Symptoms (cough, wheeze and/or dyspnea) persist
at least 3 months
- Presence of airflow obstruction on pulmonary function
testing
- Presence of non-specific bronchial hyper-responsiveness
- Other pulmonary diseases ruled out
How do I know if I have work-related asthma?
Sometimes it's obvious, sometimes very difficult to know. While
there are a variety of sophisticated tests (including blood and
breathing tests) to help physicians diagnose this condition, perhaps
the most important is the medical history. Medical history includes
information about your medical condition before the job began and
the specific relationship of your symptoms to job activities. For
example, an obvious case of occupational asthma would be a 30-year-old
woman who:
a) never smoked;
b) never had asthma or respiratory symptoms before starting a
new job;
c) after working on a new job for months to years, develops wheezing,
cough and shortness of breath;
d) notes that her symptoms get better away from work (weekends,
or vacation), and flare again back at work;
e) works with a specific chemical that is known to cause occupational
asthma (e.g., toluene diisocyante);
fe) is diagnosed with asthma by breathing tests.
A much more difficult case would be a 35-year-old
man who:
a) currently smokes, and has smoked a pack a day
for 15 years;
b) has a history of episodes of bronchitis before taking a new
job in a factory at age 34;
c) develops a respiratory infection with fever, and then notes
trouble breathing;
d) gets more short of breath when he returns to work after recovering
from the infection.
This patient may in fact have smoking-related chronic
obstructive disease exacerbated by infection, and not work-related
asthma. Only by testing and further history could a physician make
a reasonable determination.
I might have work-related asthma B What should I do?
There is one cardinal rule that every worker must remember: Your
health comes first. If asthma occurs on the job, and the job doesn't
change, the asthma won't get better. The worker must remove himself
or herself from the environment. If this is you, I recommend seeing
an asthma specialist as soon as possible. Be prepared to give a
detailed history of your symptoms and their relationship to the
job. Ideally, this information should be written down and handed
to the physician. If there is a strong suspicion based on your history,
your doctor can write a note asking for a position change within
the company (if possible), or that you stay off work while tests
are performed. Again, the diagnosis may not be obvious, and it may
take time to make a reasonable assessment.
Can I get worker's compensation for work-related asthma?
Every state runs a worker's compensation agency, and work-related
asthma is certainly compensable. The worker will have to satisfy
some stringent medical criteria. Usually, an exam will be ordered
with a state physician (i.e., someone other than your treating physician).
More often than not, the employer will dispute the diagnosis, and
may ask for yet another exam with a physician they designate. Conflicting
reports are common, making it difficult for a workers' compensation
agency to decide on a case's merits. In truth, these agencies were
originally set up to compensate injured workers, and this meant
broken limbs and other external injuries. It is much more difficult
to adjudicate a medical diagnosis like asthma: a) where the cause
is often not obvious; b) in which symptoms can be extremely variable,
and c) that is also very common in the general population. Given
the potential for disagreement, it is not surprising that the decision
of the compensation agency is often appealed. If you think you have
work-related asthma, by all means get it checked out, but don't
expect a speedy resolution. And remember: your health comes first.
Does cigarette smoking predispose to occupational
asthma? If I smoke will it be more difficult to prove I have occupational
asthma? Will my symptoms likely improve if I quit smoking?
Yes. Yes. Yes. No point in belaboring the obvious.
I have asthma and am taking several medications that
control my condition. Should I still avoid a dusty environment?
By all means, yes. The fact that you need asthma medications to
control your condition is warning flag; any dusty environment could
trigger your symptoms. Note that the offending work environment
could be outdoors, e.g., work around diesel truck fumes or dust
in an outdoor saw mill. Or, it could be indoors in a non-factory
setting, such as a smoke-filled bar. Evaluate your potential job
environment carefully if you have asthma.
Is treatment of occupational asthma different from
regular asthma?
Treatment of work-related asthma is no different from asthma unrelated
to the job, with one important exception: advice about continued
working. If a worker has developed an allergic reaction to something
in the environment (i.e., is sensitized to it), he or she must leave
that environment. The quicker they remove themselves, the better
the outcome; studies have shown that continued exposure to the sensitizing
agent is associated with further deterioration of lung function.
Masks and other devices to minimize the exposure are of no help,
and should not be relied on. Even tiny amounts of allergen can trigger
a reaction if the worker is sensitized to it. On the other hand,
if the asthma was due to a one-time irritant exposure, and the irritant
is removed completely, than there should be no contraindication
to continued working in that environment. Sometimes, though, other
pollutants in the environment may bother the worker more than before,
even though the specific agent causing the asthma is removed. Although
stopping exposure generally results in clinical improvement, this
is not invariable, particularly if the worker is a smoker or has
co-existing sinusitis (which can also trigger asthma exacerbations).
Even without these other conditions, the patient may continue to
manifest asthma symptoms and require medication for months or years
after leaving the job.
I hear what you say, and I have asthma symptoms
at work, but there is no way I can quit my job. What can I take
for it?
If that is your situation, then you must work with a physician to
find the best strategy. Generally, this is two-fold. First, some
type of airway protection (masks, changes in ventilation at the
work site, etc.) that your doctor may be able to recommend to your
employer. Second, there are numerous asthma medications on the market,
and finding the proper regimen is often a matter of trial and error.
If you continually function on two (out of 6) cylinders day in and
day out, you could end up a respiratory cripple. With attention
to airway protection, and proper medication, your physician may
be able to get you up to 4 or 5 cylinders, and still keep you on
the job.
