Asthma On the Job
How to Link Symptoms with Work Exposure
By Jennifer J. Paraschak
What do bakers, carpenters, concrete workers, health care providers, spray painters, and zoo employees all have in common? Their jobs could cause occupational asthma.
Reports of occupational asthma date back to the 4th century when Hippocrates described symptoms in tailors. In 1713, physicians identified grain workers with asthma. And, a 1911 report documented the disease in photographers working with platinum salts.
Today, researchers have identified more than 300 airborne substances linked to inducing asthma. In addition, industry is adding newer agents into the workplace where employees are being exposed, explains Michael Alberts, MD.
“I think it’s becoming a big problem because even though we’re getting a little better at identifying occupational asthma, it looks to the world like regular old asthma,” says Dr. Alberts, associate center director for clinical affairs and chief medical officer at the H. Lee Moffitt Cancer Center, University of South Florida, Tampa.
He estimates that 600,000 U.S. workers have occupational asthma. “It’s now the most prevalent occupational lung disease in developed countries.”
Typically, two patient profiles fit the description of occupational asthma. One group has a prior history of asthma with a marked increase in symptoms including chest tightness, cough and shortness of breath.
Often, these changes are associated with a change in the workplace, says Ron Balkissoon, MD, assistant professor of medicine at the University of Colorado Health Science Center, Denver. An asthma exacerbation may be related to a chemical spill or inadvertent high level exposure that is atypical for the person’s general work.
The other patient profile is someone who has no prior history of asthma and appears to have developed the disease as an adult from repeated exposure to triggers at work. “You generally require a latency period of at least weeks or months, more often two to five years of exposure, before you truly become sensitized to an agent,” Dr. Balkissoon says.
For example, health care workers may develop asthma from an underlying allergy to proteins in powdered latex gloves.
Substances that cause occupational asthma are broken down into two categories–high molecular and low molecular weight agents. High molecular agents are particles such as pollens, grain dusts, flour, molds and animal dander.
“Large agents will have an immediate response,” Dr. Balkissoon says. They can be recognized directly by an antibody that stimulates a type 1 hypersensitive response. This leads to the rapid release of histamines, esinophils and mast cell activation.
Low molecular agents can include chemical compounds, vapors and fumes, such as diisocyantes, acid anhydrides, formaldehyde, glutaraldehyde, latex and colophony fumes. These agents are in soldering fluxes, spray paints, beauty products and lacquers.
Low molecular agents cause a delayed response because it takes time for the body to process them. “Typically, they must be bound to a human protein like albumin, get processed, and act as a hapten that allows them to stimulate an antibody response leading to an immune response,” Dr. Balkissoon says.
It takes a conscientious clinician to recognize these substances as potential asthma triggers in the workplace. Patient questionnaires that include a thorough family and occupational history can help in diagnosis.
An important question to ask is, “Does your work involve the probability of inhaling chemicals because they evaporate or are sprayed or because they are dispersed as dusts?” says David Hendrick, MD, a consultant physician from the Royal Victorian Infirmary in England.
To confirm occupational asthma, physicians can use pulmonary function tests with or without a bronchodilator. Patients measure their breathing function with portable peak flow meters four to six times a day while at work and when away from work. For at least two weeks, they record work shifts, values, symptoms and exposure on a diary card. Physicians review the results and determine if an association between symptoms and work exposure is present.
“The problem is that it’s highly operator-dependent and not always reliable,” Dr. Balkissoon explains. Patient honesty is crucial. To document more accurate results, physicians can bring patients into their offices and do spirometry testing before and after work shifts to identify any changes in lung function.
In a few high molecular weight agents, like some molds and flour, physicians can perform skin testing or a radioallergosor-bent test (RAST). These tests expose a person’s serum and antibodies to a particular allergen to determine how much antibody binding is present. However, they are not well-standardized, Dr. Alberts cautions, and are not commonly used.
In difficult-to-diagnose cases, physicians can perform a methacholine challenge test that deliberately exposes a person in a controlled setting to a bronchodilator. “It measures airway responsiveness, the underlying twitchiness of the airways, the fundamental abnormality of asthma that the airways are more likely to react,” Dr. Hendrick explains.
Physicians perform the test by spirometry and administer a bronchoconstrictor through a nebulizer. The patient does an FEV1, inhales a dose of water, repeats the FEV1, inhales a very small concentration of methacholine (or sometimes histamine), and again repeats the FEV1. The process continues with progressively higher doses of methacholine until the patient’s FEV1 falls to 20 percent below the baseline level. At that point, the concentration of methacholine is calculated from the dose response curve.
“Patients with asthma typically will react at much lower doses of methacholine than people without asthma,” says William Beckett, MD, professor of environmental medicine, University of Rochester School of Medicine and Dentistry, New York.
Once occupational asthma is diagnosed, physicians prescribe the same medications used to treat asthma. However, the management is different, says Susan Tarlo, MBBS, associate professor of medicine, University of Toronto, Canada.
Physicians focus on prevention, such as encouraging strict industrial hygiene practices, instituting environmental control measures and removing the patient from further exposure.
“If someone is sensitized, if they have this immunologic response to something at work, they need to avoid the exposure,” she stresses. A person’s asthma will become progressively worse if their work environment stays the same. “The earlier the diagnosis of OA is made, and the earlier people are taken out of the exposure, the better the outcome.”
Jennifer Paraschak is associate editor of ADVANCE.