Occupational Asthma in Health Care Professionals

Replicating studies done in the industrial sector probably would find there is a higher incidence among health care workers.

ASTHMA is an illness characterized by intermittent breathing difficulty including chest tightness, wheezing, cough, and shortness of breath. It is a serious and sometimes fatal condition. Occupational asthma is defined as asthma caused by workplace exposures to biological agents.

An estimated 11 million workers in a wide range of industries and occupations are potentially exposed to at least one of the many agents known to be associated with the development of occupational asthma. Despite these facts, few specific measures have been designed to protect employees, and national attention on this issue has been sparse. However, the tide has been turning. Exposure to agents in industry has been recognized as a major contributor to asthma, highlighted by the fact that asthma has emerged as the most prevalent occupational lung disease in the developed world. Already more than 200 documented agents have been associated with the development of occupational asthma.

In the modern hospital environment, health care workers are exposed to hazardous substances--respiratory sensitizers, irritants, infectious agents, and others. Concerns are increasing about the health implications of this exposure. The increasing number of reports documenting cases of health care workers developing asthma because of workplace exposure has caused great concern and raised awareness. The reports document asthma among laboratory technicians, nurses, and in endoscopy and radiology units.

As awareness about this issue is raised further, an increasing number of health care professionals will seek advice about respiratory symptoms in the hospital environment.

The Substances . . . Exposed
Numerous substances have been identified as being prevalent within the health care setting. By convention, the substances described as causing occupational asthma among health care professionals can be divided into high molecular weight and low molecular weight substances.

High molecular weight substances
Allergens of a high molecular weight are classed as weighing over 5000 daltons (see Table 1). They are most likely to be proteins of bacterial, fungal, plant, or animal origin. Very often the patient's history of symptoms can point to high molecular weight exposure. In the majority of cases the patient's complain of allergic symptoms affecting the eyes, nose, or skin, with a clear relation between chest symptoms and occupational exposure.

In virtually all reported cases of occupational asthma caused by high molecular weight compounds, the onset of asthma symptoms is by and large preceded by symptoms such as rhinitis, conjunctivitis, or even contact dermatitis and urticaria.

Table 1. High Molecular Weight Substances








All workers

Hospital environment

Animal proteins

Laboratory workers

Research laboratory

Low molecular weight compounds
The diagnosis of occupational asthma inflicted by low molecular weight substances (see Table 2) is more difficult. In high molecular weight exposure, the onset of asthma is preceded by allergic symptoms, but this is not the case here. The majority of the low weight chemicals, in particular the biocides, irritate mucosal surfaces and so symptoms may be dismissed by health care workers as being purely irritant in nature.

Also, asthma caused by low weight chemicals may not be recognized because it tends to produce atypical, non-specific symptoms such as cough and chest discomfort. More classic symptoms such as wheeze and chest tightness may not arise until evening or night, after eight to nine hours of exposure. Problems also exist because many reports have used differing diagnostic criteria. Despite these differences there is one common denominator within these reports in that all documented low molecular weighted chemicals show changes in airway caliber following exposure and sensitization to the agent.

Indeed, the demonstration of an asthmatic response following specific bronchial inhalation challenges remains the "gold standard" for diagnosing asthma caused by low molecular weight chemicals. This is because the specific IgE response is a marker of hyper responsiveness. The IgE response is a well-recognized physiological reaction of asthma, "priming"and prolonging the life of eosinophils--the main inflammatory mediator of asthma.

Table 2. Low Molecular Weight Substances





Nurse, radiographer

Endoscopy, radiology


Lab technician


Methy Methacrylate

Theater nurse


Radiograph fixative


Diagnostic imaging

Diagnosis of Occupational Asthma
As for any condition, a thorough history is paramount for accurate diagnosis. The history should include complete details of symptoms and occupational activities.

Once there is suspicion of an agent, the duration, location, and pattern of symptoms must be related to type, nature, quantity, and intensity of exposure to suspected agents. As mentioned previously, high molecular weight compounds have a pattern of developing allergic rhinitis, conjunctivitis, urticaria, or contact dermatitis before asthmatic symptoms ensue. More specifically, sensitization to high molecular weight compounds also can be be confirmed by skin prick and bronchial inhalation tests. Indeed, the presence of recent onset work-related asthma, with confirmation of the sensitization of the suspected allergen, is considered sufficient by many physicians to make a diagnosis of occupational asthma caused by high molecular weight chemicals.

However there are a number of factors that should be borne in mind prior to diagnosing occupational asthma. Two people working in the same department may have differing levels of exposure to the chemical, if working day or night shifts. Certain chemicals may be more irritable under artificial light, and also there is natural day-to-day variation in professional activity. Hospital staff also work periodic night or weekend shifts, followed by varying periods away from work, and away from exposure to the sensitizing agent.

This natural variation in health care professionals working within a "fluid" shift system may result in intermittent and often unpredictable exposure to the sensitizing agent. As a consequence, any relation between symptoms and work maybe difficult to establish, thus making diagnosis difficult and delayed. Also, are there differences between health care professionals working in rural and urban areas? A comparative study between these two environments is a good idea.

Whether you are diagnosing low molecular weight or high molecular exposure, it is recommended that objective measurements of asthma and any relation between symptoms and work environment should be made. One such method is by recording peak flow measurements within set time intervals, followed by bronchial provocation tests. As with any study that involves active participation of subjects, great care must be take to ensure that time of starting, finishing, type of work, and substances to which the health worker has been exposed are well documented in order to interpret the airflow indices being assessed.

Evidence for Occupational Asthma in Health Care Professionals
In recent years an increasing number of researchers have tried to elucidate the extent of occupational asthma among health care professionals. In particular, they want to know the prevalence of asthma caused by specific sensitizing agents and which professionals are at greater risk from occupational asthma. Below are some of the substances likely to cause occupational asthma in health care professionals and the individuals who are most at risk.

A low molecular weight compound that has caused much interest is glutaraldehyde, which has long been recognized for its excellent biocidal activity. Exposure may be associated with nasal, eye, and skin symptoms.

Since the 1960s, endoscopy units within the United Kingdom have openly used the broad spectrum antimicrobial activity of glutaraldehyde against viruses, gram +/- bacteria, bacterial spores, mycobacterium, and fungi. Its non-corrosive nature allows universal acceptance by biomedical equipment manufacturers, and its low cost makes it the first-choice disinfectant for Britain's National Health Service. However, some 18 years after glutaraldehyde's introduction, the first publication associating glutaraldehyde exposure with work-related symptoms came to light. Since then, the reported incidence of work-related symptoms and glutaraldehyde has increased.

Glutaraldehyde has multi-faceted uses. As well as being an endoscopic disinfectant, it's a constituent of the developer in X-ray film processing. Gannon's group looked at radiographers, darkroom technicians, and a secretary who never entered the darkroom but reacted to X-ray film placed on her desk. All of these individuals worked within the context of the radiology unit. The diagnosis of occupational asthma was confirmed in all but one of the subjects, by serial peak flow and bronchial provocation tests.

Smedley's group added weight to these findings by determining the prevalence of work-related symptoms among radiographers compared with a control group of physiotherapists. There was a clear excess of work-related symptoms among radiographers. In particular, they were more likely to complain of symptoms that were worse at work, such as mouth soreness, itchy or runny eyes, stuffy nose, and lower respiratory tract symptoms. Thus, it seems radiographers are at risk: In the future, will radiologists be interpreting their own X-rays?

Radiographic fixatives contain acetic acid and hydrochloric acid as well as glutaraldehyde, but the sensitizing properties of these two, if any, have not been established. Larger studies need to be carried out becuase there has been no systematic survey of respiratory symptoms among radiographic personnel, especially given growing concern within the profession about occupational asthma. A study comparing endoscopy nurses and radiology workers is highly recommended because both use glutaraldhyde, and possibly we could see in which specialty asthma is more prevalent.

In summary, glutaraldehyde must be considered as a possible sensitizer whenever doctors are faced with health care professionals complaining of asthmatic symptoms, especially those who work in endoscopy units, where in the last 15 years greater volumes of glutaraldehyde are being used to sterilize endoscopes, and in X-ray departments, where developers contain more glutaraldehyde than previous versions to compensate for reduced silver content of the film. The best option would be to replace glutaraldehyde with a safer agent.

Psyllium, a high molecular weight gum, is a member of the plantago weed family. Psyllium is widely used as a laxative and has been shown to cause occupational asthma in employees of pharmaceutical companies who prepare the laxative, with the prevalence estimated in the region of 3 to 6 percent. There have also been reports of allergic symptoms in nurses who prepare psyllium, but the relationship between psyllium and occupational asthma is unknown.

Malo's group investigated personnel of four chronic care hospitals to assess the prevalence, evaluating by questionnaire, skin testing and specific inhalation challenges. This is of merit because previous studies have assessed prevalence by questionnaires, but with this method we can quantify whether psyllium is indeed a causative agent. Every nurse, auxiliary nurse, or assistant directly or indirectly in contact with psyllium was investigated. The study concludes psyllium is indeed IgE dependent (increased IgE antibodies), and thus with psyllium the subjects must have developed immunolgical sensitization before getting the disease in the target organ--i.e. occupational asthma. Those with positive skin prick to psyllium underwent specific inhalation challenges, with the great majority developing bronchial hyper responsiveness.

In conclusion, Malo's group showed the prevalence of occupational asthma from psyllium was 4 percent in those sampled working within the four hospitals. Psyllium is of risk to the respiratory health of personnel working within chronic care hospitals. Moves should be made to substitute psyllium use.

Latex is the milky sap of the tree Hevea brasiliensis. The allergens identified in latex have molecular weights of 14, 28 and 88kd to which specific IgE in the serum of sensitized individuals bind. The majority of cases are probably due to inhalation of cornstarch powder dusting the gloves, which has adsorbed these latex proteins.

The association between occupational asthma and latex is well documented. Swanson et al. found airborne concentrations of latex allergens between 13 and 21 mg m-3 in areas of hospitals where gloves were used regularly. The majority of cases reporting asthmatic symptoms involve nurse and laboratory technicians who had jobs involving multiple changes of latex gloves.

The problem seems to be widespread. A study by Vandenplas et al. reported the prevalence of latex allergy among workers at a Belgian hospital: 4.7 percent of the sample had immediate skin test response to latex. Many subjects reported symptoms of urticaria, rhinitis, and half reported respiratory symptoms. Inhalation testing with latex provoked an asthmatic response in 2.5 percent.

Occupational asthma due to latex has been reported to occur in 6 percent of glove manufacturing workers and 2.5 percent of hospital employees using latex gloves. Although Vandenplas's study didn't quantify the level of airborne latex, it is the first case reporting occupational asthma within a hospital administrative employee. It can be said that latex proteins are potent aeroallergens causing respiratory health hazard in subjects with direct or indirect inhalation exposure. The possibility of occupational asthma caused by latex should be suspected and properly assessed even in workers who do not directly handle latex gloves but are exposed to airborne latex allergens in medical or subsidiary environments. Importantly, if these atopic individuals are identified, appropriate adoptive measures should be employed. The table below highlights recommendations for latex sensitive individuals:

  • Use vinyl gloves
  • Use hypoallergenic latex gloves
  • Ask that co-workers use vinyl or hypoallergenic latex gloves
  • Wear a medical ID tag
  • Warn health care providers of sensitivity
  • Eliminate or minimize the use of latex
  • Respiratory therapists are another group of professionals at risk from occupational asthma. A previous cross sectional study of 315 therapists in Rhode Island revealed an excess risk of asthma developing after entry into the profession compared with other health care professionals. (This particular study was severely limited by the small study sample.) Kern and Christiani investigated a larger sample population in Massachusetts. They compared respiratory therapists with physical therapists, and when their analysis was restricted to those developing physician-diagnosed asthma after entry into the profession, the cases within respiratory therapists were significantly higher.

    Respiratory therapists are exposed to both viral and bacterial organisms in the course of treating patients. These exposures may lead to infection, airway damage, bronchial irritability, and hyper responsiveness. It may be that viral infections are more common in respiratory therapists compared to another group. However the quantitative exposure of organisms represents an unknown entity and may represent a confounding factor. More needs to be done to elucidate and identify the potential agents responsible for occupational asthma diagnosed in respiratory therapists.

    Chloramine T
    Chloramine T has been used as disinfectant in hospitals. Dijkman cites asthmatic reactions in nurses handling this substance in operating theaters in the Netherlands. Challenge studies revealed biphasic and late bronchial reactions, which were prevented by chromoglycate inhalation. The late phase was accompanied by systemic symptoms such as leukocytoisis and fever. Chloramine T is thought to pose its effects by its ability to dry very fast in well-ventilated areas such as operating theaters. Rapid drying would precipitate crystallization, with circulation of particles in the air thatare easily inhaled. Several cases have highlighted asthmatic symptoms in nurses, which explains why many hospitals have reverted to an alternative disinfectant.

    Methyl methacrylate
    Staying with the operating theater, orthopedic nurses may be at risk of occupational asthma from methyl methacrylate. It is used as bone cement in surgery. Pickering et al. reported the case of a nurse who regularly mixed poly methylate methacrylate with monomethyl metha crylate to produce the bone cement CMW. This procedure leads to a short-duration high concentration of methyl metha crylate in the atmosphere, with the peak being in the first 90 seconds. After many years, the nurse in question developed asthmatic symptoms that would remit dramatically when she was away from work. Bronchial provocation confirmed it to be asthma from occupational causes.

    Yet this is the only case reported. This could be due to the fact there is long period of time before the methyl methacrylate produces the symptoms, so fewer workers are likely to be identified. More likely is that most theaters use a small fume cabinet to reduced the atmospheric concentration of methyl methacrylate to acceptable levels. Use of a fume cabinet for the mixing is highly recommended.

    Intertwined with the hospital are laboratory research workers. Most cases of asthmatic and allergic disease are caused by rats and mice, which are important in experimental research. The major source of allergens is through secreta and excreta, which become airborne, often as dust particles, and are reinhaled by those working with the animals. The most common symptoms are rhinitis, conjunctivitis, and urticaraia, with asthma being rare. This has been mainly achieved by the ventilation systems, restriction of the number of animals used, masks, and clothing. Despite asthma being rare, it is important to recognize the possibility of this diagnosis because in severely affected cases, the workers may not be able to continue their work.

    Comparing the potential risk of occupational asthma in the categories just mentioned and health professionals in other specialist units, such as renal dialysis and cardiothoracic units, would help to answer remaining questions. Also, more needs to be done to look at other potential agents, including protein compounds, pharmaceutical agents, volatile gases, and glues.

    Glutaraldehyde and latex have been in use for decades. Thus, it is likely compounds such as these may go undetected as a cause of asthma because they have been in use for so long, but every possibility should be investigated. Better awareness is required for health care professionals, with greater access to information about the proper handling and use of substances potentially minimizing the risk of sensitization and onset of symptoms. The most significant change would involve educating personnel and retraining on supervision of these substances.

    Ultimately, early detection and removal from further exposure maybe the most useful way to prevent occupational asthma in health care workers. There is gradually a better appreciation of this condition with the health care environment, but we are lacking in studies identifying the high-risk groups in the hospital sector.

    Causal relationships for many sensitizers have not been proved. If we can replicate in the hospital setting the research that has been done in the industrial sector, it is likely to reveal a greater prevalence of occupational asthma among health professionals.

    Although we have gained insight into the likely sensitizing substances and health professionals who are at risk, we have only touched the surface of iceberg. More awareness and research are needed, otherwise if we are not careful we will be hitting that iceberg headfirst. We cannot turn a blind eye and pretending occupational asthma "doesn't happen." Recently awakened interest in causes of occupational illness should ensure fewer such conditions are missed in the future.

    This article originally appeared in the September 2003 issue of Occupational Health & Safety.

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