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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

4.1 Work-Related Asthma

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WRA is the most common respiratory disease treated in occupational health clinics in the U.S., accounting for a substantial share of all asthma among adults. A 2003 statement of the American Thoracic Society indicates that 15 percent of asthma among adults is attributable to work. Under cooperative agreements, NIOSH-funded researchers have since estimated that 29 percent to 33 percent of new-onset adult asthma is attributable to work. In addition, RDRP scientists estimate that 23 percent of existing adult asthma is exacerbated by work. Assuming that about 25 percent of asthma is attributable to work, at least 2.25 million Americans between the ages of 15 and 65 have experienced onset or exacerbation of their asthma due to workplace conditions (A4-1).

Challenges to conducting research on WRA involve issues of identification, causality, and implementation:

  • Clinicians and researchers need tools to help distinguish WRA from other forms of asthma. Although a sizable proportion of asthma among adults can be attributed to work, asthma is not a uniquely occupational disease, and exposures outside work (e.g. ambient environment, home) can also contribute to the onset and worsening of this disease.
  • WRA can be caused by a variety of agents in many different settings. Depending on the agent or venue, a different analytical approach or practical solution might be necessary. Common causes of WRA include natural rubber latex, isocyanates, and cleaning agents. In total, there are over 300 agents that can cause or exacerbate asthma at work, and they can occur in dozens of different industries and occupations. New agents are identified every year, and old agents are recognized again in new settings.
  • Existing prevention opportunities have not been fully exploited. For example, primary prevention of WRA is often overlooked as a viable option. Many clinicians, researchers, and lay people view asthma as a disease of individual susceptibility, in which exposure to allergens are of concern after onset rather than before onset. In fact, controlling exposures to sensitizers in workplaces can make a substantial difference in the number of workers who become sensitized and develop asthma. This was demonstrated in the past in the detergent industry where a spike in the incidence of WRA was successfully addressed by encapsulating the detergent enzymes and instituting other measures to limit worker exposures.  

RDRP has established a significant track record in the asthma arena, as evidenced by 3108 separate records found in NIOSHTIC-2 (the comprehensive NIOSH bibliography) that pertain to asthma and asthma-inducing agents, such as latex and isocyanates.

The following sections illustrate how RDRP has contributed to addressing these challenges through pursuing its research and prevention objectives in:

  • Preventing and reducing natural rubber latex asthma and allergy among healthcare workers
  • Preventing and reducing WRA in the isocyanate production industry
  • Preventing and reducing WRA related to non-industrial indoor environmental quality
  • Improving detection of WRA and relevant exposures

RDRP has contributed in part to documented outcomes associated with these specific objectives, which are an increased awareness that natural rubber latex is an asthma sensitizer, a decrease in the use of natural rubber latex products, and a concomitant decrease (25-fold) in WRA incidence due to exposure to natural rubber latex. In the case of isocyanates there is a growing awareness among manufacturers of products that contain isocyanates that exposure to their products carries a risk of WRA. However, it will take more time and effort to convert this to a reduction in isocyantate induced asthma.

RDRP scientists are raising awareness of the problem of methyl diisocyanate (MDI) asthma associated with spray-on truck-bed liner application. They have helped two states, Michigan and Washington to post their Alerts and RDRP has recently released a NIOSH Alert on application of spray-on bed liners.

RDRP has developed a five-year prospective collaborative project involving industry, labor, and government, in which a standardized approach to hazard and health monitoring, agreed upon by all primary producers of Toluene Diisocyanate (TDI) is to be implemented. The collaboration is undergoing formal scrutiny for feasibility and effectiveness. The protocol describes a finalized, formal analysis plan to document the level of implementation of recommended approaches and to evaluate subsequent changes in exposures and health outcomes, including the diagnosis of diisocyanate-induced asthma among plant workers (A4-2).

Asthma in relation to indoor air quality problems in schools and offices has been addressed for years and in many workplaces via RDRP responses to requests for HHEs. In recent years, RDRP has undertaken evaluations at several work locations in the northeastern U.S. under a research protocol. There is documentation that some RDRP recommendations for intervention, including provision of alternate work locations and building modifications or renovations, have been implemented at evaluated worksites. Studies are now in progress to determine if these interventions have been effective in mitigating exposures and improving health outcomes.

A major challenge in detecting WRA pertains to the high prevalence of asthma in the general population. In another activity, RDRP provided leadership in the development of a health monitoring software package designed to facilitate the evaluation of individuals at risk of WRA. This package has been made readily available to physicians, and should assist in the clinical diagnosis of WRA. The development of a standardized respiratory questionnaire will also assist physicians and researchers in addressing this problem.