Popcorn Workers Lung and Bronchiolitis Obliterans

An editorial in the New England Journal of Medicine concerning Popcorn Workers Lung and Bronchiotitis Obliterans appeared recently.  Bronchiolitis obliterans is a term applied to the widespread inflammatory and fibrotic obstruction of the small airways.

Occupational airway diseases such as occupational asthma, bronchitis, reactive airways dysfunction syndrome and byssinosis are common workplace diseases.  The involvement of the small airways, such as the bronchioles are infrequently reported in occupational airway disease, but these may lead to serious chronic lung  injury.  One such disease of the bronchioles is bronchiolitis obliterans.  This disease is initiated by damage to the epithelium of the small conducting airways and progresses to inflammation of the airways, frequently to the adjacent alveolar tissue as well.  The clinical consequence of this injury and inflammation is irreversible airway obstruction.

In the workplace, bronchiolitis obliterans has been associated with the presence of irritant gases, namely oxides of nitrogen but also chlorine, phosgene, ozone, hydrogen sulfide and sulfur dioxide as well as organic and inorganic dusts.  Unlike water-soluble irritant gases which dissolve on the mucus membranes of the upper airway, oxides of nitrogen hydrolyze slowly into acids after penetrating to deep lung tissue.  Lower respiratory symptoms become apparent only 3-24 hours after the onset of exposure.  The most common symptoms include cough, dyspnea and fever.  Exposure to very high levels of oxides of nitrogen may cause acute respiratory failure.  Following recovery, symptoms may reoccur in 3 to 6 weeks.  Histologic examination showed bronchiolitis obliterans with marked intraluminial proliferation of fibrous tissue.

Sporadic cases of bronchiolitis obliterans have been reported in the published scientific literature in unrelated industries that have not previously been linked to this disease.  This includes nylon-flock workers, workers who spray prints onto textiles (with polyamide-amine dyes), battery workers (exposure to thionyl  chloride fumes) and workers in the food flavoring industry.

Kreiss et al. (2002) investigated a clustering of cases of bronchiolitis obliterans in a microwave-popcorn packaging plant.  In 2000, a physician specializing in occupational medicine described fixed obstruction lung disease in eight former employees of the plant, all employed between 1992-2000.  Symptoms in all 8 were compatible with description of bronchiolitis obliterans.  Four of the eight worked in the mixing room and the other 4 worked in the packaging area.  Of the 425 employees during this time period (1992-2000), only 13 had worked in the mixing room.  Air sampling at the plant detected many volatile organic compounds, but diacetyl, a ketone with butter-flavor characteristics was singled out as the likely etiological agent.  Toxicity studies using rats support this association (Hubbs et al. 2002).

Kreiss et al. (2002) in a cross-sectional study evaluated 117 current workers at the plant.  This investigation concentrated on the frequency of subclinical findings in the plant.  They noted that the prevalence of respiratory symptoms and of findings of obstruction on spirometry among the current workers was approximately 3 times higher than the prevalence in the general population.  These investigators observed a strong exposure – response relation between cumulative diacetyl exposure and the frequency and extent of airway obstruction.

They speculate that these subtle subclinical findings corresponding to symptoms and lung-function abnormalities, not of a sufficient degree to cause respiratory impairment, which are most often associated with the gradient of the irritant responsible for bronchiolitis obliterans.  Moreover, it follows that these individuals may be at risk of developing bronchiolitis obliterans.

These types of cross sectional studies support the need for comprehensive biological monitoring of workers exposed to agents that are associated with adverse health effects, including any subclinical effects that cause deviations from the baseline for any given worker.

Furthermore, the follow up for the inhalation of agents that are known deep lung irritants (from animal experimentation) provides evidence in support of  the associations found in epidemiological studies.

Sources:

E. Neil Schachter 2002. Popcorn Workers Lung. (Editorial) New England Journal of Medicine 347 (5): 360-61.

Kreiss, K., gomma, A., Kullman, L., Fedank., Simocs, E.J., Enright, P.L. 2002.  Clinical Bronchiolitis obliterans in workers at a microwave-popcorn plant. New England Journal of Medicine 347(5): 330-8.

MMWR. 2002.  Fixed Obstructive Lung Disease in Workers at a Microwave Popcorn Factory – Missouri 2000-2002.  April 26, 2002: 51(16); 345-7.

Hubbs, A.F., Mercer, R.R., Batelli, L. et al. 2002. Ultrastructural changes in the airways of rats inhaling butter flavoring vapors. Toxicol. Sci. 66:Suppl. 194. Abstract

By: Arlene Weiss, MS, DABT

Contributing Editor