Researchers in the Netherlands have identified the cause of the disease, which was first acknowledged in 2001 among the workers of an American chemical plant that produced microwave able popcorn.
The research, which examined a population of workers at a chemical plant that produced diacetyl (a key component of butter flavouring), was reported in the first issue for September of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
"Our study found a cluster of [previously undiagnosed] BOS cases in a diacetyl production plant," said lead author Frits G. B. G. J. van Rooy, M.D., of the Division of Environmental Epidemiology at the Universities Utrecht in the Netherlands.
"This supports the conclusion that an agent in the diacetyl production process has caused BOS," he added.
Diacetyl was identified early on as a marker for exposure among popcorn workers. Its specific role, if any, however, in the development of BOS was not known. No cases of BOS had previously been identified outside of North America or in chemical production plants related to flavouring.
By investigating the BOS status of former workers of the diacetyl plant, researchers hoped to determine whether there was a link between diacetyl exposure and the development of BOS.
With the help of the human resources department, Dr. van Rooy and colleagues traced 196 former workers who were still living and who had been employed at the diacetyl production plant between 1960 and 2003, when the plant closed.
They identified 175 who consented to complete exposure and respiratory health questionnaires and undergo lung function tests and clinical assessments. Of the 102 process workers considered to be at the highest risk for exposure, researchers positively identified three cases of BOS, and later, a fourth, in a worker who had initially declined to participate in the research.
"This is the first study where cases of BOS were found in a chemical plant producing diacetyl," wrote Dr. van Rooy.
While the researchers were unable to rule out contributions of other chemicals to the development of BOS, the study significantly narrows the field of suspects to diacetyl and the components and byproducts of its manufacturing process.
"The spectrum of exposures is much smaller in this production plant compared with the popcorn processing plants where a wide range of chemicals was identified," the researchers wrote.
"This population-based survey establishes the presence of BOS, or popcorn worker's lung, in chemical workers manufacturing a flavouring ingredient with exposures to diacetyl, acetoin and acetyldehyde. Any or all of these exposures may contribute to the risk of this emerging occupational disease."
The novel finding of four cases of BOS in workers at the diacetyl plant has important implications for practicing physicians and public health officials.
"None of the four cases had been recognized as bronchiolitis obliterans or as occupationally related," wrote Kathleen Kreiss, M.D., in the accompanying editorial in the same issue of the journal.
"To identify flavouring-related bronchiolitis obliterans, physicians need to consider the diagnosis," she noted. Dr. Kreiss, of the Field Studies Branch of the National Institute for Occupational Safety and Health, was one of the first investigators on the scene when "popcorn worker's lung" arose as a public health issue.
Furthermore, she writes, "the collective evidence for diacetyl causing a respiratory hazard supports action to minimize exposure to diacetyl, even if contributions by other flavouring chemicals exist."