From Centre de recherche, Centre de pneummologie, Hôpital Laval, Institut universitaire de cardiologie et de pneumologie de Québec, Université Laval.
Correspondence to: Yves Lacasse, MD, Hopital Laval, Centre de Pneumologie, 2725 Chemin Ste-Foy, Québec, QC, G1V 4G5, Canada; e-mail: firstname.lastname@example.org
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
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We thank Dr Barber and colleagues for their very specific comment on the role of nontuberculous mycobacteria in metalworking fluid (MWF) hypersensitivity pneumonitis (HP) that followed our broad narrative review of HP in our recent article in CHEST.1 We also read with interest their systematic review of respiratory outbreaks associated with exposure to water-based MWF, to which they refer.2 We noted that eight of the 27 outbreaks included in their review involved patients with HP. Microbial contamination of MWF samples was variable. Mycobacteria were detected in MWF in 12 outbreaks; mycobacteria were also tested but not detected in three others. However, no detail was provided regarding the methods used to detect mycobacteria in MWF.
Although mycobacteria are ubiquitous in aqueous environments, identifying them is particularly difficult. Bacterial culture methods lack sensitivity. Establishing a link between mycobacteria and HP is further complicated by the fact that the immunogenic properties of HP agents do not seem to be linked to their viability, because animal models of HP use dead organisms or whole cell extracts.3,4
Our group developed a DNA extraction method and real-time polymerase chain reaction assay capable of quantifying mycobacterial load in environmental samples using a dual-labeled probe to specifically detect Mycobacterium immunogenum.5 This method proved more sensitive than DNA extraction alone and standard culture.6 Our group also found that MWFs are more often contaminated by bacteria (mostly Pseudomonas pseudoalcaligenes) than by mycobacteria (M immunogenum).7 In the same work environment, M immunogenum was not found in air samples.8 An explanation may be that high-level air contamination with mycobacteria in machining plants is intermittent only and depends on sporadic use of MWF-generating aerosols.
We would certainly agree that HP could occur in mycobacteria-free workplaces. However, that M immunogenum is related to MWF-HP is more than an attractive hypothesis. M immunogenum in MWF has been linked to HP outbreaks in several reports.2 Animal models clearly demonstrate that MWFs containing mycobacteria can induce granulomatous lung disease, peribronchiolar lymphocytosis, increased cell concentrations in lavage, and upregulation of several cytokines.4 These findings are consistent with HP. To our knowledge, such a model does not exist with Pseudomonas species or any other bacteria isolated from MWFs.
Contamination of MWFs with mycobacteria is often underestimated because of laboratory methods that lack sensitivity to detect them. We would be pleased to apply the methods we developed in our laboratory to MWF samples from the United Kingdom.
Other contributions: The authors thank Caroline Duchaine, PhD.
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