Abstract

Background
Outbreaks of hypersensitivity pneumonitis (HP) are not uncommon in workplaces where metal working fluid (MWF) is used to facilitate metal turning. Inhalation of microbe-contaminated MWF has been assumed to be the cause, but previous investigations have failed to establish a spatial relationship between a contaminated source and an outbreak.

Objectives
After an outbreak of five cases of HP in a UK factory, we carried out blinded, molecular-based microbiological investigation of MWF samples in order to identify potential links between specific microbial taxa and machines in the outbreak zone.

Methods
Custom-quantitative PCR assays, microscopy and phylogenetic analyses were performed on blinded MWF samples to quantify microbial burden and identify potential aetiological agents of HP in metal workers.

Measurements and main results
MWF from machines fed by a central sump, but not those with an isolated supply, was contaminated by mycobacteria. The factory sump and a single linked machine at the centre of the outbreak zone, known to be the workstation of the index cases, had very high levels of detectable organisms. Phylogenetic placement of mycobacterial taxonomic marker genes generated from these samples indicated that the contaminating organisms were closely related to Mycobacterium avium.

Conclusions
We describe, for the first time, a close spatial relationship between the abundance of a mycobacterium-like organism, most probably M. avium, and a localised outbreak of MWF-associated HP. The further development of sequence-based analytic techniques should assist in the prevention of this important occupational disease.

Metal worker’s lung: spatial association with Mycobacterium avium
Phillip L James, Julie Cannon, Christopher M Barber, Laura Crawford, Heather Hughes, Meinir Jones, Joanna Szram, Steven Cowman, William O C Cookson, Miriam F Moffatt, Paul Cullinan
doi: 10.1136/thoraxjnl-2017-210226

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Comments

This paper describes an another outbreak of hypersensitivity pneumonitis with 3 index cases where a study of the workforce identified a further 3. The metalworking fluid from a common sump was found to be heavily contaminated with bacteria including Mycobacteria. Phylogenetic analysis of high-quality HSP65 gene Sanger sequences from metalworking fluid samples grouped tightly with a representative sequence from a distinct slow-growing M. avium type strain. Unlike some other outbreaks of metalworking fluid HP attributed to mycobacteria, only weak precipitating antibodies to the used metalworking fluid were found in only 2/5 cases (and no exposed controls). No specific challenges were reported. This study falls short of identifying the mycobacteria as the cause of the HP, but does suggest that they might be. It further questions the role of precipitating antibodies in identification of cases of metalworking fluid HP

9/3/2017