Respiratory disease in workers exposed to metal working fluids

The largest UK outbreak of respiratory disease in metalworking fluid (MWF) exposed workers (Powertrain) led to a heightened awareness of the health hazards associated with MWF. A literature review identified 29 outbreaks of ill health associated with MWF exposure with a peak incidence between 1996 and 2000. Microbial contamination was suspected but no unifying causative agent could be found. Six different case definitions for extrinsic allergic alveolitis (EAA) were indentified, only one of which was validated. The process of developing an evidence based case definition for MWF-EAA required the identification of a group of patients with unequivocal MWF associated EAA. The Powertrain database (created at the time of the outbreak and subsequent follow up appointments) was utilised and an Expert Panel of five occupational lung disease consultants concluded that there was sufficient clinical evidence to diagnose 14 workers as definite cases of EAA. By calculating the positive predictive value of the data points relevant to a diagnosis of EAA combined with knowledge and experience of previous EAA diagnostic criteria, it was possible to develop a new evidence-based EAA diagnostic score (the MWF EAA Score). The MWF EAA Score was applied to the Powertrain data demonstrating agreement with the Expert Panel opinion in over 80% of the cases with a greater number of workers correctly classified than with other published diagnostic criteria1. The score was also applied to previously published case series of workers diagnosed with MWF EAA, in order to externally validate the new EAA rating system. The MWF EAA Score appeared to perform well and there was sufficient data provided in almost half of these published cases indicating that the MWF EAA Score would have shown agreement. This scoring system is a simple and reproducible tool and provides an evidence-based case definition suitable for use in future UK outbreaks.