Introduction and objectives Although a number of case definitions for MWF EAA have been used in previous outbreaks, none has emerged as an evidence-based standard. This study used data from a large UK MWF outbreak investigation, to develop and validate a new case definition for MWF EAA.
Methods Demographic and clinical data from the 37 workers with suspected EAA during a large outbreak were reviewed by an Expert Panel. A new case definition for MWF EAA was developed using significant differences between workers with and without definite clinical EAA. This MWF EAA Score was modelled to match Expert Panel opinion as closely as possible, and used clinical criteria relatively weighted by their positive predictive value for EAA in the outbreak. The performance of the new scoring system was compared with other existing case definitions, and applied to 50 cases of MWF-EAA from nine published US outbreaks.
Results The MWF EAA Score is shown in Abstract S1 table 1, where the highest score is applied in each section. A score of >26 represents definite EAA, 19–26 possible EAA, and <19 not a case of EAA. When applied to the 37 workers, the MWF EAA Score showed good correlation (coefficient=0.85) with the Expert Panel Score (per cent likelihood of EAA), and agreed with the Expert Panel opinion in 81% of cases. The MWF EAA Score appeared to perform well when compared with other established case definitions, and when applied to 50 US cases of MWF EAA.
Conclusions Although difficult to truly validate, the MWF EAA Score offers a weighted and evidence-based case definition for workers suspected of suffering from EAA in MWF outbreaks. If adopted as a standard, the MWF EAA score will facilitate comparison of the findings from future outbreaks, in terms of risk factors and causation of this interesting disease.