EspP, an Extracellular Serine Protease from Enterohemorrhagic E. coli, Reduces Coagulation Factor Activities, Reduces Clot Strength, and Promotes Clot Lysis.

BACKGROUND: EspP (E. coli secreted serine protease, large plasmid encoded) is an extracellular serine protease produced by enterohemorrhagic E. coli (EHEC) O157:H7, a causative agent of diarrhea-associated Hemolytic Uremic Syndrome (D+HUS). The mechanism by which EHEC induces D+HUS has not been fully elucidated. OBJECTIVES: We investigated the effects of EspP on clot formation and lysis in human blood. METHODS: Human whole blood and plasma were incubated with EspP(WT )at various concentrations and sampled at various time points. Thrombin time (TT), prothrombin time (PT), and activated partial thromboplastin time (aPTT), coagulation factor activities, and thrombelastgraphy (TEG) were measured. RESULTS AND CONCLUSIONS: Human whole blood or plasma incubated with EspP(WT) was found to have prolonged PT, aPTT, and TT. Furthermore, human whole blood or plasma incubated with EspP(WT) had reduced activities of coagulation factors V, VII, VIII, and XII, as well as prothrombin. EspP did not alter the activities of coagulation factors IX, X, or XI. When analyzed by whole blood TEG, EspP decreased the maximum amplitude of the clot, and increased the clot lysis. Our results indicate that EspP alters hemostasis in vitro by decreasing the activities of coagulation factors V, VII, VIII, and XII, and of prothrombin, by reducing the clot strength and accelerating fibrinolysis, and provide further evidence of a functional role for this protease in the virulence of EHEC and the development of D+HUS.

Combination pretest probability assessment and D-dimer did not reduce outpatient imaging for venous thromboembolism in a tertiary care hospital emergency department.

INTRODUCTION: Venous thromboembolism (VTE) is difficult to diagnose yet potentially life threatening. A low-risk pretest probability (PTP) assessment combined with a negative D-dimer can rule out VTE in two-thirds of outpatients, reducing the need for imaging. Real-life implementation of this strategy is associated with several challenges. METHODS: We evaluated the impact of introducing a standardized diagnostic algorithm including a mandatory PTP assessment and D-dimer on radiologic test use for VTE in our emergency department (ED). A retrospective review of all ED visits for suspected VTE in the year prior to and following the introduction of this algorithm was conducted. VTE diagnosis was based on imaging. Guideline compliance was also assessed. RESULTS: ED visits were investigated for suspected VTE in the pre- and postintervention periods (n  =  1,785). Most D-dimers (95%) ordered were associated with a PTP assessment, and 50% of visits assigned a low PTP had a negative D-dimer. The proportion of imaging tests ordered for VTE in all ED visits was unchanged postintervention (1.9% v. 2.0%). The proportion of patients with suspected VTE in whom VTE was confirmed on imaging decreased postintervention (10.2% v. 14.1%). CONCLUSION: In spite of excellent compliance with our algorithm, we were unable to reduce imaging for VTE. This may be due to a lower threshold for suspecting VTE and an increase in investigation for VTE combined with a high false positive rate of our D-dimer assay in low-pretest probability patients. This study highlights two common real-life challenges with adopting this strategy for VTE investigation.