William O. Hahn

Biomarkers of Endothelial Activation Are Associated with Poor Outcome in Critical Illness

Background Endothelial activation plays a role in organ dysfunction in the systemic inflammatory response syndrome (SIRS). Angiopoietin-1 (Ang-1) promotes vascular quiescence while angiopoietin-2 (Ang-2) mediates microvascular leak. Circulating levels of Ang-1 and Ang-2 in patients with SIRS could provide insight on risks for organ dysfunction and death distinct from inflammatory proteins. In this study, we determined if biomarkers of endothelial activation and inflammation exhibit independent associations with poor outcomes in SIRS. Methods We studied 943 critically ill patients with SIRS admitted to an Intensive Care Unit (ICU) of an academic medical center. We measured plasma levels of endothelial markers (Ang-1, Ang-2, soluble vascular cell adhesion molecule-1 (sVCAM-1)) and inflammatory markers (interleukin-6 (IL-6), interleukin-8 (IL-8), granulocyte-colony stimulating factor (G-CSF), soluble tumor necrosis factor receptor-1 (sTNFR-1)) within 24 hours of enrollment. We tested for associations between each marker and 28 day mortality, shock, and day 3 sequential organ failure assessment (SOFA) score. For 28 day mortality, we performed sensitivity analysis for those subjects with sepsis and those with sterile inflammation. We used multivariate models to adjust for clinical covariates and determine if associations identified with endothelial activation markers were independent of those observed with inflammatory markers. Results Higher levels of all biomarkers were associated with increased 28 day mortality except levels of Ang-1 which were associated with lower mortality. After adjustment for comorbidities and sTNFR-1 concentration, a doubling of Ang-1 concentration was associated with lower 28 day mortality (Odds ratio (OR) = 0.81; p<0.01), shock (OR = 0.82; p<0.001), and SOFA score (β = -0.50; p<0.001), while Ang-2 concentration was associated with increased mortality (OR = 1.55; p<0.001), shock (OR = 1.51; p<0.001), and SOFA score (β = +0.63; p<0.001). sVCAM-1 was not independently associated with SIRS outcomes. Conclusions In critically ill patients with SIRS, early measurements of Ang-1 and Ang-2 are associated with death and organ dysfunction independently of simultaneously-measured markers of inflammation.

Emergence of High-Level Daptomycin Resistance in Corynebacterium striatum in Two Patients with Left Ventricular Assist Device Infections

INTRODUCTION We describe the clinical and microbiologic courses of two patients with ventricular assist device infections secondary to Corynebacterium striatum treated with daptomycin. In both cases, the pathogen was initially susceptible to daptomycin (minimum inhibitory concentration [MIC] <0.125 mg/L) but became resistant (MIC >256 mg/L) during therapy. METHODS The clonal nature of the isolates was determined by pulse-field gel electrophoresis (PFGE). Daptomycin binding was assessed by fluorescence microscopy using daptomycin-boron-dipyrromethene (bodipy). Induction and stability of daptomycin resistance were assessed by culturing strains in the presence of low concentrations of daptomycin or passage of resistant strains on daptomycin-free medium and repeat MIC testing, respectively. RESULTS PFGE revealed that resistant clinical isolates were genetically indistinguishable from their parent strains, but the two pairs were unrelated to each other. The resistant strains had 7.5-15 times lower binding of daptomycin-bodipy compared to the related susceptible strains (p ≤ 0.0002). High-level daptomycin resistance (MIC >256 mg/L) was generated in vitro for both susceptible parent strains after overnight culture in the presence of daptomycin. One of the resistant strains maintained a high-level resistance phenotype up to 5 days of passage on daptomycin-free medium, whereas the other strain reverted back to a susceptible phenotype (MIC = 0.38 mg/L) after one passage on daptomycin-free medium, with a concomitant increase in daptomycin binding. CONCLUSIONS High-level daptomycin resistance in C. striatum was readily generated in vitro and during the course of therapy in these patients. This resistance appears to be mediated by reduced daptomycin binding. Providers should be cautious about using long-term daptomycin monotherapy for C. striatum infections.

Blood Stage Malaria Disrupts Humoral Immunity to the Pre-erythrocytic Stage Circumsporozoite Protein

Many current malaria vaccines target the pre-erythrocytic stage of infection in the liver. However, in malaria-endemic regions, increased blood stage exposure is associated with decreased vaccine efficacy, thereby challenging current vaccine efforts. We hypothesized that pre-erythrocytic humoral immunity is directly disrupted by blood stage infection. To investigate this possibility, we used Plasmodium-antigen tetramers to analyze B cells after infection with either late liver stage arresting parasites or wild-type parasites that progress to the blood stage. Our data demonstrate that immunoglobulin G (IgG) antibodies against the pre-erythrocytic antigen, circumsporozoite protein (CSP), are generated only in response to the attenuated, but not the wild-type, infection. Further analyses revealed that blood stage malaria inhibits CSP-specific germinal center B cell differentiation and modulates chemokine expression. This results in aberrant memory formation and the loss of a rapid secondary B cell response. These data highlight how immunization with attenuated parasites may drive optimal immunity to malaria.

Multidrug-Resistant Corynebacterium striatum Associated with Increased Use of Parenteral Antimicrobial Drugs

Device-related infections with this pathogen frequently require prolonged parenteral therapy.

Host derived biomarkers of inflammation, apoptosis, and endothelial activation are associated with clinical outcomes in patients with bacteremia and sepsis regardless of microbial etiology

William O. Hahn, Carmen Mikacenic, Brenda L. Price, Susanna Harju-Baker, Ronit Katz, Jonathan Himmelfarb, Mark M. Wurfelb,y, and W. Conrad Lilesa,y Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA, USA; Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Washington, Seattle, WA, USA; Department of Biostatistics, University of Washington, Seattle, WA, USA; Kidney Research Institute, University of Washington, Seattle, WA, USA

A Two-Biomarker Model Predicts Mortality in the Critically Ill with Sepsis.

Rationale: Improving the prospective identification of patients with systemic inflammatory response syndrome (SIRS) and sepsis at low risk for organ dysfunction and death is a major clinical challenge. Objectives: To develop and validate a multibiomarker‐based prediction model for 28‐day mortality in critically ill patients with SIRS and sepsis. Methods: A derivation cohort (n = 888) and internal test cohort (n = 278) were taken from a prospective study of critically ill intensive care unit (ICU) patients meeting two of four SIRS criteria at an academic medical center for whom plasma was obtained within 24 hours. The validation cohort (n = 759) was taken from a prospective cohort enrolled at another academic medical center ICU for whom plasma was obtained within 48 hours. We measured concentrations of angiopoietin‐1, angiopoietin‐2, IL‐6, IL‐8, soluble tumor necrosis factor receptor‐1, soluble vascular cell adhesion molecule‐1, granulocyte colony‐stimulating factor, and soluble Fas. Measurements and Main Results: We identified a two‐biomarker model in the derivation cohort that predicted mortality (area under the receiver operator characteristic curve [AUC], 0.79; 95% confidence interval [CI], 0.74‐0.83). It performed well in the internal test cohort (AUC, 0.75; 95% CI, 0.65‐0.85) and the external validation cohort (AUC, 0.77; 95% CI, 0.72‐0.83). We determined a model score threshold demonstrating high negative predictive value (0.95) for death. In addition to a low risk of death, patients below this threshold had shorter ICU length of stay, lower incidence of acute kidney injury, acute respiratory distress syndrome, and need for vasopressors. Conclusions: We have developed a simple, robust biomarker‐based model that identifies patients with SIRS/sepsis at low risk for death and organ dysfunction.

Malaria in the traveler: how to manage before departure and evaluate upon return.

Malaria is the clinical syndrome when a patient experiences symptoms in response to infection with one of several strains of the Plasmodium parasite. This article is intended for health care providers to become familiar with some of the basics of care of patients who are travelling to or returning from an area with ongoing malaria transmission. The specific focus is on patients from nonendemic areas who plan on travel for a finite period to an area where malaria is endemic.

cGAS-mediated control of blood-stage malaria promotes Plasmodium-specific germinal center responses

Sensing of pathogens by host pattern recognition receptors is essential for activating the immune response during infection. We used a nonlethal murine model of malaria (Plasmodium yoelii 17XNL) to assess the contribution of the pattern recognition receptor cyclic GMP-AMP synthase (cGAS) to the development of humoral immunity. Despite previous reports suggesting a critical, intrinsic role for cGAS in early B cell responses, cGAS-deficient (cGAS-/-) mice had no defect in the early expansion or differentiation of Plasmodium-specific B cells. As the infection proceeded, however, cGAS-/- mice exhibited higher parasite burdens and aberrant germinal center and memory B cell formation when compared with littermate controls. Antimalarial drugs were used to further demonstrate that the disrupted humoral response was not B cell intrinsic but instead was a secondary effect of a loss of parasite control. These findings therefore demonstrate that cGAS-mediated innate-sensing contributes to parasite control but is not intrinsically required for the development of humoral immunity. Our findings highlight the need to consider the indirect effects of pathogen burden in investigations examining how the innate immune system affects the adaptive immune response.