648. Rapid, Non-invasive Detection of Cryptic Tularemia Using a Plasma-Based Microbial Cell-Free DNA Next-Generation Sequencing Test

Background Francisella tularensis causes severe infections and is a Category A potential bioterrorism agent but its microbiological diagnosis can be challenging. The diagnosis of tularemia is limited by non-specific protean clinical symptoms that overlap with other infectious syndromes, the fastidious nature of Francisella tularensis, along with insensitivity and poor specificity of serology. Rapid, non-invasive diagnosis of tularemia by microbial cell-free DNA (mcfDNA) next-generation sequencing (NGS) of plasma offers a means to overcome these limitations. Methods The Karius Test™ (KT) detects and quantifies mcfDNA in molecules/µL (MPM) from >1400 organisms in plasma (performed at the CLIA certified/CAP accredited Karius laboratory). KT detections of Francisella tularensis were compiled from three medical centers with clinical review by healthcare providers. Results KT detected Francisella tularensis in four patients. All were adult males in whom the diagnosis was unexpected. The most common symptoms were fever and chest pain. White blood cell count neutrophilic predominance and abnormal chest X-ray findings were found in three cases. A broad infectious disease work-up was performed with the initiation of broad spectrum empiric antibiotics in all cases. KT was the first test to identify Francisella tularensis as the microbiological diagnosis with a time to diagnosis of 2.25 days (avg) +/- 0.5 from sample collection (one day from sample receipt in all cases), enabling narrowed, targeted antibiotic treatment. Francisella tularensis mcfDNA concentration was 1772 MPM (avg) +/- 1914. KT was the only test to establish the diagnosis in two cases; tularemia serologies were confirmatory in two cases, one of which had confirmatory culture from lymph node biopsy. Three patients were diagnosed with the pneumonic form of the illness and one with a visceral glandular form. Possible epidemiological exposures were identified in all cases. Conclusion KT enabled rapid, non-invasive, plasma-based diagnosis of diverse clinical manifestations of invasive tularemia against a competing broad infectious and non-infectious differential diagnosis. Timely diagnosis enabled targeted narrowing of antibiotic therapy and successful treatment of pneumonic and glandular forms of the infection. Disclosures All Authors: No reported disclosures