2139. Rickettsia typhi Detection in Clinical Infections by the Karius Test, a Plasma Microbial Cell-free DNA Next-Generation Sequencing Test

Abstract Background Rickettsia typhi typically causes a nonspecific syndrome characterized by fever, rash, and headache but can rarely progress to severe disease. R. typhi is transmitted by the rat flea and there has been an increased incidence in Houston, TX. Establishing the diagnosis can be challenging and is often made by serological studies. Prompt therapy with doxycycline is important especially in severe disease. Methods Karius Test results from the prior 2 years (Redwood City, CA) were reviewed for detections of R. typhi. The Karius Test is a CLIA-certified/CAP-accredited next-generation sequencing (NGS) plasma test that detects microbial cell free DNA (mcfDNA). After mcfDNA is extracted and NGS performed, human sequences are removed and remaining sequences are aligned to a curated pathogen database of >1,000 organisms. Organisms present above a statistical threshold are reported. Chart review was conducted on the cases of R. typhi identified by the Karius Test. Results The Karius Test detected R. typhi in 6 adult patients, 4 women and 2 men, from a medical center in Houston, TX. In 2 patients, R. typhi mcfDNA was present in the raw sequencing data but at an abundance below validated statistical thresholds. R. typhi mcfDNA was not found in negative controls run simultaneously with the samples. All patients presented with fever, 4 presented with headache, 3 presented with gastrointestinal symptoms, 3 developed rash, one presented with hypotension. Laboratory data were available for 5 patients. Four patients developed thrombocytopenia, 5 had anemia, 4 patients had WBC < 5, 4 had transaminase elevation and 3 developed hyponatremia. 3 out of 5 had R. typhi serologies sent; all 3 were positive (including two of the patients with R. typhi mcfDNA levels below threshold). In the two other patients the Karius test was the means of establishing the diagnosis. 3 out of 5 patients where data were available were treated with doxycyline. Conclusion The Karius test was able to detect R. typhi in a cluster of 6 patients in one medical center in Houston, TX. NGS for mcfDNA offers a rapid means of detecting R. typhi infection. Accurate, rapid diagnosis of R. typhi has important public health implications given its vector-borne mechanism of transmission. Disclosures All authors: No reported disclosures.