Session: 243. Bacterial Diagnostics, Saturday, 12:15-1:30 p.m.
Rickettsia typhi typically causes a non-specific 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.
Karius Test results from the prior two 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 > 1000 organisms. Organisms present above a statistical threshold are reported. Chart review was conducted on the cases of R. typhi identified by the Karius Test.
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 was 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 was available were treated with doxycyline.
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.
Fernando Centeno– Medical Student, Baylor College of Medicine, Houston, TX
Asim Ahmed– Medical Director, Karius, Inc, Redwood City, CA
David Hong– Vice President, Medical Affairs and Clinical Development, Karius, Inc., Redwood City, CA
Sudeb Dalai– Medical Director, Karius, Inc, Redwood City, CA
Laila Woc-Colburn– Associate Professor, Director of Medical Education, Medical Director, ID Faculty Group Practice, Baylor College of Medicine, Houston, TX