Use of Advanced Diagnostics for Timely Identification of Travel-associated Leptospira santarosai Infection in Four Adolescents Through Plasma Microbial Cell-free DNA Sequencing With the Karius Test

BACKGROUND

Leptospirosis is an important zoonotic infection worldwide. Diagnosis of leptospirosis is challenging given its nonspecific clinical symptoms that overlap with other acute febrile illnesses and limitations with conventional diagnostic testing. Alternative advanced diagnostics, such as microbial cell-free DNA (mcfDNA), are increasingly being used to aid in the diagnosis of infections and can be applied to pathogens with public health importance such as Leptospira , a nationally notifiable disease.

METHODS

The Karius Test uses plasma mcfDNA sequencing to detect and quantify DNA-based pathogens. This test offered through the Karius lab detected 4 cases of Leptospira santarosai during a 5-month period across the United States in 2021 and were clinically reviewed.

RESULTS

In our case series, 4 adolescents with recent travel to Central America (Costa Rica, n = 3 and Belize, n = 1) from April to August 2021 were diagnosed with leptospirosis. While a large workup was performed in all cases, mcfDNA testing was the first test to detect L. santarosai as the microbiological diagnosis in all cases.

CONCLUSIONS

Results of the Karius Test enabled rapid, noninvasive diagnosis of leptospirosis allowing for targeted therapy. Use of mcfDNA can be utilized for diagnosis of pathogens where conventional testing is challenging or limited. This in turn can enable quick diagnosis for targeted treatment and potentially aid in supporting case definitions of reportable diseases of public health concern.

546. Resolution of a Cluster of Travel-Associated Leptospira santarosai Infection in Four Adolescents by Plasma Microbial Cell-Free DNA Detection with the Karius Test®

Background

Leptospira can cause severe infections but their diagnosis can be challenging. Diagnosis is limited by nonspecific, protean clinical symptoms; the fastidious nature of Leptospira; and poor specificity, sensitivity, and long turnaround times of serologic testing. Given these limitations, identifying epidemiological clusters of leptospirosis can be challenging. Rapid, non-invasive diagnosis of leptospirosis by microbial cell-free DNA (mcfDNA) next-generation sequencing (NGS) of plasma offers a means to overcome these limitations in individual diagnosis and public health epidemiological surveillance.

Methods

The Karius Test® (KT) detects and quantifies mcfDNA in molecules/µL (MPM) in plasma from a curated genomic database of >20,000 organisms reporting on >1000 pathogens through the Karius CLIA certified/CAP accredited lab (Redwood City, CA). Four KT detections of Leptospira santarosai were identified April - August 2021 across four independent United States institutions. Clinical review was performed by pediatric infectious diseases consultants.

Results

KT detected L. santarosai in four adolescents with travel to Costa Rica or Belize (Table). A broad work-up was performed in all patients. McfDNA NGS was the first test to identify L. santarosai as the diagnosis in all cases with an average time to diagnosis of 2.5+/- 0.58 days from sample collection, enabling narrowed, targeted antibiotic treatment. L. santarosai mcfDNA was positive in three patients despite pretreatment; average L. santarosai mcfDNA concentration was 173.5+/- 186.1 MPM. Leptospira serologies were confirmatory in three patients, potential epidemiological exposures were identified in all patients, and all recovered.

Conclusion

KT enabled rapid, non-invasive diagnosis of diverse manifestations of L. santarosai against a competing broad differential in four adolescent travelers returning from Costa Rica or Belize. The resolution of the etiology of this cluster of patients with leptospirosis demonstrates the potential utility of mcfDNA to quickly diagnose and support case definitions of reportable diseases and the potential importance of plasma mcfDNA NGS in public health and epidemiological surveillance.

Disclosures

Asim A. Ahmed, MD, Karius: Employee|Karius: Stocks/Bonds Sara Saporta-Keating, MS, MD, Pfizer: Co-investigator in investigator-driven study sponsored by Pfizer.