645. Rapid Diagnosis of Disseminated Mycobacterium kansasii infection in Renal Transplant Recipients Using Plasma Microbial Cell Free DNA Next Generation Sequencing

Abstract Background Disseminated Mycobacterium kansasii infection is rare in kidney transplant recipients. The diagnosis may not be suspected readily due to non-specific clinical presentation. The diagnosis and treatment can be further delayed due to poor sensitivity of culture (especially of extra-pulmonary sites) and slow growth in culture media. Accurate and rapid diagnosis of disseminated M. kansasii infections in transplant recipients is important for antimicrobial management. Methods Two cases of disseminated M. kansasii infections with unusual presentation in which rapid diagnosis was made using the Karius test (KT) are presented. The KT 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 reads are removed, and remaining sequences are aligned to a curated database of >1400 organisms. Organisms present above a statistical threshold are reported. Results Case 1: A 31-year female kidney transplant recipient presented with a thyroglossal duct cyst, as well as swelling of her right metacarpophalangeal joint and left 3rd finger. AFB culture of the thyroglossal cyst aspiration done on post admission day (PAD) 2 took 27 days to be identified as M. kansasii (on PAD 29) whereas plasma sent for KT on PAD 5 reported a positive test for M. kansasii at 284 molecules/microliter (MPM) in 4 days (on PAD 9). Case 2: A 59-year male kidney transplant recipient presented with generalized weakness, arthralgia, pericardial effusion, cytopenia, weight loss and intermittent fevers. Plasma sent for KT on PAD 12 was reported positive for M. kansasii at 1314 MPM in 3 days (on PAD 15). PET CT done simultaneously was consistent with an infection of an old AV graft in the left upper extremity. The AFB culture of the resected graft was confirmed as M. kansasii in 22 days on PAD 36. After the KT was available (before confirmation of M. kansasii on culture), the first patient underwent modification of empiric treatment and the second patient was started on specific treatment for M. kansasii. Table of M. kansasii cases Rapid diagnosis of disseminated M. kansasii infection Conclusion Open-ended NGS plasma testing for mcfDNA identified disseminated M kansasii infection much earlier than standard microbiology and thus helped in initiation and modification of pathogen directed treatment. Disclosures All Authors: No reported disclosures


Rapid Diagnosis of Disseminated Mycobacterium kansasii infection in Renal
Background. Disseminated Mycobacterium kansasii infection is rare in kidney transplant recipients. The diagnosis may not be suspected readily due to non-specific clinical presentation. The diagnosis and treatment can be further delayed due to poor sensitivity of culture (especially of extra-pulmonary sites) and slow growth in culture media. Accurate and rapid diagnosis of disseminated M. kansasii infections in transplant recipients is important for antimicrobial management.
Methods. Two cases of disseminated M. kansasii infections with unusual presentation in which rapid diagnosis was made using the Karius test (KT) are presented. The KT 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 reads are removed, and remaining sequences are aligned to a curated database of >1400 organisms. Organisms present above a statistical threshold are reported.
Results. Case 1: A 31-year female kidney transplant recipient presented with a thyroglossal duct cyst, as well as swelling of her right metacarpophalangeal joint and left 3rd finger. AFB culture of the thyroglossal cyst aspiration done on post admission day (PAD) 2 took 27 days to be identified as M. kansasii (on PAD 29) whereas plasma sent for KT on PAD 5 reported a positive test for M. kansasii at 284 molecules/microliter (MPM) in 4 days (on PAD 9). Case 2: A 59-year male kidney transplant recipient presented with generalized weakness, arthralgia, pericardial effusion, cytopenia, weight loss and intermittent fevers. Plasma sent for KT on PAD 12 was reported positive for M. kansasii at 1314 MPM in 3 days (on PAD 15). PET CT done simultaneously was consistent with an infection of an old AV graft in the left upper extremity. The AFB culture of the resected graft was confirmed as M. kansasii in 22 days on PAD 36. After the KT was available (before confirmation of M. kansasii on culture), the first patient underwent modification of empiric treatment and the second patient was started on specific treatment for M. kansasii. Background. The American Academy of Pediatrics recommends tuberculin skin tests (TSTs) or interferon gamma release assays (IGRAs) to test for tuberculosis (TB) infection in children ≥2 years old, and prioritizes IGRA testing in Bacille Calmette-Guérin vaccine recipients due to cross-reactivity. TSTs require a return visit, which frequently results in loss to follow up. Growing evidence supports accuracy of IGRA testing in pediatric patients, including young children, leading to calls for preferential use of IGRA over TST. We sought to evaluate trends in IGRA use in children over time.
Methods. We identified all TB infection tests conducted in children 5-17 years old at 2 academic medical systems in Boston from October 2015-January 2021. TSTs were identified using medication administration records, and IGRAs were identified using laboratory records. We computed the proportion of tests per month that were IGRA and TST. We used Pearson correlation to determine the association between month of testing and proportion of tests that were IGRAs.
Results. 21,471 TB infection tests were obtained from 16,778 patients during our timeframe. Median age of testing was 13.4 years (IQR 9.2 -16.2 years). During the study period, there was a significant increase in the monthly proportion of TB infection tests that were IGRAs (Pearson correlation coefficient 0.92, P < 0.001). The total number of tests performed per month also increased, with seasonal increases in testing in late summer and early fall and a substantial decline in testing early in the COVID-19 pandemic.

Tuberculosis infection tests and proportion IGRA.
Total number of tuberculosis infection tests per month and proportion of tests that were interferon gamma release assays, from October 2015 -January 2021.
Conclusion. Use of IGRAs among patients age 5-17 years of age increased significantly overall and compared to TST in two large Boston healthcare systems over a 5-year period. These results suggest a shift towards blood-based TB infection testing in a low-burden setting, which may improve completion of the pediatric TB infection care cascade. Future research is needed to determine reasons for changing testing modalities, and similar patterns in other settings.
Disclosures. Gabriella S. Lamb, MD, MPH, Nothing to disclose

Investigation of Heteroresistance Among Klebsiella pneumoniae (KP) Inner Colonies (IC) Observed During Fosfomycin Disk Diffusion (DD) Testing
Morgan L. Bixby, BS 1 ; Amanda Krueger, n/a 2 ; Elizabeth B. Hirsch, PharmD 1 ; Background. During fosfomycin DD testing, the frequent occurrence of non-susceptible IC within the zone of inhibition of susceptible isolates has been noted. The Clinical & Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) have contradicting recommendations on how IC should be interpreted; CLSI recommends considering IC when interpreting DD results whereas EUCAST recommends ignoring them. This study sought to identify the susceptibility of these IC and to understand whether heteroresistance contributes to the appearance of IC during fosfomycin DD.
Methods. This study included a convenience sample of 71 KP clinical isolates from 3 United States locations. During DD testing, 58 (81.7%) of these isolates displayed at least one IC. Broth microdilution (BMD) minimal inhibitory concentration (MIC) testing, using extrapolated CLSI Escherichia coli breakpoints, was performed on a subset (n=32) of the IC in duplicate for comparison to the corresponding parent MIC values. This was followed by a modified disk elution screening test for heteroresistance to compare the frequency of low level resistance (LLR) and high level resistance (HLR) between the susceptible isolates that produced resistant IC (n=6) and those that did not produce any IC (n=3).
Results. The MIC range for the IC isolates (128 to > 1024 μg/mL) increased as compared to the parent isolates (< 2 to > 256 μg/mL) and MIC 50/90 increased from the parent (128/ > 256 μg/mL) to IC (1024/ > 1024 μg/mL) isolates. All IC isolates had a resistant MIC value vs. 46.5% of parent isolates, and over 90% of IC isolates had an MIC at least 2 dilutions higher than their corresponding parent isolate. Heteroresistance screening found all tested isolates to be positive for LLR, and 8 of 9 positive for HLR, while the one HLR-negative isolate was IC-producing.
Conclusion. IC were frequent during fosfomycin DD testing and were commonly more resistant than their corresponding KP parent isolates. A small subset of these isolates tested via a modified disk elution test displayed either LLR or HLR regardless of the absence of IC. These results call for further investigation among a larger isolate set to understand what mechanisms are responsible for the frequency of IC and their increased fosfomycin resistance.
Disclosures. All Authors: No reported disclosures