Citations

Abstract Background Trimethoprim-sulfamethoxazole (TS) prophylaxis can prevent Pneumocystis jirovecii (PCP) and other opportunistic infections (OIs), such as intestinal protozoa, Toxoplasma, Listeria, and Nocardia. We sought to assess the frequency, causative factors, and impact of early TS discontinuation in abdominal SOT recipients. Methods This is a single-center, retrospective cohort study of adult abdominal SOT recipients at Mayo Clinic Arizona between 1/1/2021 and 6/30/2023. Objectives included the rate and reasons behind early TS discontinuation and whether TS prophylaxis was reinitiated. Early discontinuation was defined as cessation of TS prophylaxis within 6 months post-transplant for ≥7 days. Secondary outcomes included median duration of therapy, alternative prophylactic agent utilized, and incidence of TS preventable OI. Patients were excluded if they had no TS ordered, died <180 days from transplant, or received a thoracic organ transplant. Results 942 abdominal SOT recipients were identified. Thus far 171 liver, 11 Kidney, and 29 liver/kidney have been reviewed and included in the current analysis. TS was discontinued early in 60 (28%) patients. Predominant reasons for discontinuation were hyperkalemia (45%), cytopenias (17%), and acute kidney injury (15%). Allergy was the indication for discontinuation in 1 patient. Median duration of TS before discontinuation was 39 days (IQR 66). TS was not resumed in 78% of cases. The predominant reason for non-resumption was alternative prophylaxis with no clear intent to rechallenge TS (70%). The main discontinuation reason had resolved in 70% that stopped due to cytopenias, 67% that stopped due to liver injury, and 96% that stopped due to hyperkalemia. Alternative prophylaxis included pentamidine (50%), dapsone (32%), atovaquone (5%), none (13%). No patients developed PCP or other TS preventable OI during 9-month follow-up post-SOT. Conclusion TS is discontinued prematurely in a significant number of SOT recipients and is often not resumed despite resolution of the offending cause. Given its proven track record in preventing several OIs in SOT recipients, providers should document reason(s) for TS discontinuation and consider resumption of TS after reasons for discontinuation resolve. Disclosures All Authors: No reported disclosures

Abstract Background Phage therapy is being evaluated to treat bacterial infections. Host-related factors that might abrogate phage efficacy remain incompletely characterized. Phage aggregation has been hypothesized to protect phages in harsh environments. Herein, effects of immunized rabbit sera on phage aggregation were assessed. Methods Three New Zealand rabbits were immunized weekly for 3 weeks by intramuscular injection of phage K. Serum samples were collected weekly at times 0, 7, 14, 21 and 28. Development of an antibody response was confirmed by ELISA. Phage K was exposed to immunized serum with or without heat-inactivated host bacterium (Staphylococcus aureus ATCC 19685) as follows. 45 µl of phage K (1010±1 plaque forming units/mL [pfu/ml]) was mixed with 5 µl immunized serum diluted 1:1000 with or without heat-inactivated bacterial host in phosphate buffered saline (PBS). After incubation, exposed phage was visualized using transmission electron microscopy (TEM, JEOL) at 80kV. Results Phage K immunization elicited a strong IgG response. Exposure to immunized serum led to a decrease in viable phage over time, abrogated by adding heat-inactivated bacteria (Fig 1). TEM imaging showed phage clustering with exposure to immunized serum (Fig 2A); clusters appeared disorganized with concomitant exposure to heat-inactivated host bacteria (Fig 2B). Exposure of phage to heat-inactivated bacteria without serum yielded evenly distributed phage, with minimal clustering (Fig 2C). Conclusion Phage K exposure elicited a neutralizing immune response associated with decreased phage survival in immunized serum, prolonged by adding heat-inactivated host bacteria. TEM imaging showed phage K clustering in different ways depending on the microenvironment encountered. Biological relevance and mechanistic underpinnings of these phenomena need further characterization. Disclosures Robin Patel, MD, a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, a: See above|MicuRx Pharmaceuticals and BIOFIRE: Grant/Research Support|PhAST, Day Zero Diagnostics, Abbott Laboratories, Sysmex, DEEPULL DIAGNOSTICS, S.L., Netflix, Oxford Nanopore Technologies and CARB-X: Advisor/Consultant|Up-to-Date and the Infectious Diseases Board Review Course.: Honoraria

Abstract Background Vascular graft infection (VGI) is a rare but serious condition. Pathogen identification can be difficult given the deep-seated nature. Microbial cell-free DNA next-generation sequencing (mcfDNA NGS) is an emerging tool in non-invasive microbiologic workup. One commercially available mcfDNA is the Karius Test (KT). There is a paucity of data regarding utility and impact of mcfDNA NGS testing in the evaluation of VGI. Methods We retrospectively evaluated adult patients who underwent KT for evaluation of VGI at our institution. Only patients who met the Management of Aortic Graft Infection Collaboration (MAGIC) classification for suspected or confirmed VGI were included. We investigated the concordance between KT and conventional microbiologic workup. Conventional workup (CW) included pathogen identification through blood cultures, peri-graft/graft cultures, or histopathology. Concordance was defined by identical pathogen identification on KT and CW. We examined the influence of the KT result on clinical management.Figure 1.KT Results for Confirmed and Suspected VGI. Results We identified 25 patients who met criteria for either suspected or confirmed VGI per the MAGIC criteria. Microbiology was undefined in 8 patients who had negative KT and negative CW. A total of 17 patients had positive workup with 6 having positive KT and negative CW, 3 having negative KT and positive CW, and 8 having both positive KT and positive CW (Table 1). KT was less likely to be positive for patients who met criteria for suspected infection (4/10; 40%) as opposed to confirmed infection (10/15; 66.67%), albeit non-significant (OR 0.33, p=0.188) (Figure 1). The KT led to antimicrobial de-escalation in 27.3% of patients with positive CW and 35.7% of patients with negative CW (Figure 2). Full concordance of KT and CW was noted in 3 patients (Table 2).Figure 2.Influence of KT on VGI cases with positive and negative conventional work-up. Treatment escalation was defined as the broadening of antimicrobial coverage due to KT results. Treatment de-escalation was defined as narrowing/discontinuation of antimicrobial coverage due to KT results. Conclusion We found that the positivity rate for KT was 56%. KT impacted management in 40% of cases. Patients with confirmed VGI had a higher likelihood of having a positive KT. KT was the only positive microbiological definitive test in one case. Further studies are needed to explore the utility and impact of KT in the workup of VGI. Disclosures All Authors: No reported disclosures

Abstract Background Chronic periprosthetic joint infection is commonly managed with two-stage exchange. Clinically, evaluation for persistent infection at the second stage of exchange may inform management. The aim of this study was to evaluate the yield of periprosthetic tissue and antimicrobial-containing cement spacer sonicate fluid cultures at the second stage of two-stage exchange surgeries. Methods Periprosthetic tissue and sonicate fluid cultures of hip and knee cement spacers removed at the second stage of two-stage exchange surgeries between January 2010 and December 2020 were studied. Two or more positive tissue cultures yielding the same organism were considered positive. For sonicate culture, ≥20 CFU/10 ml of sonicate fluid was considered positive. Persistent infection was defined by the presence of at least one of the following: intraoperative purulence, sinus tract, histopathology showing acute inflammation, or clinical signs of infection. Cement spacers were removed as part of spacer exchange if persistent infection was suspected or for insertion of a new implant if infection was not suspected. Results 172 cultures were evaluated, 69% from knees and 31% from hips. Median patient age was 64 years; 53% were men. 38/172 (22%) of cement spacers were removed as part of a spacer exchange and 134/172 (78%) for insertion of a new implant. Persistent infection was present in 49/172 (28%). 18/172 (10%) received antibiotics 2 weeks before culture, including 8/18 (44%) undergoing spacer exchange. For persistent infections, tissue and sonicate culture were positive in 11/49 and 5/49, respectively. In the 123 without persistent infection, no tissue or sonicate cultures were positive. When a new implant was placed, persistent infection was observed in 18/134 (13%), and tissue and sonicate cultures were positive in 4/18 and 1/18, respectively. When a new implant was placed (116) and no infection was found, all tissue and sonicate cultures were negative. After spacer exchange, persistent infection was present in 31/38 (81%), and tissue and sonicate cultures were positive in 8/31 and 3/31, respectively; in the 7 without infection, there were no positive cultures. Conclusion Sonication culture of cement spacers and periprosthetic tissue cultures have low sensitivities for persistent infection. Disclosures Matthew Abdel, MD, Stryker: Advisor/Consultant|Stryker: Royalties Nicholas Bedard, MD, Stryker: Advisor/Consultant Robin Patel, MD, a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, a: See above|MicuRx Pharmaceuticals and BIOFIRE: Grant/Research Support|PhAST, Day Zero Diagnostics, Abbott Laboratories, Sysmex, DEEPULL DIAGNOSTICS, S.L., Netflix, Oxford Nanopore Technologies and CARB-X: Advisor/Consultant|Up-to-Date and the Infectious Diseases Board Review Course.: Honoraria

Abstract Background With progressive understanding of the natural history of COVID-19 and accumulation of knowledge on clinical management, treatment guidelines recommended several options including remdesivir (RDV), a broad-spectrum antiviral. Given the evolving nature of COVID-19, it is critical to capture the totality of scientific evidence to inform clinical decision making. We conducted a systematic literature review (SLR) to summarize the mortality endpoint for RDV among hospitalized adults throughout COVID-19 eras and contrasted with evidence informing treatment recommendations in clinical guidelines. Methods We systematically searched MEDLINE, Embase and Cochrane Library databases for interventional and observational studies examining RDV efficacy. Clinical trial registries, Cochrane COVID-19 Study Register, and conference abstracts were hand-searched (Fig1). Case reports and case studies were excluded. A review of most recent RDV recommendations across guidelines was conducted. Results From Dec ’19 to Dec ’22, 123 relevant publications were identified. In ’23, the evidence grew significantly, with 70 new publications. In total, 193 publications were evaluated, and 122 unique studies were included. While early randomized clinical trials (RCT) and small sample size observational studies did not universally demonstrate a significant difference in mortality in all severity groups of RDV-treated patients, real-world studies with larger sample sizes showed a significant impact across disease severity levels, regardless of COVID-19 era (Table1). Guideline recommendations for COVID-19 treatment with RDV are based on early RCTs (Table2) and most have not been updated (Fig2). Conclusion Our comprehensive evaluation of scientific literature indicates that evidence of RDV impact on mortality in hospitalized COVID-19 patients continued to grow and cover full range of disease severity. Guideline recommendations have not evolved in parallel which may explain differing recommendations in certain subgroups (e.g. IMV/ECMO). To assure that providers in the hospital setting are aware of and deploy evidence-based optimal care for patients with COVID-19, recommendations should rely on current evidence, including real-world data. Disclosures Essy Mozaffari, PharmD, MPH, MBA, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Michele Bartoletti, MD, PhD, Advan pharma: Advisor/Consultant|Advan pharma: Honoraria|Biomereux: Honoraria|Gilead: Advisor/Consultant|Gilead: Honoraria|Infectopharma: Advisor/Consultant|Msd: Advisor/Consultant|Msd: Grant/Research Support|Msd: Honoraria|Pfizer: Honoraria Alpesh N. Amin, MD, MBA, Alexion: Advisor/Consultant|Aseptiscope: Advisor/Consultant|AstraZeneca: Advisor/Consultant|Bayer: Advisor/Consultant|Dexcom: Advisor/Consultant|Eli Lilly: Advisor/Consultant|Ferring: Advisor/Consultant|Gilead: Advisor/Consultant|GSK: Advisor/Consultant|Heartrite: Advisor/Consultant|Nova Nordisk: Advisor/Consultant|Pfizer: Advisor/Consultant|Renibus: Advisor/Consultant|Reprieve: Advisor/Consultant|Salix: Advisor/Consultant|Seres: Advisor/Consultant|Spero: Advisor/Consultant Yohei Doi, MD, PhD, bioMerieux: Lecture fees|Entasis: Grant/Research Support|Fujifilm: Advisor/Consultant|Gilead Sciences: Advisor/Consultant|GSK: Advisor/Consultant|KANTO CHEMICAL CO.,INC.: Grant/Research Support|KANTO CHEMICAL CO.,INC.: Patent for genotyping kit|MeijiSeika Pharma: Advisor/Consultant|Moderna: Advisor/Consultant|MSD: Lecture fees|Pfizer: Advisor/Consultant|Shionogi & Co., Ltd.: Grant/Research Support|Shionogi & Co., Ltd.: Lecture fees Paul LOUBET, MD, PhD, Astrazeneca: Advisor/Consultant|Gilead: Advisor/Consultant|Moderna: Advisor/Consultant|Pfizer: Advisor/Consultant Christina G. Rivera (O'Connor), Pharm.D, Gilead Sciences: Board Member Michael Roshon, MD/PhD, MD/PhD, Gilead: Honoraria Thomas F. Oppelt, PharmD, BCPS, Gilead Sciences, Inc: I am an employee of Gilead Sciences, Inc|Gilead Sciences, Inc: Stocks/Bonds (Public Company) Mel Chiang, Ph.D., Gilead Sciences: I am an employee of Gilead Sciences|Gilead Sciences: Stocks/Bonds (Public Company)

Abstract Background Recurrent Clostridioides difficile infection (rCDI) is common, with a prior CDI linked to a risk of up to 65% for subsequent recurrences. Fecal microbiota, live-jslm (RBL) is the first microbiota-based product approved in the US for the prevention of rCDI in adult patients following antibiotic treatment for rCDI. This study reports the characteristics and outcomes of patients with rCDI who were administered RBL in a real-world setting. Methods Adult patients with rCDI who received RBL either at home or a clinic from healthcare professionals affiliated with a home-care provider network were included. Patients were required to have at least 8 weeks of follow-up after RBL administration, with CDI recurrence status assessed at week 8. Patient demographics, clinical characteristics, administration setting, prior medication use, and prior healthcare resource utilization were collected. The primary outcome was CDI recurrence within 8 weeks post-RBL administration. All variables were summarized descriptively using median and interquartile range (IQR) for continuous outcomes and count and percentage for categorical variables. Results Between July 2023 and March 2024, 136 patients with rCDI received RBL, of whom 73 had at least 8-week follow up and reported CDI recurrence status at week 8. Patients had a median age of 63.0 years (IQR = 47.0, 76.0), 68.5% were female, most (74.0%) had ≥ 3 prior CDI recurrences, 5.5% had received fecal microbiota transplant, and 9.6% had received bezlotoxumab (Table). One third of patients (32.9%) had previously been hospitalized and 38.4% had prior emergency room visits due to CDI. Most patients were previously treated with antibiotics for rCDI: 39.7% with vancomycin only, 11.0% with fidaxomicin only, and 43.8% with both vancomycin and fidaxomicin. All patients, except for 4 with missing data, received RBL 24-72 hours post-antibiotics. Most patients (83.6%) received RBL at home. At week 8, the overall treatment success rate (no CDI recurrence) was 87.7% (87.3% [62/71] in RBL-naïve; 100% [2/2] in previously RBL-treated). Conclusion RBL was effective in preventing recurrence of CDI at 8 weeks in a real-world setting, where most patients received RBL at home. These results suggest that RBL is effective in managing rCDI, including in a home care setting. Disclosures Sahil Khanna, MBBS, MS, Ferring Pharmaceuticals, Inc.: Grant/Research Support|Finch: Grant/Research Support|Immuron: Advisor/Consultant|Niche: Advisor/Consultant|Pfizer: Grant/Research Support|Probio Tech, LLC: Advisor/Consultant|Seres Therapeutics: Grant/Research Support|Takeda: Advisor/Consultant|Vedanta: Grant/Research Support Sanghyuk Seo, PharmD, MS, Ferring Pharmaceuticals, Inc.: Employee Min Yang, MD, PhD, Analysis Group, Inc.: I am an employee of Analysis Group, Inc., which has received consulting fees from Ferring for the conduct of this study. Viviana García-Horton, PhD, Analysis Group, Inc.: I am an employee of Analysis Group, Inc., which has received consulting fees from Ferring for the conduct of this study. Yipeng Gao, PhD, Analysis Group, Inc.: I am an employee of Analysis Group, Inc., which has received consulting fees from Ferring for the conduct of this study. Hannah Kim, PhD, Analysis Group, Inc.: I am an employee of Analysis Group, Inc., which has received consulting fees from Ferring for the conduct of this study. Loren Ormenaj, n/a, Analysis Group, Inc.: I am an employee of Analysis Group, Inc., which has receivedconsulting fees from Ferring for the conduct of this study. Amy Guo, PhD, Ferring Pharmaceuticals, Inc.: Employee

Abstract Background The Rochester Epidemiology Project (REP) has been used to examine numerous infectious and non-infectious entities in a population-based approach in Olmsted County, Minnesota. To further investigate patterns of enterococcal bloodstream infection (BSI), we used the Expanded Rochester Epidemiology Project (E-REP) to include additional surrounding counties to conduct a retrospective population-based study of adult patients who developed enterococcal BSI, with or without infective endocarditis (IE). Methods The E-REP population under study included eight counties in southeastern Minnesota (including Olmsted County), representing a total population of over 250,000 individuals. Adults (age ≥ 18 years) diagnosed with an initial episode of enterococcal BSI with or without enterococcal IE between January 1, 2018 and December 31, 2022 were included; patients with either polymicrobial BSI with enterococci or a previous bout of enterococcal BSI before the study period were excluded. Cases of enterococcal BSI and IE were identified using ICD-10 codes and underwent complete medical record review. Patient characteristics, microbiology, antibiotic regimens, infectious complications, and outcomes were collected. Results A total of 113 cases of enterococcal BSI were identified over the five-year study period. The age- and sex-adjusted incidence rate of enterococcal BSI was 6.9 per 100,000 person-years, with a significantly higher rate among males than females (Figure 1). BSI incidence rate varied by age, with patients 80 years or older having the highest incidence rate (Figures 1 and 2). Twenty-two cases of enterococcal IE were identified, yielding an overall IE prevalence of 20.8% (Figure 3). The cumulative mortality rate at 12 months was high at 41.7% (Figure 3). Five patients (4.4%) had a relapse of enterococcal BSI, defined as recurrence of BSI after negative follow-up blood cultures and within 12 weeks of the initial BSI. Conclusion This is the first population-based investigation that has focused on the epidemiology and clinical profile of patients with enterococcal BSI and complicating IE in a US population. This included an IE prevalence of 20.8%, which should be considered when evaluating and managing patients with enterococcal BSI. Disclosures Larry M. Baddour, MD, UpToDate, Inc.: Royalty payments (authorship duties).

Abstract Background Treatment of high risk AmpC-producing Enterobacterales bloodstream infections (BSIs) is challenging due to the posibility of development of antibiotic resistance during treatment. The aim of this study was to analyze the impact of antimicrobial stewardship activity and IDSA guidelines adequacy in patients with high risk AmpC-producing Enterobacterales BSIs. Methods Patients with Citrobacter spp, Enterobacter spp and Klebsiella aerogenes BSIs were included between June 2019-March 2024. Outcomes of death and relapse of infection at 30 days were assessed. Adequacy of definitive antimicrobial treatment according to IDSA guidelines was evaluated. The impact of antimicrobial stewardship activity in treatment adequacy and outcome was analyzed. Analysis was performed using SPSS version 25. Results 2049 BSIs were evaluated and 67 were finally included. 80% were monomicrobial. Median patient age was 74 years, 73% were male. The most frequent microorganism isolated was Enterobacter cloacae (55%). 50% were nosocomial and the most frequent origen was biliary tract (35,8%). 35% met sepsis criteria. 30% of cases presented cefotaxim resistance. Empiric and definitive antibiotic treatment was prescribed according IDSA guidelinesi n 34% and 91% of cases, respectively.. Death at 30 days was 6% and a combination outcome of death and relapse of infection at 30 days was 11,9%. Definitive antibiotic treatment adequacy according to IDSA guidelines was associated with lower mortality and relapse at 30 days (OR 0,04; IC95 0,003-0,6; P=0,02). Antimicrobial stewardship team did an intervention in 34% cases. This intervention was associated with a trend toward of lower mortality and relapse (4% vs 15%, P=0,2), a trend toward of higher IDSA guidelines adequacy (100% vs 86%, P=0,08), and a higher switch to oral treatment (78% vs 52%; P=0,03). Conclusion Adequacy of definitive antimicrobial treatment in high risk AmpC producing Enterobacterales BSIs according to IDSA guidelines was associated with a better outcome. Antimicrobial stewardship is desired for management of these patients. Disclosures All Authors: No reported disclosures

Abstract Background Wound biofilm infections impact ∼2% of the United States and at-risk individuals often have underlying morbidities such as diabetes. Antibiotics and topical approaches like debridement or silver dressings have had limited success, underscoring a need for strategies that efficiently target pathogens in wound beds. Methods We developed a hydrogen peroxide (H2O2) generating electrochemical bandage (e-bandage) composed of carbon fabric electrodes separated by cotton fabric with an Ag/AgCl reference electrode (RE) placed between cotton fabric layers. The e-bandage is controlled by a wearable micropotentiostat (MP); H2O2 is generated by O2 + 2H++ 2e- → H2O2. O2 is dissolved on a primary working electrode with negative polarity compared to the RE while a positively polarized secondary counter electrode generates H+ and e-. The H2O2 e-bandage/MP device has in vitro activity against mono- and dual-species bacterial and fungal biofilms. We showed that the H2O2 e-bandage decreased the burden of methicillin-resistant Staphylococcus aureus and/or Pseudomonas aeruginosa with difficult-to-treat resistance in a murine wound infection model. Given this, we initiated a H2O2 e-bandage safety assessment on healthy human skin. Here, testing of a non-polarized, circular (2 cm diameter) device pre-loaded with biocompatible hydrogel containing 0.9% NaCl is reported. Sterilized e-bandages assessed in a shelf-life study retained activity for two weeks. Adults with intact forearm skin were then recruited to the Clinical Research Trials Unit at the Mayo Clinic. Consented individuals had a non-polarized e-bandage covered by Tegaderm placed on their forearm. A MP enclosed in a biocompatible case was connected to the e-bandage and secured using skin tape. One day later, the device was removed and a follow-up phone call made six days later to assess for adverse effects. Results Three volunteers wearing a non-polarized H2O2 e-bandage experienced no discomfort, irritation, allergic reaction, or skin discoloration after device removal and seven days post device placement. Conclusion These preliminary studies combined with the previously performed murine bacterial biofilms work support further studies of this novel device for treating wound infections caused by antimicrobial resistant pathogens. Disclosures Robin Patel, MD, a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, a: See above|MicuRx Pharmaceuticals and BIOFIRE: Grant/Research Support|PhAST, Day Zero Diagnostics, Abbott Laboratories, Sysmex, DEEPULL DIAGNOSTICS, S.L., Netflix, Oxford Nanopore Technologies and CARB-X: Advisor/Consultant|Up-to-Date and the Infectious Diseases Board Review Course.: Honoraria

Abstract Background Invasive mold infections (IMI) lead to significant morbidity and mortality in patients with hematologic malignancies. We provide patients deemed at higher risk mold active prophylaxis but still observe breakthrough IMIs. The purpose of this study was to evaluate risk factors associated with these breakthrough infections. Methods We conducted a retrospective cohort study of adult hematologic patients at 3 tertiary care medical centers from November 19, 2011 - August 6, 2021. Only IMI cases defined as proven or probable per EORTC/MSG criteria were included. Patients with IMIs who received a minimum of 7 days of mold active prophylaxis were classified as breakthrough infection. We performed logistical regression analysis to identify risk factors associated with breakthrough IMI. Results Majority of cases were probable IMIs, with 16 (28.6%) and 25 (15.7%) proven cases amongst breakthrough and non-breakthrough IMIs, respectively. Many variables indicative of weakened host immune system, including neutropenia and hypogammaglobulinemia, were associated with breakthrough IMIs, albeit not statistically significant (Table 1). Multivariate analysis revealed history of AML (OR 4.20, 95% CI 2.03-8.88; p < 0.001) and receipt of HCT (OR 3.37, 95% CI 1.46-8.11; p = 0.003) to be independent host risk factors for breakthrough IMI. Of all the pathogens, Fusarium (OR 4.38, 95% CI 1.56-12.56; p = 0.005) and Mucorales (OR 5.59, 95% CI 2.11-15.61; p < 0.001) were significantly likely to lead to breakthrough IMIs. 26 (47.3%) of the breakthrough IMIs were on appropriately dosed prophylaxis at the time of infection, with only 9 (16.4%) found to be subtherapeutic (Table 2). Overall, mortality was slightly higher amongst the breakthrough IMIs (51.8% vs 45.9%) but not significantly different (Figure 1). Conclusion In our cohort of probable/proven IMIs, we did not observe any significant difference in mortality between patients with breakthrough IMIs and those not on mold active prophylaxis. Even with appropriate prophylactic dosing, breakthrough infections occurred, irrespective of agent. Our study demonstrates that host risk factors and the causative pathogen are clinically more pertinent than the prophylaxis regimen in breakthrough IMIs. Disclosures Paschalis Vergidis, MD, MSc, AbbVie: Advisor/Consultant|Ansun Biopharma: Grant/Research Support|Cidara Therapeutics: Grant/Research Support|F2G: Grant/Research Support|Scynexis: Advisor/Consultant|Scynexis: Grant/Research Support