P-920. Free-living Ameba Infections Diagnosed by Cell-free DNA Blood Testing – United States, 2018-2023

Abstract Background Free-living amebae (FLA) including Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri live in soil and water worldwide and cause severe infections in humans. Approximately 15 people in the United States are infected by FLA each year; most do not survive. Early diagnosis and treatment improve outcomes. Targeted testing options for FLA require tissue or cerebrospinal fluid (CSF) and are offered at < 5 laboratories in the U.S., making it challenging to diagnose infections quickly and non-invasively. Detection of FLA infections via cell-free DNA testing of blood (Karius Test®) has increased in recent years. Methods The Centers for Disease Control and Prevention (CDC) maintains a database of confirmed FLA cases reported through the CDC FLA Clinical Consultation Service or national surveillance efforts. This database was used to identify and describe cases in which a Karius Test® first detected an FLA infection. Results In 2018-2023, 9 U.S. FLA infections were diagnosed with Karius Test® and reported to CDC, including 4 Acanthamoeba, 4 Balamuthia, and 1 Naegleria case. These represent 10% of FLA cases reported to CDC in this timeframe (9/93). Four of these cases were reported in 2023 (22% of FLA cases in 2023), an increase over previous years. FLA had not been suspected in 8/9 cases before receiving results. Eight patients presented with meningitis or encephalitis; 1 had only skin findings. FLA diagnoses were subsequently confirmed by other methods in 7/7 cases for which tissue or CSF was available. Duration from hospitalization or symptom onset to Karius Test® result was 5-14 days. One patient was diagnosed postmortem; the others were initiated on anti-amebic therapy. No patients ultimately survived, though 3 patients were treated for several weeks. Conclusion Cell-free DNA testing (Karius Test®) of blood is increasingly being used to diagnose FLA infections. Nearly all patients described were diagnosed by Karius Tests® before FLA infections had been suspected. Early diagnosis can allow early treatment, inform clinical decision-making, and contribute to the further understanding of FLA infections through surveillance. In patients with suspected FLA infections or encephalitis of unknown etiology, Karius Test® may be useful, particularly when tissue or CSF is not available. Disclosures All Authors: No reported disclosures