Plasma cell-free DNA testing in diagnosing Listeria rhombencephalitis in a CSF PCR-negative patient: a case report.

Background: The aetiologic identification of central nervous infections, including Listeria, remains challenging as most pathogens are not identified in meningoencephalitis cases despite advances in molecular diagnostics. Plasma next-generation sequencing (NGS) has exciting potential in the clinical setting due to the broad detection range and non-invasive testing approach. Case presentation: A 59-year-old non-binary and healthy individual presented with fever and vomiting. They were found to have nystagmus, dysphagia and hypophonia. Their course was complicated by progressive encephalopathy, thus requiring intubation. Serial brain MRIs performed days apart demonstrated rapidly progressive cerebral oedema and expanding ring-enhancing brain abscesses. Extensive diagnostic testing was unrevealing, which included multiple PCR cerebrospinal fluid (CSF) infectious tests and both dedicated serum and CSF serological testing for neuroinflammatory aetiologies. Given the rapid and significant clinical deterioration, the patient underwent plasma NGS testing and a brain biopsy. Listeria was ultimately detected with NGS multiple days before the biopsy results were available. Conclusions: This is one of the first reported cases of diagnosing Listeria in the central nervous system with plasma NGS, rather than CSF, testing. This case describes the potential to improve a patient's clinical outcomes using plasma NGS in situations of diagnostic uncertainty or high-risk biopsies.