Rapid CSF Molecular Diagnosis of Listeria monocytogenes Meningoencephalitis in an Elderly Immunocompetent Patient: A Case Report

Background/Objectives: Listeria monocytogenes is an uncommon but potentially life-threatening cause of central nervous system infection, predominantly affecting older adults and immunocompromised patients. Neurolisteriosis may present with nonspecific neurological manifestations, and the absence of classical meningeal signs may delay diagnosis. We report a case of L. monocytogenes meningoencephalitis in an elderly patient without known immunosuppression, with rapid cerebrospinal fluid (CSF) molecular testing facilitating early diagnosis and appropriate antimicrobial treatment. Case presentation: A 76-year-old man with significant cardiovascular comorbidities was admitted with a 3-day history of fever, headache, nausea, vomiting, fatigue, and gait instability. He was alert on admission, with only mild meningeal signs, and initial cranial computed tomography showed no acute intracranial abnormalities. CSF analysis revealed inflammatory changes. Empirical ceftriaxone therapy was supplemented with vancomycin, followed by the initiation of intravenous ampicillin and gentamicin after molecular identification of L. monocytogenes. The diagnosis was subsequently confirmed by CSF culture, while blood cultures remained negative. Clinical and laboratory parameters improved progressively, accompanied by marked improvement in CSF findings on follow-up examination. The patient was discharged in stable condition after 18 days of hospitalization. Conclusions: Neurolisteriosis should be considered in elderly patients presenting with fever and neurological symptoms, even in the absence of overt immunosuppression or prominent meningeal signs. This case highlights the diagnostic value of rapid CSF molecular testing, particularly when blood cultures are negative and the initial clinical presentation is nonspecific. Early recognition of L. monocytogenes infection and timely initiation of targeted antimicrobial therapy are essential to improving outcomes.