Abstract Introduction Escherichia coli meningitis is primarily a neonatal disease and is exceedingly rare in adults, particularly in immunocompetent individuals. Adult cases are typically associated with severe immunosuppression, neurosurgical procedures, or trauma. We report an unusual case of E. coli K1 meningitis in an adult with type 1 diabetes and MGUS, complicated by hypoglycemic brain injury. Case Presentation A 37-year-old woman with type 1 diabetes mellitus (A1c 7% in 8/2025) with poor glycemic control, hypertension, asthma, iron deficiency anemia, capillary leak syndrome, and MGUS was found unresponsive at home after seizure-like activity. Her mother reported last known well at 14:00 on 9/18/25. She was hypoglycemic (CBG 30 mg/dL) and unresponsive to glucagon; EMS administered D50 with minimal effect. On arrival to the ED, she was obtunded (GCS 6), drooling, and grunting, requiring intubation. Initial labs showed WBC 31 K/µL (peak 48 K), lactic acid 3.2 mmol/L, and anion gap metabolic acidosis. She was afebrile. CT head demonstrated loss of gray-white differentiation and sulcal effacement consistent with anoxic encephalopathy. MRI brain revealed mild scattered T2 hyperintensities suggestive of chronic microvascular or post-inflammatory change. Lumbar puncture revealed mild neutrophilic pleocytosis (WBC 10), protein 18 mg/dL, and glucose 171 mg/dL. The meningitis/encephalitis PCR panel was positive for E. coli K1; cryptococcal antigen was negative. She was treated with vancomycin, ampicillin, and ceftriaxone, later narrowed to meropenem for 10 days. She was extubated on hospital day 5 with improving mentation and normalization of leukocytosis (36 → 19 K). Discussion Adult E. coli meningitis is rare, and E. coli K1 infection in this population is exceptional. The patient’s diabetes and MGUS may have contributed to subtle immune dysfunction, predisposing to infection. The positive PCR result despite near-normal CSF indices raises concern for potential false positives or early-stage infection. This case underscores the importance of interpreting molecular testing in the clinical context. Concurrent hypoglycemic brain injury further complicated the diagnostic picture. Empiric broad-spectrum antimicrobial coverage was appropriate and led to recovery. Conclusion This case highlights that E. coli K1 meningitis can occur in adults with mild immune dysregulation. Clinicians should correlate PCR-based results with clinical and CSF findings. In diabetic patients presenting with altered mental status, both metabolic and infectious etiologies should be promptly considered to guide appropriate management. This abstract is funded by: None
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