To describe the first case of spontaneous Serratia marcescens monoinfection in CSF in an adult with intravenous drug abuse.  

We report this case of a 53 year old male with active intravenous drug use (IVDU) and no previous neurosurgical procedures, who presented with altered mental status and gait instability for 2 weeks along with headache, nausea and vomiting for 2 months. CT scan revealed hydrocephalus requiring urgent placement of an intraventricular catheter.  Initial CSF analysis revealed glucose of <10mg/dl, protein of 107mg/dl, WBC count of 67cells/mm³, and RBC count of 125cells/mm3. Three separate CSF cultures drawn at 48 hour intervals each grew Serratia marcescens. Metagenomic next generation sequencing from CSF confirmed the presence of Serratia without any co-infection.  MRI of the cervical spine was concerning for C1-C2 septic arthritis for which he underwent surgery but cultures were negative. Blood cultures remained negative throughout.  Patient received intravenous antibiotics that improved his clinical condition. Intrathecal gentamycin was later added for continued inflammation in CSF, which then resolved.  

Serratia marcescens is an extremely rare cause of acute meningitis in adults and reported cases have a history of cranial, spinal or otic manipulation. On the contrary, our patient had an insidious onset of meningitis resulting in hydrocephalus with no prior procedures. His IVDU was likely a risk factor, though there was no evidence of bacteremia. Atypical organisms in CSF can often be disregarded as contaminants. This can delay therapy and increase morbidity and mortality. Our case highlights an atypical presentation of meningitis caused by a rare organism.