Borrelia garinii spirochetemia in a previously healthy child presenting with Streptococcus anginosus group brain abscess: a case report

Background The clinical significance of transient Borrelia burgdorferi sensu lato complex (hereafter referred to as B. burgdorferi ) spirochetemia remains poorly understood and has rarely been documented. We report the isolation of viable B. garinii genospecies from the blood of a previously healthy child presenting with a Streptococcus anginosus group (SAG) brain abscess. Case presentation An eight-year-old girl presented with four days of headache, fever, nausea, slightly reduced general condition, and mild facial asymmetry. Initial evaluation, including lumbar puncture, raised suspicion of viral meningitis or Lyme neuroborreliosis (LNB). Based on the differential diagnosis of Lyme disease, she was enrolled in the prospective BRILLIANT study (NCT06045416), with additional blood and cerebrospinal fluid (CSF) sampling for B. burgdorferi culture and serology. Following initial outpatient management, she re-presented with clinical deterioration and signs of raised intracranial pressure. Cranial magnetic resonance imaging revealed a brain abscess requiring surgical drainage. Abscess cultures yielded SAG. Dental treatment four days before symptom onset provided a plausible source of infectious spread. Treatment with intravenous ceftriaxone and metronidazole for six weeks resulted in complete clinical recovery and radiological improvement. Borrelia burgdorferi -specific two-tier serology and CSF culture remained negative. In contrast, blood plasma culture for B. burgdorferi obtained at initial presentation yielded viable spirochetes after seven weeks. Borrelia burgdorferi DNA was confirmed by flaB -targeted qPCR, and hybrid whole-genome sequencing generated a near-complete genome identifying B. garinii genospecies. Conclusion This case demonstrates viable B. garinii spirochetemia without serological evidence of LNB, incidentally detected during investigation of a SAG brain abscess. It highlights the uncertain clinical significance of transient B. burgdorferi spirochetemia, and the importance of interpreting microbiological findings within the clinical context.