A case of pyogenic vertebral osteomyelitis and psoas abscess caused by Haemophilus influenzae: Diagnostic value of 16S ribosomal RNA gene analysis in a culture-negative case.

Haemophilus influenzae is a rare cause of pyogenic osteomyelitis, with only eleven reported adult cases. We present a case of H. influenzae vertebral osteomyelitis and psoas abscess in a 48-year-old woman who had received prior antibiotic therapy before the event. She subsequently developed worsening lower back pain, and magnetic resonance imaging revealed L4/L5 osteomyelitis with psoas abscess. Despite empiric cefazolin therapy, her condition deteriorated. All microbiological cultures remained negative, including blood and aspirated pus from the lesion. Broad-range 16S ribosomal RNA gene polymerase chain reaction and sequencing analysis identified β-lactamase-negative ampicillin-susceptible H. influenzae as the causative pathogen. After switching to cefotaxime, the patient improved and completed treatment with oral levofloxacin without recurrence. This case demonstrates the value of molecular techniques in diagnosing culture-negative infections, particularly in antibiotic-pretreated patients.