Neisseria sicca Vertebral Osteomyelitis: A Case Report and Literature Review

Background: Culture-negative vertebral osteomyelitis presents a significant diagnostic challenge. Neisseria sicca (N. sicca) is a typically benign commensal organism of the upper respiratory tract that rarely causes invasive infections, warranting cautious interpretation if isolated in a single positive culture. This case study details a 62-year-old male diagnosed with vertebral osteomyelitis caused by N. sicca, examining diagnostic challenges, treatment, and outcomes. Methods: We conducted a comprehensive search on MEDLINE using the keywords "Neisseria sicca", "osteomyelitis", and "diskitis". An additional search excluding N. gonorrhea and N. meningitidis was also performed, revealing a total of four cases of N. sicca osteomyelitis in the literature. Results: A 62-year-old male with a history of hypertension, type 2 diabetes, atrial fibrillation, and previous L5-S1 spinal fusion presented with fever and back pain in May 2023. Initial imaging revealed T8-T9 vertebral osteomyelitis. Despite a six-week course of IV daptomycin, his symptoms worsened, prompting further evaluation. A CT-guided biopsy with comprehensive testing, including histopathology and microbial cultures, initially identified N. sicca. Due to its rarity, additional biopsies were conducted, confirming the infection. IV ceftriaxone was initiated, leading to significant pain improvement, and a subsequent MRI showed near resolution. The patient transitioned to oral cefuroxime, with follow-up confirming complete infection resolution by December 2023. Conclusions: This case underscores the importance of a structured diagnostic approach in culture-negative vertebral osteomyelitis to differentiate between commensal contamination and true infection. Repeated positive cultures of N. sicca from a sterile site confirmed its role as the causative agent. Early identification and targeted antibiotic therapy are critical to improving outcomes in rare cases of N. sicca vertebral osteomyelitis.