Prevalence and Risk Factors of Deep Spinal Infection after Single-Shot Epidural Injections: A Nationwide Cohort Study of 3.8 Million Pain Outpatients

BACKGROUND: Deep spinal infection (DSI) is a rare but potentially devastating complication of epidural injections. This study aimed to determine the nationwide incidence and risk factors of DSI following single-shot outpatient epidural injections for pain management. METHODS: Using customized data from the Korean National Health Insurance Service database, all patients who underwent single-shot outpatient epidural injections between 2009 and 2018 were identified. DSI was defined as a new-onset infection within 90 days of the most recent epidural injection that necessitated hospitalization and at least 4 weeks of antibiotic therapy. Multivariable logistic regression was performed to evaluate patient- and procedure-related risk factors. RESULTS: Among 12,049,555 injections in 3,769,014 individuals, 2,422 cases of DSIs were identified (0.020% per injection). In multivariable analysis, increased risk was associated with age ≥ 65 years (odds ratio [OR], 1.04; 95% CI, 1.04 to 1.05), peripheral vascular disease (OR, 1.38; 95% CI, 1.07 to 1.78), chronic pulmonary disease (OR, 1.33; 95% CI, 1.11 to 1.61), rheumatologic disease (OR, 1.85; 95% CI, 1.41 to 2.43), peptic ulcer disease (OR, 1.42; 95% CI, 1.22 to 1.66), liver disease (OR, 1.57; 95% CI, 1.34 to 1.83), diabetes (OR, 1.44; 95% CI, 1.14 to 1.81), recent immunosuppressant or systemic steroid use (OR, 2.44; 95% CI, 1.73 to 3.45), ≥ 3 injections within 90 days (OR, 1.93; 95% CI, 1.47 to 2.55), and lumbosacral-level injections (OR, 1.70; 95% CI, 1.45 to 2.00). In contrast, selective nerve root block was associated with a lower risk of DSI (OR, 0.49; 95% CI, 0.37 to 0.64). CONCLUSION: Although DSI after single-shot epidural injections is rare, its potential severity underscores the importance of careful patient selection and risk stratification, particularly in older patients, those with comorbidities or immunosuppression, and in procedures involving the lumbosacral level.