Seasonal trends of pyogenic spondylodiscitis in Japan: a nationwide inpatient database study

Objectives: The aims of this study were 1) to investigate seasonal epidemiological variations of pyogenic spondylodiscitis, including Methicillin-resistant Staphylococcus aureus (MRSA) infection, in Japan, and 2) to evaluate associated inpatient outcomes.

Methods: We performed a retrospective nationwide study using data from the Japanese Diagnosis Procedure Combination (DPC) inpatient database, covering the period from 2010 to 2022. The parameters assessed were seasonal incidence, demographic characteristics, inpatient mortality, complications, and medical costs. Risk factors for in-hospital death were evaluated using multivariable Cox proportional hazards regression models.

Results: A total of 71,134 patients with pyogenic spondylodiscitis were identified, with 11.9% (n = 8,446) exhibiting MRSA infection. Admissions peaked in spring (n = 18,076) and were lowest in winter (n = 17,565), although no seasonal trend was observed among those with MRSA infection. The average age of patients was 71.05 years, and 60.9% of patients were male. The average hospital stay was longest in spring (53.5 days) and shortest in summer (51.6 days) (P = 0.006). Medical costs were highest in spring ($16,979) and lowest in summer ($16,437) (P < 0.001). Mortality rates were highest in fall and winter (3.0% each) and lowest in summer (2.6%) (P = 0.024). Sepsis was the most common concomitant infection, occurring in 10.4% of patients. The risk factors for in-hospital mortality were being elderly, male, having a low BMI, and high comorbidities. Among patients aged over 65, aspiration pneumonia and sepsis were risk factors for death throughout the year.

Conclusion: The findings highlight significant seasonal variations in pyogenic spondylodiscitis, with different concomitant infections but no significant difference in MRSA infection across seasons. This highlights the need for MRSA-targeted interventions regardless of season.