Lack of Seasonal and Temporal Variability in Total Hip Arthroplasty Surgical Site Infections.

Background: Surgical site infections (SSIs) are a signifi- cant cause of morbidity and mortality following total joint arthroplasty (TJA). While many risk factors are known, the seasonal and temporal associations of SSI are less under- stood. Understanding the associations can help reduce SSI rates.

Methods: We tracked rates of deep surgical site infec- tions (dSSIs) following total hip arthroplasty (THA) at a single large urban academic medical center from January 2009 through August 2018. Using a Poisson regression, we determined the monthly and seasonal variability of dSSIs. We also calculated the change in dSSI rate over the entire 9.67-year study period.

Results: In total, 15,703 THA cases between January 2009 and August 2018 were analyzed. There was no signifi- cant difference in the dSSI rate following THA in fall, winter, or spring as compared to summer. Similarly, there was no significant difference in dSSIs in July as compared to other months of the year. The average rate of dSSIs following THA was 1.04 (SD, 0.90) per 100 patients. The dSSI rate following THA decreased over the study period (r = 0.93, 95% CI: 0.84-1.03) but did not reach statistical significance.

Conclusion: This study demonstrated a non-significant, albeit decreasing, rate of dSSIs following THA over the study period. Contrary to previous reports, there was no difference in the dSSI rate in the summer months as compared to other seasons. The month of the year also does not appear to be a significant risk factor for SSIs, calling into question previous reports arguing for the importance of the "July effect."