How do we understand the disagreement in the frequency of surgical site infection between the CDC and Clavien-Dindo classifications?

To clarify the discrepancy in the incidence and severity of surgical site infections (SSI) for radical cystectomy between reports based on the CDC guideline and those using the Clavien-Dindo classification we evaluated 449 consecutive patients who underwent radical cystectomy for bladder cancer between 1990 and 2012. Of the 115 (25.6%) patients with SSI defined by the CDC guideline, 89 could be analyzed. We compared the SSI rates and severity defined by the CDC guideline and Clavien-Dindo classifications. There were 58 patients with superficial SSI, 16 with deep SSI, and 15 with organ/space SSI according to the CDC guideline. All patients with organ/space SSI were judged as "not having SSI" by the Clavien-Dindo classification. They were classified as having "intestinal prolapse", "intestinal fistula", "abdominal abscess" and "pelvic abscess." There was a significant association between the treatment duration and depth of SSI based on the CDC guideline by Spearman's rank-correlation coefficient (p < 0.001, r = 0.614) and with the grade of complications (p < 0.001, r = 0.632) in the Clavien-Dindo classification. Multivariate analysis showed that patients with grade III SSI in the Clavien-Dindo classification needed a significantly longer treatment duration. It is necessary to be aware that a discrepancy can occur automatically due to the different natures of the definitions. Using the CDC guideline, we can effectively estimate the future treatment period when SSI occurs. With the Clavien-Dindo classification, grade III SSI requires a longer treatment duration.