2121. Shifting Surgical Site Infection Denominators and Implication on NHSN Reporting

BACKGROUND: Per National Healthcare Safety Network (NHSN) rules, when multiple procedures are performed during a single operation, the operation is counted in the surgical site infection (SSI) denominator of each NHSN surgical procedure category. SSIs, however, are counted only in the highest-ranking procedure category. These rules result in procedures that are ineligible to have an associated SSI being counted in SSI denominators. METHODS: We analyzed 3 years (January 1, 2015–December 31, 2017) of laminectomy and rectal surgery SSI data from hospitals in the Duke Infection Control Outreach Network (DICON) that used ICD procedure codes to assign denominators per NHSN definitions. We compared SSI rates using two different denominators: NHSN denominators vs. reduced denominators that counted only primary laminectomy and rectal surgery procedures. We calculated rate ratios (RR) to compare the NHSN and adjusted SSI rates for each procedure for all hospitals that reported at least 1 SSI. RESULTS: Eleven hospitals reported 87 infections following 17,247 laminectomy procedures. The overall SSI rate increased by 44% when only primary procedures were counted in the denominator (RR 1.44); but individual hospital RR ranged from 1.10 to 2.20 (Table 1). 5 hospitals reported seven SSIs following 740 rectal procedures. The overall SSI rate increased by 143% when only primary procedures were counted in the denominator (RR 2.43), but individual hospital RR ranged from 2.00 to 5.00 (Table 1). CONCLUSION: NHSN’s method for calculating SSI denominators underestimates true SSI rate. The current method particularly impacts procedures that are frequently performed in conjunction with higher-ranking NHSN procedures. Counting only primary procedures in procedure category denominators would provide higher, more accurate SSI rates. DISCLOSURES: All authors: No reported disclosures.