Applying the standardized infection ratio for reporting surgical site infections in Australian healthcare facilities

Stephanie K Tanamas; Lyn-Li Lim; Ann L Bull; Michael J Malloy; Allen C Cheng; Leon J Worth

doi:10.1017/ash.2023.478

Applying the standardized infection ratio for reporting surgical site infections in Australian healthcare facilities

Antimicrob Steward Healthc Epidemiol. 2023 Nov 16;3(1):e211. doi: 10.1017/ash.2023.478. eCollection 2023.

Authors

Stephanie K Tanamas¹, Lyn-Li Lim^{1

2}, Ann L Bull¹, Michael J Malloy^{1

3}, Allen C Cheng^{4

5}, Leon J Worth^{1

6

7

8}

Affiliations

¹ Victorian Healthcare Associated Infection Surveillance System (VICNISS) Coordinating Centre, Melbourne, VIC, Australia.
² Department of Infectious Diseases, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia.
³ Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, VIC, Australia.
⁴ Department of Infectious Diseases, Alfred Hospital and Central Clinical School and School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC, Australia.
⁵ Monash Infectious Diseases, Monash Health and School of Clinical Sciences, Monash University, Melbourne, VIC, Australia.
⁶ National Centre for Antimicrobial Stewardship, Department of Infectious Diseases, The University of Melbourne, Melbourne, VIC, Australia.
⁷ Sir Peter MacCallum Department of Oncology, University of Melbourne Cancer & Department of Infectious Diseases, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
⁸ Department of Medicine, The University of Melbourne, Melbourne, VIC, Australia.

Abstract

Objective: We explored the utility of the standardized infection ratio (SIR) for surgical site infection (SSI) reporting in an Australian jurisdiction.

Design: Retrospective chart review.

Setting: Statewide SSI surveillance data from 2013 to 2019.

Patients: Individuals who had cardiac bypass surgery (CABG), colorectal surgery (COLO), cesarean section (CSEC), hip prosthesis (HPRO), or knee prosthesis (KPRO) procedures.

Methods: The SIR was calculated by dividing the number of observed infections by the number of predicted infections as determined using the National Healthcare Safety Network procedure-specific risk models. In line with a minimum precision criterion, an SIR was not calculated if the number of predicted infections was <1.

Results: A SIR >0 (≥1 observed SSI, predicted number of SSI ≥1, no missing covariates) could be calculated for a median of 89.3% of reporting quarters for CABG, 75.0% for COLO, 69.0% for CSEC, 0% for HPRO, and 7.1% for KPRO. In total, 80.6% of the reporting quarters, when the SIR was not calculated, were due to no observed infections or predicted infections <1, and 19.4% were due to missing covariates alone. Within hospitals, the median percentage of quarters during which zero infections were observed was 8.9% for CABG, 20.0% for COLO, 25.4% for CSEC, 67.3% for HPRO, and 71.4% for KPRO.

Conclusions: Calculating an SIR for SSIs is challenging for hospitals in our regional network, primarily because of low event numbers and many facilities with predicted infections <1. Our SSI reporting will continue to use risk-indexed rates, in tandem with SIR values when predicted number of SSI ≥1.