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

Retrospective chart review.

Statewide SSI surveillance data from 2013 to 2019.

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

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.

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.

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.

To evaluate time trends in surgical site infection (SSI) rates and SSI pathogens in Australia.

Prospective multicenter observational cohort study.

A group of 81 Australian healthcare facilities participating in the Victorian Healthcare Associated Infection Surveillance System (VICNISS).

All patients underwent surgeries performed between October 1, 2002, and June 30, 2013. National Healthcare Safety Network SSI surveillance methods were employed by the infection prevention staff at the participating hospitals.

Procedure-specific risk-adjusted SSI rates were calculated. Pathogen-specific and antimicrobial-resistant (AMR) infections were modeled using multilevel mixed-effects Poisson regression.

A total of 183,625 procedures were monitored, and 5,123 SSIs were reported. Each year of observation was associated with 11% risk reduction for superficial SSI (risk ratio [RR], 0.89; 95% confidence interval [CI], 0.88–0.90), 9% risk reduction for deep SSI (RR, 0.91; 95% CI, 0.90–0.93), and 5% risk reduction for organ/space SSI (RR, 0.95; 95% CI, 0.93–0.97). Overall, 3,318 microbiologically confirmed SSIs were reported. Of these SSIs, 1,174 (35.4%) were associated with orthopedic surgery, 827 (24.9%) with coronary artery bypass surgery, 490 (14.8%) with Caesarean sections, and 414 (12.5%) with colorectal procedures. Staphylococcus aureus was the most frequently identified pathogen, and a statistically significant increase in infections due to ceftriaxone-resistant Escherichia coli was observed (RR, 1.37; 95% CI, 1.10–1.70).

Standardized SSI surveillance methods have been implemented in Victoria, Australia. Over an 11-year period, diminishing rates of SSIs have been observed, although AMR infections increased significantly. Our findings facilitate the refinement of recommended surgical antibiotic prophylaxis regimens and highlight the need for a more expansive national surveillance strategy to identify changes in epidemiology.

Infect Control Hosp Epidemiol 2015;00(0): 1–8

To measure the interobserver agreement, sensitivity, specificity, positive predictive value, and negative predictive value of data submitted to a statewide surveillance system for identifying central line-associated bloodstream infection (BSI).

Retrospective review of hospital medical records comparing reported data with gold standard according to definitions of central line–associated BSI.

Six Victorian public hospitals with more than 100 beds.

Reporting of surveillance outcomes was undertaken by infection control practitioners at the hospital sites. Retrospective evaluation of the surveillance process was carried out by independent infection control practitioners from the Victorian Hospital Acquired Infection Surveillance System (VICNISS). A sample of records of patients reported to have a central line-associated BSI were assessed to determine whether they met the definition of central line–associated BSI. A sample of records of patients with bacteremia in the intensive care unit during the assessment period who were not reported as having central line–associated BSI were also assessed to see whether they met the definition of central line-associated BSI.

Records of 108 patients were reviewed; the agreement between surveillance reports and the VICNISS assessment was 67.6% (κ = 0.31). Of the 46 reported central line–associated BSIs, 27 were confirmed to be central line–associated BSIs, for a positive predictive value of 59% (95% confidence interval [CI], 43%–73%). Of the 62 cases of bacteremia reviewed that were not reported as central line–associated BSIs, 45 were not associated with a central line, for a negative predictive value of 73% (95% CI, 60%–83%). Estimated sensitivity was 35%, and specificity was 87%. The positive likelihood ratio was 3.0, and the negative likelihood ratio was 0.72.

The agreement between the reporting of central line–associated BSI and the gold standard application of definitions was unacceptably low. False-negative results were problematic; more than half of central line–associated BSIs may be missed in Victorian public hospitals.

To analyze the risk factors for surgical site infection (SSI) complicating coronary artery bypass graft (CABG) surgery and to create an alternative SSI risk score based on the results of multivariate analysis.

A prospective cohort study involving inpatient and laboratory-based surveillance of patients who underwent CABG surgery over a 27-month period from January 1, 2003 through March 31, 2005. Data were obtained from 6 acute care hospitals in Victoria, Australia, that contributed surveillance data for SSI complicating CABG surgery to the Victorian Hospital Acquired Infection Surveillance System Coordinating Centre and the Australasian Society of Cardiac and Thoracic Surgeons, also in Victoria.

A total of 4,633 (93%) of the 4,987 patients who underwent CABG surgery during this period were matched in the 2 systems databases. There were 286 SSIs and 62 deep or organ space sternal SSIs (deep or organ space sternal SSI rate, 1.33%). Univariate analysis revealed that diabetes mellitus, body mass index (BMI) greater than 35, and receipt of blood transfusion were risk factors for all types of SSI complicating CABG surgery. Six multivariate analysis models were created to examine either preoperative factors alone or preoperative factors combined with operative factors. All models revealed diabetes and BMI of 30 or greater as risk factors for SSI complicating CABG surgery. A new preoperative scoring system was devised to predict sternal SSI, which assigned 1 point for diabetes, 1 point for BMI of 30 or greater but less than 35, and 2 points for BMI of 35 or greater. Each point in the scoring system represented approximately a doubling of risk of SSI. The new scoring system performed better than the National Nosocomial Infections Surveillance System (NNIS) risk index at predicting SSI.

A new weighted scoring system based on preoperative risk factors was created to predict sternal SSI risk following CABG surgery. The new scoring system outperformed the NNIS risk index. Future studies are needed to validate this scoring system.

To measure the accuracy and determine the positive predictive value (PPV) and negative predictive value (NPV) of data submitted to a statewide surveillance system for identifying surgical site infection (SSI) complicating coronary artery bypass graft (CABG) surgery.

Retrospective review of hospital medical records comparing SSI data with surveillance data submitted by infection control consultants (ICCs).

Victorian Hospital Acquired Infection Surveillance System (VICNISS) Coordinating Centre in Victoria, Australia.

All patients reported to have an SSI following CABG surgery and a random sample of approximately 10% of patients reported not to have an SSI following CABG surgery.

The VICNISS ascertainment rate for CABG procedures in Victoria was 95%. One hundred sixty-nine medical records were reviewed, and reviewers agreed with ICCs about 46 (96%) of the patients reported as infected by the ICCs and 31 (91%) of the patients identified with a sternal SSI by the ICCs. In one-third of SSIs, the depth of SSI documented by ICCs was discordant with that documented by the reviewers. Disagreement about patients with donor site SSI was frequent. When the review findings were used as the reference standard, the PPV for ICC-reported SSI was 96% (95% confidence interval [CI], 86%-99%), and the NPV was 97% (95% CI, 92%-99%). For ICC-reported sternal SSI, the PPV was 91% (95% CI, 76%-98%) and the NPV was 98% (95% CI, 94%-100%).

There was broad agreement on the number of infected patients and the number of patients with sternal SSI. However, discordance was frequent with respect to the depth of sternal SSI and the identification of donor site SSI. We recommend modifications to the methodology for National Noscomial Infection Surveillance System-based surveillance for SSI following CABG surgery.

The Victorian Hospital Acquired Infection Surveillance System (VICNISS) hospital-acquired infection surveillance system was established in 2002 in Victoria, Australia, and collates surgical site infection (SSI) surveillance data from public hospitals in Australia.

To evaluate the association between the US National Nosocomial Infections Surveillance (NNIS) system's risk index and SSI rates for 7 surgical procedures.

SSI surveillance was performed with NNIS definitions and methods for surgical procedures performed between November 2002 and September 2004. Correlations were assessed using the Goodman-Kruskal γ statistic.

Data were submitted for the following numbers of procedures: appendectomy, 545; coronary artery bypass graft (CABG), 4,632; cholecystectomy, 1,001; colon surgery, 623; cesarean section, 4,857; hip arthroplasty, 3,825; and knee arthroplasty, 2,416. NNIS risk index and increasing SSI rate were moderately well correlated for appendectomy (γ = 0.55), colon surgery (γ = 0.48), and cesarean section (γ = 0.42). A fairly positive correlation was found for cholecystectomy (γ = 0.17), hip arthroplasty (γ = 0.2), and knee arthroplasty (γ = 0.16). However, for CABG surgery, a poor association was found (γ = 0.02).

The NNIS risk index was positively correlated with an increasing SSI rate for all 7 procedures; the strongest correlation was found for appendectomy, cesarean section, and colon surgery, and the poorest correlation was found for CABG surgery. We believe that risk stratification with the NNIS risk index is appropriate for comparison of data for most procedures and superior to use of no risk adjustment. However, for some procedures, particularly CABG, further studies of alternative risk indexes are needed to better stratify patients.