Nosocomial Infection Surveillance Risk Index Research Articles

Sternal wound infection after coronary artery bypass graft surgery: Validation of existing risk scores

Prediction of surgical site infection and mortality after cardiac surgery might allow for interventions to reduce adverse outcomes. We sought to evaluate existing risk scores. We included 809 consecutive patients undergoing coronary artery bypass surgery. Data were collected prospectively. Infections were defined as deep sternal wound infection or mediastinitis by using established criteria and evaluated 60 days after surgical intervention. All-cause mortality was assessed at 30 days and 6 months. We assessed the ability of the National Nosocomial Infections Surveillance risk index, the EuroSCORE, and the Society of Thoracic Surgeons risk score to predict infection and mortality. Discrimination was assessed using the area under the receiver operating curve. The rate of surgical site infection was 3.6% (29/809 patients). The National Nosocomial Infections Surveillance risk index showed moderate discrimination for infection (area under the receiver operating curve of 0.64) and poor ability to stratify patients into infection risk groups. The EuroSCORE predicted infection and 30-day and 6-month mortality with good discrimination (area under the receiver operating curve of 0.72, 0.78, and 0.77, respectively). Ranking patients by the EuroSCORE and dividing the cohort into 3 roughly equal risk groups yielded an ascending risk for infection of 0.7%, 3.0%, and 7.2%. The preoperative and intraoperative Society of Thoracic Surgeons risk scores showed good discrimination for surgical site infection (area under the receiver operating curve of 0.72 and 0.76, respectively) and excellent discrimination for early and late mortality (area under the receiver operating curve of >0.80). Risk grouping based on the Society of Thoracic Surgeons score yielded an ascending risk for infection of 0.7%, 3.6%, and 6.4%. The EuroSCORE and the Society of Thoracic Surgeons risk score can be used for joint risk stratification for surgical site infection and mortality. Both scores performed better than the National Nosocomial Infections Surveillance risk index.

Performance of the National Nosocomial Infections Surveillance Risk Index in Predicting Surgical Site Infection in Australia

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 gamma 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 ( gamma =0.55), colon surgery ( gamma =0.48), and cesarean section ( gamma =0.42). A fairly positive correlation was found for cholecystectomy ( gamma =0.17), hip arthroplasty ( gamma =0.2), and knee arthroplasty ( gamma =0.16). However, for CABG surgery, a poor association was found ( gamma =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.

Risk Factors for Surgical Site Infections Following Spinal Fusion Surgery at a Children's Hospital

BACKGROUND/OBJECTIVES: Postoperative infections especially surgical site infections (SSIs) are serious complications of spine fusions requiring extensive medical care and frequently additional surgical intervention. Between 1996 and 1999 at a children's hospital, a significant increase in the SSI rate was identified in patients with no known risk factors for infection preoperatively. The objectives of the study were to identify specific risk factors for SSIs in patients undergoing spinal fusion surgery and to analysis the characteristics of these infections. METHODS: A retrospective cohort study with medical chart review of all patients (ages 6 months to 21 years of age) who underwent spine fusion surgery between Jan. 1999 and Dec. 2003. Risk factors for SSI were determined using univariate analysis and multivariate logistic regression. SSIs were analyzed using CDC and NNSI guidelines. RESULTS: During the 5-year study, 234 spine fusion surgeries were performed with 19 (8%) patients developing a SSI. Univariate analysis identified diagnosis (idiopathic, neuromuscular, or structural scolotic curves), a secondary condition (such as cerebral palsy, myelodysplasia, an autoimmune condition, or genetic syndromes), and ASA score were significant preoperative risks with cut time, blood loss, blood replacement (type and amount), and bone graft used significant procedural risks. Postoperatively, hospital length of stay, antibiotic use, transfer to the ICU, and other non-infectious postoperative problems were significant. In the multivariate logistic regression, only cut time remained significant. Of the 19 SSIs, 11 (58%) occurred ≤ 30 days; 3 (16% occurred between 31 to 365 days, and 5 (26%) were identified more than 366 days postoperatively. Sixty three percent were classified as organ/space infections, requiring extensive medical intervention. Comparison of National Nosocomial Infection Surveillance risk index and study population infection rates Number of Risk Factor NNIS Rate Study Population Rate 0 1.2% 1.3% 1 3.1% 5.1% 2,3 7.2% 1.7% CONCLUSIONS: Diagnosis, cut time and ASA were found to be significant in this study. The identification of SSIs after 366 days (2 to 5 years) postoperatively is becoming an increasing concern requiring surveillance for infection to continue for several years to determine the actual SSI rate for this population of patients.

Duration of operation as a risk factor for surgical site infection: comparison of English and US data

T times are used to categorize surgical procedures into long and short durations. They constitute a part of the US National Nosocomial Infection Surveillance (NNIS) risk index that is widely used internationally in surveillance for surgical site infections (SSIs). The objective of this study was to compare the US NNIS T times with data collected in England. The Surgical Site Infection Surveillance Service in England holds data collected by 168 hospitals in 13 categories of surgical procedures between 1997 and 2002. The 75(th) percentile and corresponding T time were calculated from English data and compared with US times. Differences in rates of SSI above and below the T times were compared. Graphical methods were used to assess the cut points that exhibited an association with risk of SSI. The results show that English and US T times were the same for all surgical categories except coronary artery bypass graft and vascular surgery, where the English T time was 4 h. The 75(th) percentile time for hip hemiarthroplasties was 40 min less than for total hip replacements (THR). Although the incidence of SSI in THR was significantly higher in operations lasting for longer than the T time (P<0.05), no association between risk of SSI and T times set at 1, 1.5 or 2 h was observed for hip hemiarthroplasties. In conclusion, operations lasting for longer than the T time were associated with a higher risk of SSI in most categories. In the hip prosthesis category, this association only applied to THR.

Surgical site infection in patients submitted to digestive surgery: Risk prediction and the NNIS risk index

Some problems have been reported with the power of the National Nosocomial Infection Surveillance (NNIS) risk index to predict the risk of surgical site infections (SSI) for specific procedures. To develop an alternative risk prediction index for SSI and to compare the performance with the NNIS index. A prospective cohort study was carried out with all (609) patients submitted to digestive tract surgery in 2 general teaching hospitals in the city of São Paulo, Brazil, from August 2001 through March 2002. The final incidence rate of SSI was 24.5%; 149 cases of SSI were identified: 33 (22.1%) during hospitalization and 116 (77.9%) after discharge. Logistic multivariate analysis was used for construction of the model. Obesity, surgery risk, adjusted duration, and video laparoscopic surgery were statistically significant (P < .05) for all previous procedures. The performance of the NNIS model in this study showed a low predictive capacity for the occurrence of SSI as determined by the receiver operating characteristic (ROC) curve (0.627; 95% CI: 0.575-0.678) compared with the alternative model developed with this population (0.732; 95% CI: 0.685-0.779). The presence of obesity, adjusted duration, and surgery risk significantly increased the risk for SSI. The NNIS risk index was not significant for SSI in the sample studied, and laparoscopic access was associated with a significant reduction in the risk for SSI. Although the NNIS index is a well-known and simple index, other models depicting variables related to SSI with a better sensitivity and specificity can be developed. Additional studies are required to confirm our results.

Surgical site infection in a university hospital in northeast Brazil

We examined prevention of surgical site infection (SSI) in a tertiary teaching hospital in northeast Brazil, from January 1994 to December 2003. The survey included 5,742 patients subjected to thoracic, urologic, vascular and general surgery. The criteria for diagnosing SSI were those of the Centers for Disease Control, USA, and the variables of the National Nosocomial Infection Surveillance risk index were used. Data analysis revealed that anesthetic risk scores, wound class and duration of surgery were significantly associated with SSI. A total of 296 SSIs were detected among the 5,742 patients (5.1%). The overall incidence of SSI was 8.8% in 1994; it decreased to 3.3% in 2003. In conclusion, the use of educational strategies, based on guidelines for SSI prevention reduced SSI incidence. Appropriate management of preoperative, intraoperative, and postoperative incision care, and a surveillance system based on international criteria, were useful in reducing SSI rates in our hospital.

Incidence of surgical site infections and accompanying risk factors in Vietnamese orthopaedic patients

A cohort study of surgical site infections (SSIs) was conducted in 582 orthopaedic surgical patients at Cho Ray Hospital, a reference hospital in Ho Chi Minh City, Vietnam, in order to determine the incidence and analyse risk factors for SSIs in this population. The SSI incidence rate was 12.5% (73 of 582); 3.6% incisional SSIs, 6.8% deep incisional SSIs and 2.1% organ/space SSIs. The incidence increased from 2% in clean wounds to 44.6% in dirty wounds, or 1.3% in patients with a National Nosocomial Infections Surveillance (NNIS) risk index of 0 to 75% in patients with an NNIS risk ratio of 3. In multi-variate analysis, having a dirty wound [odds ratio (OR) 8.7; 95% confidence intervals (CI) 4.6--16.4], American Society of Anesthesiologists' score >2 (OR 3.9; 95%CI 1.8-8.8), procedures with external fixation (OR 2.9; 95%CI 1.4-5.9), emergency surgery with motor-vehicle-related trauma (OR 2.1; 95%CI 1.2-3.9), or duration of procedure >2h (OR 2.1; 95%CI 1.1-4.2) were independent risk factors for SSI. Lack of appropriate prophylaxis was of borderline significance (OR 3.2; 95%CI 0.9-11.1, P=0.06). Among 76 patients with SSIs, 22 patients were discovered during postdischarge follow-up. These late SSIs had age as an additional risk factor (OR 2.8; 95%CI 1.1-7.2). Our data show that SSIs were frequent and differed widely by wound class. The NNIS risk index was predictive of SSI for this population. With a high number of motor vehicle accidents in Vietnam, the majority of orthopaedic operations are trauma related. Emergency surgery for injuries sustained in these accidents, and procedures with external fixation were especially prone to infections.

Adverse impact of surgical site infections in English hospitals

Between October 1997 and June 2001, 140 English hospitals participating in the surveillance of surgical site infection (SSI) with the Nosocomial Infection National Surveillance Service (NINSS) reported 2832 SSIs following 67 410 surgical procedures in nine defined categories of surgery. Limb amputation had the highest incidence of SSI with 14.3 SSIs per 100 operations. For all categories of surgery, except knee prosthesis (P=0.128), there was a linear increase in the incidence of SSI when the American National Nosocomial Infections Surveillance risk index increased. Superficial incisional SSI was more common than deep incisional and organ/space SSI, and accounted for more than half of all SSIs for all categories of surgery. The postoperative length of stay (LOS) was longer for patients with SSI, and when adjusted for other factors influencing LOS, the extra LOS due to SSI ranged from 3.3 days for abdominal hysterectomy to 21.0 days for limb amputation, and was at least nine days for the other categories. The additional cost attributable to SSI ranged from pound959 for abdominal hysterectomy to pound6103 for limb amputation. Deep incisional and organ/space SSI combined incurred a greater extra LOS and cost than superficial incisional SSI for all categories of surgery, except limb amputation. The crude mortality rate was higher for patients with SSI for all categories of surgery but, after controlling for confounding, only patients with SSI following hip prosthesis had a mortality rate that was significantly higher than those without SSI [odds ratio (OR)=1.8, P=0.002]. However, the adjusted mortality rate for patients with deep incisional and organ/space SSI compared with those without SSI was significantly higher for vascular surgery (OR=6.8, P<0.001), hip prosthesis (OR=2.5, P=0.005) and large bowel surgery (OR=1.8, P=0.04). This study shows that the adverse impact of SSI differs greatly for different categories of surgery, and highlights the importance of measuring the impact for defined categories rather than for all SSIs and all surgical procedures.

Postoperative bacteremia secondary to surgical site infection.

We evaluated all surgical site infections (SSI) and postoperative bacteremias secondary to SSI as part of an ongoing active surgical surveillance program at a community hospital. Among 40,191 surgical procedures, we identified 515 patients with SSI and 47 with postoperative bacteremia secondary to SSI. Four variables were examined as potential predictors for developing postoperative bacteremia secondary to an SSI: National Nosocomial Infections Surveillance risk index, abdominal surgery, surgical procedures with an implantable device, and the presence of Staphylococcus aureus in wounds. Of these 4 variables, only one, S. aureus isolated from a wound culture, was associated with an increased risk of developing postoperative bacteremia secondary to SSI. Patients with S. aureus isolated in either pure or mixed culture from SSI were more than twice as likely to have postoperative bacteremia secondary to SSI than were those without S. aureus wound infection.

An outbreak of coagulase-negative staphylococcal surgical-site infections following aortic valve replacement.

To determine the cause of a coagulase-negative staphylococcal outbreak and to identify risk factors for surgical-site infections among patients following Medtronic Freestyle bioprosthesis implantation. Retrospective case-control study. An 800-bed university referral center. The cohort of 64 patients undergoing Freestyle valve replacement from September 1998 to December 1998. Seven patients developed infection (10.9% vs 1.1% during the preceding 8 months), including two with mediastinitis and five with endocarditis. There were no statistically significant differences between cases and controls with respect to age, gender, weight, underlying illness, preoperative hospital stay, duration of surgery, time on bypass, central venous catheter duration, National Nosocomial Infection Surveillance risk index, New York Heart Association class, albumin, or antibiotic prophylaxis. However, only three cases were documented to have received vancomycin prophylaxis. Of all staff evaluated, only surgical resident A was significantly associated with infection (odds ratio, 7.68; 95% confidence interval, 1.3-44.1; P=.02) Pulsed-field gel electrophoresis patterns on Staphylococcus epidermidis isolates from four of the six cases were identical. These cases were performed on different days. Surgical resident Awas the only staff member present in the operating room for all cases caused by the epidemic strain. This S epidermidis strain, however, was not isolated from operating room staff. A surgical resident was significantly associated with infection. However, the cause of this outbreak was likely multifactorial. Changes occurring during the investigation included institution of vancomycin as routine prophylaxis and modification of surgical technique, which contributed to the resolution of the outbreak.

Toward Further Reducing Wound Infections in Cardiac Operations

Background. Serious wound infections such as mediastinitis still occur at a rate of 0.8% to 2.0%, according to the most recently published cardiac operative series. Methods. Data from careful surveillance for infection have been collected prospectively during a 4.5-year period on 1,717 patients who underwent cardiac operations performed under direct ultraviolet C radiation. Results. The rate for mediastinitis was 0.23%, and for deep incisional infection without mediastinitis, 0.12%; these rates are significantly lower than those for eight of nine of the most recently published cardiac series. When our infection rates were stratified using the National Nosocomial Infection Surveillance risk index, they were also significantly lower in the most important risk categories than the corresponding stratified rates collected from the participating hospitals of the Centers for Disease Control and Prevention National Nosocomial Infection Surveillance system. Conclusions. Though we lack the proof that only a large, randomized study might provide, certainly, one possible explanation for our lower wound infection rate was the use of bactericidal ultraviolet C radiation during operation. This is a simple and effective means of minimizing operating room airborne bacteria as one possible source of these infections.