Risk stratification for surgical site infections in Australia: evaluation of the US National Nosocomial Infection Surveillance risk index

Risk Factors and Dynamic Nomogram Development for Surgical Site Infection Following Open Wedge High Tibial Osteotomy for Varus Knee Osteoarthritis: A Retrospective Cohort Study

Background

As the worldwide population ages, the population receiving open wedge high tibial osteotomy (OWHTO) is growing, and surgical site infection (SSI) is a rare but fatal surgical complication. This study aimed to identify risk factors independently associated with SSI following OWHTO and develop a predictive nomogram.

Methods

Clinical data of patients who received OWHTO and followed up for more than 12 months in our hospital were retrospectively reviewed. Multivariable logistic regression was performed to determine independent risk factors for SSI and to construct predictive nomograms. The study further illustrated the predictive performance of the model by using the receiver operating characteristic (ROC) curve, calibration curve, and decision curve analysis (DCA).

Results

A total of 1294 eligible patients were included in the study. Multivariate analysis revealed tobacco consumption (OR=3.44, p=0.010), osteotomy size ≥12 mm (OR=3.3, p=0.015), the use of allogeneic bone or artificial bone graft substitutes (allogeneic bone vs none, OR=4.08, p=0.037; artificial bone vs none, OR=5.16, p=0.047), Kellgren-Lawrence (K-L) grade IV (OR=2.5, p=0.046), systemic immune-inflammation index (SII) >423.62 (OR=6.2, p<0.001), high-sensitivity C-reactive protein (HCRP) >2.6 mg/L (OR=2.42, p=0.044), and a higher level of fasting blood glucose (FBG) (OR=1.32, p=0.022) were the independent predictors of SSI. The cutoff score of the model was 148, with a sensitivity of 76.0% and specificity of 81.0%. The concordance index (C-index) and Brier score of the nomogram were 0.856 and 0.017, and the corrected values after 1000 bootstrapping validations were 0.820 and 0.018, respectively. Furthermore, the ROC curve, calibration curve, and DCA exhibited excellent predictive accuracy and clinical applicability of the model.

Conclusion

This study developed a dynamic nomogram based on seven predictors, which allowed surgeons to individualize risk stratification of patients and intervene promptly to reduce SSI rates.

Early coronavirus disease 2019 (COVID-19) pandemic effects on individual-level risk for healthcare-associated infections in hospitalized patients

OBJECTIVE

We compared the individual-level risk of hospital-onset infections with multidrug-resistant organisms (MDROs) in hospitalized patients prior to and during the coronavirus disease 2019 (COVID-19) pandemic. We also quantified the effects of COVID-19 diagnoses and intrahospital COVID-19 burden on subsequent MDRO infection risk.

DESIGN

Multicenter, retrospective, cohort study.

SETTING

Patient admission and clinical data were collected from 4 hospitals in the St. Louis area.

PATIENTS

Data were collected for patients admitted between January 2017 and August 2020, discharged no later than September 2020, and hospitalized ≥48 hours.

METHODS

Mixed-effects logistic regression models were fit to the data to estimate patients' individual-level risk of infection with MDRO pathogens of interest during hospitalization. Adjusted odds ratios were derived from regression models to quantify the effects of the COVID-19 period, COVID-19 diagnosis, and hospital-level COVID-19 burden on individual-level hospital-onset MDRO infection probabilities.

RESULTS

We calculated adjusted odds ratios for COVID-19-era hospital-onset Acinetobacter spp., P. aeruginosa and Enterobacteriaceae spp infections. Probabilities increased 2.64 (95% confidence interval [CI], 1.22-5.73) times, 1.44 (95% CI, 1.03-2.02) times, and 1.25 (95% CI, 1.00-1.58) times relative to the prepandemic period, respectively. COVID-19 patients were 4.18 (95% CI, 1.98-8.81) times more likely to acquire hospital-onset MDRO S. aureus infections.

CONCLUSIONS

Our results support the growing body of evidence indicating that the COVID-19 pandemic has increased hospital-onset MDRO infections.

Clinical prediction models and risk tools for early detection of patients at risk of surgical site infection and surgical wound dehiscence: a scoping review

OBJECTIVE

Despite advances in surgical techniques, intraoperative practice and a plethora of advanced wound therapies, surgical wound complications (SWCs), such as surgical site infection (SSI) and surgical wound dehiscence (SWD), continue to pose a considerable burden to the patient and healthcare setting. Predicting those patients at risk of a SWC may give patients and healthcare providers the opportunity to implement a tailored prevention plan or potentially ameliorate known risk factors to improve patient postoperative outcomes.

METHOD

A scoping review of the literature for studies which reported predictive power and internal/external validity of risk tools for clinical use in predicting patients at risk of SWCs after surgery was conducted. An electronic search of three databases and two registries was carried out with date restrictions. The search terms included 'prediction surgical site infection' and 'prediction surgical wound dehiscence'.

RESULTS

A total of 73 records were identified from the database search, of which six studies met the inclusion criteria. Of these, the majority of validated risk tools were predominantly within the cardiothoracic domain, and targeted morbidity and mortality outcomes. There were four risk tools specifically targeting SWCs following surgery.

CONCLUSION

The findings of this review have highlighted an absence of well-developed risk tools specifically for SSI and/or SWD in most surgical populations. This review suggests that further research is required for the development and clinical implementation of rigorously validated and fit-for-purpose risk tools for predicting patients at risk of SWCs following surgery. The ability to predict such patients enables the implementation of preventive strategies, such as the use of prophylactic antibiotics, delayed timing of surgery, or advanced wound therapies following a procedure.

Surgical site infections after abdominal surgery: incidence and risk factors. A prospective cohort study

BACKGROUND

Abdominal surgeries have high rates of surgical site infections (SSIs), contributing to increased morbidity and mortality and costs for hospitalization. The aim of this study was to determine the SSI incidence rates and risk factors after abdominal surgeries.

METHODS

This prospective cohort study included all patients undergoing abdominal surgeries between 2005 and 2007 in the Western Galilee Medical Center in Nahariya, Israel. SSI incidence rates were calculated per 100 operations. Odds ratios (ORs) were estimated for each risk factor using univariate and multivariate analyses by logistic regression models.

RESULTS

Among 302 patients in the study cohort, the total SSI incidence rate was 22.2%. The univariate analysis defined 13 variables significantly associated with SSI: age > 60 years, lower functional status, diabetes mellitus, congestive heart failure, immunocompromising underlying disease, treatment with chemotherapy and other immunosuppressive medications, impaired immune system open cholecystectomy, laparotomy, an American Society of Anesthesiologists (ASA) score > 2, drain insertion, and 'dirty wound' classification. In multivariate regression analysis, treatment with immunosuppressive medications (OR = 2.5, 95% confidence interval (CI) = 1.099-143.443), open cholecystectomy (OR = 2.25, 95% CI = 2.242-40.109), and dirty wound classification (OR = 2.179, 95% CI = 3.80-20.551) were significantly associated with SSI.

CONCLUSIONS

The significant risk factors defined should be addressed preoperatively to decrease the risk for SSI. Wound surveillance in the post-discharge period is necessary for correct estimation of SSI rates.

Complex Surgical Site Infections and the Devilish Details of Risk Adjustment: Important Implications for Public Reporting

Objective.

To validate the National Nosocomial Infection Surveillance (NNIS) risk index as a tool to account for differences in case mix when reporting rates of complex surgical site infection (SSI).

Design.

Prospective cohort study.

Setting.

Twenty-four community hospitals in the southeastern United States.

Methods.

We identified surgical procedures performed between January 1, 2005, and June 30, 2007. The Goodman-Kruskal gamma or G statistic was used to determine the correlation between the NNIS risk index score and the rates of complex SSI (not including superficial incisional SSI). Procedure-specific analyses were performed for SSI after abdominal hysterectomy, cardiothoracic procedures, colon procedures, insertion of a hip prosthesis, insertion of a knee prosthesis, and vascular procedures.

Results.

A total of 2,257 SSIs were identified during the study period (overall rate, 1.19 SSIs per 100 procedures), of which 1,093 (48.4%) were complex (0.58 complex SSIs per 100 procedures). There were 45 complex SSIs identified following 7,032 abdominal hysterectomies (rate, 0.64 SSIs per 100 procedures); 63 following 5,318 cardiothoracic procedures (1.18 SSIs per 100 procedures); 139 following 5,144 colon procedures (2.70 SSIs per 100 procedures); 63 following 6,639 hip prosthesis insertions (0.94 SSIs per 100 procedures); 73 following 9,658 knee prosthesis insertions (0.76 SSIs per 100 procedures); and 55 following 6,575 vascular procedures (0.84 SSIs per 100 procedures). All 6 procedure-specific rates of complex SSI were significantly correlated with increasing NNIS risk index score (P< .05).

Conclusions.

Some experts recommend reporting rates of complex SSI to overcome the widely acknowledged detection bias associated with superficial incisional infection. Furthermore, it is necessary to compensate for case-mix differences in patient populations, to ensure that intrahospital comparisons are meaningful. Our results indicate that the NNIS risk index is a reasonable method for the risk stratification of complex SSIs for several commonly performed procedures.

An evaluation of differences in risk factors for individual types of surgical site infections after colon surgery

BACKGROUND

Most studies and national programs aggregate the different types of surgical site infections (SSIs) potentially masking and misattributing risk. Determining that risk factors for superficial, deep, and organ space SSIs are unique is essential to improve SSI rates.

METHODS

This cohort study utilized data of 59,365 patients who underwent colon resection at hospitals participating in the American College of Surgeons National Surgical Quality Improvement Program from 2007 to 2009. Four independent, multivariable, predictive models were developed to assess the unique associations between risk factors and each SSI group: Superficial, deep, organ space, and an aggregate of all 3 types of SSIs.

RESULTS

Overall, 13% of colon cases developed SSIs: Superficial (8%), deep (1.4%), and organ space (3.8%). Each model was different. Morbidly obese patients were more likely to develop SSIs than normal weight patients across all models; however, risk factors common to all models (eg, body mass index [BMI], duration of operation, wound class, laparoscopic approach) had very different levels of risk. Unique risks for superficial SSIs include diabetes, chronic obstructive pulmonary disease, and dyspnea. Deep SSIs had the greatest magnitude of association with BMI and the greatest incidence of wound disruption (19.8%). Organ space SSIs were often owing to anastomotic leaks and were uniquely associated with disseminated cancer, preoperative dialysis, preoperative radiation treatment, and a bleeding disorder, suggesting a physically frail or compromised patient may put the anastomosis at risk.

CONCLUSION

Risk factors for superficial, deep, and organ space SSI differ. More effective prevention strategies may be developed by reporting and examining each type of SSI separately.

Surgical site infections following coronary artery bypass graft procedures: 10 years of surveillance data

BACKGROUND

Surgical site infections following coronary artery bypass graft (CABG) procedures pose substantial burden on patients and healthcare systems. This study aims to describe the incidence of surgical site infections and causative pathogens following CABG surgery over the period 2003-2012, and to identify risk factors for complex sternal site infections.

METHODS

Routine computerised surveillance data were collected from three public hospitals in Queensland, Australia in which CABG surgery was performed between 2003 and 2012. Surgical site infection rates were calculated by types of infection (superficial/complex) and incision sites (sternal/harvest sites). Patient and procedural characteristics were evaluated as risk factors for complex sternal site infections using a logistic regression model.

RESULTS

There were 1,702 surgical site infections (518 at sternal sites and 1,184 at harvest sites) following 14,546 CABG procedures performed. Among 732 pathogens isolated, Methicillin-sensitive Staphylococcus aureus accounted for 28.3% of the isolates, Pseudomonas aeruginosa 18.3%, methicillin-resistant Staphylococcus aureus 14.6%, and Enterobacter species 6.7%. Proportions of Gram-negative bacteria elevated from 37.8% in 2003 to 61.8% in 2009, followed by a reduction to 42.4% in 2012. Crude rates of complex sternal site infections increased over the reporting period, ranging from 0.7% in 2004 to 2.6% in 2011. Two factors associated with increased risk of complex sternal site infections were identified: patients with an ASA (American Society of Anaesthesiologists) score of 4 or 5 (reference score of 3, OR 1.83, 95% CI 1.36-2.47) and absence of documentation of antibiotic prophylaxis (OR 2.03, 95% CI 1.12-3.69).

CONCLUSIONS

Compared with previous studies, our data indicate the importance of Gram-negative organisms as causative agents for surgical site infections following CABG surgery. An increase in complex sternal site infection rates can be partially explained by the increasing proportion of patients with more severe underlying disease.

Incidence and modifiable risk factors of surveillance of surgical site infections in Egypt: a prospective study

BACKGROUND

Surgical site infections (SSIs) contribute significantly to patient morbidity and mortality and exhaust health care system resources. The main objectives of the study were to describe the incidence rates of SSIs among patients undergoing urologic or cardiothoracic surgeries, the associated risk factors, and the common causative etiologies found at Alexandria University Hospital in Egypt.

METHODS

A prospective active surveillance study for patients undergoing urologic and cardiothoracic surgeries was implemented from July 2009 to December 2010. Patients were inspected daily for developing SSIs and with a 30-day postoperative follow-up. Wound swabs were obtained from patients who had clinical signs suggestive of infection. Swabs were cultured for bacterial identification and tested for antimicrobial sensitivity. Standard Centers for Disease Control and Prevention National Health Safety Network case definitions were used.

RESULTS

SSIs occurred in 187 (17%) of patients with complete follow-up (n = 1,062), of which 106 (57%) occurred in-hospital and 81 (43%) occurred after discharge. Higher SSI rates were observed in cardiothoracic surgeries (23.3%), compared with urologic surgeries (9%) (P < .001). A stepwise logistic model identified an increased risk of SSI for those who underwent cardiothoracic surgeries (odds ratio [OR], 4.7; 95% confidence interval [CI], 2.2-11.1), those aged >45 years (OR, 2.32; 95% CI, 1.35-4.01), increased duration of hospital stay before (OR, 1.03; 95% CI, 1.01-1.05) and after (OR, 1.07; 95% CI, 1.04-1.09) surgery, antibiotics ≤24 hours before surgery (OR, 2.54; 95% CI, 1.63-3.94), and dirty wounds (OR, 4.09; 95% CI, 1.60-10.43).

CONCLUSIONS

Measures to reduce the high rates of SSI need to be instituted through a multidisciplinary effort including infection control education and specific SSI prevention activities at Alexandria University Hospital.

Improved hospital-level risk adjustment for surveillance of healthcare-associated bloodstream infections: a retrospective cohort study

BACKGROUND

To allow direct comparison of bloodstream infection (BSI) rates between hospitals for performance measurement, observed rates need to be risk adjusted according to the types of patients cared for by the hospital. However, attribute data on all individual patients are often unavailable and hospital-level risk adjustment needs to be done using indirect indicator variables of patient case mix, such as hospital level. We aimed to identify medical services associated with high or low BSI rates, and to evaluate the services provided by the hospital as indicators that can be used for more objective hospital-level risk adjustment.

METHODS

From February 2001-December 2007, 1719 monthly BSI counts were available from 18 hospitals in Queensland, Australia. BSI outcomes were stratified into four groups: overall BSI (OBSI), Staphylococcus aureus BSI (STAPH), intravascular device-related S. aureus BSI (IVD-STAPH) and methicillin-resistant S. aureus BSI (MRSA). Twelve services were considered as candidate risk-adjustment variables. For OBSI, STAPH and IVD-STAPH, we developed generalized estimating equation Poisson regression models that accounted for autocorrelation in longitudinal counts. Due to a lack of autocorrelation, a standard logistic regression model was specified for MRSA.

RESULTS

Four risk services were identified for OBSI: AIDS (IRR 2.14, 95% CI 1.20 to 3.82), infectious diseases (IRR 2.72, 95% CI 1.97 to 3.76), oncology (IRR 1.60, 95% CI 1.29 to 1.98) and bone marrow transplants (IRR 1.52, 95% CI 1.14 to 2.03). Four protective services were also found. A similar but smaller group of risk and protective services were found for the other outcomes. Acceptable agreement between observed and fitted values was found for the OBSI and STAPH models but not for the IVD-STAPH and MRSA models. However, the IVD-STAPH and MRSA models successfully discriminated between hospitals with higher and lower BSI rates.

CONCLUSION

The high model goodness-of-fit and the higher frequency of OBSI and STAPH outcomes indicated that hospital-specific risk adjustment based on medical services provided would be useful for these outcomes in Queensland. The low frequency of IVD-STAPH and MRSA outcomes indicated that development of a hospital-level risk score was a more valid method of risk adjustment for these outcomes.

The association of preoperative anemia and perioperative allogeneic blood transfusion with the risk of surgical site infection

BACKGROUND

The purpose of the study was to investigate allogeneic blood transfusion (ABT) and preoperative anemia as risk factors for surgical site infection (SSI).

STUDY DESIGN AND METHODS

A prospective, observational cohort of 5873 consecutive general surgical procedures at Basel University Hospital was analyzed to determine the relationship between perioperative ABT and preoperative anemia and the incidence of SSI. ABT was defined as transfusion of leukoreduced red blood cells during surgery and anemia as hemoglobin concentration of less than 120 g/L before surgery. Surgical wounds and resulting infections were assessed to Centers for Disease Control standards.

RESULTS

The overall SSI rate was 4.8% (284 of 5873). In univariable logistic regression analyses, perioperative ABT (crude odds ratio [OR], 2.93; 95% confidence interval [CI], 2.1 to 4.0; p < 0.001) and preoperative anemia (crude OR, 1.32; 95% CI, 1.0 to 1.7; p = 0.037) were significantly associated with an increased odds of SSI. After adjusting for 13 characteristics of the patient and the procedure in multivariable analyses, associations were substantially reduced for ABT (OR, 1.25; 95% CI, 0.8 to 1.9; p = 0.310; OR, 1.07; 95% CI, 0.6 to 2.0; p = 0.817 for 1-2 blood units and >or=3 blood units, respectively) and anemia (OR, 0.91; 95% CI, 0.7 to 1.2; p = 0.530). Duration of surgery was the main confounding variable.

CONCLUSION

Our findings point to important confounding factors and strengthen existing doubts on leukoreduced ABT during general surgery and preoperative anemia as risk factors for SSIs.

Surveillance of healthcare-acquired infections in Queensland, Australia: data and lessons from the first 5 years

OBJECTIVE

To present healthcare-acquired infection surveillance data for 2001-2005 in Queensland, Australia.

DESIGN

Observational prospective cohort study.

SETTING

Twenty-three public hospitals in Queensland.

METHODS

We used computer-assisted surveillance to identify episodes of surgical site infection (SSI) in surgical patients. The risk-adjusted incidence of SSI was calculated by means of a risk-adjustment score modified from that of the US National Nosocomial Infections Surveillance System, and the incidence of inpatient bloodstream infection (BSI) was adjusted for risk on the basis of hospital level (level 1, tertiary referral center; level 2, large general hospital; level 3, small general hospital). Funnel and Bayesian shrinkage plots were used for between-hospital comparisons.

PATIENTS

A total of 49,804 surgical patients and 4,663 patients who experienced healthcare-associated BSI.

RESULTS

The overall cumulative incidence of in-hospital SSI ranged from 0.28% (95% confidence interval [CI], 0%-1.54%) for radical mastectomies to 6.15% (95% CI, 3.22%-10.50%) for femoropopliteal bypass procedures. The incidence of inpatient BSI was 0.80, 0.28, and 0.22 episodes per 1,000 occupied bed-days in level 1, 2, and 3 hospitals, respectively. Staphylococcus aureus was the most commonly isolated microorganism for SSI and BSI. Funnel and shrinkage plots showed at least 1 hospital with a signal indicating a possible higher-than-expected rate of S. aureus-associated BSI.

CONCLUSIONS

Comparisons between hospitals should be viewed with caution because of imperfect risk adjustment. It is our view that the data should be used to improve healthcare-acquired infection control practices using evidence-based systems rather than to judge institutions.

Economic burden of surgical site infections at a European university hospital

OBJECTIVE

To quantify the economic burden of in-hospital surgical site infections (SSIs) at a European university hospital.

DESIGN

Matched case-control study nested in a prospective observational cohort study.

SETTING

Basel University Hospital in Switzerland, where an average of 28,000 surgical procedures are performed per year.

METHODS

All in-hospital occurrences of SSI associated with surgeries performed between January 1, 2000, and December 31, 2001, by the visceral, vascular, and traumatology divisions at Basel University Hospital were prospectively recorded. Each case patient was matched to a control patient by age, procedure code, and National Nosocomial Infection Surveillance System risk index. The case-control pairs were analyzed for differences in cost of hospital care and in provision of specialized care.

RESULTS

A total of 6,283 procedures were performed: 187 SSIs were detected in inpatients, 168 of whom were successfully matched with a control patient. For case patients, the mean additional hospital cost was SwF-19,638 (95% confidence interval [CI], SwF-8,492-SwF-30,784); the mean additional postoperative length of hospital stay was 16.8 days (95% CI, 13-20.6 days); and the mean additional in-hospital duration of antibiotic therapy was 7.4 days (95% CI, 5.1-9.6 days). Differences were primarily attributable to organ space SSIs (n = 76).

CONCLUSIONS

In a European university hospital setting, SSIs are costly and constitute a heavy and potentially preventable burden on both patients and healthcare providers.