Validating a 3-point prediction rule for surgical site infection after coronary artery bypass surgery

A New Surgical Site Infection Risk Score: Infection Risk Index in Cardiac Surgery

Various scoring systems attempt to predict the risk of surgical site infection (SSI) after cardiac surgery, but their discrimination is limited. Our aim was to analyze all SSI risk factors in both coronary artery bypass graft (CABG) and valve replacement patients in order to create a new SSI risk score for such individuals. A priori prospective collected data on patients that underwent cardiac surgery (n = 2020) were analyzed following recommendations from the Reporting of studies Conducted using Observational Routinely collected health Data (RECORD) group. Study participants were divided into two periods: the training sample for defining the new tool (2010–2014, n = 1298), and the test sample for its validation (2015–2017, n = 722). In logistic regression, two preoperative variables were significantly associated with SSI (odds ratio (OR) and 95% confidence interval (CI)): diabetes, 3.3/2–5.7; and obesity, 4.5/2.2–9.3. The new score was constructed using a summation system for punctuation using integer numbers, that is, by assigning one point to the presence of either diabetes or obesity. The tool performed better in terms of assessing SSI risk in the test sample (area under the Receiver-Operating Characteristic curve (aROC) and 95% CI, 0.67/055–0.76) compared to the National Nosocomial Infections Surveillance (NNIS) risk index (0.61/0.50–0.71) and the Australian Clinical Risk Index (ACRI) (0.61/0.50–0.72). A new two-variable score to preoperative SSI risk stratification of cardiac surgery patients, named Infection Risk Index in Cardiac surgery (IRIC), which outperforms other classical scores, is now available to surgeons. Personalization of treatment for cardiac surgery patients is needed.

Ability to predict the development of surgical site infection in cardiac surgery using the Australian Clinical Risk Index versus the National Nosocomial Infections Surveillance-derived Risk Index

Surgical site infection (SSI) is a major infectious complication that increases mortality, morbidity, and healthcare costs. There are scores attempting to classify patients for calculating SSI risk. Our objectives were to validate the Australian Clinical Risk Index (ACRI) in a European population after cardiac surgery, comparing it against the National Nosocomial Infections Surveillance-derived risk index (NNIS) and analyzing the predictive power of ACRI for SSI in valvular patients. All the patients that who underwent cardiac surgery in a tertiary university hospital between 2011 and 2015 were analyzed. The patients were divided into valvular and coronary groups, excluding mixed patients. The ACRI score was validated in both groups and its ability to predict SSI was compared to the NNIS risk index. We analyzed 1,657 procedures. In the valvular patient group (n: 1119), a correlation between the ACRI score and SSI development (p < 0.05) was found; there was no such correlation with the NNIS index. The area under the receiver-operating characteristic curve (AUC) was 0.64 (confidence interval [CI] 95%, 0.5-0.7) for ACRI and 0.62 (95% CI, 0.5-0.7) for NNIS. In the coronary group (n: 281), there was a correlation between ACRI and SSI but no between NNIS and SSI. The ACRI AUC was 0.70 (95% CI, 0.5-0.8) and the NNIS AUC was 0.60 (95% CI, 0.4-0.7). The ACRI score has insufficient predictive power, although it predicts SSI development better than the NNIS index, fundamentally in coronary artery bypass grafting (CABG). Further studies analyzing determining factors are needed.

Epidemiological Surveillance of Surgical Site Infection and its Risk Factors in Cardiac Surgery: A Prospective Cohort Study

INTRODUCTION AND OBJECTIVES

Surgical site infection in cardiac surgery is uncommon. The aim of the present study was to examine the incidence of this infection, compare it with national and international data, and evaluate its risk factors.

METHODS

This prospective cohort study included patients who underwent valve surgery or coronary revascularization during a 6-year period. The incidence of surgical site infection was studied. Associations between risk factors and infection were evaluated using odds ratios (OR). The infection rate was compared with Spanish and American data using the standardized infection ratio.

RESULTS

A total of 1557 patients were included. The overall cumulative incidence of infection was 4% (95% confidence interval [95%CI], 3.6%-5.6%), 3.6% in valve surgery (95%CI, 2.5%-4.7%) and 4.3% in coronary revascularization (95%CI, 2.3%-6.3%). Risk factors for surgical site infection in valve surgery were diabetes mellitus (OR=2.8; P<.05) and obesity (OR=6.6; P<.05). Risk factors for surgical site infection in coronary revascularization were diabetes mellitus (OR=2.9; P<.05) and reoperation for bleeding (OR=8.8; P<.05).

CONCLUSIONS

Diabetes mellitus and obesity favor surgical site infection in valve surgery, whereas diabetes mellitus and reoperation for bleeding favor surgical site infection in coronary revascularization. Infection surveillance and control programs permit evaluation and comparison of infection rates in cardiac surgery.

Preoperative risk prediction of surgical site infection requiring hospitalization or reoperation in patients undergoing vascular surgery

OBJECTIVE

The objective of this study was to develop a surgical site infection (SSI) prediction score for risk assessment before elective vascular surgery.

METHODS

We conducted a nested case-control study among patients who underwent elective vascular (abdominal aortic and peripheral arterial) surgery from January 1, 2003, to December 31, 2007, at Mayo Clinic (Rochester, Minn) an academic tertiary surgical center. Cases were patients with SSI requiring hospitalization; controls (one or two per case) were matched on type of procedure and date of surgery. Clinical data were collected by chart review. A risk score based on preoperative variables was developed using multivariable logistic regression and bootstrap resampling. The C statistic, equivalent to the area under the receiver operating characteristic curve, was used to assess discrimination. Calibration was assessed by plotting percentile risk groups of model-predicted values against observed proportions of subjects with SSI.

RESULTS

Eighty-four cases were compared with 160 controls. Preoperative variables independently associated with SSI risk were critical limb ischemia, previous SSI, prior revascularization procedure, and chronic obstructive pulmonary disease. A prediction model containing these variables was developed (model and risk score C statistic of 0.737 and 0.727, respectively). The calibration curve did not appear to deviate appreciably from the 45-degree line of identity.

CONCLUSIONS

We developed an SSI risk score based on noninvasive preoperative variables with acceptable discrimination and calibration. This tool needs prospective and external validation.

The Development of Statistical Models for Predicting Surgical Site Infections in Japan: Toward a Statistical Model–Based Standardized Infection Ratio

OBJECTIVE

To develop and internally validate a surgical site infection (SSI) prediction model for Japan.

DESIGN

Retrospective observational cohort study.

METHODS

We analyzed surveillance data submitted to the Japan Nosocomial Infections Surveillance system for patients who had undergone target surgical procedures from January 1, 2010, through December 31, 2012. Logistic regression analyses were used to develop statistical models for predicting SSIs. An SSI prediction model was constructed for each of the procedure categories by statistically selecting the appropriate risk factors from among the collected surveillance data and determining their optimal categorization. Standard bootstrapping techniques were applied to assess potential overfitting. The C-index was used to compare the predictive performances of the new statistical models with those of models based on conventional risk index variables.

RESULTS

The study sample comprised 349,987 cases from 428 participant hospitals throughout Japan, and the overall SSI incidence was 7.0%. The C-indices of the new statistical models were significantly higher than those of the conventional risk index models in 21 (67.7%) of the 31 procedure categories (P<.05). No significant overfitting was detected.

CONCLUSIONS

Japan-specific SSI prediction models were shown to generally have higher accuracy than conventional risk index models. These new models may have applications in assessing hospital performance and identifying high-risk patients in specific procedure categories.

Infect. Control Hosp. Epidemiol. 2016;37(3):260–271

Risk Factors for Sternal Wound Infection After Open Heart Operations Vary According to Type of Operation

BACKGROUND

This study evaluated whether risk factors for sternal wound infections vary with the type of surgical procedure in cardiac operations.

METHODS

This was a university hospital surveillance study of 3,249 consecutive patients (28% women) from 2006 to 2010 (median age, 69 years [interquartile range, 60 to 76]; median additive European System for Cardiac Operative Risk Evaluation score, 5 [interquartile range, 3 to 8]) after (1) isolated coronary artery bypass grafting (CABG), (2) isolated valve repair or replacement, or (3) combined valve procedures and CABG. All other operations were excluded. Univariate and multivariate binary logistic regression were conducted to identify independent predictors for development of sternal wound infections.

RESULTS

We detected 122 sternal wound infections (3.8%) in 3,249 patients: 74 of 1,857 patients (4.0%) after CABG, 19 of 799 (2.4%) after valve operations, and 29 of 593 (4.9%) after combined procedures. In CABG patients, bilateral internal thoracic artery harvest, procedural duration exceeding 300 minutes, diabetes, obesity, chronic obstructive pulmonary disease, and female sex (model 1) were independent predictors for sternal wound infection. A second model (model 2), using the European System for Cardiac Operative Risk Evaluation, revealed bilateral internal thoracic artery harvest, diabetes, obesity, and the second and third quartiles of the European System for Cardiac Operative Risk Evaluation were independent predictors. In valve patients, model 1 showed only revision for bleeding as an independent predictor for sternal infection, and model 2 yielded both revision for bleeding and diabetes. For combined valve and CABG operations, both regression models demonstrated revision for bleeding and duration of operation exceeding 300 minutes were independent predictors for sternal infection.

CONCLUSIONS

Risk factors for sternal wound infections after cardiac operations vary with the type of surgical procedure. In patients undergoing valve operations or combined operations, procedure-related risk factors (revision for bleeding, duration of operation) independently predict infection. In patients undergoing CABG, not only procedure-related risk factors but also bilateral internal thoracic artery harvest and patient characteristics (diabetes, chronic obstructive pulmonary disease, obesity, female sex) are predictive of sternal wound infection. Preventive interventions may be justified according to the type of operation.

Impact of obesity on the risk of wound infection following surgery: results from a nationwide prospective multicentre cohort study in England

We sought to assess the impact of body mass index on the risk of surgical site infection in a prospective cohort study of 206 National Health Service (NHS) hospitals in England between 2007 and 2011. Body mass index was available for 159,720 of 350,089 operations among patients undergoing abdominal hysterectomy, coronary artery bypass graft, hip replacement, knee replacement, or large-bowel surgery. Among these patients, the risk of surgical site infection ranged from 0.65% for knee replacement to 11.04% for large-bowel surgery. Overall, 127,512 (79.8%) patients were overweight or obese (body mass index of ≥25 kg/m(2)). Obesity was associated with a 1.1-fold to 4.4-fold increase in the adjusted odds of developing surgical site infection as compared with normal weight, depending on the type of surgery. The population-attributable fraction (PAF) for body mass index was greatest in overweight (body mass index of 25.0-29.9 kg/m(2)) patients undergoing coronary artery bypass graft, accounting for 15% of their overall risk of surgical site infection (PAF 0.15; 95% CI 0.09-0.22). Being overweight or obese substantially increased the likelihood of patients developing surgical site infection. Given the increasingly high proportion of the surgical population who are overweight, this is likely to place a considerable additional burden on the NHS. Strategies for mitigating this excess risk need to be found.

Microbial colonization of electrocardiographic telemetry systems before and after cleaning

BACKGROUND

Nosocomial infections caused by multidrug-resistant organisms are commonly associated with longer hospital stays up to 12 to 18 days and annual estimated costs of $5.7 billion to $6.8 billion. One common mode of transmission is cross-contamination between patients and providers via surface contaminants on devices such as telemetry systems.

OBJECTIVES

To determine the effect of a cleaning protocol on colonization of surface contaminants on electrocardiographic telemetry systems in 4 cardiovascular step-down units and to compare colonization in medical vs surgical units.

METHODS

A prospective, randomized, case-controlled study (the Descriptive Evaluation of Electrocardiographic Telemetry Pathogens [DEET] study) was designed to evaluate microbial colonization on telemetry systems before and after cleaning with sodium hypochlorite wipes. Each randomly selected telemetry system served as its own control. Nurses used a standardized culture technique recommended by personnel in infection control. Colonization before and after cleaning was analyzed by using the McNemar test and frequency tables. A standard cost-comparison analysis was conducted.

RESULTS

A total of 30 telemetry systems in medical units and 29 in surgical units were evaluated; 41 telemetry systems (69%) were colonized before the intervention, and 14 (24%) were colonized after it (P < .001). Before cleaning, surface organisms were present in 14 instances (35%) in surgical units and in 27 instances (66%) in medical units (P < .001). The cleaning strategy was cost-effective.

CONCLUSIONS

The cleaning intervention was effective, and cost-comparison analysis supported implementing a cleaning strategy for reusable leads rather than investing in disposable leads.

Epidemiology and outcome of major postoperative infections following cardiac surgery: risk factors and impact of pathogen type

BACKGROUND

Major postoperative infections (MPIs) are poorly understood complications of cardiac surgery. We examined the epidemiology, microbiology, and outcome of MPIs occurring after cardiac surgery.

METHODS

The study cohort was drawn from the Society of Thoracic Surgeon National Cardiac Database and comprised adults who underwent cardiac surgery at 5 tertiary hospitals between 2000 and 2004. We studied the incidence, microbiology, and risk factors of MPI (bloodstream or chest wound infections within 30 days after surgery), as well as 30-day mortality. We used multivariate regression analyses to evaluate the risk of MPI and mortality.

RESULTS

MPI was identified in 341 of 10,522 patients (3.2%). Staphylococci were found in 52.5% of these patients, gram-negative bacilli (GNB) in 24.3%, and other pathogens in 23.2%. High body mass index, previous coronary bypass surgery, emergency surgery, renal impairment, immunosuppression, cardiac failure, and peripheral/cerebrovascular disease were associated with the development of MPI. Median postoperative duration of hospitalization (15 days vs 6 days) and mortality (8.5% vs 2.2%) were higher in patients with MPIs. Compared with uninfected individuals, odds of mortality were higher in patients with S aureus MPIs (adjusted odds ratio, 3.7) and GNB MPIs (adjusted odds ratio, 3.0).

CONCLUSIONS

Staphylococci accounted for the majority of MPIs after cardiac surgery. Mortality was higher in patients with Staphylococcus aureus- and GNB-related MPIs than in patients with MPIs caused by other pathogens and uninfected patients. Preventive strategies should target likely pathogens and high-risk patients undergoing cardiac surgery.

Surgical site infections and their prevention

PURPOSE OF REVIEW

Recent studies have assessed interventions and bundles of interventions to prevent surgical site infections (SSIs). We reviewed numerous studies to identify those with the strongest evidence supporting interventions for preventing SSIs.

RECENT FINDINGS

Bundles that included more than one intervention to decrease the risk of Staphylococcus aureus wound contamination, such as chlorhexidine bathing and nasal application of mupirocin, had the strongest supporting evidence. However, bundles should be tested to ensure that their components are not antagonistic. Vancomycin prophylaxis and extended antimicrobial prophylaxis should not be used routinely, but should be reserved for high-risk populations such as patients who carry methicillin-resistant S. aureus (MRSA). Novel interventions to prevent SSIs (e.g., topical or oral antimicrobial agents, skin sealant, and antimicrobial sutures) need further evaluation before surgeons implement them routinely.

SUMMARY

There is some evidence that bundled interventions can reduce SSIs. However, more research should be done evaluating the effectiveness of these interventions. Future studies of bundles should use robust methodologies, such as randomized controlled trials, cluster randomized trials, or quasi-experimental studies analyzed by time series analysis.

Risk factors for coronary artery bypass graft chest surgical site infections in New York State, 2008

BACKGROUND

All hospitals in New York State (NYS) are required to report surgical site infections (SSIs) occurring after coronary artery bypass graft surgery. This report describes the risk adjustment method used by NYS for reporting hospital SSI rates, and additional methods used to explore remaining differences in infection rates.

METHODS

All patients undergoing coronary artery bypass graft surgery in NYS in 2008 were monitored for chest SSI following the National Healthcare Safety Network protocol. The NYS Cardiac Surgery Reporting System and a survey of hospital infection prevention practices provided additional risk information. Models were developed to standardize hospital-specific infection rates and to assess additional risk factors and practices.

RESULTS

The National Healthcare Safety Network risk score based on duration of surgery, American Society of Anesthesiologists score, and wound class were not highly predictive of chest SSIs. The addition of diabetes, obesity, end-stage renal disease, sex, chronic obstructive pulmonary disease, and Medicaid payer to the model improved the discrimination between procedures that resulted in SSI and those that did not by 25%. Hospital-reported infection prevention practices were not significantly related to SSI rates.

CONCLUSIONS

Additional risk factors collected using a secondary database improved the prediction of SSIs, however, there remained unexplained variation in rates between hospitals.

Performance, revision, and extension of the National Nosocomial Infections Surveillance system's risk index in Brazilian hospitals

OBJECTIVE

To assess the benefit of using procedure-specific alternative cutoff points for National Nosocomial Infections Surveillance (NNIS) risk index variables and of extending surgical site infection (SSI) risk prediction models with a postdischarge surveillance indicator.

DESIGN

Open, retrospective, validation cohort study.

SETTING

Five private, nonuniversity Brazilian hospitals.

PATIENTS

Consecutive inpatients operated on between January 1993 and May 2006 (other operations of the genitourinary system [n = 20,723], integumentary system [n = 12,408], or musculoskeletal system [n = 15,714] and abdominal hysterectomy [n = 11,847]).

METHODS

For each procedure category, development and validation samples were defined nonrandomly. In the development samples, alternative SSI prognostic scores were constructed using logistic regression: (i) alternative NNIS scores used NNIS risk index covariates and cutoff points but locally derived SSI risk strata and rates, (ii) revised scores used procedure-specific alternative cutoff points, and (iii) extended scores expanded revised scores with a postdischarge surveillance indicator. Performances were compared in the validation samples using calibration, discrimination, and overall performance measures.

RESULTS

The NNIS risk index showed low discrimination, inadequate calibration, and predictions with high variability. The most consistent advantage of alternative NNIS scores was regarding calibration (prevalence and dispersion components). Revised scores performed slightly better than the NNIS risk index for most procedures and measures, mainly in calibration. Extended scores clearly performed better than the NNIS risk index, irrespective of the measure or operative procedure.

CONCLUSIONS

Locally derived SSI risk strata and rates improved the NNIS risk index's calibration. Alternative cutoff points further improved the specification of the intrinsic SSI risk component. Controlling for incomplete postdischarge SSI surveillance provided consistently more accurate SSI risk adjustment.