Use of censored data to monitor surgical-site infections

Informative Censoring-A Cause of Bias in Estimating COVID-19 Mortality Using Hospital Data

(1) Background: Several retrospective observational analyzed treatment outcomes for COVID-19; (2) Methods: Inverse probability of censoring weighting (IPCW) was applied to correct for bias due to informative censoring in database of hospitalized patients who did and did not receive convalescent plasma; (3) Results: When compared with an IPCW analysis, overall mortality was overestimated using an unadjusted Kaplan-Meier curve, and hazard ratios for the older age group compared to the youngest were underestimated using the Cox proportional hazard models and 30-day mortality; (4) Conclusions: An IPCW analysis provided stabilizing weights by hospital admission.

Examination of Risk Factors for the Development of Surgical Site Infections

INTRODUCTION

Hospital-acquired infections (HAI) and surgical site infections (SSI) are a global public health problem. The aim of the study was to determine the incidence of SSIs at the Surgical Clinics of the University Clinical Centre Banja Luka and to identify risk factors for the development of SSIs.

METHODS

In order to determine the frequency of SSIs through the incidence compared to the patients operated at the Surgical Clinics of the University Clinical Centre Banja Luka, we conducted a prospective cohort study which encompassed 11.216 operated patients, in the period from November 11^th, 2014 to September 30^th, 2015. In order to identify risk factors for the development of SSIs, a nested case-control study of risk factors for SSIs was conducted. The study group consisted of patients who were diagnosed with SSIs in the period of monitoring, while the control group was consisted of patients without SSIs who corresponded with the study group in age and sex.

RESULTS

The highest values of incidence of SSIs were observed at the Department of Anesthesia and Intensive Care (2.65%), Department of Orthopaedic Surgery (2.48%) and the Department of Vascular Surgery (2.15%), and the lowest ones at the Department of Urology (0.59%). Among the cases of SSIs, deep infections of the surgical site were the most represented (82.7%). Multivariate logistic regression was used to identify the following independent risk factors: length of pore-operative stay in hospital (p=0.000; OR=1.062; 95% CI=1.037-1.087), reintervention (p=0.000; OR=22.409; 95% CI=6.361-79.071) and cotrticosteroids (p=0.023; OR=4.141; 95%CI=1.221-14.047).

CONCLUSION

The incidence of SSIs at the Surgical Clinics of the University Clinical Centre Banja Luka is at the level of hospitals in developed countries. There are a number of risk factors for SSIs, which may be prevented.

The Standardized Incidence Ratio as a Reliable Tool for Surgical Site Infection Surveillance

Objective.

To evaluate whether the standardized incidence ratio (SIR) is a more reliable tool for comparing rates and temporal trends of surgical site infection (SSI) in surgery wards than the incidence rate among patients with an National Nosocomial Infections Surveillance system (NNIS) risk index category of 0.

Design.

Observational, prospective cohort study in a sequential SSI surveillance system.

Setting.

Volunteer surgery wards in a surveillance network in northern France that annually conducted SSI surveillance for 3 months from 1998 to 2000.

Methods.

The incidence rate was the number of SSIs divided by the number of patients included, stratified by the NNIS risk index category. SIR was the observed number of SSIs divided by the expected number computed using a multiple regression model.

Results.

Overall, 26,904 patients in 67 surgery wards were enrolled. Between 1998 and 2000, the SSI incidence rate among patients with NNIS risk index category 0 decreased from 2.1% to 1.4%, which was a 33% reduction (P = .002). The SIR decreased from 1.2 (95% confidence interval [CI], 1.1-1.3) to 0.8 (95% CI, 0.7-0.9), which was a 20% decrease per year and an overall 33% reduction. The number of SSIs was significantly higher than expected in 17 of 201 surveillance periods over the 3 years. The classification of the wards according to the 2 indicators over the 3 years showed that wards with a high SIR did not consistently have the highest SSI incidence rate among patients with NNIS risk index category 0, partly because the type of surgical procedure and the duration of follow-up are not taken into account in the NNIS risk index.

Conclusion.

SIR should be considered a reliable indicator to estimate the reduction in SSI incidence that results from implementation of infection control policies and for comparison of SSI rates between wards.

Validation of a Modified Version of the National Nosocomial Infections Surveillance System Risk Index for Health Services Research

Objective.

To validate the National Nosocomial Infections Surveillance system risk index through administrative data to predict surgical site infections.

Design.

Retrospective cohort study.

Setting.

Population-based analysis in Ontario, Canada.

Patients.

All elderly patients who underwent elective surgery from April 1, 1992, through March 31, 2006 (n = 469,349).

Methods.

Data on procedural and patient outcomes were gathered from linked population-wide hospital discharge records and physician claims. The 75th percentile of surgical duration was estimated through anesthesiologist billing fees recorded in 15-minute increments; the American Society of Anesthesiology score of at least 3 out of 5 was estimated by diagnostic codes for severe systemic illness; and all surgeries were classified as clean or clean-contaminated because of their elective nature (thus, the maximum score on the modified index was 2).

Results.

A total of 147,216 surgeries (31%) had a score of 0;246,592 (53%) had a score of 1; and 75,541 (16%) had a score of 2 on the modified index. The 30-day risk of surgical site infection increased with each increment in the modified index (score of 0, 5.4%; score of 1, 8.0%; score of 2, 14.3%; P < .001). The association was evident for surgical site infection diagnosed during the index admission (score of 0, 2.0%; score of 1, 3.7%; score of 2, 8.9%; P < .001), as well as that associated with reoperation or death (score of 0, 0.04%; score of 1, 0.23%; score of 2, 0.73%; P < .001). The modified index predicted increases in surgical site infection risk within each of 11 surgical subgroups. In accord with past research, the modified index had modest discrimination (C statistic, 0.59), and the majority of surgical site infections (72%) occurred within lower risk strata.

Conclusions.

The modified index predicts surgical site infection in population-based analyses and is associated with incremental increases in risk.

Agreement among healthcare professionals in ten European countries in diagnosing case-vignettes of surgical-site infections

OBJECTIVE

Although surgical-site infection (SSI) rates are advocated as a major evaluation criterion, the reproducibility of SSI diagnosis is unknown. We assessed agreement in diagnosing SSI among specialists involved in SSI surveillance in Europe.

METHODS

Twelve case-vignettes based on suspected SSI were submitted to 100 infection-control physicians (ICPs) and 86 surgeons in 10 European countries. Each participant scored eight randomly-assigned case-vignettes on a secure online relational database. The intra-class correlation coefficient (ICC) was used to assess agreement for SSI diagnosis on a 7-point Likert scale and the kappa coefficient to assess agreement for SSI depth on a three-point scale.

RESULTS

Intra-specialty agreement for SSI diagnosis ranged across countries and specialties from 0.00 (95%CI, 0.00-0.35) to 0.65 (0.45-0.82). Inter-specialty agreement varied from 0.04 (0.00-0.62) in to 0.55 (0.37-0.74) in Germany. For all countries pooled, intra-specialty agreement was poor for surgeons (0.24, 0.14-0.42) and good for ICPs (0.41, 0.28-0.61). Reading SSI definitions improved agreement among ICPs (0.57) but not surgeons (0.09). Intra-specialty agreement for SSI depth ranged across countries and specialties from 0.05 (0.00-0.10) to 0.50 (0.45-0.55) and was not improved by reading SSI definition.

CONCLUSION

Among ICPs and surgeons evaluating case-vignettes of suspected SSI, considerable disagreement occurred regarding the diagnosis, with variations across specialties and countries.

Decreasing time trend in SSI incidence for orthopaedic procedures: surveillance matters!

BACKGROUND

Infection is the most common reason for early revision after hip and knee arthroplasty, and the revision rate is increasing. Surgical site infection (SSI) surveillance data are important to assess the true infection rate. There is little information regarding the potential time trend in SSI incidence following orthopaedic surgery.

AIM

To evaluate whether a time trend exists in SSI incidence due to surveillance following orthopaedic surgery.

METHODS

The SSI rates after hip and knee replacements and osteosynthesis of trochanteric femoral fractures and ankle fractures were recorded prospectively from May 1998 to October 2008 according to the criteria of the US Centers for Disease Control and Prevention. In total, 4177 procedures were analysed, 65.8% of which were performed on female patients. Linear regression was used to analyse trends in SSI rates.

FINDINGS

SSI incidence decreased significantly from 7% in the first year to 3% in the last year; a 57% relative reduction. The duration of surgery was the only significant predictor for infection (P < 0.001) in a logistic regression model that also included age, American Society of Anesthesiologists' score and level of emergency.

CONCLUSION

Surveillance following orthopaedic procedures showed a significant decrease in SSI incidence over the 11-year surveillance period. The causality between surveillance and SSI incidence is difficult to prove, but surveillance with feedback probably influences several procedures that affect the quality of health care, even if duration of surgery is the only significant predictor of this effect.

Application of multistate models in hospital epidemiology: advances and challenges

Survival analysis has established itself as a major statistical technique in medical research. Applications in hospital epidemiology, however, are only beginning to emerge. One reason for this delay is that usually complete follow-up of patients in hospital is feasible. This overview discusses where survival techniques provide additional insight into hospital epidemiology, and where they are, in fact, needed even in the absence of right-censoring.

Cluster-randomized, crossover trial of the efficacy of plain soap and water versus alcohol-based rub for surgical hand preparation in a rural hospital in Kenya

Background

The aim of this cluster-randomized, crossover trial was to compare the efficacy of plain soap and water with an alcohol-based handrub for surgical hand preparation and prevention of surgical-site infection (SSI) in a Kenyan rural hospital.

Methods

A total of 3317 patients undergoing clean and clean-contaminated surgery were included. Follow-up data 30 days after discharge were available for 3133 patients (94·5 per cent).

Results

SSI occurred in 255 patients (8·1 per cent), with similar rates for both study arms: 8·3 per cent for alcohol-based handrub versus 8·0 per cent for plain soap and water (odds ratio 1·03, 95 per cent confidence interval 0·80 to 1·33). After adjustment for imbalances between study arms and clustering effects, the main outcome measure remained unchanged (adjusted odds ratio 1·06, 0·81 to 1·38). The duration of surgery and wound contamination class independently predicted SSI. The cost difference between the methods was small (€4·60 per week for alcohol-based handrub compared with €3·30 for soap and water).

Conclusion

There was no statistically or clinically significant difference in SSI rates, probably because more important factors contribute to SSI development. However, this study demonstrated the feasibility and affordability of alcohol-based handrubs for hand preparation before surgery in settings without continuous, clean water. Registration number: NCT00987402 (http://www.clinicaltrials.gov).

Discharge after discharge: predicting surgical site infections after patients leave hospital

In this population-based retrospective cohort study, we examined the frequency, severity, and prediction of post-discharge surgical site infections (SSIs). We evaluated all patients admitted for their first elective surgical procedure in Ontario, Canada, between 1 April 2002 and 31 March 2008. Procedure and patient characteristics were derived from linked hospital, emergency room and physician claims databases within Canada's universal healthcare system. The 30 day risk of SSI was derived from the initial hospital admission, outpatient consultations, return emergency room visits and readmissions. The cohort included 622 683 patients, of whom 84 081 (13.5%) were diagnosed with SSI, and more than half (48 725) were diagnosed post-discharge. Post-discharge infections were associated with an increased risk of reoperation (odds ratio: 2.28; 95% confidence interval: 2.11-2.48), return emergency room visit (9.08; 8.89-9.27), and readmission (6.16; 5.98-6.35). The most common risk index predicted incremental increases in the risk of in-hospital SSI, but did not predict increases in the risk of post-discharge infection. Patients with post-discharge infections had baseline characteristics more akin to uninfected patients than patients with in-hospital infections. Predictors of post-discharge infection included shorter procedure duration, shorter length of stay, rural residence, alcoholism, diabetes and obesity. Post-discharge SSIs are frequent, severe, scattered over time and location, and hard to predict using common risk indices. They represent an important hidden burden in our healthcare system.

Rates of surgical site infection as a performance measure: Are we ready?

With the introduction of quality assurance in health care delivery, there has been a proliferation of research studies that compare patient outcomes for similar conditions among many health care delivery facilities. Since the 1990s, increasing interest has been placed in the incorporation of clinical adverse events as quality indicators in hospital quality assurance programs. Adverse post-operative events, and very especially surgical site infection (SSI) rates after specific procedures, gained popularity as hospital quality indicators in the 1980s. For a SSI rate to be considered a valid indicator of the quality of care, it is essential that a proper adjustment for patient case mix be performed, so that meaningful comparisons of SSI rates can be made among surgeons, institutions, or over time. So far, a significant impediment to developing meaningful hospital-acquired infection rates that can be used for intra- and inter-hospital comparisons has been the lack of an adequate means of adjusting for case mix. This paper discusses what we have learned in the last years regarding risk adjustment of SSI rates for provider performance assessment, and identifies areas in which significant improvement is still needed.

Accounting for incomplete postdischarge follow-up during surveillance of surgical site infection by use of the National Nosocomial Infections Surveillance system's risk index

OBJECTIVE

We examined the usefulness of a simple method to account for incomplete postdischarge follow-up during surveillance of surgical site infection (SSI) by use of the National Nosocomial Infections Surveillance (NNIS) system's risk index.

DESIGN

Retrospective cohort study that used data prospectively collected from 1993 through 2006.

SETTING

Five private, nonuniversity healthcare facilities in Belo Horizonte, Brazil.

PATIENTS

Consecutive patients undergoing the following NNIS operative procedures: 20,981 operations on the genitourinary system, 11,930 abdominal hysterectomies, 7,696 herniorraphies, 6,002 cholecystectomies, and 6,892 laparotomies.

METHODS

For each operative procedure category, 2 SSI risk models were specified. First, a model based on the NNIS system's risk index variables was specified (hereafter referred to as the NNIS-based model). Second, a modified model (hereafter referred to as the modified NNIS-based model), which was also based on the NNIS system's risk index, was specified with a postdischarge surveillance indicator, which was assigned the value of 1 if the patient could be reached during follow-up and a value of 0 if the patient could not be reached. A formal comparison of the capabilities of the 2 models to assess the risk of SSI was conducted using measures of calibration (by use of the Pearson goodness-of-fit test) and discrimination (by use of receiver operating characteristic curves). Goodman-Kruskal correlations (G) were also calculated.

RESULTS

The rate of incomplete postdischarge follow-up varied between 29.8% for abdominal hysterectomies and 50.5% for cholecystectomies. The modified NNIS-based model for laparotomy did not show any significant benefit over the NNIS-based model in any measure. For all other operative procedures, the modified NNIS-based model showed a significantly improved discriminatory ability and higher G statistics, compared with the NNIS-based model, with no significant impairment in calibration, except if used to assess the risk of SSI after operations on the genitourinary system or after a cholecystectomy.

CONCLUSIONS

Compared with the NNIS-based model, the modified NNIS-based model added potentially useful clinical information regarding most of the operative procedures. Further work is warranted to evaluate this method for accounting for incomplete postdischarge follow-up during surveillance of SSI.

[Incidence of surgical site infections in the departments of orthopedics and traumatology]

BACKGROUND/AIM

Besides infections of urinary tract and pneumonias, as well as blood infections, surgical site infections (SSI) represent one of the most common localization of hospital infections. The aim of this study was to determine the incidence of SSI in the departments of orthopedics and traumatology as well as the SSI incidence in relation to the ASA score, surgical site contamination class and NNIS index.

METHODS

A prospective cohort study followed daily all the surgical patients hospitalized over 48 hours in the Institute for Orthopedic Surgery and Traumatology, Clinical Center of Serbia, as well as 30 days after the discharge, during the period betwen February 1 to July 31, 2002. The patients were examined and their diagnoses made according to the definition of hospital infections, i.e. upon clinical and/or laboratory analyses, using concurrently the ASA score, surgical site contamination class and NNIS index.

RESULTS

Out of 227 surgical patients, 60 were diagnosed with SSI during their hospitalization, while 3 of the patients developed SSI after the discharge. The incidence of SSI was 22.7% (95% CI = 17.8-27.6). In the patients with good health condition, i.e. ASA < or = 2, the incidence of SSI was 18.3% (43/235) and in those with ASA > 2, it was 47.6% (20/42) (chi2 = 17.4; p < 0.001). The incidence of SSI was 13.5% (25/185) in the clean wounds, 11.6% (5/43) in purely contaminated, while it was much higher in the contaminated 65.5%; (19/29) and soiled 70.0%; (14/20) wounds (chi2 = 67.6; p < 0.001). The incidence of SSI in relation to NNIS was 8.1% (13/161) in the patients with score 0, then 36.4% (32/88) in the patients with score 1, and 64.3% (18/28) in the patients with the scores 2 and 3 (chi2 = 57.3; p < 0.001). The patients with SSI stayed in the departments of orthopedics and traumatology approximately 1.8 times longer than the patients without SSI (t = 5.3; DF = 275; p < 0.0019.

CONCLUSION

It is important to emphasize the need for constant epidemiological surveillance of SSI and the implementation of preventive measures in Serbia.

Surgical site infection - a European perspective of incidence and economic burden

This retrospective review of reported surgical site infection (SSI) rates in Europe was undertaken to obtain an estimated scale of the problem and the associated economic burden. Preliminary literature searches revealed incomplete datasets when applying the National Nosocomial Infection Surveillance System criteria. Following an expanded literature search, studies were selected according to the number of parameters reported, from those identified as critical for accurate determination of SSI rates. Forty-eight studies were analysed. None of the reviewed studies recorded all the data necessary to enable a comparative assessment of the SSI rate to be undertaken. The estimated range from selected studies analysed varied widely from 1.5-20% - a consequence of inconsistencies in data collection methods, surveillance criteria and wide variations in the surgical procedures investigated - often unspecified. SSIs contribute greatly to the economic costs of surgical procedures - estimated range: 1.47-19.1 billion Euro dollars. The analysis suggests that the true rate of SSIs, currently unknown, is likely to have been previously under-reported. Consequently, the associated economic burden is also likely to be underestimated. A significant improvement in study design, data collection, analysis and reporting will be necessary to ensure that SSI baseline rates are more accurately assessed to enable the evaluation of future cost-effective measures.

Recent developments in the prevention of surgical site infections: preoperative screening and postoperative surveillance

The purpose of this review is to cover the literature on the prevention of postsurgical infections in the period January 2002 to May 2003. Only articles that address novel insights in the prevention of infections are included in this review. The most interesting findings were observed in preoperative screening of patients for nasal carriage of Staphylococcus aureus. Eradication of Staphylococcus aureus in nasal carriers resulted in reduction of postsurgical nosocomial infections due to (endogenous) S. aureus infections. Furthermore, postoperative surveillance studies revealed insight in the incidence of surgical site infections, showed the use of risk indices and identified risk factors important for the development of postsurgical infections.