Surgical site infection in patients in hospitals

Background: Surgical site infection (SSI) is highly prevalent in patients undergoing gastrointestinal operations. As patterns of wound infection in these patients are ever changing, SSI surveillance programs periodically to document the trend of SSI rate in these patients are essential. This study was conducted with the primary intention to audit our SSI rate in elective gastrointestinal operations to monitor closely and sustain good SSI rate.

Methods: We audited of patients undergoing elective clean and clean-contaminated gastrointestinal operations at a tertiary-care hospital in Singapore over four year period. The Criteria and definitions of SSI by the Centers for Disease Control, USA were used to identify and diagnose SSI. We analyzed the yearly SSI rates according to wound types and operative procedures for four consecutive years. We also studied the microbiological pattern of infection in these SSI patients.

Results: From 2006 to 2009, there were 5100 patients who underwent elective gastrointestinal operations. Forty-four SSIs were identified, giving an infection rate of 0.9 SSIs/100 operations. Colorectal operations had 2.9% SSI, upper gastrointestinal gave rise to 0.9%, hepatobiliary operations had 0.8% and hernia operations had 0.1%. Among them, 93% were superficial incisional SSI. The commonest microorganisms involved were E coli (29% among infected sites), MRSA (17%), Enterococcus (14%) and Enterobacter (14%).

Conclusion: In conclusion, our hospital surgical infection rates were lower than the average National Nosocomial Infections Surveillance (NNIS) rates. Clinical Practice Improvement Program (CPIP) is effective in sustaining good result. Appropriate management of preoperative, intraoperative, and postoperative wound care and a surveillance system based on international criteria, were useful in maintaining good SSI rates in our hospital and comparison to international data.

CLINICAL AUDIT OF OUR SURGICAL SITE INFECTION RATE FOR ELECTIVE OPERATIONS IN A DIGESTIVE SURGERY UNIT

INTRODUCTION

Surgical Infection is a preventable complication and efforts made to prevent this complication shall be the priority of every patient. Infection at or near surgical incisions within 30 days of an operative procedure, defined as Surgical Site Infection (SSI), contributes substantially to surgical morbidity and mortality. The incidence of SSI ranges from 2% to 5% for patients undergoing surgical procedures each year in the United States, resulting in 500,000 infections, 3.7 million excess hospital days, and $1.6 billion in extra hospital charges. SSI is the second commonest infective complication, accounting for 20% to 25% of the total nosocomial infection [3]. SSI has been well studied in many hospitals worldwide [4-7].

SSI is considered one of the most important problems in the surgical wards. Although complete elimination of infection in surgical patients is impossible, a reduction of its incidence to a minimal acceptable level can result in great benefits for patients and would save economic resources. The etiology of surgical infection is multifactorial, and the necessity to reduce and control it requires surveillance as well as a hospital-wide effort, with institutional support and leadership.

Accordingly, the best strategy in controlling SSIs is in their prevention. This encompasses meticulous operative technique, timely administration of appropriate preoperative antibiotics, and a variety of preventive measures aimed at neutralizing the threat of bacterial, viral, and fungal contamination posed by operative staff, the operating room environment, and the patient’s endogenous skin flora.

In 2005, our hospital statistic indicated that the infection rates for clean operations and clean-contaminated operations were 1.6% and 4% respectively [ ]. Although these figures might have underestimated the SSI rates as some of the SSI cases were not captured by our system, the surgical team felt that there was room for improving in our SSI rates for clean and clean-contaminated operations. We adopted the Clinical Practice Improvement Program (CPIP) Strategy [5] to improve our SSI rates since 2005 by implementing evidence-based practice. In 2010, we conducted a four-year period audit in a tertiary-care hospital in Singapore. We analyzed our SSI rate each year, the incidence of SSI by operative procedure, microbiological pattern in SSI cases and study the risk factors.

Materials and Methods

Our hospital is a 1440-bed tertiary care public institution. We studied all patients from the Digestive Disease Centre who had elective upper gastrointestinal, hepatobiliary and pancreatic, colorectal, abdominal cavity operations and hernia operations. All patients were followed up for 30 days after operations to identify and diagnose SSI.

Our hospital adopted the criteria put forth by the CDC. SSIs are classified as either incisional or organ/space, with incisional SSIs being further subclassified as superficial (involving only skin and subcutaneous tissue) versus deep (involving underlying soft tissue) [ ].

Surgical wounds are classified according to the level of contamination into Class I (Clean wounds), Class II (Clean-Contaminated wounds), Class III (Contaminated wounds) and Class IV (Dirty-Infected wounds).

Clean wound is defined as an uninfected operative wound in which no inflammation is encountered and the alimentary, genital, or uninfected urinary tract is not entered. In addition, clean wounds are primarily closed and, if necessary, drained with closed drainage. Examples are herniorrhaphy and hepatectomy.

Clean-contaminated wound is defined as an operative wound in which the alimentary, genital, or urinary tracts are entered under controlled conditions and without unusual contamination. Specifically, operations involving the biliary tract and gastrointestinal tract are included in this category, provided no evidence of infection or major breach in technique is encountered.

In our CPIP project launched in 2005, the team brainstormed all factors causing SSI and they were summarized in the Fish-Bone Diagram. The factors were broadly classified as environment, staff, equipment, patients and procedural factors. Using the Pareto methodology, four factors are selected based on priority and evidence-based interventions were designed.

Four interventions were introduced and embedded into our new work flow:

(1) Clippers instead of shavers were used for preoperative hair removal. Signs were used as reminder and patients were instructed not to self-shave preoperatively.

(2) Standardized prophylactic antibiotics regime that is consistent with the Ministry of Health guidelines and the Department of Surgery Prophylactic Antibiotic Regimen, and the timing of antibiotics administration within 30 minutes prior to surgical incision were strictly adhered to by anaesthetists.

(3) Individualized glucose monitoring regime for diabetic patients was implemented. Post-anaesthesia care unit (PACU) and ward nursing officers were assigned the responsibility and accountability for monitoring and control of blood glucose level to ensure that the postoperative blood glucose level is below 11.1mmol/l for all diabetic patients.

(4) Postoperative normothermia within the range of 36.0-38.0 degree Celsius was maintained using warmed forced-air blankets preoperatively, intra-operatively and postoperatively in the PACU; in addition to warmed intra-venous fluids, increased ambient temperature in the operating room and electrical warming blankets are placed under the patients on the operating table.

The workflow was redesigned to embed the above new interventions into our workflow. The project was piloted in the fourth quarter of 2005 and fully implemented in January 2006.

Studied population

All patients undergoing elective major operations in the Department of General Surgery were included in the study. Operations under local anesthesia, trauma patients, emergency operations, infected, contaminated and dirty operations and operations of anorectum, oropharynx, skin grafts, burns or scalds were excluded. All ventral hernia, inguinal hernia, upper gastrointestinal, hepatopancreaticobiliary and colorectal operations under the clean and clean-contaminated categories were included.

From January 2006 to December 2009, 5100 patients underwent elective clean and clean-contaminated gastrointestinal and hernia operations in our department. Out of the 5100 patients, 1863 (36%) patients had hernia operations, 1923 (38%) had hepatopancreaticobiliary operations, 860 (17%) had colorectal operations, 344 (7%) had upper gastrointestinal operations and 110 (2%) had operations to abdominal cavity (Figure 1).

There was both laparoscopic and open type of operations in the casemix of our study. Hernia operation included inguinal hernia, ventral hernia and recurrent hernia operations. Hepatobiliary operation included cholecystectomy, choledochoduodenectomy, common bile duct exploration, hepatectomy, pancreatectomy and splenectomy. In colorectal operations, there were anterior resection, abdominoperineal resection, hemicolectomy and colostomy operations. Upper gastrointestinal operations included total or partial gastrectomy, gastrostomy, Ivor-Lewis operation and Heller’s operation. Abdominal cavity operations comprised of exploratory laparotomy, adhesiolysis, resection of retroperitoneal tumour and abdominal sarcoma operations.

According to the data collected from July 2008 to December 2009, the study group comprised 3:2 ratio of male and female patients; median age of the patients was 59 (16-96) years. The median ASA score was II (I-IV) while median duration of operations was 90 mins (15 – 830 mins).

Data Management

Data were collected from January 1, 2006, to December 31, 2009. Electronic Operating Room reservation system was reviewed every day and the operations that met the inclusion criteria were flagged. The medical records of the patients, operative notes, anesthetic records and microbiology investigation data were reviewed. Information on operative procedure such as the type of operation, degree of wound contamination was also recorded. Medical records of discharged patients in the outpatient department and medical records of readmitted patients were also reviewed for evidence of infection that developed after hospital discharge.

Interim data analysis of SSI rate was done quarterly to evaluate the trend of SSI rates. Frequent updates in charts format were visually fedback to all staff members in the OR, PACU and wards. This allowed the staffs to see how their care could positively impact on the patient outcome and thus motivate them to continue the good practice.

Surgical Site Infection Surveillance

Patients with SSI were identified by both inpatient surveillance and post-discharge surveillance. We realized that a few patients might not be captured in our data collection when they were managed at primary care level. To improve our capture rate, we adopted two levels of surveillance. First was the physical examination of the surgical site of all inpatients with SSI by our surgeons, surgical nurse clinicians, or infection control nurses. Second level of surveillance was the detection of outpatient SSI through post-discharge phone contacts to our patients or patient’s primary care providers by our nurse clinicians or doctors. Outpatient SSI surveillance also included examination of the patients’ wounds during follow-up visits. Post-discharge phone review of our patients also helped to minimize default follow up at the clinic. This process improves our SSI pick-up rate.

Medical records of all SSI patients were thoroughly reviewed by the project leader and the team. Data was captured and SSI was confirmed before classifying it according to the criteria of the Centres for Disease Control and Prevention [6]. Any equivocal cases were moderated by a panel of independent reviewers. Wounds were swabbed for microbiological analysis if a purulent discharge was present at the time of review. Microbiology results were interpreted in conjunction with the clinical information as well as inputs from our microbiologists. A positive culture did not necessarily imply infection and a negative result might not necessarily exclude SSI.

Statistical analysis

Incidence of SSI was calculated by dividing the number of infections by the number of operations performed and then multiplied by 100. The frequency of the organisms identified as causative pathogens responsible for infection was calculated by dividing the number of isolates by the number of infections.

Results

Among 5100 patients, there were 44 SSIs identified between Jan 2006 and Dec 2009, for an overall infection rate of 0.9%. During this interval, SSI rates ranges from 0.3% to 1.9% according to quarterly audits (Figure 2). An increase in the SSI rates (spikes) were noticed in the 3rd quarter of 2008 and 4th quarter of 2009; this could be due to the admission of new staff workers who have yet to be familiarized with our guidelines and protocol for SSI prophylaxis.

Among the 44 SSIs, 41 (93%) were superficial SSIs, 1 (2%) was deep SSIs, and 2 (5%) were organ/space SSIs (Figure 4). The patients were followed for 30 days. The number of Superficial, deep and organ/space SSI in each subspecialty was shown in Table 4.

The overall SSI rate was 0.05% in patients with clean surgical sites and 1.3% in clean-contaminated surgical sites for gastrointestinal and hernia operations over four years. The SSI rates in clean operations were 0% in 2006, 2007 and 2009 and 0.2% in 2008. SSI rates in clean-contaminated operations were 1.1% in 2006, 0.7% in 2007, 1.7% in 2008 and 1.8% in 2009 respectively (Table 1).

Analysis by sub-specialty, the overall incidence of SSI within 4 years was 2.9% in colorectal operations, 0.9% in upper gastrointestinal operations, and 0.8% in hepatobiliary and pancreatic operations and 0.1% in hernia operations. There was no SSI in abdominal cavity operations within four years (Figure 3). The yearly SSI rates in subspecialties were shown in the table 2.

 In 2005, the year prior to SSI prevention CPIP implementation, the SSI rate was 3.1%, this was used as baseline for comparison. Four years after the bundle of interventions was implemented, 99.1% of the elective patients in this cohort were free from SSI, giving the overall SSI rate of 0.9% for both clean and clean-contaminated elective gastrointestinal and hernia operations. This resulted in an overall relative reduction of SSI by 71% within four years when benchmarked against 2005 data for all clean and clean-contaminated elective gastrointestinal and hernia operations (3.1% vs. 0.9%) (Figure 5).

The SSI rate for clean operations over four years was 0.05% and the overall clean-contaminated SSI rate was 1.3%. This resulted in 97% reduction of SSI in clean operations (1.6% to 0.05%) and 68% reduction in clean-contaminated operations (4% to 1.3%) following implementation of CPIP projects (Figure 6).

SSI Microbiology

In the majority of SSI cases, the pathogen source is the native flora of the patient’s skin, mucous membranes, or hollow viscera.7 When skin is incised, underlying tissue is exposed to overlying endogenous flora.8 Most typically, aerobic gram-positive cocci such as Staphylococcus aureus was the frequent contaminant, with resistant pathogens such as methicillin-resistant S aureus (MRSA) representing an increasing proportion of such infections in recent years.9,10 Surgical entry into hollow viscera exposes surrounding tissue to gram-negative bacilli such as Escherichia coli, gram-positive organisms such as enterococcus, and, occasionally, anaerobes such as Bacillus fragilis.2 There is increasing trend of hospital acquired infection in recent years, for example, ESBL represents the hospital acquired infection. In our study, we analyzed 42 culture results of SSI patients and two of the patients did not have cultures. The commonest microorganisms in our SSI patients were Escherichia coli (29%), followed by Staph aureus (26%). Among colorectal SSI cases, the top three microorganisms involved in their wounds were Escherichia coli, MRSA and anaerobes. In hepatobiliary and pancreatic operations, Enterobacter, Enterococcus and Escherichia coli formed the top three organisms (Table 3). The finding that Escherichia coli was the most common pathogen in our SSI patients was surprising as it was not the skin flora, mostly found in the other studies. However, we didn’t find ESBL in the culture of our patients. In our study, S. aureus was the 2nd most common cause of surgical wound infections accounting for 26% of SSI. Of these, 64% were methicillin resistant. Overall MRSA rate in four year period was 1.4 per 1000 operations. Yearly MRSA rates per 1000 operations were 2.8, 0, 2.2 and 3.5 in 2006, 2007, 2008 and 2009 respectively.

In colorectal SSIs, top three organisms found were E coli, MRSA and anaerobes. In hepatobiliary SSIs, microorganisms such as enterobacter, enterococcus and E coli were the commonest. Among upper GI SSIs, we found that both methicillin resistant and sensitive S. aureus and mixed growth as well.