Inadequate Prophylaxis Linked to Surgical Site Infections

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Study Will Test Treatment Bundle for Preventing SSIs

Cardiac surgery poses a higher risk for surgical site infections than arthroplasty, but both types of surgery pose a risk for potentially causing catastrophic infections, such as an infected joint or infected bone following sternotomy. The goal of prophylaxis is to drive surgical site infections as low as possible, and my associates and I have begun a study funded by the federal Agency for Healthcare Research and Quality (AHRQ), the STOP SSI study, to test a bundle of prophylactic steps aimed at achieving that, specifically targeted at reducing gram-positive infections.

Dr. Loreen A. Herwaldt

Our first step, as reported at this year’s annual meeting of the Infectious Diseases Society of America, was a literature review and meta-analysis to identify preventive steps that appeared associated with a reduced rate of SSIs in patients undergoing cardiac surgery or primary replacement of a hip or knee. We will now make available these best practices measures to all hospitals in the Hospital Corporation of America network. In addition, as part of our AHRQ project, we will identify about 20 Hospital Corporation of America hospitals that perform these two types of surgeries to participate in a pre- and postintervention study assessment. We will review data on the SSI rates at these 20 hospitals before the new intervention enters routine use, and then compare that performance with the SSI rate following implementation.

The intervention has three main components: All patients scheduled for cardiac or primary hip or knee surgery should undergo screening to determine whether they are nasally colonized with Staphylococcus aureus. Carriers receive mupirocin ointment in their nose if they are not allergic to the drug. Also, patients who carry methicillin-resistant S. aureus receive prophylactic antibiotic treatment with vancomycin in addition to the standard prophylactic antibiotic, cefazolin. Finally, all patients undergo a chlorhexidine bath before surgery. Similar bundled approaches have been successfully applied to reduce the rates of central-line–associated bloodstream infections and ventilator-associated pneumonia.

The AHRQ targeted gram-positives in this initial study because these pathogens cause the majority of SSIs in the United States following these types of surgeries. Although cefazolin provides some gram-negative coverage, its routine use may not completely prevent gram-negative SSIs. Before we embark on testing a routine intervention designed to prevent gram-negative SSIs, we should first run a study to identify risk factors that define a subgroup of cardiac surgery and arthroplasty patients at increased risk for gram-negative SSIs. If 99% of these surgery patients do not develop gram-negative SSIs, we should not routinely treat everyone with additional drugs that will increase costs and may also boost complications. A better option would be identifying the patients at risk for a gram-negative SSI who stand to benefit most from extended-spectrum prophylaxis.

Dr. Loreen A. Herwaldt is a professor of medicine and hospital epidemiologist at the University of Iowa in Iowa City. She said that she has no disclosures. Dr. Herwaldt made these remarks in an interview.



BOSTON – Just 1% of all surgical procedures are associated with complex surgical site infections, but many develop in association with ill-suited prophylactic antibiotic regimens, according to an analysis of more than 2.4 million American who underwent cardiac or orthopedic surgery during 2006-2009.

Nevertheless, "the vast majority [of surgery patients] don’t get SSIs. Do we want to modify treatment for all patients to address the small proportion who get complex SSIs?" asked Dr. Dale W. Bratzler.

The low overall rate of complex SSIs suggests that any changes to standard SSI prophylaxis regimens should proceed cautiously. "What we need most are strategies for identifying patients at high risk for SSI due to drug-resistant organisms for targeting modified antimicrobial prophylaxis regimens," said Dr. Bratzler, a professor in the department of health administration and policy of the University of Oklahoma, Oklahoma City.

The analysis he reported at the annual meeting of the Infectious Diseases Society of America used data from two large U.S. databases collected from January 2006 to December 2009. Information on the pathogen distribution of SSIs came from the National Healthcare Safety Network database of the Centers for Disease Control and Prevention, which included data from 1,389 U.S. hospitals during this period on the number and type of SSIs that occurred in patients who underwent coronary artery bypass grafting (CABG), and those who had primary total hip or total knee replacement surgery. The second database, from the Hospital Inpatient Quality Reporting Program of the Centers for Medicare and Medicaid Services, collected data on the type of antimicrobial prophylaxis received by patients who underwent these surgical procedures at 3,330 U.S. hospitals.

"Do we want to modify treatment for all patients to address the small proportion who get complex SSIs?"

The National Healthcare Safety Network data showed that a total of 3,024 patients developed a complex SSI among the 207,053 who underwent CABG (1.5%), and 3,532 patients had a complex SSI among the 495,529 patients who had primary hip or knee replacement surgery (0.7%), Dr. Bratzler reported. Complex SSIs were defined as either deep incisional infections, or infections of an organ or surgical space. Among the CABG-associated complex SSIs, 34% were caused by gram-negative bacteria, with the balance caused by gram-positive pathogens, and 17% of all SSIs involved methicillin-resistant Staphylococcus aureus (MRSA). In the arthroplasty patients, 18% of the complex SSIs involved a gram-negative pathogen, and 21% of all infections had MRSA involvement.

The data on type of antibiotic prophylaxis used showed that among 428,541 patients who underwent CABG in this dataset, 67% received "standard" prophylaxis with either cefazolin or cefuroxime; 12% received a regimen designed for patients with beta-lactam allergy with either vancomycin or clindamycin, plus an aminoglycoside added at the provider’s discretion; and 15% had prophylaxis with an extended-spectrum regimen consisting of either vancomycin plus cefazolin or cefuroxime, or an aminoglycoside plus cefazolin or cefuroxime. The remaining 6% of patients received another prophylaxis regimen.

Dr. Dale W. Bratzler

The prophylaxis data for 2,007,162 arthroplasty patients showed that the standard regimen was used in 77%, the beta-lactam allergy regimen in 13%, and the extended-spectrum regimen in 7%, with the remaining 3% of patients receiving something else.

Dr. Bratzler then compared the expected efficacy of the three most commonly used regimens against the pattern of SSIs that actually occurred in these patients. Patients who received the standard regimen could expect protection against about 40% of the types of bacteria that actually wound up producing SSIs. Patients who received the beta-lactam allergy regimens could expect protection against 56%-96% of the pathogens that actually caused the SSIs, and patients who received the extended-spectrum regimens could expect protection against 69%-96%, he said.

The researchers could not do a more detailed analysis of the relationship between the type of prophylaxis used and the pattern of SSIs that subsequently developed because both databases were anonymous, which precluded cross-referencing the information.

Dr. Bratzler said that he had no disclosures.

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