Surgical Antimicrobial Prophylaxis: Is the Glass Half Empty or More than 99% Full?

Surgical site infections (SSIs) occur relatively infrequently. However, because an estimated 51.4 million surgical procedures are performed each year in the United States, the cumulative annual morbidity and costs attributable to SSIs are huge. In fact, SSI is now the most common and most costly type of healthcare-associated infection. Compliance with process measures in the Surgical Care Improvement Project (SCIP) has been the main focus for SSI prevention efforts in most institutions. Indeed, the timing and type of antimicrobial prophylaxis (AMP) are now the cornerstones of SSI prevention. In this context, Berrios-Torres et al compared the predicted susceptibility of 6,547 pathogens causing 6,236 SSIs from 680,489 primary arthroplasty and coronary artery bypass graft (CABG) procedures reported to the National Healthcare Safety Network (NHSN) with the predicted activity of the various AMP regimens used in nearly 2.4 million arthroplasty and CABG procedures performed in more than 3,300 hospitals participating in SCIP. Two key findings in this report deserve special emphasis. First, less than half of the pathogens causing SSI were susceptible to standard AMP regimens. Second, the most common cause of AMP failure was methicillin-susceptible Staphylococcus aureus (MSSA), a pathogen that was susceptible to all regimens used for AMP in this cohort. The key strength of this study was the inclusion of data on pathogens causing SSI and AMP derived from 2 major databases. The authors also focused their analysis on "complex" SSIs and avoided the surveillance biases inherent in identifying superficial-incisional SSIs. As noted by the authors, the key weakness of the study was the fact that preoperative prophylaxis could not be linked in individual patients to the infecting organism. In addition, variables likely to predict infection due to drug-resistant pathogens, such as obesity, prior receipt of antimicrobial therapy, prior hospitalization, or known prior colonization with a resistant microorganism, were not available. Finally, the analysis utilized imputed susceptibility data for a large proportion of pathogens. This strategy may have failed to account for regional variations in the prevalence of antibiotic resistance across the United States. The authors offer 2 main strategies to decrease the rate of SSIs due to AMP-resistant pathogens: (1) expanding AMP for all surgeries and (2) expanding AMP for selected highrisk patients. The authors describe potential drawbacks with both approaches. These downsides include increased selective pressure that increases antimicrobial resistance and, more importantly, lack of evidence that SSIs would be reduced by modifying AMP. After our review of the results and thoughtful discussion of Berrios-Torres and colleagues, we believe 2 main points deserve specific emphasis. First, we discourage surgeons and epidemiologists from making wholesale changes to AMP. Second, we believe data in this report underscore the need to improve strategies for SSI prevention regardless of whether a patient is at risk for infection due to a resistant pathogen. At first glance, that slightly more than half of all SSIs following the selected surgical procedures were due to AMPresistant pathogens is remarkable. However, this relative proportion of (presumed) AMP failure due to resistant microorganisms needs to be tempered with the fact that the absolute rate of failure was extremely low. For example, the unadjusted rate of SSI among patients undergoing CABG in this cohort was 1.46%. The rate of SSI in patients undergoing arthroplasty surgery was 0.69%. Thus, even if the relative proportion of SSIs due to resistant pathogens after receipt of "standard" AMP was 59%, the absolute rate of treatment failure due to resistant pathogens was 0.86 and 0.41 per 100 procedures, respectively. In other words, more than 99% of patients did not develop a SSI due to a AMP-resistant pathogen. We can think of few therapies that have similar rates of efficacy in clinical medicine.