More than 40 million surgical procedures are performed annually in the United States, and sepsis remains a major postoperative complication [1
]. Surgical sepsis accounts for approximately 30% of all sepsis patients [13
]. The majority of published data on postoperative sepsis are derived from single institutions. Although these studies are important, they offer limited information about the demography of sepsis or temporal changes. As well, the generalizability of small series may be difficult. The use of population data for postoperative surgical sepsis is not well represented in the literature, although there have been multiple studies evaluating population data for the occurrence of medical sepsis [9
These data have demonstrated that trends in the age-adjusted rates of postoperative sepsis and the proportion of severe sepsis among all sepsis cases has increased significantly for both elective and non-elective procedures over the 17-year study period. During the study period, the overall hospital mortality rate among surgical sepsis patients with non-elective admission was reduced. Of concern is that elective surgical cases failed to show a decrease in age-adjusted rates of mortality for postoperative sepsis. Previous population data evaluating all cases of sepsis (medical and surgical) have reported that the incidence of sepsis and the number of sepsis-related deaths are increasing, although the overall mortality rate among patients with sepsis is declining [9
This population-level study demonstrates an increase in the rate of sepsis for elective surgical procedures over time with no significant improvements in the mortality rate. The proportion of cases of severe sepsis also was found to increase for elective surgery, from 32.9% to 64.6%. This significant increase suggests greater severity of sepsis as well as a higher incidence over time. The reasons for this increase in the rate and severity of sepsis after elective surgery remain unclear, but may reflect changes in the elective operative case mix over time. That is, more elective operations may be performed as outpatient procedures or with short lengths of stay, leaving sicker patients and those having more extensive procedures in the in-patient surgery cohort.
This study also demonstrates differences in the incidence of postoperative sepsis with age. Previous large population studies have looked at global sepsis rates (medical and surgical) and have demonstrated that the incidence of sepsis was disproportionately increased in elderly adults, and age was an independent predictor of death [27
]. The aged were more likely to develop sepsis and severe sepsis after surgery and had a higher mortality rate after developing sepsis. Possible reasons for this disparity may be more frequent co-morbidities, institutionalization, declining performance status, and age-associated immunosenescence with defects in immunologic function in the aged [28
]. Further analysis is needed to address procedures associated with sepsis in the elderly, as the aged are the fastest-growing segment of the U.S. population [30
Sex differences in the occurrence of sepsis are suggested by these data. We found that male patients were more likely to have postoperative sepsis. Further focused studies assessing sex disparities will be needed; we were not focused on that subject in this project. Several studies have evaluated the effect of sex and hormone concentrations on sepsis [31
], suggesting that sex may have a role in the development of sepsis. Others have suggested that sex hormones play a significant role in shaping the host response to trauma [33
]. Further analyses at a population level may help to identify procedures, co-morbidities, and other factors that influence the likelihood of developing postoperative sepsis.
These data also suggest disparities among ethnicities in the incidence of postoperative sepsis. We have demonstrated that the lowest rates of sepsis were in whites and the highest rates were in blacks. These disparities were seen with similar distributions after elective and non-elective procedures. Although other studies have evaluated the effect of race on medical sepsis [35
], there are few data evaluating ethnicity and its influence on postoperative sepsis. The reasons for these disparities remain unclear, but considerations may be more co-morbidities in blacks, different access to care, or physiological differences yet to be determined. Further, more detailed evaluations of race and postoperative sepsis are required.
With regard to the evaluation of pathogens associated with sepsis, elective surgical procedures demonstrated a significant increase in the rates of the streptococcal and staphylococcal septicemias. This finding is supported by other population studies, which have shown that the nosocomial blood stream infection rate in the hospital has nearly doubled in the past 10 years, largely secondary to an increase in primary staphylococcal bacteremia [36
]. As well, the epidemiology of severe surgical site infection (SSI) in community hospitals and the prevalence of methicillin-resistant S. aureus
SSI has increased significantly over the past years [37
]. The inpatient S. aureus
infection rate and the economic burden of S. aureus
infections for all U.S. hospitals increased substantially from 1998 to 2003 [38
This study has several limitations. The New Jersey State Inpatient Databases do not include patients in military hospitals or Veterans Affairs medical centers. Moreover, the administrative data originally were intended primarily for determination of reimbursement, although there are reports validating the use of administrative data for research purposes [9
]. In addition, the potential for inclusion bias based on limited coding schemes for the many clinical entities cannot be entirely excluded. For this analysis, we selected codes for systemic infection that were effective and unchanged during the study period, and, therefore, the addition of new codes should not have affected our selection. It is possible that there has been more thorough capture of codes by institutions based on reimbursement over time and greater emphasis on capturing sepsis events. Although the code scheme remained constant throughout the study, there may be upcoding by the institutions, and this cannot be evaluated from the dataset. We assume this change to have been slow over time and unlikely to affect the findings for the severity of sepsis.
We realize that more elective operations may now be performed on an outpatient and 23-hour admission basis, leaving patients who are sicker and are having more complex procedures in the in-hospital surgery cohort. We also acknowledge that there is a trade-off in using administrative data on hundreds of thousands of patients compared with the use of smaller cohorts with more refined clinical information. Although both types of studies have drawbacks and strengths, we believe that administrative data provide valuable population-based information on trends and severity of sepsis.
In conclusion, these population data have shown a significant increase in age-adjusted rates of postoperative sepsis over time. Despite the higher incidence of sepsis, the overall mortality rate improved, perhaps secondary to progress in surgical critical care, greater utilization of surgical intensivists, or alterations in the antibiotics or strategies employed. Of significant concern is the lack of advances in the elective surgery cohort. Elective surgery had the greatest increases in sepsis rates as well as the greatest increases in the proportion of severe sepsis cases. Elective surgery also failed to show a decrease in age-adjusted rates of death for postoperative sepsis over time. Directions for future research using population data for postoperative sepsis may include the analysis of the specific procedures associated with sepsis and the focused evaluation on the various racial and sex disparities in the development of postoperative sepsis. These data may also serve to track the effectiveness of care and function as hypothesis generating to initiate future studies focused on improvement of surgical outcomes.