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Postoperative S. aureus infections decline nearly 50% over 7 years
The incidence rate of Staphylococcus aureus infection declined nearly 50% over 7 years among veterans undergoing major surgery, according to findings from “one of the largest studies describing the long-term incidence of S. aureus in the surgical population of a national integrated health care system.”
Although preventable, postoperative infections are common and S. aureus is a “prevalent” cause. Despite this, William J. O’Brien, MS, a statistician with the VA Boston Center for Healthcare Organization and Implementation Research, and colleagues noted that there has not been enough study into the long-term burden of S. aureus infection among surgical patients.
Therefore, they conducted a retrospective cohort study that included manually reviewed data collected from the VA Surgical Quality Improvement Program and laboratory, microbiology and pharmacy data. The researchers identified surgeries in all major specialties, as well as pneumonia, UTIs, surgical site infections (SSIs) and bloodstream infections (BSIs).
The study population included 559,550 patients who were 74.6% white and 91.4% male. Among this cohort, there was a 1.5% incidence rate of S. aureus infection within 1 year following index surgery.
O’Brien and colleagues observed a yearly decrease in S. aureus incidence over the study period. In 2008, the incidence of infection 1-year after surgery was 2.1% with a decrease to 1.1% in 2015.
“The incidence rate of S. aureus infection among veterans undergoing major surgerydecreased by nearly 50% from 2008 to 2015,” O’Brien told Infectious Disease News. “Only one-quarter of the 1-year infections we identified occurred within a month after surgery, another quarter by month 3, and the remaining half during months 4 to 12. Despite a low and decreasing baseline incidence, the overall burden of S. aureus infection in surgical patients extends well beyond the conventional 30-day measurement period.”
Between 2008 and 2015, the incidence of MRSA infections within the year following surgery decreased from 0.7% to 0.4% and the incidence of methicillin-susceptible S. aureus decreased from 1.4% to 0.7%, the researchers found.
Additionally, the findings underscored the association between S. aureus infection and an increased length of stay, ED use, inpatient admissions and a fourfold increase in mortality.
“It is not known what proportion of the long-term infections are attributable to the initial surgery, therefore these outcomes should not be considered a measure of quality,” O’Brien said. “Our follow-up study, soon to be published, looks at whether surgical patients exposed to 30-day infection are at higher risk of subsequent infection and mortality in the long term.” – by Marley Ghizzone
Disclosures: O’Brien reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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S. aureus is well known to cause infection in the immediate postoperative period of 30 days, leading to increased morbidity, mortality and use of the health care system. Little is known of the burden of S. aureus infection after the 30-day reportable period in surgeries not involving implants. This retrospective cohort study of patients undergoing major surgery in the VA during 2008 to 2015 by O’Brien and colleagues shines light on the extent of the S. aureus infection in surgical patients, up to 1 year after index surgery. The biggest strength of this study is that it has a very large sample size with robust data extracted from a national VA database. Primary outcomes studied included SSI (within postoperative day 30), skin and soft tissue infection (SSTI; after day 30), BSI, UTI and pneumonia. About 75% of all infections happened after the 30-day reportable period, which infers potential underreporting and estimation of the burden of S. aureus infection in the real-world setting. The study also points to higher incidence of infection with podiatry, vascular and thoracic surgery specialties. There was also a statistically significant increase in mortality, ED visits and inpatient admissions in these patients with S. aureus infections implying increased health care costs. This study has its limitations including being retrospective, a predominantly male population and inability to distinguish infection from colonization due to data being extracted from an electronic algorithm. Finally, I am of the opinion that this study should inform designing better perioperative infection prevention strategies and not be used to attribute infections after 30 days period to index surgery.