In the JournalsPerspective

Current method of calculating SSIs underestimates rates of some procedures

Jessica L. Seidelman, MD, MPH
Jessica L. Seidelman

The current CDC National Healthcare Safety Network method of calculating rates of surgical site infection, or SSI, underestimates the SSI rate in procedures like laminectomies and rectal surgeries that are performed with higher-ranking procedures, researchers found.

Jessica L. Seidelman, MD, MPH, a medical instructor in the division of infectious diseases at Duke University School of Medicine, and colleagues from the Duke Infection Control Outreach Network (DICON) help hospitals submit data to the National Healthcare Safety Network (NHSN).

“In our process of reviewing SSIs, we realized that hospitals were calculating denominators differently and this prompted us to take a deeper look at SSI denominators,” Seidelman explained to Infectious Disease News.

Seidelman and colleagues performed a retrospective analysis of SSI surveillance data from 11 hospitals in DICON from Jan. 1, 2015, to Dec. 31, 2017, including only hospitals where 200 or more primary spinal fusions and 200 or more primary colon surgeries were performed to ensure rates were not affected by low procedure volume.

“We examined SSI rates of laminectomies and rectal procedures using two different denominators: (1) current NHSN definition or (2) only when the rectal or laminectomy procedure was the primary procedure (ie, adjusted SSI rate),” they wrote.

According to the study, infection preventionists identified 87 SSIs associated with 17,247 laminectomies and seven SSIs associated with 740 rectal procedures. After calculating percentages, the researchers found that the NHSN SSI rate and adjusted SSI rate for laminectomies were 0.5 and 0.72, respectively, showing a 30.6% increase. For rectal surgeries, the NHSN and adjusted rates were 0.95 and 2.3 respectively, representing a 58.7% increase.

“The key finding is that the current proposed method for calculating denominators is troublesome in that if you have a surgery that involves both a rectal procedure and a colon procedure, but the infection is attributed to the colon procedure, then this counts toward the colon numerator and denominator, but only the rectal denominator. This potentially leads to misleading SSI rates. If we are not going to count a procedure in the numerator, we should also not count it in the denominator,” Seidelman said. “If we want to have clinicians and hospitals make informed decisions for their patients, then we need to ensure that the data they use to make those decisions are accurate.” – by Caitlyn Stulpin

Disclosure: Seidelman reports no relevant financial disclosures.

Jessica L. Seidelman, MD, MPH
Jessica L. Seidelman

The current CDC National Healthcare Safety Network method of calculating rates of surgical site infection, or SSI, underestimates the SSI rate in procedures like laminectomies and rectal surgeries that are performed with higher-ranking procedures, researchers found.

Jessica L. Seidelman, MD, MPH, a medical instructor in the division of infectious diseases at Duke University School of Medicine, and colleagues from the Duke Infection Control Outreach Network (DICON) help hospitals submit data to the National Healthcare Safety Network (NHSN).

“In our process of reviewing SSIs, we realized that hospitals were calculating denominators differently and this prompted us to take a deeper look at SSI denominators,” Seidelman explained to Infectious Disease News.

Seidelman and colleagues performed a retrospective analysis of SSI surveillance data from 11 hospitals in DICON from Jan. 1, 2015, to Dec. 31, 2017, including only hospitals where 200 or more primary spinal fusions and 200 or more primary colon surgeries were performed to ensure rates were not affected by low procedure volume.

“We examined SSI rates of laminectomies and rectal procedures using two different denominators: (1) current NHSN definition or (2) only when the rectal or laminectomy procedure was the primary procedure (ie, adjusted SSI rate),” they wrote.

According to the study, infection preventionists identified 87 SSIs associated with 17,247 laminectomies and seven SSIs associated with 740 rectal procedures. After calculating percentages, the researchers found that the NHSN SSI rate and adjusted SSI rate for laminectomies were 0.5 and 0.72, respectively, showing a 30.6% increase. For rectal surgeries, the NHSN and adjusted rates were 0.95 and 2.3 respectively, representing a 58.7% increase.

“The key finding is that the current proposed method for calculating denominators is troublesome in that if you have a surgery that involves both a rectal procedure and a colon procedure, but the infection is attributed to the colon procedure, then this counts toward the colon numerator and denominator, but only the rectal denominator. This potentially leads to misleading SSI rates. If we are not going to count a procedure in the numerator, we should also not count it in the denominator,” Seidelman said. “If we want to have clinicians and hospitals make informed decisions for their patients, then we need to ensure that the data they use to make those decisions are accurate.” – by Caitlyn Stulpin

Disclosure: Seidelman reports no relevant financial disclosures.

    Perspective
    Michael S. Calderwood

    Michael S. Calderwood

    When discussing operative risks with a patient, it is helpful to have accurate data on both institutional and national rates of SSI following the procedure being discussed. One source of data is the procedure and infection data that hospitals report to CDC’s NHSN. These data, however, are only as good as the data being submitted.

    The article by Seidelman and colleagues raises concerns about the rates of infection being underestimated for some procedures due to how things are counted when multiple procedures are performed through the same incision. The examples used in the paper are when rectal and colon surgeries are performed through the same incision and when laminectomy and spinal fusion are performed through the same incision. If a hospital counts the case in the denominator for both procedures but only counts an SSI as attributable to the “highest-ranking” procedure (eg, colon surgery, spinal fusion), then the SSI rates following lower ranking procedures (eg, rectal surgery, laminectomy) may be underestimated.

    Because SSIs following colon surgery are publicly reported, with data on these SSIs used by the CMS to assess hospital performance in both the Hospital-Acquired Condition Reduction Program and the Hospital Value-Based Purchasing Program, attributing SSIs to colon surgery rather than other concurrent intra-abdominal surgeries helps to ensure that hospitals are compared using the same attribution rules. The downside to this practice is that it can complicate the assessment of SSI risk for the other procedures.

    Seidelman and colleagues propose including only primary procedures in the SSI denominator when calculating SSI rates and Standardized Infection Ratios. This seems like a good way to ensure more accurate data for the procedures where concerns have been raised about underestimated SSI rates, but it is also important to report on the SSI risk from more complex surgeries involving multiple procedures through the same incision. Accounting for the number and type of concurrent procedures may help to provide SSI data that are most relevant when counseling an individual patient on SSI risk. In addition, other patient risk factors (eg, obesity, diabetes, smoking) and surgical technique (eg, laparoscopic vs. open) must be considered when assessing individual risk.

    • Michael S. Calderwood, MD, MPH
    • Regional hospital epidemiologist, Dartmouth-Hitchcock Medical Center
      Associate professor of medicine, Geisel School of Medicine at Dartmouth

    Disclosures: Calderwood reports no relevant financial disclosures.