To the Editor—The Centers for Disease Control and Prevention (CDC) National Healthcare Safety Network (NHSN) uses an indirect standardization method for risk adjustment of surgical site infections (SSIs) by which procedures performed at a given hospital are assigned a risk of SSI using a logistic regression model derived from a large standard population based on historical NHSN data from 2015, or the 2015 baseline. ¹ The sum of these risks yields the expected number of SSIs, and the quotient of the observed SSIs (ie, numerator) and expected SSIs (ie, denominator) yields the standardized infection ratio (SIR). This SIR is 1 of 6 performance measures used to calculate the hospital acquired condition score, which can have severe financial repercussions for hospitals in the lowest performing quartile.

In assessing what appeared to be an increasing SIR for abdominal hysterectomy SSI for our hospital, we noted that from calendar years 2017 through 2021, the number of abdominal hysterectomy procedures reportable to the Centers for Medicare and Medicaid Services had drastically decreased from 360 to 234 procedures. ² We attributed this to a patient-centered initiative by the department of obstetrics and gynecology for patients to be discharged home on the date of surgery if the patient is undergoing a low-risk gynecological procedure (eg, laparoscopic abdominal hysterectomy with no comorbidities). This resulted in a significant increase in our outpatient abdominal hysterectomies as defined by the NHSN (ie, where surgery and discharge occur on the same calendar day) from 3% to 49% (χ² for trend P < .01), all of which were excluded from our hysterectomy SIR per the complex 30-day SIR model of the NHSN. ¹ Comparing calendar year 2021 to 2017, this resulted in a 30% decrease in our hysterectomy SSI denominator, corresponding to a 42% increase in our hysterectomy SIR per SSI. For calendar year 2021, exclusion of the same-day discharge procedures resulted in a 47% decrease in our hysterectomy SSI denominator, corresponding with a 90% increase in our hysterectomy SIR per SSI (Pearson correlation coefficient, 0.987, comparing same-day discharge exclusion to increase in SIR per SSI). These metrics are summarized in Table 1.

Table 1. Hysterectomy SSI Denominator Data for Calendar Years 2017–2021

Note. SSI, surgical site infection; SIR, standardized infection ratio.

^a χ² for trend P < .01.

^b (SIR_{with same day discharge} − SIR_{Complex 30-day})/SIR_{with same day discharge} where SIR = 1 SSI/predicted infections.

^c Pearson correlation coefficient = 0.987, comparing same day discharge exclusion to increase in SIR per SSI.

We respectfully question the NHSN risk adjustment model for hysterectomy SSI. Specifically, the exclusion of all outpatient abdominal hysterectomy as defined by the NHSN may create an inaccurate distinction between facilities that discharge on the same day versus the next day for procedures with similar SSI risk. The unintended consequence of this exclusion criterion is to bias the SIR to be higher for hospitals with a high proportion of same-day discharges. Instead, we propose that the NHSN consider patient-specific covariates in lieu of the outpatient exclusion criterion. For example, patients undergoing laparoscopic hysterectomies have a lower risk of SSI than vaginal or abdominal hysterectomies ^{Reference Meltomaa, Mäkinen, Taalikka and Helenius3} and are considered to be the best candidates for same-day discharge. ^{Reference Korsholm, Mogensen, Jeppesen, Lysdal, Traen and Jensen4,Reference Nahas, Feigenberg and Park5} Morgan et al ^{Reference Morgan, Swenson and Streifel6} also highlighted that categorizing open and laparoscopic procedures in the same stratum was a major shortcoming of the NHSN model. Thus, the NHSN might consider whether the exclusion of laparoscopic hysterectomy or stratification on laparoscopic versus other hysterectomy might provide a more accurate representation of SSI risk, rather than the calendar date of discharge following surgery.

Our department of obstetrics and gynecology will continue to advocate for same-day discharge for select gynecological procedures, as supported by mounting evidence of the safety of this practice, better stewardship of inpatient hospital resources, and most importantly, the preference of patients to be at home on the night of surgery. However, we are concerned that the NHSN has not accounted for this critical aspect of patient-centered care in their statistical model, and we propose that the implications of the exclusion of outpatient procedures be reconsidered.