Reviewed by: Valeria Fabre, MD, Johns Hopkins University School of Medicine
In 2009, the National Healthcare Safety Network (NHSN) introduced the healthcare facility-onset (HO) laboratory-identified (LabID) CDI events to objectively track nosocomial CDI. Subsequently, a standardized infection ratio (SIR) was developed to allow for inter-hospital comparisons. Two studies recently published in ICHE highlight some aspects of the definition that merit further assessment to ensure accurate measurements and reporting.
Polage and colleagues examined the impact of intensive care units (ICUs), oncology units and hematopoietic cell transplant (HCT) units on the HO-CDI SIR. Using FY 2016 data from eight medical centers in California and the published 2015 rebaseline NHSN HO-CDI SIR, the authors compared facility-wide inpatient HO-CDI events and SIRs, with and without ICU data, oncology and/or HCT unit data, and ICU bed adjustment (unmodified facility-wide SIRs were compared to SIRs where HO-CDI events identified in ICU or ONC-HCT units were removed from the SIR numerator and facility characteristic parameters and data were adjusted for the risk-adjustment model (e.g., removing ICU admissions, ICU patient days, ICU CDI events, and setting the ICU bed adjustment to zero, or similarly removing ONC-HCT unit data) to yield the appropriate number of predicted HO-CDI events in the SIR denominator). Quarterly SIR numerator and denominator data (observed and predicted HO-CDI events) were summed to create fiscal-year data. Findings: the median unmodified HO-CDI SIR was 1.24 (interquartile range [IQR], 1.15–1.34). Removal of ICU data and the ICU bed adjustment decreased HO-CDI events (median, −25%; IQR, −20% to −29%) but increased the SIR at all hospitals (median, 104%; IQR, 90%–105%). Removal of oncology-HCT unit data decreased HO-CDI events (median, −15%; IQR, −14% to −21%) and decreased the SIR at all hospitals (median, −8%; IQR, −4% to −11%). This analysis shows that ICU and ONC-HCT units contributed an excess of HO-CDI cases relative to their bed size and other wards in these hospitals but removing ICU and ONC-HCT unit data had opposing effects on the SIR. Inadequate adjustment for ONC-HCT units in the current SIR may disadvantage general hospitals with large oncology populations. Removal of the ONC-HCT unit data decreased the SIR for all 8 facilities despite the ICU bed adjustment.
In the second study, Puri and colleagues draw attention to the timing of stool collection criteria of the definition with respect to hospital admission. The authors conducted a retrospective cohort study of all LabID cases classified as HO-CDI by the current NHSN definition between June 2011 and September 2019 at 2 medical centers and compared to HO-CDI defined as any positive CDI lab specimen collected 72 hours or more from admission. The authors hypothesized that by using the NHSN >3 calendar day definition, CDI rates are overestimated. Findings: With current NHSN definition HO-CDI rate was 7.58 per 10,000 patient days compared to 6.94 per 10,000 patient days with the aforementioned change in definition, incidence rate ratio of 1.09 (95% CI, 1.00–1.19; P = .0566). Review of the 50 patients with discordant classifications, 62% received antibiotics in the 90 days prior to the positive C. difficile test, 34% came from other facilities, almost 40% had diarrhea upon admission and 30% had been prescribed laxatives upon admission. Even though the difference was not statistically significant, the observation merits further investigation.