infection control & hospital epidemiology july 2018, vol. 39, no. 7 letters to the editor


Impact of 2018 Changes in National Healthcare Safety Network Surveillance for Clostridium difficile Laboratory-Identified Event Reporting


To the Editor—Last year we reported the impact of test method (nucleic acid amplification testing [NAAT] versus toxin enzyme immunoassay [EIA]) on the Clostridium difficile laboratory-identified event (LabID-CDI event) standardized infection ratio (SIR) during a 13-month study period (February 2015–February 2016) at the University of Iowa Hospitals and Clinics (UIHC).1 Our current testing algorithm involves testing all samples with combined glutamate dehy- drogenase (GDH) and toxin EIA (C Diff Quik Chek Complete, Alere, Waltham, MA) followed by testing discordant samples with NAAT (GeneXpert C difficile/EpiPCR, Cepheid, Sunnyvale, CA). Using these data, we found that use of NAAT nearly doubled our hospital-onset LabID-CDI standardized incidence ratio (SIR; 0.5 for EIA versus 0.95 for NAAT). We concluded that the National Health Safety Network (NHSN) risk adjustment for test method failed to adequately account for the increased sensitivity of NAAT at our institution.1 Sinceweperformed this


NAAT, or both) in an effort to reduce costs, to obtain addi- tional information about toxin production (to support clinical management), and to maintain the sensitivity of NAAT testing (to help guide infection control efforts).6 We are concerned that the continued inadequacy of risk adjustment by test method, combined with new guidance about the temporal sequence of test result reporting in the event definition, will have unintended adverse consequences. Choice of test approach may be driven primarily by a desire to have LabID-CDI events defined by toxin EIA results rather than NAAT rather than by a desire to choose the test approach that best balances lab resources, clinical management, and infection prevention efforts. The 2 most common algorithms employ toxin EIA testing at different points in the algorithm. A center that starts with GDH/toxin EIA and then settles discrepant results with NAAT will report both toxin EIA- and NAAT-positive results as events, whereas a center that begins with NAAT and follows each positive NAAT with an EIA will only report toxin EIA-positive results as events. Therefore, the same result combination (NAAT-positive, toxin EIA-negative) will be counted as a LabID-CDI event at one center but not at another. If risk adjustment by test method fails to account for


study, theNHSNmodified risk


adjustment formulas for healthcare-associated infections, includ- ing LabID-CDI events, as part of their “2015 rebaseline.”2 In addition, the NHSN changed the test results that define a LabID- CDI event. Starting in 2018, “when using a multi-testing metho- dology .. .the final result of the last test finding which is placed into the patient medical record will determine if the CDI positive laboratoryassaydefinition is met.”3 We re-examined the dataset we previously used to


determine whether the new risk adjustment formula more adequately accounted for test method at UIHC. As outlined in Table 1, we found that the new LabID-CDI SIR model narrowed the difference between toxin EIA and NAAT some- what but that the SIR was still substantially higher when NAAT was the test method reported (ie, 0.89 for NAAT vs 0.61 for toxin EIA). Although the increase in the detection rate asso- ciated with NAAT use varies across centers and regions,4 our data suggest that centers using NAAT as their only CDI detection test or that use NAAT as the last test in an algorithm are being unfairly “punished” with a higher SIR than if they used toxin EIA as the primary test or as the last test in an algorithm. Several different approaches can be used to identify CDI,


and the diagnostic tests used to identify these patients will vary substantially by healthcare facility.5 More centers have now begun using algorithms for testing that include toxin EIA testing in combination with a more sensitive test (ie, GDH,


the difference, hospitals will be inclined to switch to an “NAAT first” algorithm so that they can report lower rates and SIRs. While an “NAAT first” algorithm is an adequate diagnostic


approach, it is far more expensive than the “GDH/toxin EIA first” algorithm because it requires that laboratories test all samples with the more costly NAAT rather than testing the 10%–15% of samples that are not resolved by GDH/toxin EIA testing.


findingwhich is placed into the patient medical record” rather than the lasttestperformed.3 Thus, some healthcare providers have suggested that the laboratory enter the toxin EIA results into the medical record after the other results, regardless of when the toxin EIAtestwas performedinanalgorithm.7 Themere factthatsome healthcare providers have suggested this interpretation indicates that facilities could “game the system” and that the definition must bemore specific. In summary, we found that changes in NHSN LabID-CDI


Finally, the text of the NHSN document refers to “the last test


event reporting do not adequately risk adjust for test method. Furthermore, changes in the event definition for algorithmic C. difficile testing approaches may further complicate the problem by driving laboratories to select testing approaches based upon the NHSN definition rather than on local laboratory and clinical factors. We propose that CDC address these problems (1) by further improving risk adjustment for hospitals using NAAT-only to detect C. difficile and (2) by allowing all hospitals that use toxin EIA in combination with a more sensitive test (ie, GDH EIA, NAAT, or both) for C. difficile detection to report only toxin EIA-positive results as


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