1486
performed with SAS version 9.4 software (SAS Institute, Cary, NC).
Results
From January 1, 2017, to June 30, 2018, our health system experienced 241 HO-CDI LabID events. Among these 241 events, 98 (40.7%) were NAAT-positive/EIA-positive and the remaining 143 (59.3%) were NAAT-positive/EIA-negative (Table). During the first 2 quarters of 2018, we identified 130 NAAT-positive events, of which 31 (23.8%) were EIA-positive and thus were reported as HO-CDI LabID events; the remaining 99 (76%) were EIA-negative. These changes resulted in a major decrease in HO-CDI LabID events in all 3 hospitals from 52.5 to 15.5 events per quarter before and after the NHSN methodology change, respectively. Both the NHSN methodology change (P=.0003) and the hospital (A vs. B+C; P=.0083) had an impact on the number of HO-CDI LabID events (interaction not detected). Hospital A went from 47.75 HO-CDI LabID events per quarter in 2017 to 14 events per quarter in the first half of 2018 (P<.001) (Figure 1). Hospitals B and C went from a combined mean of 2.37 to 1.5 HO-CDI LabID events per quarter (P=.049). The number of NAAT-positive/EIA-positive events remained stable before and after the NHSN definition change in all 3 hospitals (P>.05; Table 1 and Figure 1). Because the adjustment for calculating the predicted HO-CDI
LabID events changed from a NAAT-based test to an EIA-based test in January 1, 2018, the predicted number of events decreased in hospital A from 37.15 predicted events per quarter to 23.93 predicted events in the first 2 quarters of 2018 (P=.0057) (Figure 1). Hospitals B and C combined did not experience an impact in their predicted number of infections, even though hospital B went from community-nonteaching affiliated to community-teaching affiliated (6.9 vs 6.1 per quarter; P>.05). Regarding SIRs, hospital A experienced a drastic drop in SIRs after the methodology change in definition from 1.29 to 0.59 (P=.03); similarly, hospital B’s SIR dropped from 0.69 to 0.22, and hospital C’s SIR decreased from 0.64 to 0.37, before and after the methodology change, respectively (P>.5, both hospitals).
Discussion
The change in HO-CDI LabID event methodology, despite adjustment of the predicted number of events, had a major impact in the number of HO-CDI LabID events and SIRs in one of our hospitals; however, NAAT-positive/EIA-positive events remained unchanged. This change occurred in the absence of any new prevention interventions late 2017 and in 2018. This study demonstrates how changes in the interpretation of the clinical tests can play a major role in the reporting of hospital- acquired infections despite the lack of fluctuations in the underlying number of NAAT-positive/EIA-positive cases. Sev- eral years ago, more than half of the hospitals in the United States transitioned to NAAT-based testing for C. difficile with a concomitant increase in the number of CDI infections.3 Not surprisingly, we found that a reflex-EIA decreased the number of reported HO-CDIs by more than half. However, are we underreporting clinically significant CDI cases by omitting EIA- negative results? The literature is not clear: a couple of studies showed that EIA results do not correlate with disease severity.4,5
Carlos E. Figueroa et al
In contrast, a large prospective observational cohort study showed that virtually all C. difficile-associated complications and deaths occurred in patients with positive toxin immunoassay.6 A recent C. difficile guideline recommended the use of a multistep testing algorithm, such as NAAT followed by EIA.7 However, this guidance clearly recommends testing stewardship by foregoing tests in patients who had received laxatives. Even though we did not present test stewardship data, contrary to hospital A, hospitals B and C were successful in the past couple of years at decreasing inappropriate C. difficile testing. These testing stewardship initiatives included testing early on admis- sion and only when clinically indicated, not testing with laxative use, and rejecting formed stools. Also, hospital A has a large number of beds assigned to immunocompromised patients (19.5%), which are populations at higher risk for toxigenic C. difficile colonization.8,9 In summary, a change in HO-CDI LabID-event methodology
had an immediate and drastic impact in the SIR at a large academic hospital with large number of immunocompromised patients. Future studies should evaluate the impact of these methodological changes elsewhere and using longer observations times.
Acknowledgments. Financial support. No financial support was provided relevant to this article.
Conflicts of interest. L.S.M.P. has received grant funding from Cepheid. N.L. and B.B. have both been consultants for Luminex, have served as speakers for Biofire, and have received grant funding from Cepheid, Alere/TechLab, and GenePOC. All other authors report no conflicts of interest relevant to this article.
References
1. Antibiotic resistance threats in the United States, 2013. Centers for Disease Control and Prevention website.
http://www.cdc.gov/ drugresistance/pdf/ar-threats-2013-508.pdf. Published 2013. Accessed June 30, 2016.
2. Multidrug-resistant organism and Clostridium difficile infection (MDRO/CDI) module. Centers for Disease Control and Prevention website.
https://www.cdc. gov/nhsn/PDFs/pscManual/12pscMDRO_CDADcurrent.pdf. Published January 2018. Accessed July 28, 2018.
3. Lessa FC, Winston LG, McDonald LC. Burden of Clostridium difficile infection in the United States. N Engl J Med 2015;372:2369–2370.
4. Humphries RM, Uslan DZ, Rubin Z. Performance of Clostridium difficile toxin enzyme immunoassay and nucleic acid amplification tests stratified by patient disease severity. J Clin Microbiol 2013;51:869–873.
5. Guerrero DM, Chou C, Jury LA, Nerandzic MM, Cadnum JC, Donskey CJ. Clinical and infection control implications of Clostridium difficile infection with negative enzyme immunoassay for toxin. Clin Infect Dis 2011;53:287–290.
6. Polage CR, Gyorke CE, Kennedy MA, et al. Overdiagnosis of Clostridium difficile Infection in the Molecular Test Era. JAMA Intern Med 2015;175:1792–1801.
7. McDonald LC, Gerding DN, Johnson S, et al. Clinical practice guidelines for Clostridium difficile infection in adults and children: 2017 update by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA). Clin Infect Dis 2018;66:987–994.
8. Cannon CM, Musuuza JS, Barker AK, et al. Risk of Clostridium difficile infection in hematology-oncology patients colonized with toxigenic C. difficile. Infect Control Hosp Epidemiol 2017;38:718–720.
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