868 infection control & hospital epidemiology july 2018, vol. 39, no. 7


figure 1. Salmonellae- and Entamoeba histolytica–positive GPPs and overall tests per month January 2016 through December 2017.


these patients remained GPP positive in December. No copa- thogens were identified on GPP or by other routine clinical diagnostic testing (Table 1).


Retesting


A second analysis of the positive specimens was performed with another FDA-approved multiplex assay, FilmArray (BioFire Diagnostics, Salt Lake City, UT). Residual samples, when available, were also sent to the New York City and/or


New York State Department of Health for additional con- firmatory testing, which included EH and E. dispar polymerase chain reaction (PCR; suspected EH cases) and stool culture (suspected Salmonellae cases). These alternative methods did not confirm EH or Salmonella spp in any of the respective specimens. Confirmatory testing results are summarized in Table 1.


discussion


The clusters described here were initially compelling because possible outbreaks because of corroborating gastrointestinal symptoms and close temporo-spatial proximity among cases. Clinical symptoms of both Salmonella and EH are nonspecific and can mimic other types of colitis common among oncology patients such as Clostridium difficile colitis, cytomegalovirus colitis, and gastrointestinal graft-versus-host disease. Further investigation revealed no epidemiologic exposure for the identified pathogen among all patients. While confirmatory results were in progress, clinicians elected to treat patients due to their immunocompromised state and lack of alternate microbiologic explanation before ultimately attributing symptoms to medication side effects. While no adverse events related to treatment of suspected EH or Salmonella were


identified, these patients did endure unnecessary exposure to antibacterials and amebicides. Additionally, substantial personnel time and resources at the local and public health levels were required for the investigation of these pseudo- outbreaks. The associated costs may be an unanticipated expense for health systems that transition to multiplex testing from traditional methodologies. Entamoeba histolytica, the causative agent of amebiasis,


is a common parasitic infection transmitted to humans through contaminated food and water. While it is ubiquitous in many parts of the world, it remains an uncommon cause of diarrheal illness among hospitalized patients in developed countries. The clinical manifestations of intestinal EH infec- tion can range from asymptomatic colonization to severe colitis. For the xTAG GPP, poor specificity for EH was recognized in an early evaluation of the assay for multi- pathogen testing.5 Salmonellae, gram-negative bacteria, frequently cause foodborne gastrointestinal illness. Disease manifestations range from self-limited diarrheal illness to bacteremia and invasive infections especially among immunocompromised hosts. Hospital-based outbreaks due to Salmonellae have been reported, and the occurrence of any cluster should be promptly investigated.6,7 Multiplex panels have several distinct advantages, especially


in terms of turnaround time from sample collection to actionable results and the limited need for specialized labora- tory training. However, these advantages may be undercut by real-world performance in certain patient populations. Currently, data are limited in the reported literature on the real-world performance characteristics of GPP and their associated clinical implications in the evaluation of diarrheal illness in developed nations or among immunocompromised hosts. The specificity issue with Salmonellae and EH detection


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