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


The Perils of Multiplex Gastrointestinal Pathogen Panels: Pseudo-outbreaks of Salmonellae and Entamoeba histolytica in Immunocompromised Hosts


Elizabeth Robilotti, MD, MPH;1,2,4 Eleanor Powell, PhD;3 Shauna Usiak, MPH;2 Ying Taur, MD MPH;1,4 N. Esther Babady, PhD;1,3 Mini Kamboj, MD1,2,4


Two distinct clusters of gastroenteritis due to Salmonellae and Enta- moeba histolytica (EH) were identified using a multiplex gastro- intestinal pathogen panel (GPP) at a tertiary-care cancer center. Despite temporo-spatial overlap, our investigation did not corrobo- rate transmission or true infection. In clinical practice, GPPs may render false-positive results.


Infect Control Hosp Epidemiol 2018;39:867–870


surveillance for all pathogens included on the panel. The Luminex GPP has been cleared by the FDA for 14 targets: 8 bacteria, 3 viruses, and 3 parasites. Among them, 5 are reportable to the New York State Department of Health, including Salmonellae and EH. Additionally, under New York State (NYS) and New York City (NYC) Health Code laws,


laboratories are required to submit certain isolates for con- firmatory testing. According to the protocol, isolate recovery for all samples positive by GPP for Salmonellae were attempted using Hektoen Enteric agar plates (Hardy Diagnostics, Santa Maria, CA). All positive raw stool samples on GPP are routi- nely saved and frozen at −80°C.


Cluster 1


Acute diarrheal illness, common among hospitalized immuno- compromised patients has many etiologies, including infection, medications (eg, laxatives), and chemotherapy side effects.1 Rapid assessment of infection is essential to ensure timely ther- apeutic intervention and implementation of isolation precautions in vulnerable patient populations. Multiplex PCR-based panels for gastrointestinal pathogens offer rapid and simultaneous analysis of multiple bacterial, viral, and parasitic pathogens, with highly convenient same-day turnaround of results. Additionally, these assays are less dependent on the technical expertise of laboratory personnel than on traditional methods. For the 2 predominant multitarget gastrointestinal pathogen panels (GPPs) cleared by theUS Food and Drug Administration (FDA), sensitivity and specificity are high. However, clinical experience with routine implementation, particularly in specialized popula- tions and for pathogens uncommon in high-income countries, is insufficient.2–4 This report describes the investigation of 2 clusters of uncommon infections, one Entamoeba histolytica (EH) and the other Salmonellae, in hospitalized patients. Upon in-depth investigation, both clusters were determined to be pseudo-outbreaks related to GPP testing.


methods


The study was conducted at the Memorial Sloan Kettering Cancer Center, a 471-bed tertiary-care cancer hospital in New York, New York, where Luminex xTAG GPP (Luminex Diagnostics, Toronto, Canada) had been implemented in 2014 for the evaluation of stool from patients with diarrheal illness. The infection control department performs routine


From April 19, 2017, to May 4, 2017, 5 cases of EH were identified via routine laboratory evaluation of clinical cases of non–travel-related diarrhea using the Luminex xTAG GPP. Among them, 3 were adult hematopoietic stem cell transplant (HSCT) recipients; 2 cases were diagnosed 2 days apart on the same HSCT unit, while the third occurred in an HSCT reci- pient residing on another unit. The 2 additional cases occurred children with recent inpatient admission or exposure to our facility’s pediatric day hospital.


Cluster 2


Between July 1 and July 5, 2017, 3 cases of infection with Salmonella spp were identified by GPP in hospitalized patients admitted to the same oncology unit. The first 2 cases occurred within 1 day in patients residing in adjoining rooms. The third case was identified 3 days later on the same unit. The 3 patients were cared for by different clinical teams with very limited overlap of support staff. No clinical or ancillary staff reported contemporaneous diar-


rheal illness at the time of either cluster, and no common diet- or procedure-related links could be established among the cases. All patients received targeted antibacterial or antiparasitic therapy for the identified pathogen. Clinical and demographic characteristics of all cases are described below (Table 1).


results Testing


The mean overall inpatient and outpatient GPP testing volume per month for 2017 was 317, compared to 311 for 2016 (Figure 1). This difference was not significant (P=.60; 95% CI, −33.8 to 21). No selective increase in testing was detected among the units with cases. Notably, the 3 cases of Salmonella identified on GPP in October 2017 were identified in out- patients without known prior temporo-spatial overlap. One of


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