M A J O R A R T I C L E
T2 Magnetic Resonance Assay for the Rapid
Diagnosis of Candidemia in Whole Blood:
A Clinical Trial
Eleftherios Mylonakis,1
Cornelius J. Clancy,2
Luis Ostrosky-Zeichner,3
Kevin W. Garey,4
George J. Alangaden,5
Jose A. Vazquez,6
Jeffrey S. Groeger,7
Marc A. Judson,8
Yuka-Marie Vinagre,9
Stephen O. Heard,10
Fainareti N. Zervou,1
Ioannis M. Zacharioudakis,1
Dimitrios P. Kontoyiannis,11
and Peter G. Pappas12
1
Infectious Diseases Division, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence; 2
Veterans Affairs Pittsburgh
Healthcare System, Division of Infectious Diseases, University of Pittsburgh, Pennsylvania; 3
Division of Infectious Diseases, University of Texas Medical
School at Houston and Memorial Hermann Texas Medical Center; 4
University of Houston College of Pharmacy, Texas; 5
Division of Infectious Diseases,
Henry Ford Health System, Detroit, Michigan; 6
Department of Medicine, Medical College of Georgia at Georgia Regents University, Augusta; 7
Urgent Care
Service, Memorial Sloan Kettering Cancer Center, New York, New York; 8
Division of Pulmonary and Critical Care Medicine, Albany Medical College,
New York; 9
Department of Critical Care Medicine, St Vincent Hospital; 10
Department of Anesthesiology, UMass Memorial Medical Center, Worcester,
Massachusetts; 11
Department of Infectious Diseases, Infection Control and Employee Health, The University of Texas MD Anderson Cancer Center,
Houston; and 12
Division of Infectious Diseases, University of Alabama at Birmingham
Background. Microbiologic cultures, the current gold standard diagnostic method for invasive Candida infec-
tions, have low specificity and take up to 2–5 days to grow. We present the results of the first extensive multicenter
clinical trial of a new nanodiagnostic approach, T2 magnetic resonance (T2MR), for diagnosis of candidemia.
Methods. Blood specimens were collected from 1801 hospitalized patients who had a blood culture ordered for
routine standard of care; 250 of them were manually supplemented with concentrations from <1 to 100 colony-
forming units (CFUs)/mL for 5 different Candida species.
Results. T2MR demonstrated an overall specificity per assay of 99.4% (95% confidence interval [CI], 99.1%–
99.6%) with a mean time to negative result of 4.2 ± 0.9 hours. Subanalysis yielded a specificity of 98.9% (95% CI,
98.3%–99.4%) for Candida albicans/Candida tropicalis, 99.3% (95% CI, 98.7%–99.6%) for Candida parapsilosis,
and 99.9% (95% CI, 99.7%–100.0%) for Candida krusei/Candida glabrata. The overall sensitivity was found to be
91.1% (95% CI, 86.9%–94.2%) with a mean time of 4.4 ± 1.0 hours for detection and species identification. The sub-
group analysis showed a sensitivity of 92.3% (95% CI, 85.4%–96.6%) for C. albicans/C. tropicalis, 94.2% (95% CI,
84.1%–98.8%) for C. parapsilosis, and 88.1% (95% CI, 80.2%–93.7%) for C. krusei/C. glabrata. The limit of detection
was 1 CFU/mL for C. tropicalis and C. krusei, 2 CFU/mL for C. albicans and C. glabrata, and 3 CFU/mL for C. para-
psilosis. The negative predictive value was estimated to range from 99.5% to 99.0% in a study population with 5% and
10% prevalence of candidemia, respectively.
Conclusions. T2MR is the first fully automated technology that directly analyzes whole blood specimens to iden-
tify species without the need for prior isolation of Candida species, and represents a breakthrough shift into a new era
of molecular diagnostics.
Clinical Trials Registration. NCT01752166.
Keywords. T2 magnetic resonance; T2MR; Candida; fungal infections; clinical trial.
Few advances have occurred in the past decades to ad-
equately address the most severe and costly infectious
diseases affecting hospitalized patients, such as invasive
fungal infections. Candida species infections represent-
ed 6% of all hospital-acquired infections in the United
States in 2011, and ranked first among causes of pri-
mary bloodstream infections [1]. Despite antifungal
Received 18 September 2014; accepted 22 November 2014.
Correspondence: Eleftherios Mylonakis, MD, PhD, FIDSA, Infectious Diseases
Division, Warren Alpert Medical School of Brown University, Rhode Island Hospital,
593 Eddy St, 3rd Floor, Ste 328/330, Providence, RI 02903 (emylonakis@lifespan.
org).
Clinical Infectious Diseases®
© The Author 2015. Published by Oxford University Press on behalf of the Infectious
Diseases Society of America. All rights reserved. For Permissions, please e-mail:
journals.permissions@oup.com.
DOI: 10.1093/cid/ciu959
T2MR for Diagnosis of Candidemia • CID • 1
Clinical Infectious Diseases Advance Access published January 12, 2015
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therapy, candidemia has an associated mortality that is as high
as 40% or more [2,3].Along with timely control of the source of
the infection [4], early initiation of appropriate treatment is an
important intervention to improve prognosis, particularly
among patients with septic shock [5, 6]. For example, patients
who receive appropriate antifungal therapy within the first
day after blood is drawn for culture have an estimated mortality
of 24%, with the corresponding figures for treatment 1 and 2
days later being 37% and 41%, respectively [6].
Automated blood cultures, the current “gold standard” for
diagnosis of candidemia, take 2–5 days to finalize, leading to
a significant delay in the implementation of culture-driven
therapy [7, 8]. In contrast, emerging methods, such as matrix-
assisted laser desorption/ionization time-of-flight mass spec-
trometry, require the time necessary for culture to isolate the
pathogen before species identification [9], whereas molecular
methods, in particular polymerase chain reaction methodolo-
gies, have limited clinical adoption to date [10]. The com-
mercially available (1,3)-β-D-glucan assay is not specific for
Candida, and high rates of false-positive results in high-risk
populations have been reported [11].
The lack of diagnostic tools has led to the current clinical re-
ality, where the administration of antifungal agents remains
merely a “best guess” based on the local epidemiology and the
individual patient’s risk factors and clinical picture [7, 12]. This
overuse of the few available antifungal agents is concerning, in
light of the side effects [13] and the excess cost [14], as well as
the association of antifungal treatment with the rise of resistant
pathogens [15–17]. Thus, diagnostic methods that directly test
whole clinical samples and provide rapid, sensitive, and specific
results are long awaited [8, 11, 18–21].
A new nanodiagnostic method using manual application of T2
magnetic resonance (T2MR) to detect Candida species was pre-
viously found to have high sensitivity and specificity and a time to
result of <3 hours [22]. This technology was used to develop an
automated instrument platform, T2Dx, to provide a “patient
sample-to-answer” clinical diagnostic test, T2Candida, which is
currently approved by the US Food and Drug Administration
(FDA). By augmenting the T2MR technology with on-board
sample handling technology, the fully automated T2Dx increases
throughput while also enabling multiplex detection of 5 Candida
species on a single blood sample. Herein, we present the results of
the first extensive clinical trial to validate the sensitivity and spe-
cificity of the new approach to diagnose candidemia.
METHODS
T2Dx Instrument
The T2Dx instrument automatically completes all steps in the
T2Candida panel after specimen loading. Specifically, T2Dx
lyses the red blood cells, concentrates the pathogen cells and
cellular debris, lyses the Candida cells by mechanical bead beat-
ing, amplifies Candida DNA using a thermostable polymerase
(T2Biosystems, Inc) and pan-Candida primers for the interven-
ing transcribed spacer 2 region within the Candida ribosomal
DNA operon, and finally, detects amplified product by ampli-
con-induced agglomeration of supermagnetic particles and
T2MR measurement. The internal control, a synthetic DNA tar-
get, monitors the integrity of the T2Candida results and is pro-
cessed with each clinical specimen. If the internal control is
invalid and there are no positive T2MR signals, an “invalid” re-
sult is displayed, indicating that the specimen could contain in-
hibitors that would interfere with Candida detection. The
readout of the test is positive or negative without any quantifiable
data report. Also, positive and negative T2Candida external con-
trols were run each day before loading clinical specimens for
quality-control checks of the reagents and the T2Dx instrument.
Patients and Data Collection
The clinical trial was conducted from 31 July 2013 to 24 April
2014 at 12 centers (Supplementary Table 1). The institutional
review board of each center approved the study protocol. Writ-
ten informed consent was obtained from all patients. Patients
aged 18–95 years with a blood culture ordered per routine stan-
dard of care during their current hospitalization were enrolled
(ClinicalTrials.gov identifier: NCT01752166).
Sample Collection and Outcomes
A set of aerobic and anaerobic blood cultures and 3 whole blood
T2MR specimens were collected. T2MR clinical specimens were
collected in prelabeled and de-identified K2 ethylenediaminetet-
raacetic acid plastic blood collection vacutainers. Tube A was
stored at room temperature (20°C–25°C) and was analyzed
within 12 hours of collection, whereas tubes B and C were
maintained in frozen storage (−70°C to −80°C).
A total of 300 samples (also collected from patients referred
for a blood culture per routine standard of care) were used for
the contrived arm of the study. More specifically, 250 were man-
ually supplemented (contrived samples) with clinically relevant
titers of the 5 Candida species targeted by the T2MR technology
(C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, and C.
krusei), and 50 were used as negative controls. Different clinical
isolates were used for each specimen. The contrived arm of the
study was developed in collaboration with the FDA prior to the
beginning of the study due to the expectation that the prospec-
tive arm would not recruit candidemic patients representative of
the full range of titer levels in infected patients, and due to the
limitations of blood culture as a comparator, including its poor
sensitivity. Contrived specimens were spiked at known concen-
trations of the targeted Candida species based on FDA input
regarding the range of clinically relevant concentrations. Colo-
ny-forming units (CFUs) were confirmed by culture on yeast
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peptone dextrose agar media. Contrived specimens were de-
identified as to the Candida species and concentration, and
were shipped under refrigerated conditions (2°C–8°C) to each
test site. Each specimen was analyzed within 48 hours of receipt,
after having been placed at room temperature for 1–12 hours to
equilibrate. This incubation at room temperature for up to 12
hours was previously shown to have no effect on the CFUs
per milliliter of the specimens (data not shown). The specimens
of the contrived arm of the study were randomly inserted into
the clinical specimens with which they were tested at the same
time. Finally, the limit of detection (LOD) for the assay was de-
termined by 10 different isolates (2 each from the 5 different
Candida species) using quantified spiked samples. The LOD
was defined as the lowest CFU per milliliter of Candida species
in a specimen that was detected with ≥95% positive detection
for ≥20 replicates. When a different LOD was observed across
the 2 tested strains, the higher level of CFUs per milliliter was
determined as the LOD for that species.
T2Candida panel results are grouped on the basis of antifun-
gal resistance patterns of different Candida species [7], and 3
results are reported: C. albicans/C. tropicalis, C. krusei/C. glab-
rata, and C. parapsilosis. The blood culture specimens were
promptly processed in accordance with routine institutional
practice for a period of 5–7 days, using one of the following
FDA-cleared methods: BacT/Alert 3D system (bioMérieux,
Durham, North Carolina), BacTec FX system (BD Diagnostics,
Sparks, Maryland), and Versatrek system (TREK Diagnostic
Systems, Cleveland, Ohio).
Statistical Analysis
The sensitivity and specificity of the T2MR technology, both per
patient and per assay, were examined by comparing the T2Can-
dida results to the blood culture results and the known Candida
state of the contrived specimens. For the calculation of the sen-
sitivity and specificity per patient, each patient was considered
positive or negative based on all 3 results of the T2Candida
panel, whereas for the per-assay estimations, the 3 results of
each patient were considered separately. The sensitivity and spe-
cificity along with the 2-sided 95% confidence intervals (CIs)
were calculated using the exact Clopper–Pearson method. Con-
tinuous variables were presented as means and standard devia-
tions, and categorical data as relative frequencies. Time to result
of T2MR technology and automated blood cultures was com-
pared using the Student t test. Statistical significance was set
at P = .05.
RESULTS
Study Patients
Overall, 2264 patients were enrolled and 463 were excluded
from the final analysis. In 245 of 463 cases, T2MR yielded an
indeterminate result due to either a technical error (90 cases)
or an invalid result (155 cases) (Figure 1). Therefore, 1801 re-
sults were included in the final analysis. Specifically, 1501 pa-
tients had blood cultures drawn concurrently and from the
same anatomical sites as the T2MR specimens, 250 gave sam-
ples that were spiked with known and clinically relevant con-
centrations of different Candida species, and 50 provided
Candida-negative control samples for the contrived arm of
the study. Table 1 shows the demographic characteristics of
patients.
Sensitivity and Specificity
Results of the primary analysis are shown in Table 2. Among the
250 specimens spiked at concentrations from <1 CFU/mL to
100 CFU/mL for the 5 different Candida species and the 6 pro-
spectively collected specimens that had positive blood culture
results for Candida species, the T2MR technology had an over-
all sensitivity per assay of 91.1% (95% CI, 86.9%–94.2%) and
per patient of 91.0% (95% CI, 86.8%–94.2%). The subgroup
analysis showed a sensitivity of 92.3% (95% CI, 85.4%–96.6%)
for C. albicans/C. tropicalis, 94.2% (95% CI, 84.1%–98.8%) for
C. parapsilosis, and 88.1% (95% CI, 80.2%–93.7%) for C. krusei/
C. glabrata. The LOD was found to be 1 CFU/mL for C. tropi-
calis and C. krusei, 2 CFU/mL for C. albicans and C. glabrata,
and 3 CFU/mL for C. parapsilosis (Supplementary Table 2).
The overall specificity was found to be 99.4% (95% CI,
99.1%–99.6%) per assay and 98.1% (95% CI, 97.3%–98.7%)
per patient. Subanalysis on different Candida species showed
a specificity of 98.9% (95% CI, 98.3%–99.4%) for C. albicans/
C. tropicalis, 99.3% (95% CI, 98.7%–99.6%) for C. parapsilosis,
and 99.9% (95% CI, 99.7%–100.0%) for C. krusei/C. glabrata.
The mean time to negative result, among the prospectively col-
lected samples, was 4.2 ± 0.9 hours compared with ≥120 hours
for blood cultures per institutional protocols. With an overall
sensitivity of 91.0% and specificity of 98.1% per patient, the pos-
itive predictive value of T2MR technology is estimated to range
from 71.6% to 84.2% in a study population with 5% and 10%
prevalence of candidemia, respectively. The corresponding fig-
ures for the negative predictive value (NPV) are 99.5% and
99.0% in respective settings (Table 3).
Among the prospectively collected samples, there were 4
patients characterized as candidemic with the same Candida
species both from T2MR and the companion blood cultures.
The mean time to species identification was 4.4 ± 1.0 hours
for T2MR and 129.9 ± 26.3 hours for the blood cultures
(P < .001). One patient presented with a coinfection of C. albi-
cans and C. parapsilosis in blood culture, and both species were
detected by T2MR technology in a single test.
There were 31 discordant cases (1.7%) between the T2MR
and blood cultures. In 2 cases, the blood cultures identified
the patients as candidemic and the T2Dx instrument did not;
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in 29 cases Candida was detected by the T2Dx instrument but
not by routine blood cultures. Both cases of discordant T2MR-
negative blood culture–positive results were in oncology pa-
tients with central lines who were on antifungal agents prior to
blood draw. In both cases, the identified species was C. albicans.
In the 29 discordant T2MR-positive, blood culture–negative
samples, 18 C. albicans/C. tropicalis, 12 C. parapsilosis, and 1
C. krusei/C. glabrata were identified. Among these cases, there
was 1 with proven candidiasis based on the European Organi-
zation for the Treatment of Cancer (EORTC) criteria [23]. More
specifically, the patient had intra-abdominal C. albicans infec-
tion, which was detected by the T2MR technology and was
proven later with culture of tissue obtained during surgery
after >12 negative blood cultures. Finally, in 4 of 29 cases, Can-
dida species was isolated from other clinical samples (respirato-
ry secretions [3 patients] and urine [1 patient]), but these
patients did not meet established criteria for invasive candidia-
sis. Another 6 patients were receiving systemically antifungal
therapy but had no other evidence of fungal infection.
Among the remaining 18 patients, 5 had a central line, 4 had
undergone stem cell or solid organ transplant (1 patient also
had a central line), and 3 were oncology patients (1 was also a
transplant recipient). The individual characteristics of the pa-
tients with T2MR-positive, blood culture–negative results are
presented in Supplementary Table 3.
Reproducibility of T2MR
Two individual samples spiked with each one of C. albicans,
C. parapsilosis, and C. glabrata, one at a concentration of 1–2
times the LOD and one at 3–4 times the LOD, as well as 1 neg-
ative sample, were tested in triplicate, twice daily for a total of 6
days across 3 different sites. Overall, T2MR was found to be
98.5% reproducible (Table 4).
DISCUSSION
Candida species infections are increasing [24], currently ac-
counting for 6% of all hospital-acquired infections [1]. The
T2MR technology was able to correctly characterize 98.1% of
patients as noncandidemic, with a mean time to negative result
Figure 1. Enrollment and outcomes for the prospective and the contrived arm of the study. *Subjects are counted only once within each main protocol
deviation category, but may be counted multiple times across protocol deviation categories. **Contrived samples delayed by weather or delivery service,
personnel not available to run the specimens, T2Dx instrument not available due to a performance issue, contrived specimen did not load into the sample
inlet due to a clot, or T2 enrollment closed. †
Indeterminate results were due to invalid internal controls (149), instrument malfunction (82), invalid T2 channel
(6), failure of external control (3), sample inlet failure (4), and T2Dx drawer error (1). Abbreviation: CFUs, colony-forming units.
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of 4.2 hours. In a patient population with 6% prevalence of
Candida infections [1], this estimation would correspond to
an NPV of 99.4%. The ability to rapidly and accurately exclude
the possibility of candidemia can have significant implications
in clinical practice, by decreasing the number of patients who
need to be on empiric antifungal therapy [7, 12], and thus de-
creasing the incidence of resistant strains [15–17], the potential
of side effects of antifungal treatment [13], and substantial
healthcare costs [14, 20].
In 29 cases, T2Candida panel results were in discordance
with negative blood cultures. This discordance can represent ei-
ther false-positive T2MR, or false-negative blood culture results.
Blood culture methods, although currently the gold standard
for candidemia diagnosis, are known to have poor sensitivity
in clinical samples and are shown to be positive in only 38%
of proven and probable cases of invasive candidiasis [10], as de-
fined by the EORTC criteria [23]. These discordant results
Table 1. Baseline Characteristics of Study Participants
Characteristic
Prospective
Cohort
(n = 1501)
Contrived
Cohort
(n = 300)
Demographic characteristics
Male sex 840 (56.0%) 180 (60.0%)
Female sex 661 (44.0%) 120 (40.0%)
Age, y, mean ± SD 55.4 ± 15.7 56.9 ± 17.0
Race/ethnicity
White 1170 (77.9%) 251 (83.7%)
Black 302 (20.1%) 26 (8.7%)
Other 29 (1.9%) 23 (7.7%)
Medical history
Immunocompromised subjects 720 (48.0%) 102 (34.0%)
Cancer 379 (52.6%) 62 (60.8%)
Transplant 302a
(41.9%) 20 (19.6%)
Stem cell 130 (43.0%) 2 (10.0%)
Solid organ 171 (56.7%) 17 (85.0%)
Otherb
2 (0.7%) 1 (5.0%)
HIV/AIDS 51 (7.1%) 12 (11.8%)
On steroid therapy 306 (42.5%) 36 (35.3%)
Other IC states 41 (5.7%) 2 (2.0%)
Nonimmunocompromised
subjects
781 (52.0%) 198 (66.0%)
Diabetes mellitus 270 (34.6%) 66 (33.3%)
Abdominal surgeryc
129 (16.6%) 8 (4.0%)
Renal failurec
100 (12.8%) 32 (16.2%)
Cardiovascular 490 (62.7%) 124 (62.6%)
Burnsc
6 (0.8%) 0 (0.0%)
Data are presented as No. (%) unless otherwise indicated.
Abbreviations: HIV, human immunodeficiency virus; IC, immunocompromised;
SD, standard deviation.
a
1 patient had both solid organ and bone marrow transplant.
b
2 patients with islet cell transplant (prospective cohort), 1 patient with right
iliac crest bone graft (contrived cohort).
c
During current hospitalization.
Table 2. Overall Sensitivity and Specificity of the T2 Magnetic
Resonance Method
Sensitivity No. % 95% CI
Overall per patienta
233/256 91.0 86.8–94.2
Overall per assaya
234/257 91.1 86.9–94.2
Per Candida speciesa
C. albicans/tropicalis 96/104 92.3 85.4–96.6
C. parapsilosis 49/52 94.2 84.1–98.8
C. krusei/glabrata 89/101 88.1 80.2–93.7
Per Candida species and per CFU/mLb
C. albicans
<1 CFU/mL 8/10 80.0 44.4–97.5
1–10 CFU/mL 18/18 100.0 81.5–100.0
11–30 CFU/mL 17/17 100.0 80.5–100.0
31–100 CFU/mL 5/5 100.0 47.8–100.0
Overall 48/50 96.0 86.3–99.5
C. tropicalis
<1 CFU/mL 8/10 80.0 44.4–97.5
1–10 CFU/mL 16/18 88.9 65.3–98.6
11–30 CFU/mL 17/17 100.0 80.5–100.0
31–100 CFU/mL 5/5 100.0 47.8–100.0
Overall 46/50 92.0 80.8–97.8
C. parapsilosis
<1 CFU/mL 8/10 80.0 44.4–97.5
1–10 CFU/mL 17/18 94.4 72.7–99.9
11–30 CFU/mL 17/17 100.0 80.5–100.0
31–100 CFU/mL 5/5 100.0 47.8–100.0
Overall 47/50 94.0 83.5–98.7
C. krusei
<1 CFU/mL 6/10 60.0 26.2–87.8
1–10 CFU/mL 18/18 100.0 81.5–100.0
11–30 CFU/mL 17/17 100.0 80.5–100.0
31–100 CFU/mL 5/5 100.0 47.8–100.0
Overall 46/50 92.0 80.8–97.8
C. glabrata
<1 CFU/mL 5/10 50.0 18.7–81.3
1–10 CFU/mL 16/18 88.9 65.3–98.6
11–30 CFU/mL 16/17 94.1 71.3–99.8
31–100 CFU/mL 5/5 100.0 47.8–100.0
Overall 42/50 84.0 70.9–92.8
Specificity
Overall per patienta
1516/1545 98.1 97.3–98.7
Overall per assaya
5114/5146 99.4 99.1–99.6
Per speciesa
C. albicans/tropicalis 1679/1697 98.9 98.3–99.4
C. parapsilosis 1736/1749 99.3 98.7–99.6
C. krusei/glabrata 1699/1700 99.9 99.7–100.0
Abbreviations: CFU, colony-forming unit; CI, confidence interval.
a
Based on the prospective and the contrived arm of the study.
b
Based only on the results of the spiked samples.
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motivated a post hoc analysis of the individual patients’ notes.
This analysis showed that there was 1 case with later proven in-
vasive candidiasis, and 4 cases with Candida species isolation
from other clinical samples, but these patients did not meet es-
tablished criteria for invasive candidiasis. The above findings
indicate that at least some of these discordant results may rep-
resent cases of Candida species infections that were missed by
the blood culture. Importantly, cultures can be inhibited by an-
tifungal agents, and some Candida species may need more than
the typical 5-day culture time to grow [25, 26]. In contrast,
T2MR technology performance has not been shown to be al-
tered by antifungal agents [22].
A significant percentage of the cohort had high-risk host
factors for invasive Candida infections, such as current cancer
or neutropenia, steroid therapy, solid or stem cell transplant,
or current abdominal surgery (Table 1) [23, 27]. Of note,
there were no clinical or mycological inclusion criteria, other
than a blood culture order per routine standard of care. There-
fore, the anticipated prevalence of Candida infections in
our population was low. This allowed the evaluation of NPV
of the new technology to be done with high precision
among a population with high-risk characteristics. The low
Table 3. Positive and Negative Predictive Values of T2 Magnetic
Resonance Method for a Range of Prevalence of Candidemia
Prevalence of
Disease
91.0% Sensitivity/98.1%
Specificity
PPV NPV
1% 32.6% 99.9%
2% 49.4% 99.8%
5% 71.6% 99.5%
10% 84.2% 99.0%
20% 92.3% 97.8%
35% 96.3% 95.3%
50% 98.0% 91.6%
Abbreviations: NPV, negative predictive value; PPV, positive predictive value.
Table 4. Results of the Reproducibility Study
Candida Species Concentration Test Site No. Detected No. Not Detected % Agreement With Expected
C. parapsilosis 1–2× LOD Site 1 36 0 108/108 (100%)
Site 2 36 0
Site 3 36 0
All sites 108 0
3–4× LOD Site 1 36 0 108/108 (100%)
Site 2 36 0
Site 3 36 0
All sites 108 0
C. glabrata 1–2× LOD Site 1 35 1 105/108 (97.2%)
Site 2 34 2
Site 3 36 0
Total 105 3
3–4× LOD Site 1 36 0 106/108 (98.1%)
Site 2 35 1
Site 3 35 1
Total 106 2
C. albicans 1–2× LOD Site 1 35 1 103/108 (95.4%)
Site2 35 1
Site 3 33 3
Total 103 5
3–4× LOD Site 1 35 1 107/108 (99.1%)
Site 2 36 0
Site 3 36 0
Total 107 1
Negative NA Site 1 0 36 108/108 (100%)
Site 2 0 36
Site 3 0 36
Total 0 108
Abbreviations: LOD, limit of detection; NA, not defined.
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anticipated prevalence and the limitations of blood culture as a
gold standard comparator created the need to investigate con-
trived samples for determining the sensitivity of the T2MR
technology.
The T2MR technology was found to have an overall sensitiv-
ity per patient of 91.0%, with a mean time to species identifi-
cation of only 4.4 hours, compared to the 2–5 days typically
needed by the automated blood culture systems [8]. This differ-
ence in time of identification could impact the mortality of can-
didemic patients [5, 6]. Another important aspect of the rapid
speciation is the potential for appropriate choice of antifungal
therapy, as the 5 target Candida species of the T2MR technol-
ogy account for >95% of cases of candidemia [28],and have dis-
tinct antifungal susceptibility profiles [29, 30]. Notably, T2MR
technology was found to have an LOD as low as 1 CFU/mL
for 2 Candida species. This may prove specifically useful in
the diagnosis of candidemia coming from the gastrointestinal
tract, where the burden of organisms is low, especially among
patients on antifungals [31]. Also, T2MR has the potential of
simultaneously identifying >1 species, a unique characteristic,
and particularly interesting in the light of 2%–5% prevalence
of mixed candidemia [32]. However, this high yield needs to
be verified in prospective samples and in comparison with a
combination of clinical, imaging, and autopsy results [23].
Importantly, this new technology has a high sensitivity in
identifying non-albicans Candida species. During recent
years, there has been a shift in the Candida epidemiology,
with non-albicans species representing >50% of clinical isolates
[29]. Among them, C. glabrata is reported to be isolated in as
many as 26% of candidemic patients [33, 34]. Although culture
methods are shown to identify some Candida species in spiked
blood samples with an adequate sensitivity [35–38],this has not
been the case for C. glabrata, with reported sensitivities as low
as 60% in samples spiked with 100 CFU/mL [35–37, 39]. This
might be explained by its slow growth in the blood/broth mix-
ture, which results in a long time to culture positivity, frequently
beyond the typical 5-day culture period [25, 26]. The T2MR
technology was shown to be able to detect C. glabrata at an un-
precedented LOD of 2 CFU/mL with an overall sensitivity of
84.0%.
As a limitation of this study, it should be noted that in 245
cases the T2MR result was indeterminate. We can assume
that rerunning the sample could be a reasonable fix in the
36.7% (90/245) of cases that were due to a technical error. How-
ever, further studies are needed to clarify if this will also happen
in the cases where the T2MR result was invalid. Also, due to the
limited number of candidemic patients who were enrolled in
our study, the clinical sensitivity of T2MR should be assessed
in future studies.
This study presents the results of the first extensive clinical
trial using the T2MR technology. This technology represents
an example of the emerging era of molecular diagnostics,
where rapid, accurate, and species-specific diagnosis directly
on the clinical sample is feasible. A key advantage of T2MR
over other biosensors is that it does not require culture and sam-
ple purification or preparation, making T2MR a promising can-
didate for point-of-care diagnostics of infectious pathogens and
certain noninfectious diseases [9]. T2MR managed to identify
91% of Candida-positive samples and >98% of noncandidemic
patients. Because mortality due to invasive candidiasis has re-
mained high and unchanged for the past 2 decades [29], and
early initiation of appropriate antifungal therapy has been re-
ported to reduce mortality by at least two-thirds [5], the rapid
and accurate diagnostic capability offered by this novel technol-
ogy has the potential to change the management and prognosis
of the disease.
Supplementary Data
Supplementary materials are available at Clinical Infectious Diseases online
(http://cid.oxfordjournals.org). Supplementary materials consist of data pro-
vided by the author that are published to benefit the reader. The posted ma-
terials are not copyedited. The contents of all supplementary data are the
sole responsibility of the authors. Questions or messages regarding errors
should be addressed to the author.
Notes
Acknowledgments. The authors acknowledge Drs Robert Langer and
Tom Lowery for helpful discussions.
Financial support. This work was supported by T2 Biosystems.
Potential conflicts of interest. E. M. has received grant support from
Boehringer Ingelheim, T2 Biosystems, and Astellas and has served on an ad-
visory board for Astellas. C. J. C. has received investigator-initiated research
funding from Merck, Pfizer, and CSL-Behring. L. O.-Z. has received research
grants, consulting, and speaking honoraria from Merck, Pfizer, and Astellas,
and research grants from Associates of Cape Cod and T2 Biosystems.
K. W. G. has received grant support from T2 Biosystems. J. A. V. has served
on the speakers’ bureaus for Astellas and Pfizer, as a consultant for Astellas
and Miravista, and on the advisory board of Astellas, and has received
honoraria from Astellas and research grants from Merck. J. S. G. is on the
clinical advisory board of T2 Biosystems. M. A. J. is a consultant for Celgene,
Novartis, Mitsubishi-Tanabe, Questcor, and Janssen and has received royal-
ties from Springer and UpToDate. D. P. K. is on the advisory board of Merck
and has received research support from Merck, Pfizer, and Astellas and
honoraria from Merck, Astellas, Gilead, and Pfizer. P. G. P has received
grants/research support from T2 Biosystems, Astellas, Gilead, and Merck
and is on an ad hoc scientific advisory committee for T2 Biosystems,
Merck, Astellas, and Gilead. All other authors report no potential conflicts.
All authors have submitted the ICMJE Form for Disclosure of Potential
Conflicts of Interest. Conflicts that the editors consider relevant to the con-
tent of the manuscript have been disclosed.
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