Update of non-culture methods for laboratory identification of fungal infections

Ref ID: 19350

Author:

G. Quindos and T. Rogers

Author address:

Universidad del Pais Vasco (UPV/EHU), Bilbao, Spain and
Clinical Microbiology, Trinity College Dublin, St James’s Hospital
Campus, Ireland

Full conference title:

6th Trends in Medical Mycology 2013

Date: 11 October 2014

Abstract:

Invasive fungal diseases (IFD) are serious complications in immuno-
compromised patients. Most diseases are caused by Candida and
Aspergillus but emerging fungi are changing the clinical spectrum.
Absence of specific symptoms complicates diagnosis. Recovery of
fungi from blood and deep specimens remain insensitive, leading to
delayed treatment and undesirable mortality. To facilitate early and
safe diagnosis, some useful diagnostic tools or biomarkers, such as
1,3-b-D-glucan, galactomannan, glucuronoxylomannan and man-
nan, anti-Candida antibodies, or fungal DNA, have been developed or
are under development. Some of these biomarkers have been
included in relevant diagnostic guidelines, such as those from ECIL-4,
ESCMID, IDSA, SEIMC, etc. Their main advantage is fastness, as they
do not need 24-48 hours or even weeks for fungal isolation. Con-
versely, rapid elimination and/or low production of some biomarkers
are disadvantages that could be avoided by analyzing serial samples.
Moreover, an important setback is that the etiological agent is not
isolated for additional studies, such as antifungal susceptibility testing
or epidemiological typing. b-glucan is a panfungal marker that can
be present early in the blood and fluids from patients suffering from
IFD. This biomarker is valuable in the diagnosis of invasive candidia-
sis, aspergillosis or pneumocystosis. Its utility is lower or null for
cryptococcosis or mucormycosis. Serum b-glucan concentrations
show a constant rise before clinical and microbiological evidence of
infections, then decrease, and eventually become negative if patients
respond to antifungal therapy. Conversely, patients not responding
do not show a decrease or show a continuous rise. Recent meta-
analyses have reported sensitivity and specificity of 50-90% and 70-
100%, respectively, and high negative predictive values, for proven
or probable IFD.
b-glucan detection is more useful in patients without haematologi-
cal diseases, such as surgical or medical ICU patients. The interpreta-
tion of b-glucan among paediatric patients is difficult because of
false-positives and limited data. Galactomannan may be detected in
the course of invasive aspergillosis and be positive prior to the clini-
cal and radiological suspicions. However, this test has shown contro-
versial results depending on the clinical specimen (serum,
bronchoalveolar lavage or cerebrospinal fluid) and on the specific
patient population: sensitivity is higher among onco-haematologic
patients than in solid organ transplant recipients. Of interest, declin-
ing galactomannan has been observed in patients who responded to
antifungal therapy and rising concentrations in those with fatal out-
comes. Recently, a novel lateral-flow device that uses a monoclonal
antibody, which targets an extracellular glycoprotein of Aspergillus,
has been developed for diagnosis. This device removes most technical
requirements, reducing processing time (<30 min) and preliminary clinical results are promising. Glucuronoxylomannan is essential in the diagnosis of cryptococcal meningitis and tests for its detection are considered paradigmatic. Mannan and anti-Candida antibody detec- tions are helpful for the diagnosis of invasive candidiasis. Detectable concentrations of mannan are of short duration and antimannan antibodies are detected many times after mannan disappearance. Thus, combined detection of mannan and antimannan antibodies is recommended for the diagnosis of candidaemia in adults and neo- nates as it can be positive prior to blood cultures, with sensitivity and specificity rates around 70-85%. Fungal DNA detection in blood, bronchoalveolar lavage or other clinical specimens is a very promis- ing diagnostic tool. Meta-analyses of the use of PCR from blood, serum, or plasma samples for the detection of invasive aspergillosis and invasive candidiasis have reported sensitivity and specificity val- ues of >75% and >85%, respectively. Sensitivity and specificity were
very good for patients with proven IFD, but sensitivity decreased for
patients with probable or possible infections. However, it has a num-
ber of drawbacks that include the lack of standardization and reliable
validation of methods and results obtained among laboratories. To
overcome these problems and to optimize PCR findings, a real-time
quantitative PCR assay based on minimum information for the publi-
cation of real-time quantitative PCR experiments (MIQE) guidelines
has been proposed. Moreover, the introduction in the market of a
number of kits offers the opportunity of testing their actual diagnos-
tic usefulness and their validation before recommendation for clinical
use. Combining methods could improve diagnosis; for instance, PCR
with galactomannan surveillance appears to have best diagnostic
accuracy for invasive aspergillosis.
Although some questions, such as kinetics of biomarkers, assay
performances in different groups, etc., need to be solved, the broader
use of these assays could improve the diagnosis, treatment and prog-
nosis of IFD. A consensus will be necessary for facilitating clinical tri-
als focused on the integration of these techniques into clinical
decision-making. In conclusion, the implementation of non-culture
based methods, alone or in combination with other tests, into the
clinical setting could improve therapeutic approaches and outcome,
by personalizing therapy.

Abstract Number: m12

Conference Year: 2013

Link to conference website: NULL

New link: NULL

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