New Diagnostic Strategies for Fungal Infections

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New Diagnostic Strategies for Fungal Infections Ostrosky-Zeichner,

MD H. Rex, MD Disclosures San Diego, Saturday,

September 28, 2002 -- Medical mycology has faced an enormous obstacle

for decades: timely and accurate diagnosis of invasive fungal

infections. These infections are difficult to diagnose because cultures

are often negative, or they become positive late in the disease. If a

culture is positive, accurate identification of the organism is

laborious and time-consuming, relying on macroscopic and microscopic

morphologic characteristics, biochemical tests, and serotyping.

Physicians and microbiologists have recognized these limitations and

have been intensively developing alternative diagnostic methods for

decades. Some of these have been very successful, such as the

cryptococcal and histoplasma antigen detection methods, which have

become diagnostic standards due to their availability and diagnostic

performance.[1-4] Some, on the other hand, have been frustrating and

laid to rest, such as Candida antibodies and metabolites.[5,6] More

recent advances include the detection of genetic material of organisms

by polymerase chain reaction (PCR) and detection of the fungal cell

components such as galactomannan and beta-glucan. The 42nd ICAAC

showcased important examples in this field. Fungal PCR has been a venue

with intense research. Aspergillus has been by far the most explored

fungus, but assays are now being developed for multiple organisms.[7-8]

There are now a multitude of techniques that include both quantitative

and qualitative methods, real-time PCR, and a combination of PCR and

enzyme-linked immunosorbent assay (ELISA). These assays can be carried

out on blood and other fluids, such as bronchoalveolar lavage.[9-11]

Once the techniques are fully standardized, the primers decided on, and

the tests readily available in clinical laboratories, this area holds

promise as the standard for diagnosis of these infections.

The detection of fungal cell wall components is also very promising. The

galactomannan assay for Aspergillus has shown repeated good performance

in a variety of settings and hosts, and widespread use is

anticipated.[12] Detection of beta-glucan showed very good sensitivity

and specificity, but more important, it showed an impressive negative

predictive value.[13]

Finally, advances were also reported in culture methods and conditions.

Researchers at MD Cancer Center, Houston, Texas, suggested that

cultures in a microaerophilic environment at 35oC may improve the

recovery chances for Aspergillus from clinical specimens, since it may

be similar to the tissue microenvironment.[14] The future holds faster

and more reliable diagnostic techniques, which in turn may improve

patient outcomes. Advances in the field are very encouraging.

Becki

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