New Diagnostic Strategies for Fungal Infections
Author:
Ostrosky-Zeichner L, Rex JH
Date: 3 October 2002
Abstract:
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 Anderson 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.
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