Molecular Diagnostic Testing for Aspergillus

Abstract

The direct detection of Aspergillus nucleic acid in clinical specimens has the potential to improve the diagnosis of aspergillosis by offering more rapid and sensitive identification of invasive infections than is possible with traditional techniques, such as culture or histopathology. Molecular tests for Aspergillus have been limited historically by lack of standardization and variable sensitivities and specificities. Recent efforts have been directed at addressing these limitations and optimizing assay performance using a variety of specimen types. This review provides a summary of standardization efforts and outlines the complexities of molecular testing for Aspergillus in clinical mycology.

Non-culture based assays for the detection of fungal pathogens

“…Timely and accurate diagnosis and early initiation of appropriate antifungal treatment significantly improve disease prognosis [93]. Diagnosis of invasive pulmonary aspergillosis is traditionally based on the isolation of fungi of the genus Aspergillus in culture in combination with CME or radiographic findings [95]. However, the sensitivity of culture is low and may take a long time to results.…”

“…On the other hand, ME, as inexpensive and easy-to-perform complementary diagnostic method, improves positive predictive value by confirming positive culture results and provides information about the infecting cell morphology, the state of infected tissues, and biofilm formation, but is not organism specific [41]. Immuno assays which are based on the detection of fungal cell wall biomarkers, such as BDG or Aspergillus GM, have significantly reduced turn-around times compared with ME, but it has been shown that they can be low sensitive and specific in certain patient groups [95].…”

“…Currently, PCR is the most widely applied molecular diagnostic test, which enables amplification and detection of extremely low concentrations (from 1 to 10 pg) of Aspergillus DNA in various clinical specimens such as BAL fluid, serum, plasma, whole blood and biopsy material [94,96]. Also, PCR assays can quickly identify species within the genus Aspergillus from cultures and non-cultured samples which is of great significance for epidemiologic studies and clinical practice given the fact that newly described species such as Aspergillus lentulus and Aspergillus calidoustus have been shown to have elevated minimum inhibitory concentrations (MICs) to several antifungal drugs, including azoles [95]. Due to the lack of standardization and potential false-positive results, PCR was in 2002 excluded from European Organization for the Research and Treatment of Cancer/ Mycoses Study Group (EORTC/MSG) definitions [97].…”

“…Studies have shown that performance of molecular tests varies depending on the specimen type and patient population [95,96]. PCR analysis of blood fractions is the most desired testing modality given that it requires minimally invasive sampling procedure [95].…”

“…Studies have shown that performance of molecular tests varies depending on the specimen type and patient population [95,96]. PCR analysis of blood fractions is the most desired testing modality given that it requires minimally invasive sampling procedure [95]. Also, it is important to emphasize that this method is less exposed to accidental contamination and, in comparison with PCR on BAL samples, offers higher diagnostic sensitivity when screening [94].…”