Has Aspergillus PCR Come to the Age of Maturity?

Abstract

The diagnosis of invasive aspergillosis (IA) has always been a challenge in immunocompromised patients. Until recently, classical mycological tests were the only diagnostic tools available in this highly lethal condition. However, fungal culture and antibody detection are known for having a low diagnostic sensitivity. Histopathological examination is difficult, because biopsies in such immunocompromised hosts are risky and commonly not obtained, due to low platelet counts. Galactomannan (GM) testing has completely modified this scenario, allowing for an early, sensitive (78 %) and specific (81 %) diagnosis of IA, particularly in the neutropenic population [1]. In conjunction with computed tomography of the thorax, GM has become the backbone of preemptive antifungal therapy. Nowadays, most patients with IA enroll clinical trials or receive antifungal therapy based on GM testing. Nevertheless, there are a number of caveats that sometimes cloud the interpretation of GM results, including a high rate of false-positive results, cross-reaction with fungi other than the Aspergilli, and the reduced sensitivity of serum testing in nonneutropenic patients [2]. Therefore, the scientific community has been at a constant search for alternative non-culture-based and noninvasive diagnostic tests. Polymerase chain reaction (PCR) tests seem to fit quite well these requirements.The diagnostic performance of PCR in IA has been evaluated in several studies. A previous meta-analysis included 1618 at-risk patients from 16 studies to reveal that PCR had a sensitivity of 88 % in the diagnosis of IA [3]. Specificity was 75 % (increased to 87 % if two positive results are obtained). Most studies included in the meta-analysis used whole blood, and sample volume and DNA extraction protocols varied considerably, compromising reproducibility. More recently, a meta-analysis published at the Cochrane Library revealed that the mean sensitivity and specificity of Aspergillus PCR were 80 and 78 % for single positive test results, and 58 % and 96 %, respectively, for two consecutive positive results [4]-a performance very similar to what is known for GM. The elevated negative predictive value of Aspergillus PCR allows for IA to be virtually excluded in the presence of a negative test result. The performance of GM and PCR has been compared in a recent publication. The study showed that the highest diagnostic odds ratio (DOR) was obtained when GM was combined with PCR

A New Age in Molecular Diagnostics for Invasive Fungal Disease: Are We Ready?

“…Assuming a mean prevalence of IA of 13% in a particular patient population, the PPV of Aspergillus PCR increased from 36 to 70% when two positive results were used to define a "PCR positive" episode, while the NPV remained at 96 to 94%. The high NPV of Aspergillus PCR allows IA to be ruled out in the presence of a negative test result with little need for empiric antifungal therapy (Cruciani et al, 2015;Pasqualotto and Falci, 2016). These results were confirmed in a large prospective study to determine the efficacy of PCR screening for early diagnosis of IA in 213 high risk patients undergoing hematopoietic stem cell transplantation or chemotherapy for acute leukemia (Springer et al, 2016a).…”

Consensus guidelines for the diagnosis and management of invasive aspergillosis, 2021

“…Methodology based on that used by the Fungal PCR Initiative consortium is strongly preferred (see the FPCRI website: http://www.fpcri.eu/). 124 In antifungal drug‐naïve patients, a negative PCR result is sufficient to rule out IA (NPV 98%); however, in patients receiving mould‐active prophylaxis, the PPV of PCR is only around 5% 121,123,125 . Using the criteria of two positive results to define a ‘PCR positive’ test improves specificity and accuracy, as does the use of PCR in combination with GM; the latter is associated with earlier diagnosis 108,111,123 …”

The Curious Case of “Case Report” of Infections Caused by Human and Animal Fungal Pathogens: An Educational Tool, an Online Archive, or a Format in Need of Retooling

“…In Table 7, we present the analysis of a few Mycopathologia articles covering clinical and experimental mycology, and the opinions. The articles were from Brazil [95], China [96,97], Colombia [98], Japan [99], the Netherlands [100], and Poland [101]. Interestingly, an impressive number of downloads of a recent article did not lead to high citations [101], while high downloads of a 2016 article garnered impressive citations.…”