Circulating Aspergillus fumigatus DNA Is Quantitatively Correlated to Galactomannan in Serum

Abstract

The performance of antigen galactomannan (GM) for diagnosing invasive aspergillosis (IA) is hampered by the occurrence of false-positive results. Quantitative PCR has been proposed to improve the diagnosis of IA. Therefore, we analyzed the value of performing a PCR test to the GM-positive serum sample. Using a quantitative PCR assay specific for Aspergillus fumigatus 28S ribosomal DNA, we retrospectively tested 422 GM-positive (Platelia Bio-Rad kit) serum samples collected over 1 year from 147 patients. The cases were classified based on EORTC criteria as "proven," "probable," and "no-IA" before availability of the PCR results. After exclusion of 65 samples for non-reproducibility of GM positivity (n = 62) or PCR inhibition (n = 3), 75 (21.0%) of the remaining 357 samples were PCR-positive. GM and fungal DNA showed a significantly positive correlation (p < 0.0001, R² = 0.27, slope = 0.98 ± 0.19). At least one PCR-positive result was observed in 63.3% (31/49) of IA patients and in 13.2% (13/98) of non-IA patients (p < 0.0001). The PCR positivity was also associated with the presence of other microbiological criteria among the 44 patients with IA and complete mycological workup (p = 0.014), as well as a higher mortality rate at six months among the 135 patients with hematological conditions (p = 0.0198). Overall, we found a quantitative correlation between serum GM and circulating DNA with an increased likelihood of IA when both were positive. A PCR-positive result also supported a higher fungal load when GM was already positive. We advocate adding a PCR test for every confirmed GM-positive serum sample.

Keywords: Aspergillus fumigatus; circulating DNA; galactomannan; invasive aspergillosis; quantitative real-time PCR.

FIGURE 1

Results of the duplicates performed for each PCR-positive sample. The positive duplicates (+/+) had lower mean Cq values than the sample (+/–) with only one duplicate positive (t-test; p < 0.001).

FIGURE 2

Correlation between galactomannan index (GM-ODI) and quantification cycle (Cq) of Aspergillus fumigatus PCR assay in GM-positive serum samples obtained before (A) or after (B) initiation of antifungal therapy.

FIGURE 3

Survival curves according to the presence or not of a PCR-positive result on GM-positive samples (A), to the presence or not of a PCR-positive result associated with EORTC/MSG criteria for IA diagnosis (B), and according to the circulating fungal load as expressed as a Cq value (C).