The impact of anti-mould prophylaxis on Aspergillus PCR blood testing for the diagnosis of invasive aspergillosis.

BACKGROUND: The performance of the galactomannan enzyme immunoassay (GM-EIA) is impaired in patients receiving mould-active antifungal therapy. The impact of mould-active antifungal therapy on Aspergillus PCR testing needs to be determined. OBJECTIVES: To determine the influence of anti-mould prophylaxis (AMP) on the performance of PCR blood testing to aid the diagnosis of proven/probable invasive aspergillosis (IA). METHODS: As part of the systematic review and meta-analysis of 22 cohort studies investigating Aspergillus PCR blood testing in 2912 patients at risk of IA, subgroup analysis was performed to determine the impact of AMP on the accuracy of Aspergillus PCR. The incidence of IA was calculated in patients receiving and not receiving AMP. The impact of two different positivity thresholds (requiring either a single PCR positive test result or ≥2 consecutive PCR positive test results) on accuracy was evaluated. Meta-analytical pooling of sensitivity and specificity was performed by logistic mixed-model regression. RESULTS: In total, 1661 (57%) patients received prophylaxis. The incidence of IA was 14.2%, significantly lower in the prophylaxis group (11%-12%) compared with the non-prophylaxis group (18%-19%) (P < 0.001). The use of AMP did not affect sensitivity, but significantly decreased specificity [single PCR positive result threshold: 26% reduction (P = 0.005); ≥2 consecutive PCR positive results threshold: 12% reduction (P = 0.019)]. CONCLUSIONS: Contrary to its influence on GM-EIA, AMP significantly decreases Aspergillus PCR specificity, without affecting sensitivity, possibly as a consequence of AMP limiting the clinical progression of IA and/or leading to false-negative GM-EIA results, preventing the classification of probable IA using the EORTC/MSGERC definitions.

Multicenter comparison of serum and whole-blood specimens for detection of Aspergillus DNA in high-risk hematological patients.

Samples from patients at high risk for invasive aspergillosis (IA) were prospectively collected and analyzed for the presence of molecular markers of fungal infection. Serum specimens were screened for galactomannan and Aspergillus DNA, and whole-blood specimens were screened only for Aspergillus DNA. Fungal infections were categorized according to the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group, National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) criteria. Forty-seven cases (proven and probable IA) and 31 controls (no evidence of IA) were selected retrospectively for this case-control study, comprising 803 samples, in order to determine the performance of whole-blood PCR, serum PCR, and serum galactomannan testing. Although no single assay was able to detect every case of IA, a combination of different assays provided the best performance. There was no significant difference between the use of whole-blood and serum specimens for PCR-based diagnosis of IA, but there was a trend for whole blood to be more sensitive (85% versus 79%) and to yield an earlier positive result (36 days versus 15 days) than for serum. However, DNA extraction from serum specimens is easier and faster than that from whole-blood specimens, and it allows the same specimen to be used for both galactomannan and PCR assays. In conclusion, the appropriate sample type for DNA extraction should be determined by the local requirements and the technical platforms available at each individual center. A combination of biomarker tests offered the best diagnostic utility for detecting IA.

Dynamics of extracellular release of Aspergillus fumigatus DNA and galactomannan during growth in blood and serum.

Aspergillus fumigatus is the major cause of invasive aspergillosis (IA), a disease associated with high rates of morbidity and mortality in patients undergoing treatment for haematological malignancies. This study investigated A. fumigatus growth in vitro and in a murine model of IA in order to provide insights into the dynamics of extracellular DNA and galactomannan (GM) release and their relevance to early diagnosis of IA. Following inoculation of whole blood with 20 A. fumigatus conidia ml(-1), DNA that corresponded to the inoculum could be detected by PCR but GM was not detected in plasma separated from the blood sample, indicating that the fungus did not grow in whole blood. The quantities of DNA detected by PCR, and GM, were proportional to the amount of fungal biomass present in vitro. Fungal DNA could be detected in the sera of mice experimentally infected with A. fumigatus with maximum detection in cyclophosphamide-treated mice.