Aspergillus PCR in serum for the diagnosis, follow-up and prognosis of invasive aspergillosis in neutropenic and nonneutropenic patients

Abstract

We evaluated the usefulness of a serum Aspergillus PCR assay for the diagnosis and prognosis of invasive aspergillosis in a study involving 941 patients for a total of 5146 serum samples. Fifty-one patients had proven/probable aspergillosis. We compared galactomannan (GM), PCR and mycologic analysis of pulmonary samples in both neutropenic and nonneutropenic patients. PCR performed in serum yielded 66.7% sensitivity, 98.7% specificity, 75.6% positive predictive value and 98.0% negative predictive value, while the GM index yielded 78.4% sensitivity, 87.5% specificity, 27% positive predictive value and 98.6% negative predictive value. The inclusion of PCR in the European Organization for Research and Treatment of Cancer (EORTC) and the Mycosis Study Group (MSG) mycologic criteria permitted the reclassification of nine other cases from possible to probable aspergillosis and increased the sensitivity to 71.7%. Combining the GM index with serum PCR increased the detection rate of invasive aspergillosis with 88.2% sensitivity. PCR was systematically negative in 16 patients with noninvasive forms of aspergillosis (namely aspergilloma and chronic aspergillosis). Remaining PCR positive after a period of 14 to 20 days of treatment was related to poor outcome at 30 and 90 days. Our results also indicate that, unlike the determination of the GM index, the initial fungus load as determined by PCR was highly predictive of 90-day mortality, with the rate of the latter being 15.8% for patients with <150 copies/mL vs. 73.2% for patients at or above that cutoff (p <0.0001). Therefore, PCR appears to be a powerful and interesting tool for the identification of patients with invasive aspergillosis who might benefit from more intense care.

Keywords: Aspergillus fumigatus; fungal infection; galactomannan; haematology; solid organ transplant.

Fig. 1

Flow chart showing number of patients and samples. ¹Extended EORTC/MSG criteria included host factors as published in 2008 plus several other host factors now recognized as leading to risk of developing IA, namely alcoholic liver cirrhosis, severe acute respiratory syndrome, long stay in intensive care unit and solid organ cancer. ²Study design did not include exhaustive collection of possible cases; we present only possible cases with positive PCR results that were considered as IA by clinicians and treated as such. EORTC/MSG, European Organization for Research and Treatment of Cancer/Mycosis Study Group; IA, invasive aspergillosis.

Fig. 2

Venn diagram showing data for patients with invasive aspergillosis (n = 60). Diagram shows data for patients for whom PCR products and GM in sera as well as mycologic analysis of respiratory samples were available. Among ten patients with only positive PCR, one was positive for GM in bronchoalveolar lavage samples. GM, galactomannan.

Fig. 3

Serum Aspergillus PCR is highly predictive of 90-day mortality in IA. (a) ROC curve for evaluation of PCR (square) or GM (triangle) as marker of 90-day mortality in IA. Cutoff of 150 copies/mL offers most efficient value and area under curve of 0.837. For GM index cutoff of 2 (most efficient value) is related to small area under curve of 0.546. (b) Patients with initial fungus loads <150 copies/mL (n = 41, 73.2% survival) have more favourable outcomes than other patients (n = 19, 15.8% survival); p <0.0001 by log rank (Mantel-Cox) test, hazard ratio 0.14 (95% CI of ratio 0.05 to 0.34). (c) Patients with initial GMs below 2 (n = 28, 50% survival) appear to have more favourable outcomes than others (n = 12; 25% survival), but difference is not statistically significant (p 0.19 by log rank (Mantel-Cox) test; hazard ratio 0.5, 95% CI of ratio 0.20 to 1.29). CI, confidence interval; GM, galactomannan; IA, invasive aspergillosis; ROC, receiver operating characteristic.