Development and optimization of quantitative PCR for the diagnosis of invasive aspergillosis with bronchoalveolar lavage fluid

Background: The diagnosis of invasive pulmonary aspergillosis (IPA) remains challenging. Culture and histopathological examination of bronchoalveolar lavage (BAL) fluid are useful but have suboptimal sensitivity and in the case of culture may require several days for fungal growth to be evident. Detection of Aspergillus DNA in BAL fluid by quantitative PCR (qPCR) offers the potential for earlier diagnosis and higher sensitivity. It is important to adopt quality control measures in PCR assays to address false positives and negatives which can hinder accurate evaluation of diagnostic performance. Methods: BAL fluid from 94 episodes of pneumonia in 81 patients was analyzed. Thirteen episodes were categorized as proven or probable IPA using Mycoses Study Group criteria. The pellet and the supernatant fractions of the BAL were separately assayed. A successful extraction was confirmed with a human 18S rRNA gene qPCR. Inhibition in each qPCR was measured using an exogenous DNA based internal amplification control (IAC). The presence of DNA from pathogens in the Aspergillus genus was detected using qPCR targeting fungal 18S rRNA gene. Results: Human 18S rRNA gene qPCR confirmed successful DNA extraction of all samples. IAC detected some degree of initial inhibition in 11 samples. When culture was used to diagnose IPA, the sensitivity and specificity were 84.5% and 100% respectively. Receiver-operating characteristic analysis of qPCR showed that a cutoff of 13 fg of Aspergillus genomic DNA generated a sensitivity, specificity, positive and negative predictive value of 77%, 88%, 50%, 96% respectively. BAL pellet and supernatant analyzed together resulted in sensitivity and specificity similar to BAL pellet alone. Some patients did not meet standard criteria for IPA, but had consistently high levels of Aspergillus DNA in BAL fluid by qPCR. Conclusion: The Aspergillus qPCR assay detected Aspergillus DNA in 76.9% of subjects with proven or probable IPA when the concentrated BAL fluid pellet fraction was used for diagnosis. There was no benefit from analyzing the BAL supernatant fraction. Use of both extraction and amplification controls provided optimal quality control for interpreting qPCR results and therefore may increase our understanding of the true potential of qPCR for the diagnosis of IPA.Supported by NIH grant R01 AI054703 from the National Institute of Allergy and Infectious Diseases

“Es fundamental que la información que se transmita sea confiable”

El flamante Doctor Honoris Causa de la UNLP, Emilio Luque Fadón, de la Universidad Autónoma de Barcelona, fue uno de los conferencistas de CACIC 2017. Durante su estadía por la ciudad de La Plata, el español habló acerca de las nuevas tecnologías, su tolerancia a los fallos y el consumo energético.Facultad de Informátic

Invasive aspergillosis: Clinical and Pathological features of a new animal model

A new animal model of invasive aspergillosis is described in which female New Zealand White rabbits were immunosuppressed with corticosteroids and cyclophosphamide and were given an intratracheal inoculation of 4 × 104 conidia of Aspergillus fumigatus. Thirteen of 15 animals survived during a 10-day-period of observation. Most had clinical signs of a respiratory infection (dyspnoea) and at autopsy there was macroscopic and microscopic evidence of invasive pulmonary aspergillosis. Six control animals (infected but not immunosuppressed) showed no such signs. The extent of hyphal invasion was assessed histologically and quantified by calculating the number of colony forming units (c.f.u.) g-1 of tissue: in the experimental group the mean c.f.u. value for the lungs was 1·25 × 103compared to 73·3 c.f.u. g-1 of lung for the control group (P=0·003). The infection was also quantified by a whole lung chitin assay: in the experimental group the mean chitin content (expressed as a glucosamine equivalent) was 3·05 μg g-1 lung tissue compared to a 0·53 μg g-1 lung tissue for the control group (P=0·01). We conclude that this model of invasive aspergillosis in rabbits reflects closely the pathological features of the disease in man and that it may prove useful for studies of the pathogenesis and the treatment of invasive aspergillosis