Comparison between plasma and whole blood specimens for detection of Aspergillus DNA by PCR

Comparison of different protocols for DNA preparation and PCR for the detection of fungal pathogens in vitro

Although a large number of different PCR protocols for the detection of fungal DNA from clinical samples have been described, a generally recognised standardisation has not yet been developed. In a first step, we compared six different methods to isolate DNA under in vitro conditions from Aspergillus fumigatus, Candida albicans and Saccharomyces cerevisiae with respect to efficiency and expenditure of time. To this end, methods were tested that are based on both mechanical and enzymatic/thermic lysis. Thereby, enzymatic/thermic lysis were shown to be superior to mechanical lysis, although these methods of DNA isolation were more time consuming. The subsequent comparison of three different PCR protocols showed real-time PCR to be the most sensitive method.

In vitro release by Aspergillus fumigatus of galactofuranose antigens, 1,3-beta-D-glucan, and DNA, surrogate markers used for diagnosis of invasive aspergillosis

Aspergillus markers are becoming increasingly important for the early diagnosis of invasive aspergillosis. The kinetics of release of these surrogate markers, however, is largely unknown. We investigated the release of beta-(1-5)-galactofuranosyl (galf) antigens (Platelia Aspergillus), 1,3-beta-D-glucan (BG) (Fungitell), and DNA (PCR) in an in vitro model of Aspergillus fumigatus. The results showed that release is correlated to the growth phase of the fungus, which depends on available nutrients. Whereas galf antigens and BG are released during logarithmic growth, DNA is released only after mycelium breakdown. During early logarithmic growth, galf antigens seem to be released somewhat earlier than BG. Furthermore, galf antigen concentrations of more than 120,000 times the serum cutoff value (0.5 ng/ml) can be measured, while BG concentrations reach a value only 978 times the serum cutoff value (60 pg/ml). During lytical growth, release of galf antigens further increased to a maximum level, which depended on pH. After that, the concentration of galf antigens stayed high (pH 7.4) or decreased to zero within 4 days (pH 5.0). In contrast to galf antigens, BG concentration decreased after 1 day of growth. The decrease of galf components seems to be due to the enzyme beta-galactofuranosidase, which is able to destroy galf epitopes and whose activity fluctuates in the culture filtrates in parallel with galf antigen concentration. Fungal DNA seems to be released only due to autolysis caused by nutrient limitation. In conclusion, several factors clearly influence the release of surrogate markers in vitro. These same factors might also play a role at the infection site of Aspergillus disease in humans.

Evaluation of the role of real-time PCR in the diagnosis of invasive aspergillosis

Recently, two developments relating to the diagnosis of invasive aspergillosis (IA) have occurred. First, the standardisation of criteria for determining the category of this disease according to the European Organisation for Research and Treatment of Cancer/Mycosis (EORTC) Study Group consensus definitions has allowed comparison of results from different studies to be undertaken. The second development is the generation of PCR assays based on real-time technologies that are able to quantify Aspergillus DNA. In this review the benefits and limitations of these new published assays are compared with nested-PCR assays and enzyme immuno assays. Results from studies where these real-time assays have been used and patient's infections were classified according the EORTC definitions are examined. The effect of anti-fungal treatment is noted. The requirement for both international standards and a consensus protocol that is sensitive enough for IA diagnosis, particularly in blood, is discussed.

The evolution and evaluation of a whole blood polymerase chain reaction assay for the detection of invasive aspergillosis in hematology patients in a routine clinical setting

BACKGROUND

Invasive aspergillosis (IA) is associated with high mortality. Successful outcome with treatment is linked to early diagnosis. The utility of classic diagnostic methods, however, is limited.

METHODS

To aid in the diagnosis of IA, we retrospectively assessed our diagnostic service, using real-time polymerase chain reaction (PCR) and galactomannan sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 203 patients at risk of invasive fungal infection were screened by PCR, and 116 of the patients were also tested by ELISA. The patient group comprised 176 patients with hematological malignancy and 28 control patients with evidence of invasive candidal infection. Consensus European Organisation for Research and Treatment of Cancer and Mycoses Study Group criteria were used to classify fungal infection, which, by definition, excluded the PCR result. The PCR method was sensitive (up to 92.3% sensitivity) and specific (up to 94.6% specificity) and had good agreement with the galactomannan ELISA (76.7%) and high-resolution computed tomography scan results.

CONCLUSIONS

A negative PCR result can be used to rule out IA and to limit the need for empirical antifungal therapy; thus, it has a role in diagnosing IA infections, especially in combination with antigen testing. PCR-positive cases classified as "false positives" regularly reflect the limitations of classic microbiological procedures or restricted use of consensus clinical methods employed to classify infection.

Evaluation of pan-fungal PCR assay andAspergillusantigen detection in the diagnosis of invasive fungal infections in high risk paediatric cancer patients

Profound and prolonged neutropenia following chemotherapy is a major risk factor for systemic fungal infection. As the early diagnosis of invasive fungal infection (IFI) is difficult, these infections are still associated with high morbidity and mortality. Recently, Pan-fungal polymerase chain reaction (PCR) has been a promising aid in rapid, early diagnosis of IFI. During the past few years, increasing numbers of suspected IFIs were encountered at our institution in patients with prolonged neutropenia after intensified immunosuppressive chemotherapy. The aim of this study was to investigate the diagnostic utility of both the aspergillus galactomannan (GM) antigen and the pan-fungal PCR assay in the diagnosis of IFI in high risk febrile neutropenic paediatric cancer patients. During one year period, 91 febrile neutropenic (FN) paediatric cases at high risk for developing IFI while receiving chemotherapy were investigated at National Cancer Institute, Egypt. These patients were subjected to clinical evaluation, chest CT scan, conventional blood cultures for bacterial and fungal pathogens, aspergillus GM antigen detection and PCR assay utilizing pan-fungal primers. Of the 91 FN episodes, 15 were proven IFI; whereas 27 cases were either probable (n=13) or possible IFI (n=14), and 49 were unlikely to be IFI episodes. Based on positive results for proven/probable IFI and compared to culture results, Pan-fungal PCR showed sensitivity, specificity, positive and negative predictive values of 75%, 92%, 84% and 87%; respectively. Aspergillus antigen test showed a sensitivity of 79%, specificity of 61%, positive and negative predictive values of 54% and 83%; respectively. A negative PCR in the proven and probable cases was closely related to previous antifungal therapy for a prior history of IFI. In patients at high risk for IFI, neither the sensitivity, nor specificity of the GM test was sufficient. The results of PCR assay was reasonably specific but not very sensitive and had a chance of missing the diagnosis of IFI. The PCR assay seems a promising test for objectively defining IFI, but is not recommended as the only tool for diagnosing IFI. Combining microscopy, culture, and PCR may improve the diagnostic outcome.

Laboratory diagnosis of invasive aspergillosis

Invasive aspergillosis occurs in a wide range of clinical scenarios, is protean in its manifestations, and is still associated with an unacceptably high mortality rate. Early diagnosis is critical to a favourable outcome, but is difficult to achieve with current methods. Deep tissue diagnostic specimens are often difficult to obtain from critically ill patients. Newer antifungal agents exhibit differential mould activity, thus increasing the importance of establishing a specific diagnosis of invasive aspergillosis. For these reasons, a range of alternate diagnostic strategies have been investigated. Most investigative efforts have focused on molecular and serological diagnostic techniques. The detection of metabolites produced by Aspergillus spp and a range of aspergillus-specific antibodies represent additional, but relatively underused, diagnostic avenues. The detection of galactomannan has been incorporated into diagnostic criteria for invasive aspergillosis, reflecting an increased understanding of the performance, utility, and limitations of this technique. Measurement of (1,3)-beta-D glucan in blood may be useful as a preliminary screening tool for invasive aspergillosis, despite the fact that this antigen can be detected in a number of other fungi. There have been extensive efforts directed toward the detection of Aspergillus spp DNA, but a lack of technical standardisation and relatively poor understanding of DNA release and kinetics continues to hamper the broad applicability of this technique. This review considers the application, utility, and limitations of the currently available and investigational diagnostic modalities for invasive aspergillosis.

Advances and challenges in management of invasive mycoses

Invasive mycoses pose a major diagnostic and therapeutic challenge. Advances in antifungal agents and diagnostic methods offer the potential for improved outcomes in patients with these infections, which are often lethal. Many fungal pathogens occur almost exclusively in opportunistic settings--in the immunocompromised host--and these infections are the focus of this review. Several areas of ongoing challenge remain, including the emergence of resistant organisms and the absence of reliable markers for early identification of patients at risk of developing invasive fungal disease. This Seminar reviews the changing epidemiology of invasive mycoses, new diagnostic methods, and recent therapeutic options and current management strategies for these opportunistic pathogens.

Clinical evaluation of Aspergillus-PCR for detection of invasive aspergillosis in immunosuppressed patients

We evaluated the utility of Aspergillus PCR as a tool in diagnosing invasive aspergillosis in patients at risk. Aspergillosis was assessed according to the European Organization for Research and Treatment of Cancer (EORTC), Mycosis Study Group definitions. Nine and seven patients with proven and probable aspergillosis respectively were evaluated. Whole blood samples prior (n = 41) and during antifungal treatment (n = 67), and tissue specimens (n = 9) and/or bronchoalveolar lavage fluids (n = 7) were investigated. In patients with proven infections, the sensitivities of PCR of lung samples were 100%, of blood samples prior treatment were 66%, and during treatment 55%. Clearance of fungal DNA from blood was associated with resolution of clinical symptoms in two of four patients with proven infection. Consecutive positive PCR results for Aspergillus are fatal as two of five patients died. In patients with probable infections, the sensitivities of PCR of lung fluids were 85%, of blood samples prior treatment were 57%, and during treatment 42%. The benefits of PCR diagnosing and screening of whole blood are limited if sampling takes place once treatment has started. The performance of Aspergillus PCR from tissue samples should be recommended in addition to microscopic examination and culture technique for sensitive detection of fungal infection.

Comparison of non-culture-based methods for detection of systemic fungal infections, with an emphasis on invasive Candida infections

The accepted limitations associated with classic culture techniques for the diagnosis of invasive fungal infections have lead to the emergence of many non-culture-based methods. With superior sensitivities and quicker turnaround times, non-culture-based methods may aid the diagnosis of invasive fungal infections. In this review of the diagnostic service, we assessed the performances of two antigen detection techniques (enzyme-linked immunosorbent assay [ELISA] and latex agglutination) with a molecular method for the detection of invasive Candida infection and invasive aspergillosis. The specificities for all three assays were high (> or = 97%), although the Candida PCR method had enhanced sensitivity over both ELISA and latex agglutination with values of 95%, 75%, and 25%, respectively. However, calculating significant sensitivity values for the Aspergillus detection methods was not feasible due to a low number of proven/probable cases. Despite enhanced sensitivity, the PCR method failed to detect nucleic acid in a probable case of invasive Candida infection that was detected by ELISA. In conclusion, both PCR and ELISA techniques should be used in unison to aid the detection of invasive fungal infections.

Genetic identification and detection of human pathogenic Rhizopus species, a major mucormycosis agent, by multiplex PCR based on internal transcribed spacer region of rRNA gene

BACKGROUND

Mucormycosis is an invasive opportunistic infection caused by fungi belonging to the order Mucorales. Due to the lack of laboratory tests, the diagnosis of mucormycosis is notoriously difficult. Added with its rapid progression as well as the debilitated state of the patients who contract the disease, mortality is extremely high.

OBJECTIVE

The goal of this study was to genetically identify human pathogenic Rhizopus species, a major mucormycosis agent, by the internal transcribed spacer (ITS) region of rRNA gene.

METHODS

Primers were designed to identify five Rhizopus species known to cause human disease by multiplex PCR. PCR was done not only with test strains and clinical isolates, but also with clinical samples from cutaneous mucormycosis patients. Sporangiospore morphology was observed by scanning electron microscopy to confirm the correlation of phenotypic and genotypic features.

RESULTS

Multiplex PCR identified five Rhizopus species including Rhizopus oryzae, where R. azygosporus could only be distinguished from R. microsporus by certain polymorphisms that were present in its sequence. When this multiplex PCR was applied to clinical samples from three mucormycosis patients (paraffin sections from all and sera from one patient), Rhizopus DNA corresponding to the isolated pathogens were specifically detected.

CONCLUSION

While fungal DNA detection from clinical samples is a rigorously studied area, this is the first report to genetically identify and detect Rhizopus species from human mucormycosis specimens. This may expand the possibility of this multiplex PCR system not only to identify isolated fungi, but also as a screening method for visceral mucormycosis.

Diagnosing invasive aspergillosis during antifungal therapy by PCR analysis of blood samples

We evaluated the value of Aspergillus PCR as a tool for diagnosing invasive aspergillosis from whole-blood samples during antifungal therapy. In a 3-year study, 36 patients receiving antifungal therapy due to chest radiographic findings highly suggestive of fungal pneumonia were evaluated. The PCR results from whole-blood samples were compared to those obtained from bronchoalveolar lavage fluids and/or tissue specimens. A total of 205 whole-blood samples, 15 fine-needle aspirations or tissue biopsy specimens, and 21 bronchoalveolar lavage fluids and tracheal secretions were analyzed using PCR. Of the 36 patients, 15 had proven, 9 had probable, and 12 had possible invasive Aspergillus infection according to European Organization for Research and Treatment of Cancer/Mycosis Study Group definitions. For patients with proven infection the sensitivity values of PCR in lung and blood samples were 100 and 40%, respectively. The negative predictive value of blood monitoring under conditions of antifungal treatment was 44%. Clearance of fungal DNA from blood was associated with resolution of clinical symptoms in six of nine patients with proven infection. Repeated positive PCR results for Aspergillus were associated with fatal outcome, as three of six patients died. For patients with probable infection the sensitivity values of PCR in lung fluid and blood were 66 and 44%, respectively. The benefit of PCR diagnosis using whole-blood samples is limited when sampling takes place after treatment has been started. Performance of Aspergillus PCR using tissue samples is recommended in addition to microscopic examination and culture technique for sensitive detection of fungal infection.

Development of a serum-based Taqman real-time PCR assay for diagnosis of invasive aspergillosis

We compared an Aspergillus fumigatus-specific Taqman real-time PCR assay for the diagnosis of invasive aspergillosis (IA) with the enzyme-linked immunosorbent assay Platelia Aspergillus method. Patients with proven or probable IA had positive results with at least one of the two methods. The PCR method seems to be more specific, and a combination of the two should improve the diagnosis of IA.

Diagnosing and monitoring of invasive aspergillosis during antifungal therapy by polymerase chain reaction: an experimental study in mice

This study evaluated the value of polymerase chain reaction (PCR) for diagnosing and monitoring of invasive aspergillosis during amphotericin B therapy. PCR, microscopy and culture of tissues samples (n = 126) and blood samples (n = 78) of experimentally infected mice (n = 42) were performed. The PCR results of treated were compared to those of untreated animals; Aspergillus fumigatus and A. terreus were used in this study. In the amphotericin B treated group the sensitivities of PCR, microscopic examination and culture of the various tissues were 69, 58, and 53%, respectively; the specificities of all examinations were 100%. In the untreated group the sensitivities of PCR, microscopic examination, and culture were 72, 64, and 57%, respectively; the specificities of all examinations were 100%. The 78 blood samples taken from mice under therapy were tested by PCR over a period of 8 days following Aspergillus infection. The test sensitivity was 77%, the specificity 46%, the positive predictive value 59%, and the negative predictive value 67%. In the untreated group the sensitivity was 92%, the specificity 46%, the positive predictive value 63%, and the negative predictive value 86%. The results suggest that this PCR method has possible clinical value for improving the diagnosis of invasive Aspergillus infection. Monitoring of blood under antifungal therapy is not recommended.

Real-time automated polymerase chain reaction (PCR) to detect Candida albicans and Aspergillus fumigatus DNA in whole blood from high-risk patients

We report the development and evaluation of a real-time PCR assay using the LightCycler instrument for the detection of C. albicans and A. fumigatus DNA in whole blood. Recently published consensus criteria for the diagnosis of invasive fungal infection (IFI) were used for all patient samples. Unique and published primer pairs were developed and assessed for sensitivity, specificity, and reproducibility to detect C. albicans and A. fumigatus DNA in samples spiked with purified DNA, and whole blood samples from 8 high-risk patients and 45 negative controls. The real-time assay demonstrated an analytical sensitivity of 10 fg of purified C. albicans and A. fumigatus DNA and was found to be specific for each species. The standardized approach was highly reproducible and detected C. albicans and A. fumigatus DNA in two patients with proven IFI and in one patient with a possible IFI. In addition, we report for the first time the use of recently published international consensus criteria for the diagnosis of IFI in the evaluation of a mildly invasive fungal diagnostic assay. Standardized clinical criteria and a more standardized approach to detect fungal DNA in less invasive patient samples, may permit a more reliable comparison of future studies. A rapid real-time detection of fungal DNA in whole blood, combined with standard clinical markers of response, may be more useful for monitoring patients at risk of developing IFI than other diagnostic methods currently available.

Semiquantitative detection by real-time PCR of Aspergillus fumigatus in bronchoalveolar lavage fluids and tissue biopsy specimens from patients with invasive aspergillosis

A real-time PCR method was developed and used to detect Aspergillus fumigatus mitochondrial DNA (mtDNA) in bronchoalveolar lavage (BAL) fluids and tissue biopsy specimens. The analytical sensitivity of the assay was one A. fumigatus conidium per reaction, and the assay was linear at least over 4 orders of magnitude above the detection limit. BAL fluids from 66 immunocompromised patients at risk of invasive pulmonary aspergillosis (IPA) and 33 immunocompetent controls and tissue biopsy specimens from 10 immunocompromised patients were analyzed. The results were related to the clinical diagnosis established according to recently published consensus criteria. A. fumigatus mtDNA positivity was encountered in 16 of 81 (20%) BAL fluid specimens from patients at risk and 1 of 33 (3%) specimens from immunocompetent controls. PCRs were positive in six of seven, two of four, and four of five of the patients with proven, probable, and possible IPA, respectively, as well as in four patients at risk but without any other evidence of IPA. With qualitative detection, the diagnostic sensitivity of PCR was 73%, specificity was 93%, and predictive values of positive (PPV) and negative (NPV) results were 73 and 95%, respectively. Using a threshold cycle of <35 as a limit for positive PCR, the specificity and PPV of PCR in the diagnosis of invasive aspergillosis were 100%, but its sensitivity was only 45% and NPV was 92%. PCR was positive in tissue biopsy specimens from all patients with invasive aspergillosis caused by A. fumigatus. Semiquantitative detection of A. fumigatus mtDNA in BAL fluid may be helpful in the diagnosis of IPA. PCR is well suited for the verification of the presence of A. fumigatus in tissue biopsy specimens.

The prospective evaluation of a nested polymerase chain reaction assay for the early detection of Aspergillus infection in patients with leukaemia or undergoing allograft treatment

Patients with acute leukaemia or undergoing allogenic bone marrow transplantation at University College London Hospital Trust were screened for the presence of aspergillosis by polymerase chain reaction (PCR). Aspergillus DNA, from whole blood samples, was amplified by nested PCR to detect a 135 bp fragment in the mitochondrial region of Aspergillus fumigatus or A. flavus (121 bp). One colony-forming unit (CFU) per 2 ml of blood or 1-10 fg DNA could be detected. Patients at risk of aspergillosis were classified as probable or possible based on the European Organization for Research and Treatment of Cancer definitions. Antifungal drugs given were recorded. In four of 17 patients studied, infection was not suspected and the PCR was negative. Four patients were considered to have possible aspergillosis infection and were PCR positive on at least one occasion. Of the three patients in the probable group, four of the nine samples tested PCR positive from one patient and in another patient only one of nine samples tested positive. The remaining six patients were not suspected of having fungal infection but each had one or two PCR-positive results. In summary, six of seven patients thought to have clinical evidence of infection were PCR positive on at least one occasion and treatment with antifungals may have reduced infection below detectable levels.

A review of nucleic acid-based diagnostic tests for systemic mycoses with an emphasis on polymerase chain reaction-based assays

Nucleic acid-based assays have good potential to complement and enhance the sensitivity and rapidity of conventional methods used in diagnostic mycology. The majority of molecular tests are polymerase chain reaction (PCR)-based assays focusing mainly on the detection of Candida and Aspergillus spp. from clinical samples. DNA extraction and purification procedures should be standardized and can be facilitated by using commercial extraction kits. In general, protocols that target multi-copy genes provide the greatest sensitivity. Objective endpoint assessments of PCR tests using enzyme-linked immunosorbent assays (ELISA) or commercial quantitative systems are capable of rapidly detecting and identifying Candida and Aspergillus spp. Sequencing of PCR products can be used to confirm the identity of amplicons. In cases of suspected invasive aspergillosis, PCR should be performed on both blood and bronchoalveolar lavage fluid to maximize test sensitivity and the positive predictive value. At least two blood specimens should be tested if PCR is undertaken on blood samples alone. In situ hybridization techniques have been used with success to identify fungi in tissue specimens. The wide application of PCR-based assays relies on the introduction of standardized protocols following their evaluation in multicentre, prospective studies.

Current status of nonculture methods for diagnosis of invasive fungal infections

The incidence of invasive fungal infections has increased dramatically in recent decades, especially among immunocompromised patients. However, the diagnosis of these infections in a timely fashion is often very difficult. Conventional microbiologic and histopathologic approaches generally are neither sensitive nor specific, and they often do not detect invasive fungal infection until late in the course of disease. Since early diagnosis may guide appropriate treatment and prevent mortality, there has been considerable interest in developing nonculture approaches to diagnosing fungal infections. These approaches include detection of specific host immune responses to fungal antigens, detection of specific macromolecular antigens using immunologic reagents, amplification and detection of specific fungal nucleic acid sequences, and detection and quantitation of specific fungal metabolite products. This work reviews the current status and recent developments as well as problems in the design of nonculture diagnostic methods for invasive fungal infections.

Critical assessment of issues in the diagnosis of invasive aspergillosis

Invasive aspergillosis remains a devastating disease, which is partly because of the inability to identify infected patients at an early stage of the disease. Recently, new diagnostic tests and procedures have been developed to help in identifying high-risk patients. High-resolution computed tomography has been shown to be a potent tool for detecting pulmonary abnormalities in neutropenic patients. Assays for the detection of circulating markers such as fungal antigens or Aspergillus DNA have been developed and show that markers can be detected in the blood at an early stage of infection. Also, the markers correlate with the fungal burden in the tissue, which allows monitoring of response to antifungal therapy. The tests and procedures that are now available need to be incorporated into management strategies for at-risk patients and evaluated in clinical trials. Although we now have markers that allow the early detection of fungal products, many questions remain unanswered with respect to the kinetics of the markers in different patient groups, the optimal management strategy and the effect of prophylaxis and treatment on the markers. Nevertheless, the implementation of new approaches for the management of invasive aspergillosis offers opportunities to improve outcome of patients.

Utilization of the internal transcribed spacer regions as molecular targets to detect and identify human fungal pathogens

Advances in molecular technology show great potential for the rapid detection and identification of fungi for medical, scientific and commercial purposes. Numerous targets within the fungal genome have been evaluated, with much of the current work using sequence areas within the ribosomal DNA (rDNA) gene complex. This section of the genome includes the 18S, 5.8S and 28S genes which code for ribosomal RNA (rRNA) and which have a relatively conserved nucleotide sequence among fungi. It also includes the variable DNA sequence areas of the intervening internal transcribed spacer (ITS) regions called ITS1 and ITS2. Although not translated into proteins, the ITS coding regions have a critical role in the development of functional rRNA, with sequence variations among species showing promise as signature regions for molecular assays. This review of the current literature was conducted to evaluate clinical approaches for using the fungal ITS regions as molecular targets. Multiple applications using the fungal ITS sequences are summarized here including those for culture identification, phylogenetic research, direct detection from clinical specimens or the environment, and molecular typing for epidemiological investigations. The breadth of applications shows that ITS regions have great potential as targets in molecular-based assays for the characterization and identification of fungi. Development of rapid and accurate amplification-based ITS assays to diagnose invasive fungal infections could potentially impact care and improve outcome for affected patients.

Development of two real-time quantitative TaqMan PCR assays to detect circulating Aspergillus fumigatus DNA in serum

Several PCR assays have been developed for detecting Aspergillus fumigatus DNA in blood of patients with invasive aspergillosis. However, the best blood fraction to be assayed has not been defined and the multicopy genes used as the DNA targets for amplification not characterized. Firstly, we developed a real-time PCR assays based on the TaqMan technology targeted to a single copy gene. To compare serum, white cell pellet, and plasma for effectiveness as blood assay fractions, we spiked whole blood with A. fumigatus DNA and processed these fractions similarly. The difference between white cell pellet and serum was not significant. In contrast, the yield from plasma was 10 times lower than from serum. Then, we compared serum processed immediately or after 24 h at room temperature and observed a lower yield after 24 h. Secondly, a real-time PCR assay targeted to a mitochondrial gene was also developed. The copy number was estimated between 9 and 10 mitochondrial genes per single copy gene. Therefore, we recommend serum, stored and frozen as soon as possible, to be used for detecting circulating A. fumigatus DNA for diagnosis. Moreover, the mitochondrial multicopy gene was characterized in order to compare results from different patients.