Diagnostics of Pulmonary Aspergillosis in Critically Ill Hematological and Non-Hematological Patients in the Intensive Care Unit By Combined Use of Galactomannan, 1-3-Beta-D-Glucan, Aspergillus Specific PCR and Conventional Culture in Concurrent Blood and Bronchoalveolar Lavage Samples — Results of a Multicenter Prospective Pilot Study

Invasive pulmonary aspergillosis (IPA) is a life-threatening infectious complication mainly affecting immunocompromised hematological patients. Therapeutic success requires early and precise diagnostics. Few data are available on the performance of current diagnostic tests in patients admitted to the intensive care unit (ICU) as the majority of diagnostic studies is conducted in hematological patients and results cannot readily be transferred to patients in the ICU setting.

In a prospective multicenter study, we evaluated concurrent bronchoalveolar lavage (BAL) samples and concurrent blood samples from 44 patients admitted to the ICU who required mechanical ventilation and therefore underwent a diagnostic work-up including chest CT scan and BAL (NCT01695499). The subsequent diagnostic work-up comprised of conventional methods for direct detection of Aspergillus spp. as well as biomarkers such as galactomannan (GM) and 1-3-beta-D-glucan (BDG) and an Aspergillus specific nested polymerase chain reaction (PCR).

14 patients (32%) suffered from a hematological/hematooncological disease, of which 7 had received allogeneic stem cell transplantation. 6 patients (14%) had a solid tumor requiring chemotherapy. The remaining 24 patients (54%) had no hematological or oncological disease. 11 patients were neutropenic with ANC <1.0/nl (10 belonged to the hematooncological group). According to AspICU classification (Blot et al., Am J Respir Crit Care Med 2012) 9 patients (20%) had putative IPA (3 patients with hematological malignancy). Other invasive fungal diseases (IFD) besides IPA were observed: positive growth of Rhizopus microsporus in BAL was seen in one patient. Furthermore, two cases of disseminated candidiasis with positive growth in blood culture (C.albicans, C.krusei) and one case with positive growth in ascites (C.albicans). Additionally, two cases of Pneumocystis jirovecii pneumonia (PcP) were diagnosed.

Diagnostic performance of each single test and of test combinations was analyzed. GM and PCR showed superior performance in BAL (sensitivity/specificity of 56%/94% (GM) and 44%/94% (PCR) compared to 33%/97% and 11%/94% in serum). Despite a better sensitivity of 89%, BDG showed a specificity of only 31% in BAL and 26% in serum, reducing the diagnostic odds ratio (DOR) to 3.7 and 2.8, respectively. For hematological patients the mean GM optical density index (ODI) in BAL was 0.97 and in serum 0.58 compared to 0.59 and 0.16 in non-hematological patients. The strength of agreement between GM in BAL and GM in serum as calculated by Cohen's kappa intertest coherence analysis was 0.62 [0.29-0.95], which is considered to be good. BDG levels and performance of the PCR assay did not differ between hematological and non-hematological patients. The combined use of biomarkers in BAL showed a diagnostic performance of sensitivity/specificity/PPV/NPV and DOR of 89%/31%/25%/92% and 3.67. Testing of GM and BDG solely in serum resulted in a combined test performance of 89%/26%/ 24%/ 90% and 2.77. GM (BAL) combined with BDG (serum) showed high joint sensitivity of 100% with specificity of 25% (DOR 6.81). Using PCR instead of GM dropped sensitivity to 89% (specificity 23%, DOR 2.37). Diagnostic performance of combined GM and PCR testing in BAL showed sensitivity/specificity/PPV/NPV and DOR 67%/89%/60%/91% and 15.0. Cohen's kappa for PCR (BAL) vs. GM (BAL) was 0.49 [0.145 to 0.840], which is considered to be moderate. If a diagnostic algorithm defines BDG (serum) as an initial test that is, in case of a positive result, followed by a confirming test combination from BAL with strong or even exclusive specificity for Aspergillus spp. (GM, PCR and culture) a diagnostic performance is achieved with sensitivity/specificity/positive predictive value/negative predictive value of 88%/97%/88%/97% and DOR >100.

This study intended as a pilot study underscores the concept of combined testing in serum and BAL for optimized detection of IPA and provides valuable data for the emerging cohort of critically ill patients, both hematological and non-hematological. Further studies with hematological ICU patients in larger cohorts are planned.