Kieren A. Marr

Summary: Invasive fungal infections (IFIs) continue to cause considerable morbidity and mortality in haematopoietic stem cell transplant (HSCT) recipients. This review focuses on the risks for, and diagnosis of, IFIs (candidiasis, aspergillosis and other mould infections), and factors that affect current outcomes. Diagnosis of IFI is difficult, with the sensitivity of the gold standard tests (culture and histopathology) often <50%. Therefore, physicians rely on a constellation of clinical signs, radiography, culture, histopathology and adjunctive tests to establish diagnosis. HSCT recipients often have multiple co‐morbidities, and understanding the current outcomes and prognostic variables is therefore important for overall management. This paper reviews historical trends and current data.

Aspergillus fumigatus has been understood to be the most common cause of invasive aspergillosis (IA) in all epidemiological surveys. However, recent studies have uncovered a large degree of genetic heterogeneity between isolates morphologically identified as A. fumigatus , leading to the description of a new species, Aspergillus lentulus . Here, we examined the genetic diversity of clinical isolates identified as A. fumigatus using restriction enzyme polymorphism analysis and sequence-based identification. Analysis of 50 clinical isolates from geographically diverse locations recorded the presence of at least three distinct species: A. lentulus , Aspergillus udagawae , and A. fumigatus . In vitro, A. lentulus isolates demonstrated decreased susceptibility to antifungal drugs currently used for IA, including amphotericin B, voriconazole, and caspofungin; A. udagawae isolates demonstrated decreased in vitro susceptibility to amphotericin B. Results of the present study demonstrate that current phenotypic methods to identify fungi do not differentiate between genetically distinct species in the A. fumigatus group. Differential antifungal susceptibilities of these species may account for some of the reported poor outcomes of therapy in clinical studies.

Clinical failure associated with reduced susceptibility to caspofungin has been described in Candida albicans and C. parapsilosis . We report a case of Candida krusei infection that progressed despite caspofungin therapy. Reduced microbial susceptibility to all three echinocandins (caspofungin, anidulafungin, and micafungin) was noted but was not associated with mutations in FKS1 .

Candida glabrata , which can become resistant to fluconazole, is a common cause of bloodstream infection. This study was performed to determine the significance of cross-resistance to new azole drugs among C. glabrata isolates recovered as a cause of infection in azole-treated hematopoietic stem cell transplant (HSCT) recipients. Seven cases of invasive candidiasis caused by C. glabrata occurred in HSCT recipients who were receiving azole therapy between January 2000 and December 2004 in our institution. Case characteristics were ascertained. Sequential colonizing and invasive isolates were examined to determine susceptibilities to fluconazole, itraconazole, and voriconazole, and molecular relatedness by restriction fragment length polymorphism (RFLP) analysis. Twenty-three C. glabrata isolates were recovered from 4 patients who developed candidemia while receiving fluconazole and three patients who developed candidemia while receiving voriconazole. The mode MICs of fluconazole, itraconazole, and voriconazole for these isolates were ≥64 μg/ml (range, 4 to ≥64 μg/ml), 2 μg/ml (range, 0.25 to ≥16 μg/ml), and 1 μg/ml (range, 0.03 to ≥16 μg/ml), respectively. Kendall tau b correlation coefficients demonstrated significant associations between the MICs of voriconazole with fluconazole ( P = 0.005) and itraconazole ( P = 0.008). Colonizing and invasive isolates exhibiting variable susceptibilities had similar RFLP patterns. These observations suggest that C. glabrata exhibits considerable clinically significant cross-resistance between older azole drugs (fluconazole and itraconazole) and voriconazole. Caution is advised when considering voriconazole therapy for C. glabrata candidemia that occurs in patients with extensive prior azole drug exposure.

Sir—Ostrosky-Zeichner et al. [1] have investigated the utility of the (1→3) β-D-glucan assay in the diagnosis of fungal infections using a case-control methodology. They report a sensitivity and specificity of 64.4% and 92.4%, respectively, with a positive predictive value (PPV) of 89% and a negative predictive value (NPV) of 73% when a cutoff value of 80 pg/mL was employed. Although the results of this study would appear to support the utility of this assay in diagnosing invasive fungal infections (IFIs), we question the choice of control patients and the presentation of predictive values.

Aspergillus ustus is a mold that rarely infects humans; only 15 systemic cases have been reported. We report the first outbreak of invasive infection caused by A. ustus among hematopoietic stem cell transplant (HSCT) recipients. Six patients with infections were identified; 3 infections each occurred in both 2001 and 2003. Molecular typing by using randomly amplified polymorphic DNA (RAPD) and antifungal drug susceptibility testing were performed on clinical and environmental isolates recovered from our hospital from 1999 to 2003. The highest overall attack rate in HSCT patients was 1.6%. The overall death rate was 50%, and death occurred within 8 days after diagnostic culture collection. Clinical isolates exhibited decreased susceptibility to antifungal drugs, especially azoles. RAPD and phylogenetic analysis showed genetic similarity between isolates from different patients. Based on the clustering of cases in space and time and molecular data, common-source acquisition of this unusual drug-resistant species is possible.

Invasive fungal infections caused by Neosartorya pseudofischeri S. W. Peterson [anamorph Aspergillus thermomutatus (Paden) S. W. Peterson] are extremely rare. Phenotypically, the anamorphic state of N. pseudofischeri resembles Aspergillus fumigatus , the predominant agent of invasive aspergillosis in immunocompromised hosts. We report the recovery of three clinical isolates of N. pseudofischeri , all initially misidentified by morphological characteristics as A. fumigatus . All three isolates were correctly identified by sequencing portions of the β-tubulin and the rodlet A genes. Only one of the three isolates produced the confirmatory fruiting bodies and was thus classified as N. pseudofischeri ; the other isolates did not produce asci and were therefore identified as A. thermomutatus . All three isolates had higher MICs to voriconazole in vitro compared to A. fumigatus Af293. This report emphasizes that phenotypic identification of filamentous fungi may not identify morphologically similar, but genetically distinct, members of the genus Aspergillus section Fumigati . Accurate identification of these organisms may be clinically meaningful, given their potential differences in antifungal susceptibilities.

Although invasive aspergillosis is recognized as an increased concern for immunosuppressed patients, establishing an early diagnosis remains a challe