Aspergillus ustus Infections among Transplant Recipients

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 aspergillosis (IA) has become a devastating opportunistic fungal infection among immunocompromised hosts, with a 357% increase in death rates reported in the United States from 1980 to 1997). The most common cause of IA is Aspergillus fumigatus. However, in recent years, IA has been increasingly caused by non-fumigatus Aspergillus species. For example, at the Fred Hutchinson Cancer Research Center in Seattle, the proportion of infections caused by non-fumigatus Aspergillus species increased during the latter 1990s. Most of these infections were caused by A. flavus, A. nidulans, A. terreus, and A. niger. Aspergillus ustus is a group of filamentous hyalohyphomycetes consisting of 5 species: A. ustus, A. puniceus, A. panamensis, A. conjunctus, and A. deflectus. Members of this group are rare human pathogens; only 15 cases of systemic infection have been reported in the literature since 1970, and more than half of these occurred in the past 10 years). Infections caused by A. ustus may be of particular concern, as the organisms exhibit low susceptibility to multiple antifungal drugs, and outcomes have been uniformly poor. Recognition of invasive infections that occurred in 2 clusters of hematopoietic stem cell transplant (HSCT) recipients in our institution prompted us to perform a more thorough clinical investigation and environmental sampling to identify potential sources of acquisition.

Emerging Infectious Diseases
March 14, 2006

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