Journal Review

Rare outbreak may signal an emerging infection

High mortality rate in transplant patients

Panackal AA, Imhof A, Hanley EW, et al. Aspergillus ustus infections among transplant recipients. Emerg Infect Dis 2006; 12:403-408.

Investigators have confirmed the first outbreak of invasive infection caused by Aspergillus ustus. The mold rarely infects humans, as only 15 systemic cases have been reported among hematopoietic stem cell transplant (HSCT) recipients. In the outbreak, six patients with infections were identified. Three 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 the 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 eight 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.

In the six HSCT patients described in the article, infection developed late after HSCT, with a high proportion of deaths. The patients also possessed classic risk factors for IA in that most had graft-vs.-host disease that required corticosteroid and other immunosuppressive therapy. Overall death rates of patients with A. ustus infection was high in this cohort, as in previous cases. Whether death was attributable to the fungal infection, coinfections, or underlying diseases is unclear.

"A common source for the A. ustus infections appears possible, since case-patients clustered in space and time, and a high degree of genetic similarity was noted between isolates from case patients," the authors surmised. "Since these patients resided in rooms within close proximity, common source acquisition (e.g., air, water, or surface) is credible."

"A. ustus is rare; however, it may be emerging as a cause of systemic disease among immunocompromised hosts in the appropriate setting," the authors conclude. "A combination of factors, including severity of underlying host immunosuppression and common source acquisition, likely played a role in the reported outbreaks. Active laboratory, environmental, and clinical-based surveillance for A. ustus has been implemented at our hospital based on the results of this investigation; no additional isolates have been identified subsequently. Such intensive monitoring may show similar outbreaks in other facilities."