James E. Kirby, Westyn Branch-Elliman, Mary T. LaSalvia, Lorinda Longhi, Matthew MacKechnie, Grigoriy Urman, Linda M. Baldini, Fatima R. Muriel, Bernadette Sullivan, David S. Yassa, Howard S. Gold, Trevor K. Wagner, Daniel J. Diekema, Sharon B. Wright

Candida guilliermondii was isolated from sterile specimens with increasing frequency over a several-month period despite a paucity of clinical evidence suggesting true Candida infections. However, a healthcare-associated outbreak was strongly considered due to growth patterns in the microbiology laboratory more consistent with true infection than environmental contamination. Therefore, an extensive investigation was performed to identify its cause. With the exception of one case, patient clinical courses were not consistent with true invasive fungal infections. Furthermore, no epidemiologic link between patients could be identified. Rather, extensive environmental sampling revealed C. guilliermondii in an anaerobic holding jar in the Clinical Microbiology Laboratory, where anaerobic plates were pre-reduced and held prior to specimen inoculation. C. guilliermondii grows poorly under anaerobic conditions. Thus, we postulate that anaerobic plates became intermittently contaminated. Passage from intermittently contaminated anaerobic plates to primary quadrants of aerobic media during specimen planting yielded a colonial growth pattern typical for true specimen infection, thus obscuring laboratory contamination. Molecular evaluation of the C. guilliermondii isolates confirmed a common source for pseudo-outbreak cases but not for the one true infection. In line with Reason's model of organizational accidents, both active and latent errors coincided to contribute to the pseudo-outbreak. These included organism factors (lack of growth in anaerobic conditions obscuring plate contamination); human factors (lack of strict adherence to plating order, leading to only intermittent observation of aerobic plate positivity) and laboratory factors (novel equipment). All of these variables should be considered when evaluating possible laboratory-based pseudo-outbreaks.