Pseudooutbreak of Candida versatilitis fungemia in a microbiology laboratory

Investigation of a Candida guilliermondii Pseudo-outbreak Reveals a Novel Source of Laboratory Contamination

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 health care-associated outbreak was strongly considered due to growth patterns in the microbiology laboratory that were 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 was identified. Rather, extensive environmental sampling revealed C. guilliermondii in an anaerobic holding jar in the clinical microbiology laboratory, where anaerobic plates were prereduced and held before inoculating specimens. C. guilliermondii grows poorly under anaerobic conditions. Thus, we postulate that anaerobic plates became intermittently contaminated. Passaging 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. A 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, 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.

Central venous catheter infection associated with Pseudozyma aphidis in a child with short gut syndrome

Pseudozyma aphidis is a heterobasidiomycetous yeast related to the smut fungi in the genus Ustilago. Pseudozyma species are usually isolated from plants and rarely from clinical specimens. We report what is believed to be the first paediatric case of central venous catheter (CVC)-related fungaemia associated with P. aphidis. Prompt removal of the CVC in conjunction with anti-fungal therapy resulted in a successful outcome.

DNA and the classical way: Identification of medically important molds in the 21st century

The advent of the 21st century has seen significant advances in the methods and practices used for identification of medically important molds in the clinical microbiology laboratory. Historically, molds have been identified by using observations of colonial and microscopic morphology, along with tables, keys and textbook descriptions. This approach still has value for the identification of many fungal organisms, but requires expertise and can be problematic in determining a species identification that is timely and useful in the management of high-risk patients. For the increasing number of isolates that are uncommon, atypical, or unusual, DNA-based identification methods are being increasingly employed in many clinical laboratories. These methods include the commercially available GenProbe assay, methods based on the polymerase chain reaction such as single-step PCR, RAPD-PCR, rep-PCR, nested PCR, PCR-RFLP, PCR-EIA, and more recent microarray-based, Luminex technology-based, and real-time PCR-based methods. Great variation in assay complexity, targets, and detection methods can be found, and many of these methods have not been widely used or rigorously validated. The increasing availability of DNA sequencing chemistry has made comparative DNA sequence analysis an attractive alternative tool for fungal identification. DNA sequencing methodology can be purchased commercially or developed in-house; such methods display varying degrees of usefulness depending on the breadth and reliability of the databases used for comparison. The future success of sequencing-based approaches will depend on the choice of DNA target, the reliability of the result, and the availability of a validated sequence database for query and comparison. Future studies will be required to determine sequence homology breakpoints and to assess the accuracy of molecular-based species identification in various groups of medically important filamentous fungi. At this time, a polyphasic approach to identification that combines morphologic and molecular methods will ensure the greatest success in the management of patients with fungal infections.

Delayed recognition of a pseudo-outbreak of Mycobacterium terrae

Pseudo-outbreaks of mycobacteria are difficult to recognize because of long incubation periods for growth and species identification. We report our experience with one clinical microbiology laboratory that isolated a species of nontuberculous mycobacteria from 14 patient specimens. These specimens came from 12 patients at 2 hospitals over a 6-day period and included 6 different fluids or tissues. Because of the delay between mycobacterial specimen submission and growth in culture, the outbreak was not noted until more than a month later. Initial species determination by a reference laboratory indicated that these isolates were Mycobacterium fortuitum. One patient received treatment for presumed M fortuitum brain infection, and it was not effective in changing her clinical course. The isolates were sent to the Centers for Disease Control and Prevention (CDC) for identification and typing by pulsed-field gel electrophoresis. The CDC determined that the isolates were an identical strain of M terrae, thus confirming a pseudo-outbreak. Combining pseudo-outbreak isolates with those correctly identified initially as M terrae during the 6-day period in question, there were 22 samples from 20 patients with M terrae. Since the pseudo-outbreak, the number of cultures of M terrae in the clinical laboratory has returned to baseline levels without any specific intervention.

Fungemia caused by Zygoascus hellenicus in an allogeneic stem cell transplant recipient

Zygoascus hellenicus (Candida hellenica) was isolated from a blood culture from a patient who had received an allogeneic stem cell transplant. The isolate displayed an antifungal susceptibility pattern of decreased susceptibility to fluconazole and itraconazole, high susceptibility to voriconazole, and low susceptibility to caspofungin. The organism was misidentified by a commercial yeast identification system. This is the first reported case of human infection with this rare ascomycetous yeast.