Results

Four patients met the case definition (Table 1). All patients involved had undergone surgical procedures but otherwise had no clear epidemiologic link. Surgical procedures involved different surgeons on different days and in varied operating rooms over a 24-day period. Gram stains of original specimens showed a heavy burden of yeast with the first, third, and fourth cases and a low burden in the second case. All isolates grew only on plate media incubated at 30°C from tissue that had been ground in commercial BHI broth. Plate media incubated at 35°C showed no evidence of fungal growth. Specimens from the first two cases were replated to media and incubated at 30°C a few days after bacterial growth was detected due to the positive Gram stains for yeast, despite no fungal growth at 35°C. Subsequently, all specimens from the operating rooms were plated at 30°C and 35°C until the cause of the pseudo-outbreak was determined, leading to the recognition of the additional cases which also grew only at the lower temperature. No C. famata was recovered from blood, fluid, or specimens that did not require grinding or processing in BHI broth. Isolates sent to the commercial laboratory for antifungal sensitivities all failed to yield growth for testing at the recommended temperature for testing Candida species 35°C. All patients had an alternative infectious diagnosis to explain their clinical presentation and were successfully treated without antifungals. One patient received an empiric echinocandin until such time as the nature of the pseudo-outbreak was identified.

Table 1.

Patient characteristics

Table 1. Long description

A table with four rows and four columns detailing patient characteristics and clinical diagnoses. The columns are labeled Age (decade), Sex, Surgical service, Procedure/Culture site, and Clinical diagnosis. Row 1: Age 20s, Sex Male, Surgical service Orthopedics, Procedure/Culture site Open reduction internal fixation (ORIF), Clinical diagnosis E.coli prosthetic infection. Row 2: Age 70s, Sex Female, Surgical service Oral maxillofacial, Procedure/Culture site Jaw landD/osteomyelitis biopsy, Clinical diagnosis S. anginosus jaw osteomyelitis. Row 3: Age 20s, Sex Male, Surgical service Plastics, Procedure/Culture site Nerve transfer reconstruction, Clinical diagnosis E.coli infection of seroma. Row 4: Age 60s, Sex Male, Surgical service Orthopedics, Procedure/Culture site Total knee arthroplasty (TKA), Clinical diagnosis Methicillin-sensitive S. aureus prosthetic joint infection.

Laboratory inspection revealed intermittent contamination of one BHI broth lot (Figure 1). Turbidity was not obvious on side view; a white sediment ring appeared only at the tube base that became obvious with agitation. Tubes within the same lot varied significantly in burden of contamination by sight and subculture. Yeast from uninoculated tubes from the same lot grew C. famata as identified by MALDI-TOF. Whole-genome sequencing confirmed clonal identity between broth contaminant and all four patient isolates. There were no insertion, deletion, or single nucleotide polymorphism differences detected between the isolates. Following resolution of the pseudo-outbreak investigation two additional tissue cultures were also discovered to be contaminated, bringing the total number of contaminated cultures to six. These last two cultures were not sent for sequencing as the outbreak investigation had been completed and the isolates were determined to be laboratory contamination. The reports for those cultures were not entered into the patients’ medical records.

Figure 1.

Tubes on left (1) and right (3) are contaminated, with the center tube (2) serving as an uncontaminated reference. (A) The left tube has been mixed and is visibly cloudy against an appropriate background. The contamination in the right tube has settled to the bottom and is not readily apparent without agitation of the tube. (B) The same tubes without contrast card.