A yeast the automated system calls Candida haemulonii
A 70-year-old man has been in a long-term acute care hospital for 6 weeks, receiving broad-spectrum antibiotics through a central line after a prolonged surgical stay. He develops fever and hypotension; two blood culture sets grow a yeast at 30 hours. On Sabouraud dextrose agar the colonies are pale, slightly dry, and nonwrinkled. Gram stain shows budding yeast with no pseudohyphae, and the organism grows at 42 °C. The VITEK 2 card identifies it as Candida haemulonii with 98% probability. MALDI-TOF gives a score of 1.68, below the accepted cutoff, and the laboratory's library version predates any Candida auris entries. The hospital has 12 other ventilated patients on the same unit.
1. Why should the automated identification be treated with suspicion, and what is the most likely organism?
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The identification is not reliable and must not be reported as C. haemulonii. Reasons:
- MALDI score of 1.68 is below the acceptance cutoff for genus/species-level confidence; the system is telling you it does not know.
- Library gap: a database without C. auris entries will forcibly return the nearest neighbor, and C. auris is a well-recognized source of misidentification as C. haemulonii, C. famata, C. sake, or Rhodotorula on both biochemical and older MALDI platforms.
- Phenotype: pale, dry colonies, growth at 42 °C, and budding yeast without pseudohyphae are all consistent with C. auris.
- Epidemiology: prolonged broad-spectrum antibiotics, a central line, and a long-term acute care unit with ventilated patients is precisely the niche where C. auris colonizes and spreads.
The working identification is Candida auris, presumptive, pending confirmation.
2. List the actions the laboratory and infection prevention team should take in the next 24 hours.
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Laboratory
- Report as Candida auris, presumptive, with an explicit comment that identification is pending reference confirmation. Do not release the C. haemulonii call.
- Subculture to a differential chromogenic medium designed to detect C. auris (e.g., a C. auris-capable chromogenic agar) and perform a repeat MALDI after updating the library, plus sequencing at a public health or reference laboratory.
- Perform antifungal susceptibility testing (broth microdilution preferred) or send to a reference laboratory; C. auris frequently carries elevated fluconazole MICs and variable amphotericin B activity.
- Notify the local public health authority; C. auris is a reportable, alert organism in most jurisdictions.
Infection prevention
- Place the patient on contact precautions immediately, ideally in a single room, with dedicated equipment.
- Screen unit contacts with composite swabs (axilla, groin, and other sites as locally defined) to detect colonization.
- Review shared equipment, glucose meters, and environmental cleaning with a sporicidal agent - C. auris survives on dry surfaces and resists some quaternary ammonium products.
- Notify the receiving facility at transfer and flag the record for readmission.
Speed matters: point-source amplification on a ventilated unit is the usual failure mode.