Friday, 15 July 2016 10:30

One microbial pathogen 'disguised' as another leads to misdiagnoses

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Published in mBiosphere

If it looks like a duck and quacks like a duck, it’s likely a duck – so goes the saying that illustrates the simplest explanation is usually the right one. But what about duck decoys used in conjunction with bird calls? Misidentification can be a deadly error – and the same goes for microbes. Misdiagnosed infectious disease etiologies can be a very dangerous mistake for sick patients. Most clinical microbiology labs are able to use sophisticated biochemical and genetic tests to differentiate microbial species and strains, but newly emerging pathogens can be misidentified if they closely mimic another. That appears to be the case with the newly emerging fungal pathogen, Candida auris.

Screen Shot 2016-07-15 at 6.34.45 PM
Candida auris cell from initial descriptive report

Candida auris was first described in 2009 from a 70-year-old patient in Japan. The species is unable to form hyphae or pseudohyphae, differentiating it from Candida species such as C. albicans or C. tropicalis, and molecular tests can differentiate the isolate from C. glabrata but often misidentify it as C. haemulonii. This is a dangerous mix-up, as C. auris is resistant to fluconazole and has lower susceptibility to voriconazole, amphotericin B, and caspofungin. The basis of C. auris’ higher basal resistance isn’t yet fully understood, but the draft genome of two isolates will help scientists investigate this question, including the identification of many potential transporter homologs that may play a role.

The emergence of several outbreaks of C. auris in health-care settings, originally misdiagnosed, suggests person-to-person transmission is possible and emphasizes the importance of a simple diagnostic test to differentiate C. auris infection. Commercial identification systems such as the Vitek AST-YS07 card have misidentified 90% of C. auris as C. haemulonii, and this misidentification can lead to inaccurate treatment. A C. auris infection requires higher antifungal doses, due to its higher MICs, to ensure effective therapy. Until automatic ID systems are improved, MALDI-TOF mass spectrometry, as described in a recent Journal of Clinical Microbiology report, has most accurately differentiated between unique Candida species infections.

Tracking C. auris infections is also an issue with misdiagnosis: just as Zika infection was likely misdiagnosed as dengue due to poor diagnostics, C. auris infection may be more common than previously thought. Mass spectrometry may be accurate, but many clinical labs don’t have the capability to run this assay. An accessible diagnostic tool is therefore needed to help clinicians address this problem.

Thus far, C. auris has been reported only in Asian countries, but there’s no reason to think it won’t spread. The dispersal of Zika via globalized travel has demonstrated that infectious disease has no respect for geography, and microbes can quickly become endemic under the right conditions. Furthermore, the identification of E. coli harboring mcr-1 plasmids in U.S. patients demonstrates that the problem could already be among us, lurking quietly until detected. Waiting to address this problem will only lead to further misdiagnosis, a deadly but ultimately avoidable outcome.

Photo credits: C. auris cells from Microbiology and Immunology report

Julie Wolf

ASM Communications Social Media Specialist Julie Wolf spent her research career focused on medical mycology and infectious disease. Broadly interested in microbiology and scientific communication, she has taught at Long Island University and the community biolab Genspace and has written for the Scientista Foundation and Scholastic’s Science World magazine. Follow her on Twitter for more ASM and Microbiology highlights at @JulieMarieWolf.