BOSTON – An investigation into 18 nosocomial Candida auris infections at a tertiary care center in Venezuela showed that isolates of the emerging fungal pathogen obtained during the outbreak were resistant to fluconazole and voriconazole. However, the isolates were intermediately susceptible to amphotericin B and susceptible to 5-fluorocitosine, and demonstrated high susceptibility to the candin antifungal anidulafungin.
Dr. Belinda Calvo, an infectious disease specialist at the University of Maracaibo, Venezuela, and her collaborators reported these findings, related to a 2012-2013 C. auris outbreak at the hospital. Dr. Calvo and her coinvestigators noted that other invasive C. auris outbreaks have been reported in India, Korea, and South Africa, but that “the real prevalence of this organism may be underestimated,” since common rapid microbial identification techniques may misidentify the species.
In a poster session at the annual meeting of the American Society of Microbiology, Dr. Calvo and her collaborators reported that the 18 patients involved in the Venezuelan outbreak were critically ill, of whom 11 were pediatric, and all had central venous catheter placement. All but two of the pediatric patients were neonates, and all had serious underlying morbidities; several had significant congenital anomalies. The median patient age was 26 days (range, 2 days to 72 years), reflecting the high number of neonates affected. One of the adult patients had esophageal carcinoma. Overall, 10/18 patients (56%) had undergone surgical procedures, and all had received antibiotics.
As has been reported in other C. auris outbreaks, isolates from blood cultures of affected individuals were initially reported as C. haemulonii by the Vitek 2 C automated microbial identification system. Molecular identification was completed by sequencing the internal transcribed spacer (ITS) of the rDNA gene, with analysis aided by the National Institutes of Health’s GenBank and the Netherland’s CBS Fungal Diversity Centre , in order to confirm the identity of the fungal isolates as C. auris. Dr. Calvo and her associates were able to generate a dendrogram of the 18 isolates, showing high clonality, a trait shared with other nosocomial C. auris outbreaks.
Susceptibility testing of the C. auris cultured from blood samples of the affected patients showed that fluconazole had a minimum inhibitory concentration to inhibit the growth of 50% of the organisms (MIC50) of greater than 64 mcg/mL. For fluconazole, the MIC90, range, and geometric mean were all also above 64 mcg/mL, indicating a high level of resistance. For voriconazole, the MICs, range, and mean were all 4 mcg/mL. For amphotericin B, the MIC50 was 1 mcg/mL, the MIC90 was 2 mcg/mL, the range was 1-2, and the geometric mean was 1.414 mcg/mL.
The high number of pediatric patients affected, as well as early pathogen identification with speedy and appropriate antifungal therapy and prompt removal of central venous catheters, likely contributed to the relatively low 30-day crude mortality rate of 28%, said Dr. Calvo and her coauthors.
“C. auris should be considered an emergent multiresistant species,” wrote Dr. Calbo and her collaborators, noting that the opportunistic pathogen has a “high potential for nosocomial horizontal transmission.”
In June 2016, the Centers for Disease Control issued a clinical alert to U.S. healthcare facilities regarding the global emergence of invasive infections caused by C. auris.
The study authors reported no external sources of funding and no conflicts of interest.
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