Surveillance urine cultures in the ICU: prospective markers for the phenotypic and genotypic drift of emerging yeast pathogens?

Surveillance for yeast infections in the ICU is essential to define their burden and trends, to provide the infrastructure needed for epidemiological studies, to evaluate therapeutic interventions and to detect new pathogens. The present 12-month prospective observational study was conducted on a defined ICU population including 56 (24%) patients among 240 (100%) ICU admissions with distinct predisposing factors [1], mean age 52 ± 6 years, mean length of ICU stay 9 ± 6 days, APACHE II score 14 ± 5 and SOFA score 5 ± 2. Urine samples were tested by microscopy and culture on selective media. Each isolate was identified to species level, tested for phenotypic characteristics, such as susceptibility to current and novel antifungal agents and studied for genotypic similarities through identifying DNA subtypes with PCR followed by restriction fragment length polymorphism analysis (RFLP) [2] and with minisatellite length polymorphism analysis (MLP), to distinguish epidemic isolates.

Among the patient population, only 18/56 had negative urine cultures, whereas candiduria (>1000 CFU/ml) was detected in 38/56 patients and two different yeast species were isolated from 7/38 patients. Candida albicans was the main aetiology for candiuria (27%), followed by C. parapsilosis (20%), C. tropicalis and C. famata (11.3%) respectively. Emerging yeast pathogens, such as C. lusitaniae, C. dubliniensis, Trichosporon asahii and T.mucoides were isolated from 18/38 patients, while C. krusei was isolated from only 2/38 patients. All isolates were susceptible to amphotericin B, except T. asahii, for which the lowest minimum inhibitory concentrations (MICs) were recorded for itraconazole (Janssen) and voriconazole (Pfizer). Resistance to fluconazole (Pfizer) was only detected in C. krusei, in two C. famata isolates and in a subpopulation of one C. lusitaniae strain, which however were susceptible to both itraconazole and voriconazole. Identical DNA subtypes were identified among C. albicans, C. parapsilosis, C. famata, C. dubliniensis and Trichosporon species, whereas intense genetic heterogeneity was recorded among C. lusitaniae isolates.

Additional fixed-time surveillance studies in the ICU, using specific markers linked with phenotypic and genotypic analyses, may be employed to recognize outbreaks, to formulate emerging pathogen case definition and exclusion criteria leading to prevention of further cases, and to evaluate azole-based pre-emptive or targeted treatment when such criteria are fulfilled.