Community-Scale Wastewater Surveillance of Candida auris during an Ongoing Outbreak in Southern Nevada

Abstract

Candida auris is an opportunistic fungal pathogen and an emerging global public health threat, given its high mortality among infected individuals, antifungal resistance, and persistence in healthcare environments. This study explored the applicability of wastewater surveillance for C. auris in a metropolitan area with reported outbreaks across multiple healthcare facilities. Influent or primary effluent samples were collected over 10 weeks from seven sewersheds in Southern Nevada. Pelleted solids were analyzed using an adapted quantitative polymerase chain reaction (qPCR) assay targeting the ITS2 region of the C. auris genome. Positive detection was observed in 72 of 91 samples (79%), with higher detection frequencies in sewersheds serving healthcare facilities involved in the outbreak (94 vs 20% sample positivity). Influent wastewater concentrations ranged from 2.8 to 5.7 log₁₀ gene copies per liter (gc/L), and primary clarification achieved an average log reduction value (LRV) of 1.24 ± 0.34. Presumptive negative surface water and wastewater controls were non-detect. These results demonstrate that wastewater surveillance may assist in tracking the spread of C. auris and serve as an early warning tool for public health action. These findings provide the foundation for future application of wastewater-based epidemiology (WBE) to community- or facility-level surveillance of C. auris and other high consequence, healthcare-associated infectious agents.

Keywords: Candida auris; antifungal resistance; healthcare-associated infections (HAIs); public health surveillance; wastewater-based epidemiology (WBE).

Figure 1

C. auris concentrations (log₁₀ gene copies per liter) in Southern Nevada wastewater samples. Data are shown by wastewater treatment facility and sample type (for Facility 1), sampling date, and qPCR outcome. Solid circles represent quantifiable detections (≥2 qPCR reactions; >LoQ), open circles represent nonquantifiable detections (≥2 qPCR reactions; <LoQ), asterisks represent singular detections (1 qPCR reaction; <LoQ or >LoQ), and red crosses represent non-detects (0 qPCR reactions).

Figure 2

Map of Southern Nevada sewersheds in the context of C. auris wastewater surveillance. Sewershed coloring represents average influent wastewater concentration of C. auris (in log₁₀ gc/L) from July through September of 2022. Average concentrations exclude the Facility 1 primary effluent and the Facility 4 composite influent. Recall that Facility 4A receives all solids and bypass flows from Facility 2. Black diamonds denote locations of state-licensed healthcare facilities (n = 22) reporting C. auris clinical or colonization cases between August 2021 and August 2022. For visualization purposes (i.e., relative comparisons), samples below the LoQ were set to 1 log₁₀ gc/L and non-detects were set to 0 log₁₀ gc/L. Note that some healthcare facility locations overlap, making it difficult to distinguish them on the map.