Authors (including presenting author) :
Lui ETL (1), Ho AYM (2), Chan JSW (2), Lee KP (2), To WK (2), Cheung WS (3), Chow VCY (1), Luk S (2)
Affiliation :
(1) Department of Microbiology, Prince of Wales Hospital, (2) Department of Pathology, Princess of Margaret Hospital, (3) Infection Control Team, Princess Margaret Hospital
Keyword 1: :
Candida auris screening
Keyword 2: :
Pooled testing
Keyword 3: :
Test evaluation
Keyword 4: :
PCR optimization
Keyword 5: :
Antimicrobial resistance surveillance
Keyword 6: :
MDRO surveillance
Introduction :
Since its first discovery in Japan in 2009, Candida auris has been implicated in a wide range of hospital-acquired infections. Genomic analysis identified six clades of C. auris. In Hong Kong, the first imported case was reported in 2019, and the incidence of C. auris has been increasing since then. The isolates belonged to Clade I, and were resistant to fluconazole and amphotericin B. Early identification of colonization of C. auris has become crucial to halt the transmission.
Objectives :
Candida auris is a threat to public health globally. Our goal is to validate the real-time PCR assay performed on the fully automated cobas® 6800 system, using sonication to augment DNA extraction from surveillance clinical samples. Pooled sample testing was also evaluated.
Methodology :
Analytical aspects of the assay were assessed by testing on a series of dilutions of a C. auris standardized suspension. Sensitivity was tested using 235 dual swabs with and without prior sonication. Enrichment culture was the gold standard. Fifty-nine RT-PCR positive samples were subjected to 4-in-1 pooled PCR testing after sonication pre-treatment.
Result & Outcome :
The limit of detection of the cobas® 6800 PCR was 7.51 CFU/mL (95 % CI: 5.27- 20.22 CFU/mL), without cross-reactivity to other microorganisms. Out of 48 culture positive samples, 46 (95.8 %) and 44 (91.7%) samples were RT-PCR positive with and without the sonication step respectively. Sonicated samples had a lower median Ct value by 2.07 (p < 0.05). Pooled testing of sonicated samples had a positive agreement of 79.7% (95 %CI: 67.7 %-88.0 %). At a positive rate of 0.53 %, pooled testing could reduce the cost by three-fold; and the incremental cost would be US$ 242,995 for further identification of 14 positive samples among 12978 samples using individual testing. The fully automated system is a reliable platform for C. auris PCR testing. Pre-sonication enhances PCR sensitivity. Pooled PCR testing is a cost-effective approach to identify C. auris carriers with high fungal load in low prevalence settings.
