ABSTRACT
Background: Since the beginning of the COVID-19 pandemic veterinary diagnostic laboratories have tested diagnostic samples for SARS-CoV-2 not only in animals, but in over five million human samples. An evaluation of the performance of those laboratories is needed using blinded test samples to ensure that laboratories report reliable data to the public. This interlaboratory comparison exercise (ILC3) builds on two prior exercises to assess whether veterinary diagnostic laboratories can detect Delta and Omicron variants spiked in canine nasal matrix or viral transport medium. Methods: Inactivated Delta variant at levels of 25 to 1,000 copies per 50 microliters of nasal matrix were prepared for participants by the ILC organizer, an independent laboratory, for blinded analysis. Omicron variant at 1,000 copies per 50 microliters of transport medium was also included. Feline infectious peritonitis virus (FIPV) RNA was used as a confounder for specificity assessment. A total of 14 test samples were prepared for each participant. Participants used their routine diagnostic procedures for RNA extraction and real-time RT-PCR. Results were analyzed according to International Organization for Standardization (ISO) 16140 - 2:2016. Results: The overall results showed 93% detection for Delta and 97% for Omicron at 1,000 copies per 50 microliters (22-200 copies per reaction). The overall specificity was 97% for blank samples and 100% for blank samples with FIPV. No differences in Ct values were significant for samples with the same virus levels between N1 and N2 markers, nor between the two variants. Conclusions: The results indicated that all ILC3 participants were able to detect both Delta and Omicron variants. The canine nasal matrix did not significantly affect SARS-CoV-2 detection.