Proficiency test of SARS-CoV-2 Omicron variant detection in diagnostics samples by veterinary diagnostic laboratories

Veterinary diagnostic laboratories (VDLs) play a critical role in screening both human and animal samples for SARS-CoV-2. To evaluate the SARS-CoV-2 detection methods used by VDLs, a proficiency test was performed by the US Food and Drug Administration’s Veterinary Laboratory and Investigation and Response Network in collaboration with two other organizations. Thirty-two sets of 12 blind-coded samples were prepared by fortifying Molecular Transport Medium (MTM) or feline feces with SARS-CoV-2 Omicron variant or non-SARS-CoV-2 equine coronavirus RNA at various concentrations and shipped to 32 participants for blinded (unbiased) analysis. Results were analyzed according to the principles of International Organization for Standardization 16140-2:2016 using two approaches such as establishing the rate of detection (ROD) and the success rate by applying the analysis of binary outcome by logit approach. ROD provided the overall assessment of laboratories performance, whereas the novel logit approach provided an insight to more specific analysis based on the complexity of each sample. The ROD was 83% and 98% for MTM samples at 200 and 20000 genome copies per 100 µL, respectively. Fecal samples were classified as challenging exploratory, and results were not included in the assessment of performance but discussion purposes only. Fecal samples exhibited matrix interference impacting the performance. The ROD was 44% and 89% for fecal samples at 2000 and 20000 genome copies per 100 µL, respectively. The non-COVID coronavirus RNA, which was used to address the specificity, did not interfere with methods used. Establishing the success rate by evaluating the qualitative results (detected/not detected) applying a logit approach revealed that, out of thirty-two participants, twenty-eight had satisfactory results, one participant had unsatisfactory results, and three participants had questionable results for MTM samples. For fecal samples, three participants out of thirty-two did not meet the expectations at higher concentrations. Lower concentrations of fecal samples were excluded from this analysis. Again, the fecal samples were considered as challenge samples and the results were provided to assist participants in their continuous efforts to improve their performance and not to evaluate their performance.