[National external quality assessment for molecular detection of severe acute respiratory syndrome coronavirus 2...

Objective: To clarify the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant on the performance of existing molecular diagnostic assays, and investigate the detection ability of clinical laboratories across China. Methods: The first nationwide external quality assessment (EQA) for molecular detection of Delta variant was carried out based on the non-infectious phage virus-like particles samples, which were prepared by genetic engineering methods and distributed to 8 488 laboratories nationwide. The EQA panel was composed of three Delta variant samples (7.5×10², 1.5×10³ and 6.0×10³ copies/ml), one non-variant weak positive sample and one negative sample. The percentage of agreement (PA) of Delta variant samples with different concentration, the PA of Delta variant and non-variant samples with 7.5×10² copies/ml, the PA of assays used by more than 100 laboratories for Delta variant samples with different concentration and the PA of Delta variant and non-variant samples with 7.5×10² copies/ml were calculated and analyzed. Results: The data from 8 127 laboratories were available for evaluation. The testing capability of 98.77% (8 027/8 127) of the participating laboratories was found to be competent in reporting correct results for all samples. The overall percentage of agreement (OPA), negative percentage of agreement (NPA) and positive percentage of agreement (PPA) of the samples were 99.64% (40 490/40 635), 99.73% (8 105/8 127), 99.62% (32 385/32 508), respectively. With the decrease of the concentration of the samples, the PPA of Delta variant samples decreased. The PPAs were 99.41% and 99.51% for Delta variant and non-variant samples with 7.5×10² copies/ml, respectively, with no statistical difference (P=0.392). The OPA, NPA and PPA of the assays used by more than 100 laboratories were all greater than 98%, and no statistical difference of the PPAs was identified between Delta variant and non-variant samples with 7.5×10² copies/ml (P>0.05). Conclusions: Delta variant fails to impair the performance of current molecular diagnostic assays in China. The clinical laboratories have the same detection capabilities for Delta variant and non-variant samples. However, in certain laboratories, further improvement is required to ensure the accurate detection of weak positive samples.