Repurposing Positive SARS-CoV-2 Antigen Test Devices for Variant Tracking.

From the very beginning of the SARS-CoV-2 pandemic, one of the very few common opinions was that to control the expansion of the virus as many as the possible test had to be done. Antigen tests, being affordable and easy and fast to use, represented a great opportunity to expand the testing capacities of many healthcare systems. However, in 2021 with the appearance of the new SARS-CoV-2 variants, variant tracking strategies had to be implemented, which often included needing a second test to determine the variant of the patients diagnosed with antigen tests or not taking these samples into consideration at all. Therefore, we proposed recovering the positive antigen test devices to include them in our routine variant tracking strategy. The recovered positive antigen test devices obtained from 1st April 2021 to 15the January 2022 were analysed following the variant tracking protocol in force. The results obtained were compared to the positive samples detected by RT-PCR which were processed for variant tracking during the same period. 21,304 samples were processed, 6297 from the recovered positive antigen devices and 15,007 from the standard nasopharyngeal swabs. Only 773 (3.63%) samples were no conclusive, 104 (1.65%) from the recovered antigen devices and 669 (4.46%) from the RT-PCR positive group. This difference was statistically significant (p < 0.01). Taking this into account the proposed method is suitable and very recommendable, as it is an important measure to have a better and immediate picture of the circulating variants in every community.