Evaluation of 3-D printed swabs for respiratory sampling and testing for SARS-CoV-2 during the early pandemic period

Appropriate collection of respiratory samples is essential for accurate diagnostic testing of respiratory pathogens such as, SARS-CoV-2. Early in the pandemic, there was a shortage of nasopharyngeal (NP) swabs and difficulty in sampling suspected cases. Therefore, we developed a 3D printed nasal swab for anterior nares, paired with in-house viral transport medium (VTM). The utility of this 3D swab kit was investigated in comparison with the standard NP commercial swab and VTM, in 200 individuals between August and September 2021. Subjects were those presenting for diagnostic testing for SARS-CoV-2 using the RT-PCR (cobas Roche assay) assay. NP samples were taken from each subject using the standard NP and 3D swabs followed by RT-PCR on paired specimens. CT values for amplification of gene targets were evaluated to determine assay parameters based on viral load cut offs of ≤ CT 35 or, ≤ CT 37. For high to medium viral loads, 3D swab based PCR testing had a sensitivity of 93%, specificity of 99%, positive predictive value (PPV) of 98.5% and negative predictive value (NPV) of 96.2% respectively. For low viral loads, 3D swab testing had a sensitivity of 88%, specificity of 99%, with a PPV of 98.5% and NPV of 93.2%.%. 3D swab sampling of anterior nares was comparable with NP sampling using standard swabs for SARS-CoV-2 specimens with a medium to high viral load. Therefore, 3D swab based sampling is a reliable and convenient local solution for collecting respiratory samples for SARS-CoV-2 diagnostic testing