Comparison of pre-analytical characteristics for molecular and serological diagnostics of COVID-19

Background: The diagnosis of SARS-CoV-2 infection relies on RT-PCR from nasopharyngeal swabs. The pre-analytical value of different methods of material harvesting for SARS-CoV-2 are unknown. Methods: We conducted a comprehensive investigation of the pre-analytical performance for different pharyngeal sampling procedures in hospitalized patients with confirmed SARS-CoV-2 infection. In addition to swabs taken simultaneously from different locations, saliva and pharyngeal lavages were also analyzed using RT-PCR. Results: In 10 COVID-19 patients, standard nasopharyngeal swabs detected 8 out of 10 positive patients, whereas swabs taken from the palatoglossal arch resulted in 9 correct-positive results. Brushing the posterior pharynx wall with swabs resulted in detection of 9 out of 10 positive patients with no difference using either dry swabs or liquid Amies medium. A strong correlation between Ct values of both swab materials was observed. Pharyngeal lavages yielded 6 out of 10 positive results in concordance with 85% of nasopharyngeal swabs in late-stage COVID-19 patients. Investigating 23 patients with early SARS-CoV-2 infection, pharyngeal lavages showed a concordance rate of 100% compared to nasopharyngeal swabs. Conclusions: The diagnostic performance of swabs taken from the palatoglossal arch in detecting SARS-CoV-2 infection is similar to that of specimens taken from the nasopharyngeal region. However, the former sampling method is associated with less discomfort and much easier to perform. Pharyngeal lavages may replace swabs for mass screening in early stages of SARS-CoV-2 infection. The predictive values are comparable, and the procedure is performed without exposing healthcare workers to transmission risks.