Sample collection and preparation
Eighty-three nasopharyngeal (NP) and an oropharyngeal swabs (OP) were obtained by trained health staff at the isolation units. Based on recommendation from Center for Disease Control and Prevention (CDC) (CDC, 2020) and to maximize sensitivity and to limit the use of test resources, the two NP and OP swabs taken from one participant were admixed in a 3-ml tube containing viral transport medium (VTM, Ismailia free zone, Egypt. Ref: 1/V T01.001.0001) and stored at -80 °C until further analyses.