Why use a throat swab?

There are many sites or secretions that can be collected by nucleic acid testing, such as nasopharyngeal sites, lavage fluid from bronchial and bronchoalveolar lavage, sputum, and blood.

Blood is generally unlikely to detect the new coronavirus. What the blood can detect is the antibody produced by the body against the new coronavirus, but the production of antibodies can only indicate that the subject has been infected with the virus, and cannot determine whether he is currently infected.

Bronchial and bronchoalveolar lavage fluids had the highest sensitivity, reaching 93%; sputum samples were slightly weaker, at 72%.

However, these three methods are obviously more suitable for patients who have been diagnosed and hospitalized, and sampling personnel need a higher level of safety protection, which is not realistic for large-scale screening. According to research, the receptor ACE2 of the new coronavirus is abundantly expressed on epithelial cells and smooth muscle cells. In the upper respiratory tract (including the nose, pharynx, and larynx), the virus replicates at high levels. Therefore, the virus can be captured in the extracts of nasal swabs, throat swabs, and secretions of epithelial cells of the upper respiratory tract.