A nasopharyngeal swab is a device used for collecting a sample of nasal secretions from the back of the nose and throat.[1][2] The sample is then analyzed for the presence of organisms or other clinical markers for disease. This diagnostic method is commonly used in suspected cases of whooping cough, diphtheria, influenza, and various types of diseases caused by the coronavirus family of viruses, including SARS, MERS, and COVID-19.[3][4][5][6][7][8]
^"Influenza Specimen Collection"(PDF). Centers for Disease Control and Prevention. n.d. Retrieved 25 March 2020. A nasopharyngeal (NP) swab is the optimal upper respiratory tract specimen collection method for influenza testing.