The collection quality of microbial

The collection quality of microbial samples can strongly affect the detection results.Respiratory tract samples are often used in the detection of COVID-19. Upper-respiratory-tractsamples include nasopharyngeal and/or oropharyngeal swabs and aspirates, andlower-respiratory-tract samples include phlegm, respiratory aspirates, bronchoalveolar lavage fluid,and lung biopsy samples. According to SARS treatment experience, the viral loads and genomefractions of lower-respiratory-tract samples are high [2] , so lower-respiratory-tract samples shouldbe used for testing, followed by nasopharyngeal and/or oropharyngeal swabs. It was reported thatfor one patient, before hospitalization, the three nucleic acid detection results on oropharyngealswabs were all negative, and after hospitalization, the result of nucleic acid detection using thebronchoalveolar lavage fluid collected during rescue was positive. However, the collection oflower-respiratory-tract samples is very difficult. In addition, due to the specific clinical conditions,such as the clinical procedures of medical personnel and patient tolerance (for example, thesputum sample should be a sputum produced by deep coughing after clearing the mouth, but manyseverely ill patients are very weak and fail to provide such samples, instead producing mostlysaliva), currently, nasopharyngeal and oropharyngeal swabs are the main samples used for nucleicacid detection of SARS-CoV-2.