Nucleic acid testing of nasal swabs and nucleic acid testing of pharyngeal swabs are the two main methods for confirming the diagnosis of novel coronavirus pneumonia (COVID-19).
There have been reports of three or more consecutive negative pharyngeal swab virus nucleic acid tests in patients with COVID-19.
In clinical practice, it has been found that patients with negative pharyngeal swab nucleic acid tests have positive nasal swab nucleic acid tests when repeated, possibly because the pharyngeal swab and nasal swab samples are different, resulting in biased test results.
Below you will find an explanation of nasal and pharyngeal swabs and their application and differences in the diagnosis of COVID-19.
Nasal swabs, also known as nasopharyngeal swabs, are sampling tools for extracting epithelial cells and secretions from the nasopharynx.
The secretions extracted from nasal swabs can be used for pathogenic testing, such as viral nucleic acid testing and bacterial culture.
It is commonly used for the diagnosis of respiratory infectious diseases, such as influenza, purulent sinusitis, and nasal boils.
Sampling is performed by using a sterilized nasal swab to penetrate deep into the nasal cavity and reach the nasopharynx to extract secretions and nasopharyngeal epithelial cells by rotating or wiping, etc. The section with the secretions is then placed into a sterile container for pathogenic testing.
Pharyngeal swab is a sampling tool for extracting mucosal cells and secretions from the oropharynx.
The secretions extracted from the pharyngeal swab can also be used for pathogenic testing, such as bacterial culture and viral nucleic acid testing.
It is commonly used for the diagnosis of respiratory infectious diseases including pharyngeal lesions, such as influenza, purulent tonsillitis, acute bacterial pharyngitis, etc.
The sampling method is to use sterilized pharyngeal swabs and other items to penetrate deep into the pharynx, through the root of the tongue to the posterior pharyngeal wall, tonsillar crypt, and lateral wall, repeatedly wiping left and right 2 to 3 times, and gently removing the swabs. The extracted mucosal cells and one end of the secretion are then placed into a sterile container or a container with culture fluid and sent for pathogenic testing.
When sampling the pharyngeal swab, the patient should open the mouth as much as possible, and the medical staff should observe the pharynx repeatedly before taking the sample.
To avoid affecting the test results, pharyngeal swab sampling for bacterial culture should be done before taking antibiotic medications if possible. Pharyngeal swab sampling is best done before eating, in addition to rinsing the mouth before sampling, and avoiding touching the tongue, pendulous gland, oral mucosa and saliva when sampling and removing the swab.
The virus can be detected in the upper respiratory tract shortly after the onset of illness.
Nasopharyngeal swabs sample the mucosal epithelial cells and endocrine secretions of the nasopharynx; pharyngeal swabs sample the mucosal epithelial cells and secretions of the oropharynx. Separate viral nucleic acid tests were performed, and if positive is one of the gold standards for confirming the diagnosis of COVID-19.
Among the sampling methods used to diagnose COVID-19, nasal swab and pharyngeal swab sampling are easier than sputum, bronchoalveolar lavage fluid, and stool nucleic acid testing.
When using pharyngeal swab sampling, medical personnel directly face the patient's mouth, and the patient is prone to irritating cough and vomiting during the collection process, thus making the collector easily exposed to the virus-bearing aerosol produced and at greater risk of infection; in addition, patients have coughing and nausea reactions during pharyngeal swab collection, which can affect the quality of the collected specimen and may result in "false negative "False negative" results.
When using nasal swabs for sampling, medical personnel can stand to the side of the patient, the probability of exposure to droplets and other respiratory-produced substances is smaller, and the risk of being infected is lower; in addition, the reaction during collection is relatively small, and the amount of samples that can be collected may be relatively adequate.
Some studies have found that the amount of virus in the nasopharynx of COVID-19 patients may be more than that in the pharynx.
It has also been found that nasopharyngeal swabs have a higher rate of positive nucleic acid testing than pharyngeal swabs.
Therefore, nasopharyngeal swabs may reduce the risk of infection in medical personnel while reducing the rate of missed COVID-19 tests relative to pharyngeal swabs.
