New coronavirus nucleic acid test results are an important reference for the diagnosis and efficacy evaluation of novel coronavirus pneumonia. Nucleic acid test screening specimens are mostly derived from deep cough sputum or pharyngeal swabs, which are divided into nasopharyngeal swabs and oropharyngeal swabs. So, what is the difference between the two?
Guangzhou Daily reporter learned from Sun Yat-sen Memorial Hospital of Sun Yat-sen University on March 3 that the second batch of the hospital's medical team to support the prevention and control of the epidemic in Hubei, three deputy chief physicians, Liang Faya, Tian Peng and Cai Yuexin of the Department of Otorhinolaryngology, as well as two nurses, Chen Wen and Lu Zhiyin, recently carried out training and sampling of nasopharyngeal swabs at the West Campus of the Union Hospital of Huazhong University of Science and Technology.
Deputy Chief Physician Cai Yuexin introduced that the pharyngeal partition includes nasopharynx, oropharynx and laryngopharynx, and the mucous membranes of the three are continuous and all belong to the area of the upper respiratory tract. Nasopharyngeal swabs and oropharyngeal swabs just take different paths, sampling through the mouth is an oropharyngeal swab, sampling through the nose is a nasopharyngeal swab.
Liang Faya, deputy chief physician, introduced that oropharyngeal swabs are more commonly used in clinical practice because they are relatively simple to perform with an open mouth. However, the risk of exposure is higher for those who take samples through the oropharynx. The operator often needs to face the patient's mouth, and the patient is prone to irritating dry cough, vomiting and other symptoms during the collection process, exposing the collector to the aerosol with the virus.
Nasopharyngeal swabs have several advantages over oropharyngeal swabs. The sample can be left in the pharynx for a longer period of time to obtain a more adequate amount of specimen, which is the reason why its positive rate has been reported in the literature to be higher than that of oropharyngeal swabs.
In addition, it is well tolerated by patients and can usually be preceded by surface anesthesia and constriction of the nasal mucosa, which allows skilled samplers to sample patients without anesthesia.
Since the operator can stand behind the patient's side during nasopharyngeal sampling, the patient pulls down the mask to expose only the nostrils and cover the oral cavity without looking directly into the patient's mouth, and there is essentially no gag reflex, the risk of exposure is considerably lower. Individual patients may have a sneeze reflex after sampling, which can also be covered immediately with an elbow or tissue.
If the pharyngeal swab nucleic acid test specimen collection is not done properly, it may result in a "false negative" result, which may delay the patient's treatment.
So, what is the key to pharyngeal swab nucleic acid test specimen collection? Dr. Tian Peng, deputy chief physician, said that whether it is a nasopharyngeal swab or an oropharyngeal swab, the depth of collection and the length of contact with the mucosa are key. If the nasopharyngeal swab is not collected deep into the nasopharyngeal cavity, or if the patient vomits when the oropharyngeal swab is collected, resulting in insufficient sampling time, the majority of the cells collected may be cells that do not contain the virus, which may result in a "false negative" nucleic acid test.
In some cases, the negative nucleic acid test is followed by a "re-positive" test, which is sometimes associated with inaccurate sampling.
A small number of patients may experience a small amount of nosebleed after sampling, but this can usually be stopped on its own, if necessary by slightly constricting the bleeding site with an epinephrine swab.
