1. Pathogenic diagnosis is the gold standard for infectious diseases. In the early stage, because there were too many patients in Wuhan and too few laboratories could perform nucleic acid testing, a large number of patients were waiting for testing, and the results were not as reliable as expected, so some clinicians in Wuhan called for "replacing" viral nucleic acid testing with chest CT; it was also reported that the sensitivity of sputum specimens was higher than that of pharyngeal swabs, but it would increase the liquefaction of sputum. It has also been reported that sputum specimens are more sensitive than pharyngeal swabs, but the liquefaction of sputum is added to the process (2 ml of proteinase K in the sampling cup), which can also lead to false-negative results due to unsatisfactory liquefaction; bronchoalveolar lavage fluid specimens are difficult to collect (≥5 ml aspirated by clinicians under aseptic operation);
collecting stool for nucleic acid testing is inconvenient (3-5 g of soybean-sized stool specimens in a collection tube containing 2 ml of saline); in patients with no or difficult access to respiratory secretions In patients with no or difficult access to respiratory secretions, blood specimens can be collected for testing. At present, the diagnosis is still confirmed by the positive nucleic acid of the novel coronavirus isolated at home and abroad.
The sixth edition of the treatment protocol no longer emphasizes the specimen tested, as long as the new coronavirus test is positive, it can be used as a confirmed case. However, nasopharyngeal swab is still the easiest and most popular method.
2. The positive rate of pharyngeal swabs in confirmed patients is roughly 30%-50%. Some time ago, academician Wang Chen suggested in an interview with CCTV that the positive rate of pharyngeal swabs among confirmed patients was only 30%-50%; according to the literature first published by Yanbin Liu of West China Hospital of Sichuan University, pharyngeal swabs and nasal swabs were taken from 100 cases of novel coronavirus pneumonia in Wuhan Red Cross Hospital at the same time, and the positive detection rate of pharyngeal swabs was 54%, while the positive rate of viral nucleic acid in nasal swab specimens was 89%. 89%; and a typical case reported in the media was a patient with 3 negative nucleic acid tests for pharyngeal swab specimens and positive nucleic acid tests for alveolar lavage fluid specimens collected during the resuscitation process after admission to hospital. The comprehensive analysis is as follows.
Common objective reasons are: nasal and pharyngeal swabs are most commonly used, but they are closely related to the course of the disease. In the early stage, the virus is distributed in the upper respiratory tract, and as the disease progresses, the upper respiratory tract virus is cleared, while the viral load in the lower respiratory tract increases instead, and may not be easily detected from nasal and pharyngeal swabs at a later stage.
Common subjective reasons are: if the medical staff sampling is not skilled or inaccurate location; scraping specimens when the patient's reaction is relatively large; collection of medical staff facing the patient's mouth, there is a risk of droplet and aerosol transmission route, sampling time is short or not strong enough, it is difficult to collect enough specimens, resulting in the detection of false negatives appear.
3. The difference between cotton swabs and nylon flocked swabs
The material and quality of the sampling swab is also important to the quality of the sample. Velvet on nylon flocked swabs increases the surface area of the swab in contact with the pharynx and can maximize the transfer of cells to the surface of the swab. A foreign study found that flocked swabs were 20% to 60% more efficient at transferring surface microorganisms than cotton swabs.
4. Nasal swab sampling standing on the side of the patient is less risky than swabbing the pharynx standing on the front of the patient.
To collect pharyngeal swab specimens, three levels of protection are required. During the sampling process, patients may suddenly become nauseous and cough due to pharyngeal discomfort, resulting in splattering of droplets. Even though some workplaces for collecting pharyngeal swabs are arranged outdoors to ensure effective ventilation, the high risk of this operation is not guaranteed. Nasal swab sampling, on the other hand, can be performed standing to the side of the patient and avoiding the triggering of the patient's sensitive pharyngeal reflex (often manifested as nausea and, in severe cases, vomiting, with the posterior pharyngeal wall, the root of the tongue and the bilateral palatal arches as the triggering areas).
Therefore, the risk of nasal swab sampling is lower than that of pharyngeal swab sampling. The following is the procedure for collecting nasopharyngeal swabs and oropharyngeal swabs from the same patient according to the requirements of the treatment protocol (Trial Version 5, Revised).
