Multiple rounds of nucleic acid testing are being carried out repeatedly in high-risk areas of the epidemic.
Nucleic acid testing requires repeated scraping of the throat with a swab, and many people have been "stabbed" many times.
Some enthusiastic netizens found that it was mentioned in the "New Coronary Virus Pneumonia Diagnosis and Treatment Plan (Trial Ninth Edition)" that nucleic acid detection can be carried out by testing sputum.
If "sputum" can also yield results, wouldn't it be okay not to be "stabbed"?
So, which part of the test specimen is more effective?
Can this trick actually work?
The reporter of Science and Technology Daily exclusively interviewed Peng Niancai, an expert in the field of nucleic acid detection, professor of Xi'an Jiaotong University and founder of Tianlong Technology.
Which part of the test specimen is the most effective
"No matter what part of the specimen is selected, as long as nucleic acid can be obtained from it, the enrichment, purification and amplification of nucleic acid can detect whether there is virus in it, and then reflect whether a person has the virus or not, it is a qualified sample." Peng Niancai told A reporter from Science and Technology Daily, for the new coronavirus transmitted by the respiratory tract, throat swabs, nasal swabs, anal swabs, sputum and bronchoalveolar lavage fluid can all be valid samples.
Taking a throat swab as an example, in addition to obtaining pharyngeal secretions during scraping, enough epithelial cells encapsulating the virus should be scraped out.
The sputum contains not only the mucous secretions of the bronchial mucosal epithelium, but also the exfoliated mucosal epithelial cells, inflammatory cells, etc. These exfoliated cells of the infected person will contain the virus, and can be detected positive after nucleic acid extraction.
In addition, different sampling sites often have different representations.
Some experts said that nasopharyngeal swabs represent upper respiratory tract infections, sputum represents lower respiratory tract infections, and anal swabs represent the load of nucleic acid in the body.
For example, it was previously clinically found that some confirmed cases only have gastrointestinal symptoms, and respiratory tract testing may be missed.
Therefore, in some special cases, the detection of samples from different parts can complement and confirm each other.
Sputum has a long history as a test specimen
"In the early stage of the epidemic two years ago, the new coronavirus mainly caused inflammation in the lungs, so nucleic acid testing was performed on the bronchoalveolar lavage fluid." Peng Niancai said that with the scientific understanding of the new coronavirus, for example, it was isolated from the feces of infected persons. Live virus, suggesting that the virus can also be detected by anal swabs, and the detection samples are gradually enriched.
According to the information inquired by the reporter of Science and Technology Daily, the "New Coronary Virus Pneumonia Diagnosis and Treatment Plan (Trial Fifth Edition)" generally categorizes samples into respiratory specimens and blood specimens.
It was not until the sixth edition that respiratory specimens were divided into nasopharyngeal swabs, sputum and other lower respiratory tract secretions, and it was specially proposed that in order to improve the positive rate of nucleic acid testing, it is recommended to collect sputum as much as possible, and collect sputum from patients undergoing tracheal intubation. Lower respiratory tract secretions should be sent for inspection as soon as possible after specimen collection.
It can be seen that for the new coronavirus at that time, the sputum test was superior to the nasopharyngeal swab test, which helped to reduce the false negative rate of nucleic acid tests.
Sputum testing is not necessarily better
"Sampling for nucleic acid testing is like 'cutting bean sprouts', which is related to the course of infection and viral load. It is necessary to choose the right time and place for 'bean sprouts germination' and 'scissors' to detect positive or negative. "Peng Niancai said, therefore, in order to obtain effective samples during sampling, the "scissors" should be cut in the right place.
"With the deepening of people's understanding of the Omicron variant strain, it is found that it infects the upper respiratory tract more. In theory, the detection of Omicron variant strain and the selection of upper respiratory tract specimens will obtain the positive rate of viral nucleic acid detection." Peng Niancai Said, therefore, now, compared with sputum as a lower respiratory tract sample and nasopharyngeal swab, which has a higher detection rate and the highest detection rate a few days after infection, further research is needed.
The specific guiding principles are reflected in the ninth edition of the diagnosis and treatment plan.
In addition, for large-scale screening, the optimal sampling method should not only be non-invasive, convenient, and have a high detection rate, but also facilitate collection, avoid contact, and avoid cross-infection caused by aerosol formation.
The data show that the methods of collecting sputum samples include natural expectoration, tracheal puncture and suction, and extraction through bronchoscopy.
Some methods are complicated and painful to operate.
Natural expectoration of sputum is also more complicated than taking a swab. It is necessary to rinse the mouth with water several times, cough up the sputum deep in the trachea, and keep it in a glass, plastic cup or wax-coated carton, which is not convenient for further collection and testing.
Therefore, nucleic acid detection through the collection of throat swabs is more conducive to standardized sampling throughout the process.
In order to ensure the safety, effectiveness and standardization of nucleic acid testing, at the press conference of the Joint Prevention and Control Mechanism of the State Council on April 6, Wang Guiqiang, director of the Department of Infectious Diseases at Peking University First Hospital, suggested that the public should not eat within two hours before nucleic acid testing and avoid sampling. Vomiting and nausea occurred during the process; do not drink water for 30 minutes, do not eat chewing gum, and avoid drinking.
Our reporter Zhang Jiaxing