For nucleic acid testing, you must read these 10 points!

◎ Dai Xiaopei, a reporter from Science and Technology Daily

What are the precautions when doing nucleic acid testing? Science and Technology Daily reporter interviewed Li Dongzeng, chief physician of the Respiratory and Infectious Diseases Department of Beijing You'an Hospital. The expert answered in detail these 10 questions that should be paid attention to when doing nucleic acid testing.

Medical staff collect nucleic acid samples from citizens at a temporary nucleic acid testing sampling point in Zhongguancun Street, Haidian District, Beijing. Photo by Xinhua News Agency reporter Ren Chao

1. Does it make sense not to drink hot water within 30 minutes before doing a nucleic acid test?

Li Dongzeng: Drinking hot water before nucleic acid testing may dilute the virus attached to the throat, and the virus is not heat-resistant, so drinking hot water will inhibit the activity of the virus. In order to improve the accuracy of throat swab nucleic acid testing, it is recommended that the test subject should not drink hot water within 30 minutes before the test. In addition, drinking beverages will dilute the virus, and chewing gum will secrete more saliva to dilute the virus, which may also lead to missed detection.

But it cannot be said that drinking hot water, beverages, or chewing gum will definitely lead to inaccurate test results.

Because the test results are affected by many factors. For example, the amount of virus in the body of the person being tested. If the amount of virus in the body of the person being tested is low, drinking hot water to dilute it may result in less virus being collected, affecting the test results; if the amount of virus in the body of the person being tested is high, even if the person drinks hot water, the test result may still be positive.

In fact, the sampling method has a greater impact on the test results. The specific locations of the pharyngeal swabs for nucleic acid collection are on both sides of the pharyngeal isthmus, the tonsillar crypts, and the posterior pharyngeal wall. Normally, the pharyngeal swabs for nucleic acid collection need to be wiped repeatedly 3-5 times to ensure that mucosal cells are collected. During this period, the swabs should be prevented from contacting the tongue, uvula, oral mucosa, and saliva to avoid affecting the test results.

However, in actual testing, some samplers may only scratch it two or three times, or just wipe the pharynx without reaching the posterior pharyngeal wall, which will increase the error in the test results.

In summary, inadequate testing methods may lead to a decrease in the positive rate, and if the subject drinks hot water, it will have a greater impact on the results.

2. Can drinking water reduce infectiousness?

Li Dongzeng: For people infected with the new coronavirus, drinking water may temporarily dilute the virus in the mouth, but the virus may replicate again half an hour later. Because the virus replicates very quickly, the infectiousness of the virus will not be reduced by drinking water.

3. Can I brush my teeth or rinse my mouth within 30 minutes before the nucleic acid test?

Li Dongzeng: Just like drinking hot water, brushing your teeth and rinsing your mouth can also reduce the amount of virus in your mouth. If you brush your teeth and rinsing your mouth one or two hours in advance, it will definitely not have an impact.

If the sampling personnel collect samples from the posterior pharyngeal wall in a standardized manner, brushing teeth and rinsing the mouth will have little effect on the test results. What is worrying is that after brushing teeth and rinsing the mouth, the nucleic acid test sampling personnel only collect samples from the front half of the mouth, which may affect the results.

How to judge whether the sampling is reliable? In fact, when the sample of the posterior pharyngeal wall is actually collected, it usually causes the subject to feel like vomiting.

4. Why should you try not to drink alcohol before nucleic acid testing?

Li Dongzeng: Alcohol, like hot water, can affect the activity of the virus, thereby reducing the accuracy of nucleic acid test results. In addition, drinking alcohol within half an hour before nucleic acid testing may make it easier to cause some digestive tract reactions during nucleic acid testing, such as vomiting.

5. When doing nucleic acid testing, try not to clear your throat, speak loudly, take deep breaths, or make "ah" sounds?

Li Dongzeng: Yes. It is mainly to prevent the spread of the virus and cause cross infection. Because when the infected person exhales, the virus may spread, increasing the risk of infection for people around them. The same is true for clearing the throat and making sounds. When taking a deep breath during the test, if there is a virus in the air at this time, you may be infected by the virus when you inhale.

Therefore, try to hold your breath when doing the nucleic acid test, finish the test quickly, put on a mask, and leave the scene as soon as possible.

6. Is it necessary to change the mask after each nucleic acid test?

Li Dongzeng: The probability of a mask being contaminated during nucleic acid testing is low, so you can generally continue to wear it. We recommend that you bring a spare mask when doing nucleic acid testing, but we do not require that you change it after the nucleic acid test.

Now Beijing requires people to keep a distance of two meters when queuing for nucleic acid testing. Everyone is facing the same direction when queuing, so the probability of masks being contaminated is very small. In addition, we generally require nucleic acid testing sites to set up one-way channels, so that people who leave the channel and wait in line do not cross each other, so as to avoid people who have finished the test and those who are waiting to be tested face to face.

However, if you place the mask on a test surface that is easily contaminated during the test, or if the mask falls to the ground, it is recommended to replace it. If someone is face to face with you during the test and he coughs or sneezes, the mask may be contaminated and it is recommended to replace it.

7. Why should you try to avoid eating 2 hours before nucleic acid testing?

Li Dongzeng: The main consideration is the comfort of the test subject. Generally, we worry that eating within two hours before the nucleic acid test may easily lead to vomiting during the nucleic acid test, especially if you poke your throat after eating too much, which is more likely to cause vomiting.

8. Some people lift up their masks from the chin to ensure that their noses are covered during nucleic acid testing. Is this necessary?

Li Dongzeng: This is not necessary. The mouth is exposed, and the nose is not bad. When doing nucleic acid testing, your mouth is so wide open. If there is a risk, the whole mouth is an exposed point. Therefore, pushing the mask from the bottom up does not reduce the risk of virus infection.

When doing nucleic acid testing, many people pull down or push up when taking off their masks. In fact, these are wrong actions because your hands touch the surface of the mask, and your hands may be contaminated. We recommend that you do not touch the mask itself when taking off or putting on the mask, and hold the straps on both sides of the mask to take it off or put it on.

More importantly, we must minimize exposure time. After the sampling personnel have finished testing a person, they must disinfect their hands, take a cotton swab, and tear off the packaging. To reduce exposure time, they should wait until the sampling personnel have completed these procedures before taking off their masks. If you move over and take off your mask and wait as soon as the person in front of you has finished testing, you may have to wait half a minute longer, and the exposure time will be longer.

9. What precautions should be taken when taking a nasal swab?

Li Dongzeng: The nasal swab is less susceptible to interference. Because the nucleic acid in the nasal swab is transmitted from the nasal cavity to the posterior pharyngeal wall by a cotton swab, it is less susceptible to interference from the mouth, tongue, etc. The effects of gargling, drinking beverages, drinking hot water, etc. on the test results of the nasal swab can be ignored.

Of course, if there is trauma to the nose, a deviated nasal septum, or coagulation dysfunction, etc., which are not suitable for nasal swabs, you should communicate with the sampling personnel in a timely manner.

10. What are the precautions for antigen testing?

Li Dongzeng: Antigen testing is generally done by the person being tested at home, and the procedure must be done according to the standard.

Generally speaking, antigen testing collects samples from 1-1.5 cm of the nasal cavity, and requires collecting samples from both sides of the nasal cavity, rotating each side of the nasal cavity 5 times and staying for a while. However, some people only do it on one side, which may affect the accuracy of the results.

It should be noted that if the antigen test is positive, it must be reported immediately, and you and your co-residents should not go out, and wait for the community to come to your door for nucleic acid testing and disinfection. The items used for sampling should not be thrown away, they can be sealed and handed over to community staff for disposal as medical waste.

Li Dongzeng finally emphasized that during the nucleic acid sampling process, the sampling personnel must ensure that the actions are standardized to reduce missed diagnoses. Citizens should actively cooperate. It is precisely because Beijing has conducted full-staff testing that infected people in the society were discovered, providing conditions for early detection, early reporting, early isolation, and early treatment, and providing a basis for cutting off the transmission chain.

Source: Science and Technology Daily

Editor: Wang Yu

Review: Yue Liang

Final judge: Wang Tingting

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