Continuous nucleic acid screening is required for some patients with low viral load

When the community completes a round of nucleic acid screening, those infected with a high viral load are usually screened, but some infected with a low viral load will show negative nucleic acid results. Therefore, continuous nucleic acid screening is needed to dynamically detect positive infections as soon as possible.

Nucleic acid testing is an important basis for epidemic prevention and treatment. What is the accuracy rate of nucleic acid testing? Some residents think that there is no need to do nucleic acid frequently, self-test antigen is ok, can you answer?

In response, Hu Xiaobo, Director of Shanghai Clinical Laboratory Center, said at a press conference on epidemic prevention and control held on April 25 that nucleic acid test is mainly used to determine whether an individual is infected with novel coronavirus, which is a highly sensitive test method. The novel Coronavirus nucleic acid test has always been the diagnostic standard for COVID-19 in China.

The current nucleic acid detection method is mainly to extract the viral RNA from the sample, and then use polymerase chain reaction (PCR) to amplify the viral gene sequence. This method has high sensitivity and specificity. “Under ideal conditions, nucleic acid testing accuracy can reach a very high level if all the steps of sampling, transportation, verification, testing, result interpretation and reporting are accurate,” Hu said.

However, the accuracy of nucleic acid detection is also affected by relevant factors, such as the cooperation of the subject when taking samples, the temperature and time of sample storage, and the standardization of the detection process. In order to ensure the accuracy of nucleic acid test results, the laboratory will take a variety of measures, such as setting internal standards to confirm whether the sample is qualified, through indoor quality control to monitor.

Shanghai launched nine campaigns to eliminate social encounters from April 22, in which the combined screening mode of “antigen + nucleic acid” was adopted in the screening campaign.

Compared with nucleic acid tests, antigen tests are fast and easy to use, and can be used for home tests, but their sensitivity is lower than nucleic acid tests, because nucleic acid tests are exponential amplification processes that make viruses easier to detect by appropriately amplifying the concentration of virus fragments, he said.

“So if a person is in the early stages of infection and the signs are not there, then the antigen test may be negative and nucleic acid testing is needed to confirm that.” Hu xiaobo said, “The accuracy of antigen testing also depends on the standardization of individual operations. Antigen testing is not a substitute for nucleic acid testing.”

He pointed out that the recent continuous screening is based on such considerations, as there is a certain incubation period in terms of the course of novel coronavirus infection, and the viral load varies from individual to individual. When the community completes a round of nucleic acid screening, those infected with a high viral load are usually screened, but some infected with a low viral load will show negative nucleic acid results. Therefore, it is necessary to carry out nucleic acid screening for many times in order to dynamically detect positive infections as soon as possible and achieve dynamic social clearance as soon as possible.