Sample collection swab:How much do you know about nucleic acid testing
The spread of the covid-19 is continuing worldwide. Although the global scientific and medical circles are making every effort to fight the epidemic, it is difficult to predict how the epidemic will develop in the future, and its impact on social development has appeared in many aspects.
In order to fully control covid-19, the general screening of local areas shall be carried out if necessary.
After identifying the detection object, how to detect it?
1、 What specimen to choose?
According to the recommendations of the American infectious diseases association, the following specimens were used:
- Nasopharyngeal swab
- Middle turbinate swab
- Anterior nostril swab
- saliva
- Anterior nostril + oropharyngeal swab
- Alveolar lavage fluid
- Anal swab
The sensitivity of simple oropharyngeal swab may not be enough, so it is relatively easy to miss diagnosis.
The sensitivity of alveolar lavage fluid is the highest, but it is obviously not suitable for universal screening.
Nasopharynx swabs and other operations should also be standardized.
Improper operation may make the quality of collected samples not high, thus increasing the risk of missed diagnosis.
2、 Select the time of detection
It is very important for COVID-19 to measure RNA and choose the right time. One analysis included 7 studies, including 2 unpublished reports, to evaluate the detection efficiency of RT-PCR at different time points after exposure to virus :
On the day of exposure to the virus, the possibility of detecting viral RNA is almost zero;
On the fifth day after exposure, that is, the first day after infection, the detection probability was 62%
About the 8th day after exposure, i.e. the 4th day after infection, the probability of detection was 80%
On the 21st day after exposure, i.e. the 17th day after infection, the detection probability was 34%
In conclusion, exposure to COVID-19 may require multiple tests to avoid missed diagnosis. However, it is not recommended to repeat the test within 24 hours of the previous test; The interval between two tests shall be at least 24 hours.
After 28 days of exposure to the virus, if the infection has not been diagnosed, it is not necessary to continue the detection; At this time, it is almost certain that it is not infected.
Nucleic acid detection throat swab sampling process
The COVID-19 nucleic acid was novel coronavirus, which was collected from sputum or lower respiratory tract by real-time fluorescent RT-PCR. If positive, the new coronavirus could be diagnosed. This is the basis for the diagnosis of new type of pneumonia. In addition to detecting the nucleic acid of the virus, it can also detect whether the virus in the specimen is highly homologous with New Coronavirus. If so, it can be diagnosed as New Coronavirus pneumonia. The virus is highly infectious and has the characteristics of human to human transmission, but the virus is sensitive to temperature and sunlight and ultraviolet rays.
The flocked swab is the best raw material for sampling swabs.
reference
1,Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19, updated December 23, 2020. https://www.idsociety.org/practice-guideline/covid-19-guideline-diagnostics/ (Accessed on January 14, 2021).
2,Kucirka LM, Lauer SA, Laeyendecker O, et al. Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction-Based SARS-CoV-2 Tests by Time Since Exposure. Ann Intern Med 2020; 173:262.