Views:2 Author:Site Editor Publish Time: 2020-03-30 Origin:Site
Thare are usually two strategies for detecting infectious diseases: detecting the pathogen itself, or detecting antibodies produced by the body in order to resist the pathogen. Detection of pathogens can detect both antigens (generally pathogen surface proteins, and some use internal nuclear proteins), as well as nucleic acids.
If any of the antibodies, antigens, or nucleic acids is detected in the patient's body fluids, it means that they are infected. Because antibodies take time to produce, generally ranging from a few days to a few weeks, some patients with weak immune functions may have low antibody levels, which can easily cause false negatives (already infected, but the test results do not appear to be infected).
At the beginning of the infection, the pathogen antigen content is also low, and it is also not easy to detect. Therefore, it is currently widely used to detect the nucleic acid sequence of a pathogen, and the signal is amplified by an amplification reaction, and the detection has high sensitivity and specificity.
Since the new coronavirus is an RNA virus, the kit basically uses reverse transcription plus real-time polymerase chain reaction (RT-PCR) to amplify the nucleic acid (RNA) of the pathogen, and at the same time detects the amplified product in real time with a fluorescent probe . This method is very sensitive and can be well quantified.
The World Health Organization (WHO) website lists the detection methods and primer sequences used by the CDC in Germany, Hong Kong, Thailand, Japan, and China, which basically target 2 to 3 sequences that are highly conserved among viral sequences-such as coding nucleic acid sequences of replicase or necleocapsid-for detection.
But the sequence used by each method is not exactly the same. Some methods use multiplex, that is, multiple target sequences are amplified in the same reaction tube; others use step-by-step, first screen with one target sequence, and then confirm with another sequence.
The accuracy of the detection response depends on the accuracy of the published gene sequence and the design of primers, probes, etc. From the limited data currently published, the accuracy of these kits is good. Because the patients that can now be detected are highly clinically suspect, the positive predictive value is very high.