The probability of a single positive result is generally small. In nucleic acid detection, fluorescence is used to report whether it is positive or not. Different colors of fluorescence represent a target. "Single positive" means that only one kind of fluorescence was "alarmed" at that time.
In the "novel coronavirus Prevention and Control Plan (Eighth Edition)", the technical guidelines for sample collection and detection in COVID-19 (hereinafter referred to as the guidelines) are clearly defined: the nucleic acid detection method in the laboratory adopts the "real-time fluorescence RT-PCR" method, and the nucleic acid detection is carried out in COVID-19. So, why does COVID-19's nucleic acid fluoresce when it appears?
Special matching "primers" are specified in the guide, which are designed for unique genes in COVID-19 genome (two COVID-19 reporter genes: open reading frame 1ab and core-shell protein). Primers are like "undercover" When you go to "check the signal" with "enemy" COVID-19, a pair will excite fluorescence.
The fluorescence is very weak. In order to avoid false detection, fluorescence PCR equipment monitors the curve law of target fluorescence rising (called Ct value) in the process of nucleic acid amplification in real time. If the law meets the characteristics of the standard (COVID-19 positive), it will report positive. Two goals means sending two "undercover" in this investigation system.
Is Shan Yang's report wrong? Judging from the results, "single positive" means that two "undercover" gave completely different answers, one positive and the other negative. Is this "split" answer because there is something wrong with the examination system?
I don't think this can be wrong. In order to solve many problems that may occur in the process of automatic nucleic acid extraction and detection, such as cross-contamination, temperature edge effect, cross-talk of fluorescence detection channels, leading domestic enterprises and R&D teams have developed technologies with core patents, which have also obtained professional certification from the United States and the European Union.
With regard to the quality control of nucleic acid detection, the guidelines stipulate that China CDC should evaluate the quality control of laboratories of provincial CDC at least once a year, and provide the quality control plan for laboratory detection in COVID-19. Before testing clinical specimens, the laboratory will also verify the detection system composed of nucleic acid extraction reagents, extraction instruments, amplification reagents and amplification instruments before use.
In large-scale population screening, the guidelines clearly stipulate that once a positive result occurs, another nucleic acid detection reagent with more sensitivity of 1-2 should be used to recheck the original sample, and the rechecked positive sample can be reported. It can be seen that the results of nucleic acid detection have "three risks" in technical equipment, laboratory assessment and review.
Is "Shan Yang" masculine? The appearance of "single positive" is related to many factors, including the infection status of the virus, the type of samples tested, and the standardization of sample sampling operations. Whether Shan Yang is nucleic acid positive or not needs further research, verification and expert knowledge. At present, most manufacturers have put forward corresponding solutions to this situation, that is, to determine whether the samples are positive or not mainly through re-inspection to improve the accuracy of detection.
The guideline also stipulates "case confirmation": if a single target is positive, it needs to be re-sampled and re-tested. When the real-time fluorescence RT-PCR of two samples shows single target positive at the same time, or the detection results of two samples of the same type show single target positive, it can be judged as positive.
In addition, fluorescent nucleic acid detection can be qualitative or quantitative. In addition to simply answering yes and no, how many questions can be answered to provide more data for positive discrimination. As for why a single gene is positive, it needs to be explored.