The global response to COVID-19 is still facing severe challenge
Recently in the global fight against COVID-19 in the process of the outbreak, due to the economic downturn, while the Omicron strain is less pathogenic than the previous strain, with anti-epidemic fatigue mentality and other complex factors, some countries and regions have cancelled the wearing masks, isolating infected and strict control measures such as tracking contact person, in addition to strengthen the vaccination basic do not take other measures for prevention and control.
In response, WHO issued a new warning to the world: " Although in many countries all restrictions have been lifted and life looks much like it did before the pandemic, reported cases are increasing in almost 70 countries in all regions." Experts believe that due to the spread of the COVID-19 variant, which is more capable of transmission, and the premature relaxation of quarantine measures in some countries, the future trend of the epidemic remains uncertain.
To help end the emergency phase of the COVID-19 outbreak, WHO calls on countries to continue to strengthen their virus surveillance capabilities to detect early warning signs of significant virus evolution, while nucleic acid testing is an important part of virus surveillance. Nucleic acid test is a mature, international general laboratory diagnosis method, editor is here to do some simple popular science.
The nucleic acid testing of COVID-19
PART 01
Principles of nucleic acid testing for COVID-19
The nucleic acid test is a test for the presence of COVID-19 nucleic acid (RNA) in the human body. Each virus contains ribonucleotides inside its nucleic acid, and different viruses contain different numbers and sequences of ribonucleotides, making each virus specific.
Nucleic acid detection is the specific detection of the nucleic acid of the COVID-19. Prior to nucleic acid testing, sputum, throat swabs, alveolar lavage fluid, blood and other samples need to be collected, which can be tested to find what bacteria the respiratory tract infection of the subject. The COVID-19 nucleic acid test is usually performed ona throat swab sample, which will be purified by lysis to extract the possible COVID-19 nucleic acid.
COVID-19 nucleic acid detection is mainly performed by fluorescence quantitative RT-PCR. In the detection process, RT-PCR is first used to reverse transcribe the nucleic acid (RNA) of the COVID-19 into its corresponding deoxyribonucleic acid (DNA). Then, the obtained DNA was replicated in large quantities by fluorescence quantitative PCR technology. At the same time, the cloned DNA was detected and labeled with specific probes. If COVID-19 nucleic acid is present, the instrument can detect the fluorescence signal, and, as the DNA replicates, the fluorescence signal increases, thus indirectly detecting the presence of COVID-19.
PART 02
Nucleic acid test is the "gold standard" of diagnosis
Regarding nucleic acid testing, it is a mature and internationally accepted laboratory diagnostic method. In the past, we detected the pathogens of viruses mainly by culture, and we identified them through staining, morphological observation, biochemical test, immune test and other methods. Viruses take a long time to grow, some pathogens are difficult to grow in the lab, and then we have nucleic acid testing. Nucleic acid detection method is highly sensitive, the specificity in methodology can reach 100 percent. In other words, a positive result of nucleic acid test is the gold standard of diagnosis, which is the same as the result of pathogen culture. Not only COVID-19, but also common pathogens such as hepatitis B virus and HIV can be diagnosed by nucleic acid testing as well as monitored for treatment.
In most countries, COVID-19 nucleic acid tests are carried out on double or triple target genes of COVID-19. Since two or three target genes do not mutate at the same time, it is unlikely that the virus mutation will affect the detection ability of nucleic acid tests.
PART 03
A positive nucleic acid test in an environmental sample does not mean the presence of live virus
Nucleic acid positive detection in environmental samples does not necessarily mean that there is live virus in the environmental samples. In order to identify the presence of live virus, it is necessary to do cell virus isolation, or virus isolation in sensitive mice, to determine whether there is live virus. Because both dead and live viruses in environmental samples and the inactivated COVID-19 vaccine we are using now contain nucleic acid, nucleic acid test can be positive, so a positive nucleic acid test does not mean that it has live virus, it needs to be evaluated comprehensively.
PART 04
Nucleic acid test sampling swab belongs to medical equipment, not cotton swab, non-toxic and harmless
A swab looks like a cotton swab, but it is not. It is made of polyester or nylon fibers. During the process of making a swab, millions of tiny fibers are vertically and evenly covered on the tip of the swab handle. When you take a sample, an oropharyngeal swab, just like a toothbrush when you brush your teeth, you brush the back wall of the pharynx in your mouth to get cells, and then you put the swab in a tube, and then you remove the sample into a preservation solution, and then you test it in the laboratory.
Sampling swab is a medical device, its production environment and requirements are very strict, there are relevant quality supervision standards, the most basic standard is non-toxic and harmless, and the production process does not produce harmful substances.
PART 05
Large population screening is usually performed with oropharyngeal swabs
Depending on the location of sampling, samples are divided into upper respiratory tract samples (e.g. nasopharyngeal swabs, oropharyngeal swabs) and lower respiratory tract samples (e.g. sputum). The sputum virus content and positive test rate were highest among the swabs, followed by nasopharyngeal swabs and oropharyngeal swabs. In the early stage of COVID-19 infection, the main symptoms are dry cough, and sputum is not saliva, it is difficult to obtain. Nasopharyngeal swab collection requires a high level of operation of the sampler, and the sampling process is slow. Although the positive rate is high, it is generally not used for screening of most of the population but can be used for sampling of isolated population. Oropharyngeal swab sampling is relatively simple and fast, so we usually use it in large-scale population screening.
PART 06
A positive nucleic acid test is a diagnosis?
A positive nucleic acid test can confirm the presence of viral nucleic acid in a person's body but does not directly confirm COVID-19 patients. If the nucleic acid test is positive, the participant should be further diagnosed based on the epidemiological history. If the participant has symptoms such as fever, sore throat, cough, fatigue, and contact history with confirmed infected persons, the participant can be diagnosed as a confirmed case.
If the participant does not have any symptoms, the participant may be diagnosed as asymptomatic carrier. Asymptomatic carriers are also contagious, and some asymptomatic infected people later develop symptoms and become confirmed patients.
PART 07
Why does false negatives happen?
False negative means that the person tested has been infected with the COVID-19, but no viral nucleic acid has been detected, that is, the nucleic acid test is negative. If a person shows no symptoms and the nucleic acid test is negative, it is easy to let his guard down, potentially leading to a wider spread of the virus.
There are three main reasons for false negative:
First, the COVID-19 nucleic acid content in the original test specimens is too low, which is below the limit of detection. This is related to the type of samples collected and the time of collection.
Secondly, if the position of the COVID-19 nucleic acid binding to the probe changes, the binding efficiency of the probe in the detection may be affected and the fluorescence signal cannot be detected.
Third, false negatives are also related to the sensitivity of the test technique. In the early stage of the epidemic, the clinical kits were not mature and sensitive enough, and there were frequent reports of false negatives. Later, with the improvement of technology, the accuracy of the test increased rapidly, and the false negative rate continued to decrease.
PART 08
Positive Nucleic acid tests after repeated negative
There are three types of positive nucleic acid tests after repeated negative tests.
In the first case, the person who was initially uninfected becomes infected at some later point in time, and then tests positive.
The second case is in the incubation period, nucleic acid test is not detected, after the onset of the test is positive.
In the third case, although the virus was present at the beginning, the load did not reach the limit of detection. Currently, the test result was negative, but after the load was high, the test was positive.
Hecin’s Rapid PCR Solution
As of 1 July 2022, COVID-19 infections have caused more than 540 million infections and more than 6 million deaths worldwide. In human host, in order to adapt to the environment in vivo, the virus will accelerate the mutation and evolution, and the mutated virus may change in infectivity, latency, transmissibility, pathogenicity, persistence time in vivo, antigenicity and other aspects. COVID-19 variants are occurring frequently, spreading rapidly and with a high infection rate across the globe, making the epidemic situation more complex and severe. Therefore, professional monitoring and judgment methods are very important.
Hecin actively responds to the global demand for COVID-19 prevention and control by launching the new set of Rapid PCR Solution, including Specimen Release Agent, 2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method) and UltraFast QPCR Instrument. Compared with traditional protocols, this protocol can save 70% of the time and produce results efficiently and quickly. In terms of performance, the sensitivity and specificity are greater than or equal to 98%. It can detect a variety of mutant strains such as Delta and Omicron, providing high-quality, stable and convenient nucleic acid testing services for supporting the global response to COVID-19. The products have been certified by the European Union, Brazil, Indonesia, Thailand, The United Kingdom, Bolivia and other countries and regions, and can be exported smoothly.
Long-distance cold chain logistics and transportation is one of the biggest obstacles to the overseas export of Nucleic Acid Test Kit. For conventional liquid testing reagents, the temperature control link in the transportation process greatly affects the performance of reagents, and the transportation cost doubles. Hecin's 2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method) uses freeze-dried powder technology, which does not require a cold chain, and can be stably transported and stored at room temperature, greatly reducing the cost of transportation.
Meanwhile, Hecin's 2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method) has passed the performance verification of the system and can be adapted to a variety of PCR instruments (ABI7500, HC 1600 etc.) to ensure the stability and accuracy of 2019-nCoV Nucleic Acid Test Kit results.
Up to now, Hecin has successfully developed a variety of respiratory detection reagents, including:
2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method),
2019-nCoV/IAV/IBV Nucleic Acid Test Kit(PCR- fluorescence probe method),
2019-nCoV Antigen Test Kit (colloidal gold method),
2019-nCoV Neutralizing Antibody Test Kit (Fluorescent immunochromatography),
2019-nCoV IgM/IgG Antibody Test Kit(colloidal gold method),
2019-nCoV and Delta Strain Nucleic Acid Test Kit (PCR- fluorescence probe method),
2019-nCoV and Omicron Variant Nucleic Acid Test Kit (PCR- fluorescence probe method), etc.
Hecin is committed to creating a full set of respiratory detection solutions suitable for multiple scenarios. Hecin will continue to follow the changes of the global epidemic, strictly control the quality of products, and continue to contribute to the epidemic prevention and control work of countries around the world.
