For the first time, the Guangzhou scientific research team accurately described the complete transmission chain of the delta variant on a global scale

2021-09-15: [Original Article Link].

Covid-19 is still a worldwide pandemic, and the new coronavirus Delta variant has rapidly become the prevailing strain. The team of Professor Tang Xiaoping and Li Feng from the Eighth Hospital Affiliated to Guangzhou Medical University, and the team of Academician Zhong Nanshan and Professor Chen Ruchong of Guangzhou Respiratory Health Research Institute, the First Affiliated Hospital of Guangzhou Medical University, for Delta variation strains cause the "5 · 21 the Covid pneumonia outbreak", in combination with epidemiological and virus genome sequencing technology for the first time on a global scale accurate depiction of the Delta mutant dissemination of full chains, combined with clinical resources, the clinical characteristics and viral dynamics of the cases in the epidemic were described in multiple directions. Recently, the research results were published in the international authoritative journal "The Lancet" Journal of Electronic Clinical Medicine. According to previous epidemiological investigation and viral nucleic acid gene sequencing "5 · 21 the Covid pneumonia outbreak" for Delta variation strains cause, with a clear chain. For the first time, the study tracked and fully reported the clear chain of transmission of this outbreak. In the beginning of the 75-year-old woman accidentally exposed infection and close family contact or dinner and infected another 3. The researchers observed that the transmission of the virus in the epidemic was mainly through direct and indirect close contact, of which 30.8% of the infected were transmitted through meals, followed by family contact (30.13%), community communication (18.59%), and other routes of transmission including work and social contact (19.87%). At the same time, the researchers included the "5 · 21" epidemic in a cohort of patients infected with the wild strain of the new coronavirus in the 2020 COVID-19 epidemic, the clinical characteristics and viral dynamics of the "5 · 21" epidemic cases were analyzed in multiple directions, and the characteristics of Delta variants were summarized, and the risk factors for severe illness were sought. The researchers found that the Delta variant had a short incubation period and a rapid spread, with a median incubation period of only 4.7 days, which was significantly shorter than that of the wild strain (6.3 days). Further subgroup analysis showed that in the non-severe Group, the latency of the virus (4.0 days) was significantly shorter in the non-severe group than in the wild strain (6.0 days). The Delta variant can spread 4 generations in 10 days, of which the fastest intergenerational transmission does not exceed 24 hours. Compared with the wild strain, the viral load of the Delta variant was significantly higher (the median CT value is 34.0, the latter is 20.6, the higher the viral load), the time of nucleic acid conversion of Delta mutant strains was also significantly longer than that of wild strains. The researchers also found that infection with the Delta variant was a risk factor for predicting critical illness. The risk of critical illness was 1.45 times higher in the Delta mutant group than in the wild strain group among elderly patients aged 60 years and older; moreover, the development of infected Delta mutant strains is 2.98 times faster than that of infected wild strains. Researchers believe that this study revealed that the Delta variant has the characteristics of short incubation period, fast transmission speed, high viral load, long nucleic acid conversion time, and easier development into critical illness. Therefore, it is very important to quickly track, isolate and detect virus infected persons in time, implement timely control of key places and implement nucleic acid screening for all staff in local areas under special circumstances. The practice of quickly discovering the source of infection and cutting off the route of transmission provides the "Guangzhou experience" for the prevention and control of the Delta variant of the Covid virus ".

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