The new crown pneumonia is still a pandemic worldwide, and the delta variant of the new crown virus has quickly become the prevailing strain.

  The team of Professor Tang Xiaoping and Professor Li Feng of the Eighth Affiliated City Hospital of Guangzhou Medical University, together with the team of Academician Zhong Nanshan and Professor Chen Ruchong of the Guangzhou Institute of Respiratory Health, the First Affiliated Hospital of Guangzhou Medical University, aimed at the "5.21 New Coronary Pneumonia Epidemic" caused by the Delta mutant strain, combined For the first time, epidemiology and viral genome sequencing technologies accurately portray the complete transmission chain of delta variants on a global scale, and combined with clinical resources, multi-directional portrayal of the clinical characteristics and viral dynamics of the cases in the epidemic.

Recently, the research results were published in the sub-issue of the international authoritative journal "The Lancet", "Journal of Electronic Clinical Medicine".

  According to previous epidemiological investigations and viral nucleic acid gene sequencing, the "5.21 New Coronary Pneumonia Outbreak" was caused by the Delta mutant strain and has a clear chain of transmission.

The study tracked and fully reported the clear chain of transmission of this epidemic for the first time.

The outbreak began when a 75-year-old woman was exposed to the infection accidentally and infected another 3 people through close family contact or gatherings.

The researchers observed that the main route of transmission of the virus in the epidemic was through direct and indirect contact. Among them, 30.8% of the infected were spread through meals, followed by family contact (30.13%) and community transmission (18.59%). , And other means of transmission including work and social contact (19.87%).

  At the same time, the researchers included those infected with the "5.21" epidemic into the cohort of patients infected with the wild strain of the new coronavirus in the 2020 new coronary pneumonia epidemic, and analyzed the clinical characteristics and virus dynamics of the "5.21" epidemic cases from multiple perspectives. Characteristics, summarize the characteristics of Delta mutant strains, and seek risk factors for progression to severe illness.

  The researchers found that the incubation period of the Delta mutant strain is short and the spread speed is fast. The median incubation period is only 4.7 days, which is significantly shorter than that of the wild strain (6.3 days).

Further subgroup analysis showed that in the non-severe group, the virus incubation period (4.0 days) of the delta mutant strain was significantly shorter than that of the wild strain (6.0 days).

Delta mutant strains can be transmitted for 4 generations within 10 days, and the fastest intergenerational transmission does not exceed 24 hours.

  Compared with the wild strain, the viral load of those infected by the delta mutant strain was significantly higher (the median CT value of the former was 34.0, and the latter was 20.6. The lower the CT value, the higher the viral load), the delta mutant strain The time for the infected person to turn negative for nucleic acid is also significantly longer than that of the wild strain.

  The researchers also found that infection with the delta variant is a risk factor for predicting that the disease will turn into a critical illness.

Among elderly patients with new coronary pneumonia aged 60 and over, the delta variant group has a 1.45 times higher risk of critical illness than the wild strain group; and infection with the delta variant strain develops into a critical illness 2.98 times faster than the wild strain.

  Researchers believe that this study reveals that the delta mutant has the characteristics of short incubation period, fast transmission, high viral load, long time for nucleic acid to become negative, and more likely to develop into critical illness.

Therefore, it is very important to quickly track, isolate and find people infected with the virus in a timely manner, implement timely control of key places, and implement nucleic acid screening of all employees in some areas under special circumstances.

The method 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 new crown virus nationwide.

(CCTV reporter Chen Xuting)

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