Pengpai News reporter Hu Danping
Recently, the New England Journal of Medicine published a new study by the Central University Hospital of South Korea. The study conducted viral culture of the new coronavirus in the respiratory samples of his hospitalized COVID-19 patients and found that although the patient continued to be positive for viral nucleic acid (PCR) after infection for a long time (median 34 days), the virus in the body quickly lost its infectivity (median 7 days).
virus culture found that the infectiousness of the new coronavirus lasted for the longest 12 days
This study by Korean scholars included new coronavirus patients who tested positive for nucleic acid RT-PCR from February to June 2020 and were hospitalized in the hospital. All patients were isolated until two consecutive times (at least 24 hours apart) of nucleic acid negative.
A total of 21 patients were included in the study, with the median age of 62 years and 76% of them were male. Of all the patients included, pneumonia developed in 71% and 38% received oxygen therapy. According to scientific scoring results, all patients included in this study had mild to moderate infections. All patients received RT-PCR test for the new coronavirus nucleic acid 1 to 5 days intervals (median time: 2 days), and a total of 165 samples were collected.
Researchers conducted virus cultures on 29 samples out of 165 samples, which are the gold standard experiments for identification of viral infectivity.
was found through the culture of viruses in 29 samples. The median time from the onset of symptoms (onset of the disease) to the clearance of viruses in the virus culture was 7 days; the median time from the onset of symptoms to the negative nucleic acid RT-PCR test was 34 days (minimum 24 days). The longest-lasting virus culture in all samples was 12 days.
study also found that the Ct values detected by nucleic acid RT-PCR of samples with positive virus culture were below 28.4. As the onset time is prolonged and the RT-PCR Ct cycle increases, the positive rate of virus culture becomes lower and lower, and the infectivity of residual viruses in patients' bodies is lower.
Virus detoxification time ≠ virus infectious time
There has been no determination on the duration of the spread of the new coronavirus and the related infection level.
Currently, the guidance of the formulation of the isolation time for COVID-19 patients around the world is mostly determined based on the previous detoxification time for COVID-19 patients.
Previously, many scholars in my country have also published research on the detoxification of the new coronavirus in international authoritative medical journals. The earliest study on the time of virus detoxification in new coronavirus patients can be traced back to March 9 last year. The Lancet published a cohort study on the clinical process and risk factors of death in adult new coronavirus patients in Wuhan led by Cao Bin, deputy director of the Sino-Japanese Friendship Hospital. The study describes new data on coronavirus detoxification for the first time, covering 191 patients (137 were discharged and 54 died). The median duration of virus detoxification in surviving COVID-19 patients was 20 days (range 8 days-37 days).
On June 19, 2020, the international authoritative medical journal Nature-Medical published the "Clinical and Immunological Evaluation of Asymptomatic SARS-CoV-2 Infections" from a research team at Chongqing Medical University in China. The study found that the median duration of detoxification in 37 patients with mild symptoms was 14 days, which was relatively shorter than previous studies. Compared with symptomatic patients, the detoxification time in the asymptomatic group increased significantly, reaching 19 days.
In the above study, the researchers pointed out that the measurable detoxification time is not equivalent to the time when the virus is contagious, and further virus culture is needed for evaluation.
It is worth mentioning that although most patients with COVID-19 infection show relatively strong contagiousness within about 7 days, there are also some more extreme cases, especially those with low immunity. On November 4, 2020 local time, Cell published online. . A study jointly completed by researchers from the National Institute of Health, . The Institute of Allergy and Infectious Diseases and other institutions reported a special case of COVID-19: A woman with leukemia who is immune-deficient in the new coronavirus was infected with the new coronavirus for at least 105 days, and detoxification for at least 70 days is potentially contagious, and remains asymptomatic.
Editor in charge: Zhong Yuhao
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