Recently, research on asymptomatic infections has frequently appeared in well-known medical journals including NEJM, JAMA, medRxiv. The latest research, led by Shen Hongbing, an academician of the Chinese Academy of Engineering, deputy secretary of the Party Committee and principal of Nanjing Medical University, pointed out that the infection period of asymptomatic infection of the new crown virus is as long as 29 days.
Asymptomatic COVID-19 Infected
On February 18, 2020, NEJM published a newsletter Evidence of SARS-CoV-2 Infection in Returning Travelers from Wuhan, China, reporting on boarding the German Air Force New coronavirus screening of 126 personnel evacuated from Hubei.
According to the article, in addition to the planned steps to check for signs and symptoms of infection, and observe the asymptomatic cohort in the quarantine area, the researchers decided to provide 115 travelers with a throat swab to detect SARS-CoV-2, and 114 passengers agreed to the test. Two of the 114 travelers (1.8%) were tested positive for SARS-CoV-2 (the cycle thresholds for these two samples were 24.39 and 30.25, respectively).
Subsequently, the researchers used two commercially available kits (LightMix Modular SARS and Wuhan CoV E-gene and LightMix Modular Wuhan CoV RdRP-gene, both produced by TIB MOLBIOL) to perform a secondary test on positive samples. Phillips, Marburg, Germany The Philipps University Marburg Institute of Virology also tested the positive samples again, confirming the positive results.
In addition, in Caco-2 cell culture, SARS-CoV-2 was isolated from both samples, indicating a potential infectivity.
In other words, the two travelers mentioned above had no clinical symptoms, but the virological test was positive, and this also coincided with the definition of asymptomatic infection in the fifth edition of the New Coronary Pneumonia Diagnosis and Treatment Program and the fourth edition of the Prevention and Control Program in China.
Viral load in asymptomatic patients is similar to asymptomatic patients
In fact, NEJM also published another newsletter on asymptomatic infections.
On February 19, 2020, NEJM published a newsletter from Guangdong CDC, Zhuhai CDC, Fifth Hospital Affiliated to Sun Yat-sen University, and Hong Kong University. Researchers used the New Coronavirus Nucleic Acid Assay Kit (real-time fluorescent RT-PCR method) provided by the Chinese Center for Disease Control and Prevention to monitor 18 patients (9 males and 9 females) in Zhuhai, Guangdong, of which 4 were secondary cases. 1 case had SARS-CoV-2 viral load in each of 1-9 upper respiratory tract samples (nasal swabs, throat swabs) without symptoms .
Yam's Board learned that the above-mentioned asymptomatic infected persons have been in close contact with confirmed cases. Although there are no clinical symptoms, nasal swabs (circulation threshold 22-28) and laryngeal swabs (circulation threshold 30) -32) Positive on days 7, 10 and 11 after close contact.
At the same time, the viral load detected in respiratory samples of asymptomatic patients was similar to that of symptomatic patients-this indicates that asymptomatic patients also have the potential to spread, confirming earlier conclusions about asymptomatic infections.
People with asymptomatic infection can be infected for up to 29 days
Based on this, the researchers specifically analyzed a group of asymptomatic infections.
On February 25, 2020, the team of Academician Shen Hongbing of Nanjing Medical University published the name Clinical Characteristics of 24 Asymptomatic Infections with COVID-19 Screened among Close Contacts in Nanjing, China on the preprinted website medRxiv. 19 Clinical characteristics of asymptomatic patients).
It is reported that, through pharyngeal swab nucleic acid test, 24 asymptomatic patients were positive for COVID-19 virus. The research team analyzed their clinical records, laboratory evaluations, and chest CT scan results.
The paper states that the median time from the first positive nucleic acid test to two consecutive negative tests is 9.5 days, and during this time, they also have the potential to spread-asymptomatic patients have already been transmitted to their families, Some infected persons also developed severe illness.
According to the analysis of the research team, the 24 asymptomatic infections are mainly divided into two categories-one is the patient's family members, and the other is the person who is less than two meters away from the confirmed patient who is still in the incubation period and has been in contact for more than one hour. Moreover, 8 out of 24 people have travel history in Hubei (details are shown below).
It is worth mentioning that the symptoms in most of the 24 people were mild and did not develop into severe cases. However, six asymptomatic infections turned positive after a negative nucleic acid test, and one case turned positive even after consecutive negative results.
Yam's Board learned that the 13th patient was in a special condition-after the infection of the family member and the family member was confirmed, the symptoms did not appear. Until February 18, the patient's nucleic acid test did not turn negative, which means that his infection period may be as long as 29 days.
Based on the results of the above analysis, the research team emphasized the importance of tracking close contacts of confirmed patients and the use of viral nucleic acid testing for longitudinal monitoring.
However, as mentioned above, most of the asymptomatic infections found so far have been in close contact with confirmed patients, so we need not be too alarmed. But at the same time, the virus is fierce and should not be underestimated.