ABSTRACT
ObjectiveAge-dependent asymptomatic and symptomatic transmission dynamics of COVID-19 have not been well quantified due to limited data. MethodsThrough a population-based surveillance network, we collected data on 1342 confirmed cases with a 90-days follow-up for all asymptomatic cases. ResultsThe difference in transmissibility of a symptomatic and asymptomatic case depended on age and was most distinct for the middle-age groups. The asymptomatic cases had a 66.72% lower transmissibility rate than symptomatic cases, and 74.10% (95%CI: 65.85% - 80.72%) of all asymptomatic cases were missed in detection. The average proportion of asymptomatic cases was 28.22% (95%CI: 22.97% - 34.56%). Simulation showed that the burden of asymptomatic transmission increased as the epidemic continued and could potentially dominate the spreading. ConclusionAsymptomatic COVID-19 cases play a significant role in transmission. Vaccine Strategies prioritizing the population between 30-60 years old are likely to have the most population-level benefits.
Subject(s)
COVID-19ABSTRACT
An outbreak of novel coronavirus (SARS-CoV-2) was identified in China in December 2019, and has spread rapidly to more than 200 countries and areas in four months. A few studies have reported that transmissibility exists during the late incubation period based on one single infection cluster caused by SARS-CoV-2. Here based on 178 SARS-CoV-2 clusters confirmed in Zhejiang Province, we analyzed the epidemic link between all 212 secondary cases with their previous cases, and found 49 secondary cases (from 26 clusters), which were 23.11% (49/212) of the total secondary cases infected from previous cases during the latter’s incubation period. The median days from the last exposure of secondary cases to the onset of previous cases was 2.0 days (IQR: 1.00~5.00 days, 90th percentile: 9.00 days) .This study has shown transmission of the SARS-CoV-2 during the incubation period and indicated that some cases might be infectious soon after they were exposed to a prior transmitter. The results highlight the importance of extending the contact group for medical observation and isolation to those in contact with the index case nine (90th percentile) or more days before the latter’s illness onset, when medical resources were sufficient.
Subject(s)
Cluster HeadacheABSTRACT
Objective@# To conduct an epidemiological investigation on the first reported case of coronavirus disease 2019 （COVID-19） in Zhejiang Province, so as to provide reference for prevention and control of the disease.@*Methods @#According to the COVID-19 Diagnosis and Treatment Program （Trial） and the COVID-19 Prevention and Control Program （Trial） issued by National Health Commission of China, a field investigation was employed on a case of fever from Wuhan reported by Wenzhou in January 15, 2020; the real-time reverse transcription polymerase chain reaction （RT-PCR） assay was performed to detect the nucleic acid of severe acute respiratory syndrome coronavirus 2 （SARS-CoV-2） from the sputum specimens or throat swabs of the case; the close contacts of the case were tracked down; relevant prevention and control measures were implemented. @*Results @#The case had lived in Wuhan for long. On January 4 of 2020, he felt cold and uncomfortable without obvious inducement, and drove back to Wenzhou with his wife. He had fever （up to 39 ℃）, cough and expectoration on the next day. On January 9, the chest computed tomographic （CT） scan showed bilateral high-density patchy shadowing with blurred edges. On January 16, his throat swab and sputum samples were collected and sent to Zhejiang Provincial Center for Disease Control and Prevention （CDC） for detection of SARS-CoV-2. The result turned out to be positive on January 17, then was rechecked and confirmed by Chinese CDC on January 20. Two weeks before the onset of the disease, the patient was engaged in the door-to-door persuasion of installing elevators in an old residential area of Wuhan, and he denied any connection with other COVID-19 cases,markets,（sick or dead） poultry or poultry products. Totally 26 close contacts were identified and kept in quarantine. During this period,three of them developed fever or respiratory symptoms, but were excluded from COVID-19. On the afternoon of January 16,the health system of Zhejiang Province and Wenzhou City launched an emergency plan and implemented a series of prevention and control measures such as isolation and treatment of cases,screening and isolation of close contacts,and public health education. @*Conclusion @#According to the epidemiological history,clinical features and laboratory test Results,the patient was identified as the first reported case of COVID-19 in Zhejiang Province.