Research On The SARS-Cov-2 Nucleic Acid Screening In Nearly Ten Million Residents Of Wuhan

Objective Since the outbreak of the Corona Virus Disease 2019（COVID-19）epidemic,Wuhan had been under lockdown measures from January 23 until April 8,2020.However,after the city’s reopening,there were newly confirmed COVID-19 cases and some asymptomatic cases in Wuhan.In order to find out all potential COVID-19 cases and asymptomatic cases,the Wuhan city government carried out a comprehensive citywide nucleic acid screening of Severe Acute Respiratory Syndrome Coronavirus 2（SARS-Co V-2）infection from May 14,2020 to June 1,2020.In this study,we aimed to explore the prevalence of COVID-19 in Wuhan after the reopening and to provide scientific evidences for the adjustments of the COVID-19 epidemic prevention and control strategies.Methods A general investigation for nucleic acid screening of SARS-Co V-2 was conducted in Wuhan,the study population were the permanent residents who were 6years old or older and had not been tested for SARS-Co V-2 nucleic acid.Before the screening work,a citywide nucleic acid screening group and five specialized task teams were formed for the management of the screening work.All personnel received standard training,and we also made norms for the sampling,transportation and testing.Before the sampling work,residents self-uploaded their basic information,including their ID card number,name,sex,age,and residence places,then the trained staff interviewed each individual regarding the history of COVID-19 and previous SARS-Co V-2 nucleic acid testing.For the newly asymptomatic cases,the Centers for Disease Control and Prevention in their region carried out the epidemiological survey（including their occupation,life track,close contacts and other information）.Besides,Wuhan Institute of Virology,Chinese Academy of Sciences and Hubei Province Center for Disease Control and Prevention would extract their sputum and throat swab samples for virus culture and sequencing analysis.SPSS 22.0 software was used for the statistical analysis of collected data.The basic information was descriptively analyzed,and used the number of cases or percentages for counting data.The Chi-square test and Fisher’s exact probability method were used to analyze the differences from the genders and ages detection rate of asymptomatic patients.Spearman rank correlation analysis was used to analyze the association between the detection rate of asymptomatic cases in each region and the prevalence of previously diagnosed patients.The detection rate of asymptomatic infections and the re-positive rate were estimated with the Pearson-Klopper exact method to calculate the 95%confidence interval（95%CI）of estimated proportions,and implemented by R package“binom”version 1.1-1^[1].A two-sided test P<0.05 was considered statistically significant.Results A total of 9,899,828 residents participated in the SARS-Cov-2 nucleic acid screening program in Wuhan,accounting for 92.9%of all the eligible residents.No new COVID-19 cases and 300 asymptomatic cases（detection rate was 0.303/10,000,95%CI:0.270/10,000–0.339/10,000）were identified.There were no positive SARS-Cov-2 nucleic acid results among the 1,174 close contacts of asymptomatic cases.In the 300asymptomatic cases,132 were males（detection rate was 0.256/10,000）and 168 were females（detection rate was 0.355/10,000）.The asymptomatic positive rate of children or adolescents aged 17 and below was the lowest（detection rate was 0.124/10,000）,while the highest detection rate was for the elderly aged 60 years and above（detection rate was 0.442/10,000）.The asymptomatic cases were mainly domestic and unemployed residents（24.3%）,retired older adults（21.3%）and public service workers（11.7%）.In addition,107 of 34,424 previously recovered COVID-19 patients tested positive again（re-positive rate 0.310%,95%CI:0.252%–0.370%）.In this screening program,single and mixed testing were performed,respectively,for 76.7%and 23.3%of the collected samples,and the asymptomatic detection rates were 0.321（95%CI:0.282–0.364）/10,000 and 0.243（95%CI:0.183–0.315）/10,000,respectively.Only 3.6%residential communities were found asymptomatic cases.The detection rate of asymptomatic cases in each administrative region was basically consistent with the previous prevalence rate of confirmed COVID-19 cases,and correlation analysis results showed that there was a significant positive correlation between the previous prevalence rate of COVID-19 confirmed cases and the detection rate of asymptomatic cases in the administrative regions（r_s=0.729,P=0.002）.Conclusion After the reopening,the prevalence of COVID-19 infection in Wuhan was extremely low,newly detected asymptomatic cases in Wuhan and their close contacts were unlikely to be infectious,and the virulence of the SARS-Cov-2 might be weakened.Districts with a high prevalence of confirmed COVID-19 cases were likely to had a high detection rate of asymptomatic persons.The citywide screening of SARS-Co V-2 infection in Wuhan was a mass screening program,it could provide a scientific evidence for Wuhan to adjust the prevention and control strategies of COVID-19epidemic and promote the city economic recovery,and it also could give invaluable experiences or lessons to other countries and cities worldwide.