Epidemiology, Duration of Virus-Carrying, Infectivity, and Management of Asymptomatic SARS-CoV-2 Carriers in Wuhan, China

SARS-CoV-2 carriers have the underlying ability to spread the virus and seed new outbreaks, which has been given public concerns. 178 asymptomatic SARS-CoV-2 carriers between March 1 and May 1,


SARS-CoV
Following a containment phase from January to April in 2020, Wuhan has transitioned to the mitigation phase. The Wuhan city reopened, and citizens were allowed to resume working since April 8, 2020.
Meanwhile, people must accept temperature tests before entering public places (e.g., such as supermarkets, restaurants, and hotels) and patients with clinical symptoms and signs (e.g., fever, dry cough, fatigue, and sore throat) onset must be reported to the healthcare organizations for further testing. The effectiveness of symptom-based interventions may largely depend on the infectiousness and fraction The empirical studies have indicated that the potential contribution of the asymptomatic carrier to total infection is 17.9 to 30.8 % [3,4], and some studies have reported the contagious capacity of asymptomatic carriers [5][6][7]. This evidence revealed the transmission of asymptomatic carriers and highlighted that fulminating cases were not only viral sources. But the limited number of cases necessitated the interpretation of the generalizability of their findings, and they did not differentiate whether these asymptomatic carriers were only asymptomatic initially or throughout the infection. Therefore, it is essential to fully understand the asymptomatic SARS-CoV-2 carriers to control the pandemic of COVID-19.
Wuhan is still faced with the risk of COVID-19 outbreak due to asymptomatic carriers since massive resuming work and school are in progress. It is crucial to fully identify and isolate asymptomatic infected citizens. The 10-days (from May 15 to May 24, 2020) of universal nucleic acid testing covered more than 9 million citizens had been conducted by committing proactive case-identification and a total of 320 asymptomatic carriers were confirmed, according to the reports from the Wuhan Municipal Health Commission [8]. We aimed to characterize the epidemiology, assessment the duration of viruscarrying, infectivity, management, and outcomes of asymptomatic SARS-CoV-2 carriers.

Participants
This is a retrospective study conducted in the Wuchang District of Wuhan. Asymptomatic carriers tested positive for SARS-CoV-2 in throat-swab using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) were extracted from the municipal Notifiable Disease Report System. We selected participants who met the following criteria: a) had tested and retested positive nucleic acid testing; b) had lived in Wuhan for more than half a year; c) had no self-reported influenza disease three months before they were confirmed SARS-CoV-2 infection; d) had full information on demographic, epidemiological, clinical features, and management; e) had been followed-up more than 2 months after they were released from quarantine. All asymptomatic SARS-CoV-2 carriers were divided into two subgroups: one was the cases who had a history of signs or symptomatic onset before infection confirmed, the other refers to the cases without symptoms all the time.

Data collection
For all asymptomatic carriers, their information on demographic (e.g., age, gender, and occupations), epidemiology (e.g., exposure history, close-contact information, and timelines of events), clinical symptoms data (e.g., fever, and respiratory symptoms onset), management (e.g., isolation, treatment, and follow-up), and outcomes (signs and symptoms onset, and results of rechecked nucleic acid tests) were collected by our investigators through direct communication and interview. In the epidemiological investigation, to acquire the above information, asymptomatic carriers were asked the following question in the interview: (1) What do you do for a living? Their answers were then divided into five categories, including healthcare workers (doctors, nurses, hospital cleaners, and medical technicians), bank staff (bank clerk, manager, and security), nucleic acid or IgM/IgG antibody test? If "yes", they were further asked the date and results of these tests.

Follow-up and management
Once infection confirmed, these asymptomatic carriers were immediately isolated and therapied in the designated hospitals for at

Statistical analysis
The underlying duration of SARS-CoV-2 carrying was defined as the days between the date of previous symptoms onset or the date of contacting COVID-19 cases and the date of confirmed infection by RT-PCR.
Descriptive data were displayed as frequencies (percentages) for categorical variables and as means (standard deviations or ranges) for continuous variables. The differences in the distribution of demographic, epidemiological characteristics, and history of chronic disease between asymptomatic carriers with and without previous symptoms onset were tested by the student's t-test or Chi-square test, respectively. A two-sided with the p-value < 0.05 was considered as the level to reject the null hypothesis. All statistical analyses were performed with the SAS program (version 9.4; SAS Institute, Carry, NC).

Demographical and epidemiological characteristics of asymptomatic carriers
A total of 178 asymptomatic carriers between March 1 and May 1, 2020, were enrolled (see Table). The mean age of the population was

Duration for carrying SARS-CoV-2
The underlying duration of virus-carrying was shown in Figure 1,

Transmission of asymptomatic carriers
There were 4 asymptomatic carriers within 4 families revealed a typical asymptomatic transmission to their family members, respectively (Figure 2). The epidemiological investigation showed that carrier 1, carrier 3, carrier 5, and carrier 7 had a history of contacting suspected or confirmed cases, while carrier 2, carrier 4, carrier 6, and carrier 8 reported they had never contacted other COVID-19 cases, except for their family members, since they were self-isolated at home during the lockdown of Wuhan.
In family 1: carrier 1 (wife) had a fever and cough that lasted for 2 weeks since January 23, 2020, while as the close contact, carrier 2 (husband) also had 2 days of fever since January 26, 2020. Then, they had no signs and symptoms onset that lasted for over two months. On

Management and follow-up of asymptomatic carriers
After asymptomatic SARS-CoV-2 carriers were confirmed, they were immediately put into the designated hospitals. Vitamins and some

Discussion
This study of asymptomatic SARS-CoV-2 carriers in Wuhan, China, provides insight into characterizing the epidemiology, duration of virus-carrying, infectivity, management, and outcomes of this population. Our study of 178 asymptomatic carriers was younger than the largest epidemiological study of 32583 confirmed COVID-19 cases (47.5 vs. and diabetes) were more common in those carriers who had a history of symptoms onset. This suggests that comorbid conditions were also associated with the risk of symptoms onset in asymptomatic carriers.

years) in Wuhan, China
Knowledge of the virulence, transmissibility, and immune system response of SARS-CoV-2 remains largely unknown. There was a study that reported asymptomatic carriers and symptomatic patients had a similar transmission potential since they had a comparable viral load [20]. In this study, family cluster infections due to human-to-

Conclusions
In summary, our analysis of a regional study in Wuhan, China, reveals that most asymptomatic SARS-CoV-2 carriers were over 18  epidemic. Fourth, the relatively strong infectivity of asymptomatic carriers was reported in the incubation-period [6], which possibly became weak as time goes on, the long duration of virus-carrying may not indicate highly contagious throughout the period. However, our results arouse concern about the prolonged duration of carrying SARS-CoV-2 in asymptomatic carriers. The dynamics of virus-carrying and infectious period of asymptomatic SARS-CoV-2 carriers need to be further clarified.

Prevention and Control in Wuhan] under Grant [number EG20B05].
We thank all patients involved in the study.