ABSTRACT
Background Novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is pandemic. However, data concerning the epidemiological features, viral shedding, and antibody dynamics between asymptomatic SARS-CoV-2 carriers and COVID-19 patients remain controversial.Methods A total of 193 subjects in Ningbo and Zhoushan, Zhejiang, China, were enrolled in this study from January 21 to March 6, 2020. All subjects were tested positive for SARS-CoV-2 genomic RNA by quantitative reverse transcription PCR and then followed up to monitor the dynamics of serum antibody immunoglobulin M (IgM) and immunoglobulin G (IgG) against SARS-CoV-2 using enzyme-linked immunosorbent assays. Scatter diagram to demonstrate the distribution of IgM and IgG among asymptomatic carriers and COVID-19 patients were generated by R.Results Of the 193 subjects, 31 were asymptomatic SARS-CoV-2 carriers, 149 were symptomatic COVID-19 patients, and 14 were COVID-19 patients during the incubation. Compared to symptomatic COVID-19 patients, asymptomatic SARS-CoV-2 carriers were younger and had higher levels of white blood cell and lymphocyte, lower levels of C-reactive protein (CRP) and viral load, and shorter viral shedding time. Seroconversion of IgM against SARS-CoV-2 from positive to negative in asymptomatic carriers took 7.50 (IQR, 4.75–11.50) days, which was significantly shorter than 25.50 (IQR, 6.75–56.75) days in COVID-19 patients (P = 0.030). The proportion of those persistently seropositive for IgG against SARS-CoV-2 was higher in COVID-19 patients than in asymptomatic carriers (66.1% vs. 33.3%, P = 0.037). Viral load was higher in symptomatic than presymptomatic COVID-19 patients. Viral shedding was longer in presymptomatic COVID-19 patients than in asymptomatic carriers. In 4 familial clusters of SARS-CoV-2 infection, asymptomatic carriers were mainly children and young adults while severe COVID-19 was mainly found in family members older than 60 years with underlying diseases. Asymptomatic carriers acquired infection more from intra-familial transmission than did COVID-19 patients (89% vs. 61%, P = 0.028).Conclusion Asymptomatic carriers might have a higher antiviral immunity to clear SARS-CoV-2 than symptomatic COVID-19 patients and this antiviral immunity might not be contributable to humoral immunity. The severity of COVID-19 is associated with older age and underlying diseases in familial clustering cases.
Subject(s)
COVID-19 , Coronavirus InfectionsABSTRACT
Background: A novel coronavirus (SARS-CoV-2) has spread widely and led to high disease burden around the world. This study aimed to explore key parameters of SARS-CoV-2 infection and to assess the effectiveness of interventions to control the coronavirus disease 2019 (COVID-19).Methods: A susceptible – exposed – infectious – asymptomatic – recovered (SEIAR) model was developed for the assessment. Data of symptomatic and asymptomatic infection of SARS-CoV-2 were collected to calculate the key parameters of the model in Ningbo City, China.Results: A total of 157 confirmed COVID-19 cases (including 51 imported cases and 106 secondary cases) and 30 asymptomatic infections were reported in Ningbo City. The proportion of asymptomatic has an increasing trend. The proportion of asymptomatic of elder people was lower than younger people, and the difference was statistical significant (Fisher’s Exact Test, P = 0.034). There were 22 clusters associated with 167 SARS-CoV-2 infections, among which 29 cases were asymptomatic, with a proportion of 17.37%. We found that the secondary attack rate of asymptomatic was almost the same as that of symptomatic cases, and no significance was observed (χ2 = 1.350, P = 0.245) by Kruskal-Wallis test. The effective reproduction number (Reff) was 1.43 which revealed that the transmissibility of SARS-CoV-2 was moderate. If the interventions were not strengthened, the duration of the outbreak would last about 16 months with a simulated attack rate of 44.15%. The total attack rate and duration of the outbreak would increase along with the increasing delay of intervention.Conclusions: SARS-CoV-2 had moderate transmissibility in Ningbo City, China. Asymptomatic infection has the same transmissibility as symptomatic. The integrated interventions were implemented at different stages during the outbreak, which found to be exceedingly effective in China.