Seroprevalence and Epidemiological Characteristics of Immunoglobulin M and G Antibodies Against SARS-CoV-2 in Asymptomatic People in Wuhan, China

Abstract

Background: The World Health Organization (WHO) recommends monitoring changes in seroprevalence of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) over time from the beginning of an epidemic to predict and plan accordingly for public health responses. At present, few domestic and foreign reports exist on the diagnosis of COVID-19 patients through serological tests. To detect and assess asymptomatic infections of COVID-19 among people in Wuhan, the epicenter of the COVID-19 pandemic in China, and provide a basis for planning an adequate public health response, we analyzed the records in a Wuhan general hospital of medical examinations mandatory for 16- to 64-year-old asymptomatic people to resume their job-related work. This retrospective study estimated the seroprevalence of IgM and IgG and compared the epidemiological characteristics of asymptomatic SARS-CoV-2- infected workers. Methods: Medical examination data were collected from the Wuhan General Hospital between March 26 and April 28, 2020. Serological tests for the presence of antibodies (IgM and IgG) against SARS-CoV-2 used a colloidal gold method. Nucleic acid sequence of viruses were detected with a fluorescent PCR method. Demographical and radiological data were collected. Statistical analyses were conducted using SPSS 20.0 software. Findings: Between March 26 and April 28, 2020, a total of 18,391 asymptomatic back-to-work participants were enrolled. Among them, 89 had positivity for IgM (0·48%, 95% confidence interval (CI): 0·38–0·58%); 620 cases had IgG positivity (3·37%, 95% CI: 3·11–3·64%), and 650 cases had either IgG positivity or IgM positivity (3·53%, 95% CI: 3·26–3·80%). After standardizing for the genders and ages in the population of Wuhan, the overall standardized seroprevalence of IgG was 3·33% (95% CI: 3·07–3·59%) and the standardized seroprevalence of IgG was 3·01% (95% CI: 2·69–3·33%) among males and 3·66% (95 % CI: 3·23–4·09%) among females. The standardized seroprevalence of IgG was higher in women than in men with a significant difference (x 2 = 2060·3, p < 0·01). By a detection method adjustment, the seroprevalence of IgG was 1·57% (95% CI: 1·39–1·75%) in all medical records, of which males were 1·96% (95% CI: 1·64–2·28%), and females were 1·19% (95% CI: 0·99–1·39%). The assayadjusted seroprevalence of IgG was higher in women than in men, and the difference was significant (x 2 = 5871·0, p < 0·01). The differences were significant for seroprevalence of IgG among people who went back to work in different categories of work place (x 2 = 198·44, p < 0·01). The differences in seroprevalence for IgG positivity or IgM positivity among people who went back to work in different urban and rural areas was also significant (x 2 = 45·110, p < 0·01). Calculated as IgG and/or IgM antibody positivity, the number of new infections was reduced by 64·8% from March 26 to April 28, 2020. Based on the census population aged 16–64 years in Wuhan in 2017, we estimated that 172,340 (95% CI: 157,568–187,112) asymptomatic people aged 16–64 years were infected with SARS-CoV-2 in Wuhan between March 25 and April 28 2020. This estimate was 3·4-times higher than the officially reported 50,333 infections on April 28. Interpretation: The seropositivity rate in Wuhan indicated that RT-PCR-confirmed patients only represented a small part of the total number of cases. Seropositivity progressively decreased in the Wuhan population from March 26 to April 28, 2020, comparable to Japan and Denmark, but well below the level reported in New York, Iran, Italy, and Germany. The prevalence of asymptomatic infection was higher in women than in men among people who went back to work in Wuhan. The low seroprevalence suggests that most of the population remains susceptible to COVID19. Funding: Emergency Management Project of the National Natural Science Foundation of China (81842035) ; Advisory Research Project of the Chinese Academy of Engineering in 2019 (2019-XZ-70) Declaration of Interests: All authors declare no conflicts of interest. Ethics Approval Statement: This study was approved by the Ethics Committee of the Hubei Provincial Hospital of Integrated Chinese & Western Medicine. This was a retrospective and observational study and informed consent was obtained.