Liu, et al. (2020) say that a large number of individuals with coronavirus disease 2019 (COVID-19) infections might present with no or only mild symptoms, and the reported numbers of patients with COVID-19 do not reflect the true scale of the outbreak; therefore, population-based serological studies are urgently needed to understand the epidemiological characteristics of the outbreak and the population’s immunity to COVID-19.
This cross-sectional study was conducted in Tongji Hospital of Huazhong University of Science and Technology between March 27 and May 26, 2020. This study was approved by the ethics committee of Tongji Hospital of Huazhong University of Science and Technology. Informed consent was waived because deidentified data were used. This study follows the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.
Adult participants aged 18 years or older were enrolled in the current study. None of the participants had a history of COVID-19. Demographic data, including age, sex, and residential region, were collected. The participants were screened for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection by serological tests for IgM and IgG antibodies to SARS-CoV-23 and by real-time reverse transcriptase–polymerase chain reaction tests for SARS-CoV-2 RNA.
A total of 35,040 individuals (17,269 men [49.3%] and 17,771 women [50.7%]) were enrolled in this study. The median (interquartile range) age was 36 (30-45) years. The positivity rate for IgM antibodies only was 0.0%, that for both IgM and IgG antibodies was 0.7%, and that for IgG antibodies only was 3.2%. Most individuals (1100 of 1360 individuals [80.9%]) tested positive for IgG antibodies only. The overall seropositivity rate was 3.9% (95% CI, 3.7%-4.1%). The researchers observed that very few individuals (15 of 35,040 individuals [0.04%]) had detectable SARS-CoV-2 viral nucleic acid sequence and tested negative during their quarantine period, and none of their close contacts had positive nucleic acid test results. The seropositive prevalence in the urban districts was higher than that in the suburban and rural areas (4.4% [95% CI, 4.0%-4.8%] vs 2.9% [95% CI 2.3%-3.6%]; P < .001), demonstrating an urban to suburban gradient. Moreover, women had higher seropositive prevalence than did men (4.4% [95% CI, 4.1%-4.6%] vs 3.3% [95% CI, 3.1%-3.6%]; P < .001). The researchers did observe that seropositive prevalence was associated with increasing age, with the highest rates among individuals aged 60 years and older (9.2% [95% CI, 7.1%-11.3%]; P < .001).
Reference: Liu A, et al. Seropositive Prevalence of Antibodies Against SARS-CoV-2 in Wuhan, China. JAMA Netw Open. 2020;3(10):e2025717. doi:10.1001/jamanetworkopen.2020.25717