Seroprevalence and epidemiological characteristics of immunoglobulin M and G antibodies against SARS-CoV-2 in asymptomatic people in Wuhan, China: a cross-sectional study

  1. Ruijie Ling
  2. Yihan Yu
  3. Jiayu He
  4. Jixian Zhang
  5. Sha Xu
  6. Renrong Sun
  7. Wangcai Zhu
  8. Mingfeng Chen
  9. Tao Li
  10. Honglong Ji
  11. Huanqiang Wang

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Abstract

Objectives

Population screening for IgG and IgM against SARS-CoV-2 was initiated on March 25 and was open to all residents of Wuhan who were symptom-free. All ages with no fever, headache or other symptoms of COVID-19 among residents in Wuhan were included.

Methods

This study adopted a cross-sectional study. Pearson Chi-square test, T-test, and Mann-Whitney test were used in comparison between different groups. To correct the effects of gender and age, the seroprevalence of IgM positivity, IgG positivity, and IgM and/or IgG positivity were standardized according to the gender and age-specific population of Wuhan in 2017.

Results

The seroprevalence of IgG and IgM standardized for age and gender in Wuhan showed a downward trend. No significant correlation was observed between the seroprevalence of IgG and the different age groups. The seroprevalence was significantly higher for females than males (x 2 =35.702, p < 0.001), with an odds ratio of 1.36 (95% CI: 1.24–1.48). A significant difference was seen in the seroprevalence of IgG among people from different geographic areas and different types of workplaces (respectively, x 2 = 42.871, p < 0.001 and x 2 = 202.43, p < 0.001). The IgG antibody-positive cases had a greater number of abnormalities in CT imaging than IgG-negative cases (30.7% vs 19.7%).

Conclusions

Our work found the reported number of confirmed patients in Wuhan only represents a small proportion of the total number of infections. There was a significant aggregation of asymptomatic infections in individuals from some occupations, and based on CT and laboratory findings, some damage may have occurred in asymptomatic individuals positive for IgG antibody.

    Strengths and limitations of this study

  • This study has the important feature of having been designed as repeated five-day serosurveys, which allowed for the monitoring of seroprevalence progression.

  • This study applied scientific statistical methods accounting for the demographic structure of the general population and imperfect diagnostic tests to estimate seroprevalence in the overall population.

  • This study had selection bias since the analyzed medical records were based on examinees directed by their work units.

  • People under the age of 19 and over age 65 were too few to be fully covered in analyses.

Article activity feed

  1. Version published to 10.1101/2020.06.16.20132423v3 on medRxiv
  2. Version published to 10.1101/2020.06.16.20132423v2 on medRxiv
  3. ScreenIT

    SciScore for 10.1101/2020.06.16.20132423: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variableFrom March 25 to April 28, 2020, a total of 18,712 (89.4%) people met the inclusion criteria with a median age of 40 years (range 4–81 years old), including 11,391 males (60.9%) with a median age of 42 years and 7,321 females (39.1%) with a median age of 37 years.

    Table 2: Resources

    Antibodies
    SentencesResources
    Subjects for serology testing: Before starting the screening for antibodies against SARS-CoV-2, we validated the serological assay with serum samples from 105 patients with COVID-19 confirmed by a SARS-CoV-2 fluorescent PCR kit with nasopharyngeal swabs collected between January 18 and February 22, 2020 (Supplementary materials-Serology Test Validation).[
    SARS-CoV-2
    suggested: None
    After centrifugation, serum was taken for SARS-CoV-2-specific IgG and IgM antibody detection within 2h.
    SARS-CoV-2-specific IgG
    suggested: None
    IgM
    suggested: None
    Software and Algorithms
    SentencesResources
    Statistical analysis: All analyses were conducted using SPSS software (version 22.0, IBM Corporation, Armonk, NY, USA), the R software package (version 3.6.2; 2019, The R Foundation for Statistical Computing), and GraphPad Prism (Version 8.0
    SPSS
    suggested: (SPSS, RRID:SCR_002865)
    GraphPad Prism
    suggested: (GraphPad Prism, RRID:SCR_002798)
    , GraphPad Software, LLC, La Jolla, CA, USA).
    GraphPad
    suggested: (GraphPad Prism, RRID:SCR_002798)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    This study had a few limitations. First, this study had selection bias since the analyzed medical records were based on examinees directed by their work units. Most of the examinees came from government-owned institutions and agencies instead of private businesses. Therefore, the sample was incompletely randomized and insufficiently representative, compromising the assessment accuracy of the prevalence of asymptomatic infections in Wuhan. Second, as the examinees were only from the back-to-work population, people under the age of 19 and over age 65 were too few to be fully covered in analyses. This study has the important feature of having been designed as repeated five-day serosurveys, which allowed for the monitoring of seroprevalence progression just after the end of the first epidemic. Further, our study applied scientific statistical methods accounting for the demographic structure of the general population and imperfect diagnostic tests to estimate seroprevalence in the overall population, while capturing uncertainty in the estimates. Our study will provide useful information for the investigation of herd immunity and help design targeted strategies for prevention. Additionally, the study of IgG and IgM against SARS-CoV-2 among asymptomatic infections can provide scientific basis for vaccine development.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  4. Version published to 10.1101/2020.06.16.20132423v1 on medRxiv