Context, Covert severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections could be seeding new outbreaks. How to identify asymptomatic SARS-CoV-2 infections early has become a global focus.

Objective, To explore the roles of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies detection, nucleic acid tests and computed tomography (CT) scanning to identify asymptomatic SARS-CoV-2 infection.

Design, The clinical data of 389 individuals with close contacts including in general characteristics, SARS-CoV-2 etiology, serum-specific IgM and IgG antibody detection and CT imaging results, were systematically analyzed.

Results, The present study showed that only 89 of the 389 individuals with close contacts were positive after the first nucleic acid test, while 300 individuals were still negative after two nucleic acid tests. Among the 300 individuals, 75 did not have pneumonia, and the other 225 individuals had pulmonary imaging changes. A total of 143 individuals were eventually diagnosed as having asymptomatic infection through IgM antibody and IgG antibody detection. The sensitivity, specificity and false-negative rate of IgM and IgG antibody detection were approximately 97.1% (347/357), 95.3% (204/214) and 4.67% (10/214), respectively. It also indicated that over approximately 2 weeks, most individuals were both IgM positive and IgG positive, accounting for 68.57% (72/105). Over approximately 3 weeks, the proportion of IgM-positive and IgG-positive individuals decreased to 8.57% (9/105), and the proportion of IgM-negative and IgG-positive individuals increased to 76.19% (80/105).

Conclusions, There are highlighted prospects of IgM/IgG antibody detection as a preferred method in identifying the individuals with asymptomatic SARS CoV-2 infection, especially combined with nucleic acid tests and pulmonary CT scanning.

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Author notes

This work was supported by grants from the National Natural Science Foundation of China (No. 81870028, 81900029 and 81470241) and the Zhejiang provincial program for the Cultivation of High-level Innovative Health Talents (No. A-2017-CXCR02).

The authors have no relevant financial interest in the products or companies described in this article.