Background:COVID-19 has become a global epidemic, close contacts and asymptomatic patients are worthy of attention. Methods:A total of 1844 people in close contact with 76 COVID-19 patients were investigated, and nasopharyngeal swabs and venous blood were collected for centralized medical quarantine observation. Real-time fluorescence used to detect 2019-nCoV nucleic acid in nasopharyngeal swabs of all close contacts, and colloidal gold method used to detect serum specific antibodies. Levels of IgM and IgG specific antibodies were detected quantitatively through chemiluminescence from the first nucleic acid negative date (0 wk) within weekly periods of:1, 1-2, 2-3, and 6-7 weeks. Results:The total positive rate of the colloidal gold method (88.5%,23/26) was significantly higher (χ2=59.182,P< 0.001) than that of the healthy control group (2.0%, 1/50). There was significant difference in IgG concentration at different time points (0-7week) after nucleic acid turned negative (χ2=14.034,P=0.029). Serum IgG levels were significantly higher within weekly timepoints 4-5 wk(Z=-2.399, P=0.016), 5-6 wk(Z=-2.049,P=0.040), and 6-7 wk(Z=-2.197,P=0.028), compared to 1-2 wk after nucleic acid negative conversion. However, there was no significant difference (χ2=4.936,P=0.552) in IgM concentration between timepoints tested (0-7 weeks) after nucleic acid conversion. The positive rates of IgM and IgG in asymptomatic patients (χ2=84.660,P<0.001) were significantly higher than the controls (χ2=9.201,P=0.002) within 7 weeks of nucleic acid negative conversion. Conclusions: The IgG concentration in asymptomatic cases remained at a high level after nucleic acid turned negative. Nucleic acid combined with IgM and IgG antibody detection is a more effective way to screen asymptomatic infections.