Abstract Background COVID‐19 has become a global pandemic, and close contacts and asymptomatic patients are worthy of attention. Methods A total of 1844 people in close contacts with 76 COVID‐19 patients were investigated, and nasopharyngeal swabs and venous blood were collected for centralized medical quarantine observation. Real‐time fluorescence was used to detect SARS‐CoV‐2 nucleic acid in nasopharyngeal swabs of all close contacts, and the colloidal gold method was used to detect serum‐specific antibodies. Levels of IgM‐ and IgG‐specific antibodies were detected quantitatively through chemiluminescence from the first nucleic acid turned negative date (0 week) and on weekly intervals of ≤1 week, 1–2 weeks, 2–3 weeks, 3–4 weeks, 4–5 weeks, 5–6 weeks, and 6–7 weeks. Results The total positive rate of the colloidal gold method (88.5%, 23/26) was significantly higher (χ 2 = 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 (0–7 weeks) after negative nucleic acid conversion (χ 2 = 14.034, p = 0.029). Serum IgG levels were significantly higher at weekly time points of 4–5 weeks (Z = −2.399, p = 0.016), 5–6 weeks (Z = −2.049, p = 0.040), and 6–7 weeks (Z = −2.197, p = 0.028) compared with 1–2 weeks after negative nucleic acid conversion. However, there was no significant difference (χ 2 = 4.936, p = 0.552) in IgM concentration between time points tested (0–7 weeks) after negative nucleic acid conversion. The positive rates of IgM and IgG in asymptomatic patients (χ 2 = 84.660, p < 0.001) were significantly higher than those in the healthy control group (χ 2 = 9.201, p = 0.002) within 7 weeks of negative nucleic acid conversion. Conclusions The IgG concentration in asymptomatic cases remained at a high level after nucleic acid turned negative. Nucleic acid detection combined with IgM and IgG antibody detection is an effective way to screen asymptomatic infections. COVID‐19 has become a global epidemic, close contacts and asymptomatic patients are worthy of attention. 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. 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.
【저자키워드】 IgG, IgM, COVID‐19, SARS‐CoV‐2, Asymptomatic, 【초록키워드】 antibodies, antibody, quarantine, COVID‐19, SARS‐CoV‐2, global pandemic, asymptomatic infections, Nasopharyngeal swab, nucleic acid, Epidemic, Antibody detection, Asymptomatic case, positive rate, chemiluminescence, asymptomatic patient, Blood, Concentration, close contact, IgM and IgG, colloidal gold, observation, significant difference, control group, no significant difference, effective, venous, Result, tested, was used, detect, collected, investigated, remained, significantly higher, different time point, Level, interval, COVID‐19 patient, IgG level, the healthy, 【제목키워드】 antibody, change, asymptomatic patient, IgM and IgG, SARS‐CoV‐2 infection, dynamic, effective, detect,