1.3 Quantitative dynamic changes in serum SARS-CoV-2 antibody in asymptomatic cases
To further detect serum SARS-CoV-2 specific IgM and IgG antibodies, 17 cases screened from 26 asymptomatic patients to detect viral nucleic acid for several times with monitor on dynamic changes of antibodies. Among 17 cases of asymptomatic cases, male (n=11) and female (n=6) age ranged from 8-77 years old, averaging 31.5 years old (IQR 14.5-45.5). The comparison of SARS-CoV-2 antibody levels between groups at different time periods (0-7 week) after nucleic acid negative transformation showed as follows:
There was no significant difference in IgM concentration between time points tested (0-7 week) after nucleic acid conversion (p>0.05) (Figure 2a). However, a significant difference was found in IgG concentrations with time changed (χ2=14.034, p=0.029) (Figure 2b). The levels of serum IgM and IgG antibodies in different time periods (0-7 weeks) after nucleic acid negative conversion were showed in table 2.
Serum IgG levels were significantly higher within weekly time points 4-5 week (Z =-2.399,p=0.016), 5-6 week (Z=-2.049,p=0.040), and 6-7 week (Z=-2.197,p=0.028), respectively, compared to 1-2 weeks after nucleic acid negative conversion. The serum IgG level within weeks 4-5 of nucleic acid negative conversion was significantly higher than that of 3-4 week (Z = -2.038, p = 0.042).
There was no significant difference in serum IgG levels within 4 weeks, as well as exceeding the first month after nucleic acid negative transformation (p > 0.05).
Among the 17 asymptomatic cases, 46 times of dynamic detection were performed on SARS-CoV-2 antibodies after the nucleic acid turned negative, including 10 times of positive results in IgM and 43 times of positive results in IgG (Figure 2). The positive detection frequencies of IgM and IgG were 21.7% (10/46) and 93.5% (43/ 46), respectively. Among the 50 healthy individuals, only one case was IgM positive with a concentration of 17.5 AU/mL, and all IgG antibodies were negative. The positive detection rates of IgM and IgG in healthy individuals were 2.0% (1/50) and 0% (0/50), respectively.
The positive rates of IgM and IgG in asymptomatic group were significantly higher than that of the control group within 7 weeks of nucleic acid negative conversion, the statistics value was χ2=84.660, p<0.001 and χ2=9.201, p=0.002, respectively (Table 3).