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).