In total, 3062 individuals were enrolled in this study, of whom 1652 were males, and 1410 were females. Of 3062 samples, seroprevalence for IgM and IgG were 86(2.81%) and 230 (7.51%), respectively. In persons with seropositive, 97 persons had positive CT scan results (3.16%); only four persons (0.13%) had NA positive, including two convalescent COVID-19 patients recovered in the observation period and two asymptomatic infection cases. The rate of specific antibody IgG was significantly higher in women than in men (P < 0.05).
Seroprevalence for IgM was significantly different among age group, from high to low: 41–60 years of age (44 [3.49%]), > 60 years of age (23 [3.36%]), < 20 years of age ( 2 [3.57%]), and 21–40 years of age (17 [1.61%]), respectively(P < 0.05). Seroprevalence for IgG among persons > 60 years of age were 59 (8.61%), 41–60 years of age were 104 (8.24%), 21–40 years of age were 65 (6.14%), and persons < = 20 years of age were 2 (3.57%), respectively (P = 0.098).
We then grouped all subjects by their consulting department (Table 1), including Fever Clinic for patients (an outpatient clinic especially for the treatment of febrile or suspected patients), Fever Clinic for medical staff (clinic especially for screening highly suspected medical staff or the treatment of confirmed cases), Internal Medicine, Surgery department, Obstetrics/Gynecology/Fertility Clinic, Pediatric department, Oncology department, and another department. The highest seroprevalence for IgM observed in the Fever clinic, from high to low: Fever clinic for patients(10.34%), Internal medicine (1.51%), Surgery department (1.37%), Oncology department (1.15%), General department or other (1.01%), Obstetrics/Gynecology/Fertility department (0.74%), Fever clinic for medical staffs (0%), and Pediatric department (0%), respectively (P < 0.001). IgG positive rate (from high to low): Fever clinic for medical staffs (25.0%), Fever clinic (23.73%), General department or other (8.08%), internal medicine (5.02%), Oncology department (3.07%), Obstetrics/Gynecology/Fertility department (2.96%), and Surgery department (2.73%) (P < 0.001) (Table 1).
Table 1
Positive Rate of SARS-CoV2 Among Different roups.
| | N (%) |
Characteristics | No.P | IgM (+) | IgG (+) | NA(+) | CT(+) |
Sex | | | | | |
Male | 1652 | 41 (2.48) | 104 (6.30) | 1(0.06) | 34 (2.06) |
Female | 1410 | 45 (3.19) | 126 (8.94) | 3 (0.21) | 63 (4.47) |
P | | 0.141 | 0.004 | 0.256 | 0.000 |
Age | | | | | |
<=20 | 56 | 2 (3.57) | 2 (3.57) | 0 | 0 |
21–40 | 1059 | 17 (1.61) | 65 (6.14) | 0 | 15 (1.42) |
41–60 | 1262 | 44 (3.49) | 104 (8.24) | 3 (0.24) | 49 (3.88) |
> 60 | 685 | 23 (3.36) | 59 (8.61) | 1 (0.15) | 33 (4.82) |
P | | 0.035 | 0.098 | 0.461 | 0.000 |
Consulting room | | | | | |
Fever clinic for patient | 493 | 51 (10.34) | 117 (23.73) | 1 (0.20) | 64 (12.98) |
Fever clinic for medical staff | 16 | 0 | 4 (25.00) | 1 (6.25) | 3 (18.75) |
Internal Medicine | 1395 | 21 (1.51) | 70 (5.02) | 1 (0.07) | 23 (1.65) |
Surgery department | 659 | 9 (1.37) | 18 (2.73) | 1 (0.15) | 2 (0.30) |
Obstetrics/Gynecology/Fertility | 135 | 1 (0.74) | 4 (2.96) | 0 | 2 (1.48) |
Pediatric department | 4 | 0 | 1 (25) | 0 | 0 |
oncology department | 261 | 3 (1.15) | 8 (3.07) | 0 | 2 (0.77) |
General department/Other | 99 | 1 (1.01) | 8 (8.08) | 0 | 1 (1.01) |
P | | 0.000 | 0.000 | 0.000 | 0.000 |
Patient classification | | | | | |
COVID-19 convalescent | 110 | 35 (31.82) | 85 (77.27) | 2 (1.82) | 51 (46.36) |
SSC | 355 | 12 (3.38) | 28 (7.89) | 0 | 14 (3.94) |
SAC | 1295 | 22 (1.70) | 74 (5.71) | 1 (0.08) | 19 (1.47) |
Attendance for other diseases | 1302 | 17 (1.30) | 43 (3.30) | 1 (0.08) | 13 (1.00) |
P | | 0.000 | 0.000 | 0.000 | 0.000 |
Comorbidity | | | | | |
Tumor | 387 | 7 (1.81) | 14 (3.62) | 0 | 5 (1.29) |
CCD | 146 | 2 (1.37) | 5 (3.42) | 0 | 2 (1.37) |
Digestive diseases | 259 | 2 (0.77) | 11 (4.25) | 0 | 2 (0.77) |
Urogenital diseases | 141 | 0 | 3 (2.13) | 0 | 1 (0.71) |
Nervous diseases | 51 | 2 (3.92) | 2 (3.92) | 1(1.96) | 1 (1.96) |
haematological diseases | 24 | 1 (4.17) | 1 (4.17) | 0 | 0 |
Other respiratory diseases | 64 | 1 (1.56) | 0 | 0 | 1 (1.56) |
External injury | 90 | 1 (1.11) | 2 (2.22) | 0 | 0 |
Pregnancy check-up | 68 | 1 (1.47) | 2 (2.94) | 0 | 1 (1.47) |
AIDS | 13 | 0 | 0 | 0 | 0 |
Other | 59 | 0 | 3 (5.08) | 0 | 0 |
P | | 0.584 | 0.881 | 0.006 | 0.967 |
SSC: Screening for symptomatic condition (the most common symptoms related to COVID-19 including fever, cough, chest tightness, diarrhea) SAC: Screening for asymptomatic condition (health examination professionals were asymptomatic currently, but didn't rule out close contacts or had a symptom related to COVID-19) CCD: Cardiovascular and Cerebrovascular diseases Other: including autoimmune diseases, skin diseases, stomatitis, laryngeal eyewinker, poisoning, etc. |
The criteria for discharging patients, i.e., being afebrile for 14 days, clinical improvement, and the NA tested negative. In this study, we also included 110 patients discharged from the hospital to evaluate their immunity. The seroprevalence for IgM and IgG in the patients was 35 (31.82%) and 85 (77.27%), respectively, which was significantly higher as compared with those in other groups (Table 1). Among the 110 COVID-19 patients, most of the patients were convalescent, and their positive rate of IgG was marked higher than that of IgM. Fourteen patients had IgM and IgG negative, while 11 cases were IgM positive, but IgG negative, maybe the newly infectious patients. CT scan showed that 46.36% of patients still have inflammatory lesions, indicating that it takes some time to absorb pulmonary inflammation. Forty-one patients with positive antibody detected the NAbs the second time for dynamic observation. Among them, 16 patients with IgM positive changed to negative on an average of 5 days, while six patients with IgG negative changed to positive in an average of 4.3 days. Three hundred fifty-five individuals with suspected syndromes, including fever, cough, chest congestion, and headache of undetermined origin, were included. The positive rate of IgM and IgG of them were 12 (3.38%) and 28 (7.89%), respectively. Their NA tests were negative, but 14 cases (3.94%) had lung abnormality by CT. 1295 participants were currently asymptomatic. Still, some of them had recalled they might have a suspected symptom, without particular diagnosis due to mild symptoms, and chose to stay-at-home quarantine. Their seroprevalence for IgM and IgG were 22 (1.71%) and 74 (5.74%), respectively. Only one showed NA tests positive, and 19 (1.47%) cases had lung abnormality by CT (Table 1).
When we re-classify the participants according to their comorbidity, in 13 cases of AIDS patients, none of them had positive results in IgM, IgG, NA, and CT tests (Table 1). Three hundred eighty-seven tumor patients had IgM and IgG positive rate 7 (1.81%) and 14 (3.62%), respectively. One hundred forty-six patients with cardiovascular and cerebrovascular diseases, hypertension, and diabetes (CCD) had IgM and IgG positive rate 2 (1.37%) and 5 (3.42%), respectively. Two hundred fifty-nine patients with digestive system diseases had high levels of IgG 11 (4.25) but low levels of IgM (0.77). One hundred forty-one patients with urogenital system diseases had levels of IgG 3 (2.13%), but none of IgM. Fifty-one patients with nerve system disease, including coma, syncope, disturbance of consciousness, dizziness, headache, epilepsy, spasm, neuralgia, and Alzheimer's disease, etc., had IgM and IgG positive rate 2 (3.92%) and 2 (3.92%), respectively. Twenty-four patients with hematological disease had IgM and IgG positive rate, were 1 (4.17%), and 1(4.17%), respectively. Sixty-four patients with other respiratory disorders, including COPD, asthma, rhinitis, pharyngitis, bronchitis, and other pathogens lung infection, had IgM and IgG positive rate, were only 1 (1.56%), and 0 (0.00%), respectively. Ninety patients with external injury had IgM and IgG positive rate, were 1 (1.11%), and 2(2.22%), respectively. Sixty-eight patients for pregnancy check-up had IgM and IgG positive rate, were 1 (1.47%) and 2 (2.94%), respectively. At last, another disease including autoimmune diseases, skin diseases, stomatitis, laryngeal eyewinker, poisoning, etc., had IgM and IgG positive rate, 0 (0.00%) and 3 (5.08%), respectively (Table 1).
The variation of IgM and IgG in COVID-19 patients.
The percentage of patients who were IgM positive reduced after March 22, keeping at a low level after that. Seroprevalence for IgG peaked at 25.93% on March 23 due to many COVID-19 patients tested the NAbs on those days. As time passed, the positive rates of IgG remained at a low level; the range was from 2.82–14.08% (Fig. 1A). Most patients were convalescent, and the positive rate of IgG was greater than that of IgM (Fig. 1A). As for subgroups, the positive rate of IgM had a higher level in the COVID-19 convalescent group (mean ± SE: 33.41 ± 0.34) than SSC (mean ± SE: 4.41 ± 0.09) and SAC groups (mean ± SE: 1.28 ± 0.09). During all study periods, the COVID-19 convalescent group showed a higher IgG positive rate (mean ± SE: 81.19 ± 0.26) than SSC (mean ± SE: 7.35 ± 0.05) and SAC groups (mean ± SE: 4.62 ± 0.09) (Fig. 1B).