Public screening for COVID-19 in Wuhan, China and beware of the antibody positive in women and tumor patients.

The novel coronavirus disease 2019 (COVID-19) has become a global health emergency. Early detection and intervention are key factors for improving outcomes in patients with COVID-19. Real-time reverse transcriptase polymerase chain reaction-based molecular assays and antibody for detecting SARS-CoV-2 in respiratory specimens are the current reference standard for COVID-19 diagnosis. Clinical implications of different specimen types for nucleic acid and antibody testing of COVID-19 in Zhongnan hospital of Wuhan University were analyzed. Compared with health groups, tumor patients had higher rate of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (+/-) immunoglobulin M (IgM) (+) immunoglobulin G (IgG) (+). The rate of SARS-CoV-2 (-) IgM (+) IgG (-) or SARS-CoV-2 (-) IgM (-) IgG (+) in female was significantly higher than that in male. These results can help governments to take screening measures to prevent the COVID-19 pandemic again.

INTRODUCTION

Coronavirus disease 2019 (COVID‐19) spread rapidly around the world and caused death of hundreds of thousands of patients. The epidemic situation is well controlled in some countries, such as China, but the occurrence of asymptomatic individuals may pose a significant public health issue. Therefore, it is necessary to take effect screening methods, such as nucleic acid and antibody detection, to find out those asymptomatic individuals. The reflections on COVID‐19 screening results can help us to figure out the real status of COVID‐19 currently and at the same time assist governments to take severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) nucleic acid positive screening measures for the public to prevent the COVID‐19 pandemic again.

METHODS

SARS‐CoV‐2 nucleic acid tests and serum antibody tests (immunoglobulin G [IgG], immunoglobulin M [IgM]) were performed on 21 398 persons to screen COVID‐19 patients, from March 1, 2020 to June 30, 2020 in Zhongnan hospital of Wuhan University, Wuhan, China. The cases are consisted of those individuals: state‐funded COVID‐19 screening, screening before factories and companies reopened, and pre‐hospital screening for patients and their escorts. The hospitalized patients were classified into patient groups. Other cases were classified into health groups. All cases had temperature and symptoms of COVID‐19 screened before entry. Informed consent was received from all patients in the study. This study was approved by the institutional ethics board at Zhongnan Hospital of Wuhan University (No. 2020074).

SARS‐CoV‐2 viral nucleic acid was test by high throughput sequencing or real‐time reverse‐transcriptase–polymerase‐chain‐reaction (RT‐PCR) assay of nasal and pharyngeal swab specimens, which were performed following a previously method. IgM/IgG test kits included recombinant SARS‐CoV‐2 antigens (spike protein and nucleocapsid protein) labelled with magnetic beads (tested on a fully‐automated chemiluminescence immunoassay analyzer) or colloidal gold (test card), anti‐human IgM monoclonal antibody, and anti‐human IgG monoclonal antibody. These test kits were reported to have high sensitivity and specificity. , According to the manufacturers, the sensitivity and specificity are ~90% and >99% for IgM, and ~98% and ~98% for IgG, respectively.

Basic information including case category (patient groups, health groups), sex, age, testing results and data of COVID‐19 IgM/IgG and nucleic acid were collected from system of laboratory medicine. For hospitalized patients, diseases were divided into different categories: including patients with malignant tumor, chronic diseases, or immune‐related diseases (such as Crohn's Disease, Inflammatory Bowel Disease, Connective Tissue Disease). Distribution characteristics were compared between cases with nucleic acid or IgM/IgG positive and negative.

RESULTS

Characteristics of participants

Of the 21 398 cases, there were 4093 hospitalized patients and 17 305 health cases. The number of male (52.5%) was slightly higher than that of female (47.5%). Median age was 40.0 years (interquartile range: 31.0–53.0) (Table 1). In total, only 12 (0.056%) cases were SARS‐CoV‐2 positive, 254 (1.19%) cases were IgM positive and 978 (4.57%) cases were IgG positive. There are some suspected cases, which is difficult to distinguish whether IgM/IgG is positive or negative. The positive prevalence of IgM/IgG antibodies to SARS‐CoV‐2 and nucleic acids are shown in Table 2.

Table 1

Baseline characteristics of study participants

	Total number (%) or
	Median (IQR)
Time
March	4034 (18.85)
April	11 517 (53.82)
May	5111 (23.89)
June	736 (3.44)
Sex
Male	11 230 (52.48)
Female	10 168 (47.52)
Age	40.0 (31.0–53.0)
Case category
Health group	17 305 (80.87)
Patient group	4093 (49.13)
Disease classification of hospitalized patients
Diagnose disease (2102)
Tumor	473 (22.50)
Chronic disease	315 (14.99)
Immune‐related disease	38 (1.81)

Table 2

Overall positive proportion of SARS‐CoV‐2 and IgM/IgG antibodies to SARS‐CoV‐2 among all cases (n = 21 398)

	number	% (95% CI)
SARS‐CoV‐2 (+)	12	0.056 (0.03–0.11)
IgM (+)	254	1.19 (1.05–1.35)
IgG (+)	978	4.57 (4.3–4.86)
SARS‐CoV‐2 (suspected)	0	0
IgM (suspected)	40	0.19 (0.14–0.26)
IgG (suspected)	111	0.52 (0.43–0.63)

Abbreviations: CI, confidence interval; IgG, immunoglobulin G; IgG, immunoglobulin M; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2.

Prevalence of IgM/IgG antibodies to SARS‐CoV‐2 and virus nucleic acid status

There were no statistically different for SARS‐CoV‐2 (+) IgM (+/−) IgG (+/−) prevalence in different time intervals, case category, age groups or sex (Figure 1A–C). The prevalence of SARS‐CoV‐2 (−) IgM (+) IgG (+) in March/April (p < 0.001), hospitalized patients (p = 0.020) and older people (p = 0.027) were significantly higher. The same is true for the prevalence of SARS‐CoV‐2 (−) IgM (−) IgG (+) (Figure 1D). No statistical difference was found in sex for SARS‐CoV‐2 (−) IgM (+) IgG (+) prevalence, but the prevalence of SARS‐CoV‐2 (−) IgM (+) IgG (−) or SARS‐CoV‐2 (−) IgM (−) IgG (+) was higher in female (Table 3). For patient groups, compared with health groups, tumor patients had higher rate of SARS‐CoV‐2 (+/−) IgM (+) IgG (+) (p = 0.003) and SARS‐CoV‐2 (−) IgM (−) IgG (+) (p = 0.007, Figure 1E).

Figure 1

The positive rate of SARS‐CoV‐2, IgM and IgG. The positive rate of SARS‐CoV‐2, IgM and IgG per month (A). The positive rate of SARS‐CoV‐2, IgM and IgG in different age groups (B). The positive rate of SARS‐CoV‐2, IgM and IgG in male and female (C). The positive rate of SARS‐CoV‐2, IgM and IgG in patients group and health group (D). The positive rates of SARS‐CoV‐2, IgM and IgG in different diseases (E)

Table 3

Comparison of SARS‐CoV‐2 (+) IgM (+/−) IgG (+/−), SARS‐CoV‐2 (−) IgM (+) IgG (+), SARS‐CoV‐2 (−) IgM (+) IgG (−) and SARS‐CoV‐2 (−) IgM (−) IgG (+) among different category groups (n = 21 398)

	SARS‐CoV‐2 (+) IgM (+/−) IgG (+/−)	P value	SARS‐CoV‐2 (−) IgM (+) IgG (+)	P value	SARS‐CoV‐2 (−) IgM (+) IgG (−)	P value	SARS‐CoV‐2 (−) IgM (−) IgG (+)	P value
Time (n)
March (4034)	3 (0.074)	0.710	52 (1.29)	<0.001	34 (0.84)	<0.001	198 (4.91)	0.001
April (11 517)	7 (0.061)		81 (0.70)		66 (0.57)		424 (3.68)
May (5111)	2 (0.039)		9 (0.18)		10 (0.20)		177 (3.46)
June (736)	0		0		0		22 (2.99)
Case category (n)
Patient group (4093)	2 (0.049)	0.828	38 (0.93)	0.020	21 (0.51)	0.992	205 (5.01)	<0.001
Health group (17 305)	10 (0.058)		104 (0.60)		89 (0.51)		616 (3.56)
Age groups, years (n)
≤14 (73)	0	0.917	0	0.027	0	0.326	2 (2.74)	<0.001
15–49 (14 330)	7 (0.049)		80 (0.56)		66 (0.46)		468 (3.27)
50–64 (5438)	4 (0.074)		45 (0.83)		33 (0.61)		253 (4.65)
≥65 (1557)	1 (0.064)		17 (1.09)		11 (0.71)		98 (6.29)
Sex (n)
Male (11 230)	9 (0.080)	0.064	72 (0.64)	0.670	36 (0.32)	<0.001	401 (3.57)	0.033
Female (10 168)	3 (0.030)		70 (0.69)		74 (0.73)		420 (4.13)

Abbreviations: IgG, immunoglobulin G; IgG, immunoglobulin M; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2.

SARS‐CoV‐2 (−) IgM (+) IgG (−) prevalence in different groups

For different age groups, no SARS‐CoV‐2 (−) IgM (+) IgG (−) was found in child. SARS‐CoV‐2 (−) IgM (+) IgG (−) prevalence is higher in female than in male only in the 15–59 age group (p < 0.001, Table 4). In terms of cases with 15–59 age group, the prevalence of SARS‐CoV‐2 (−) IgM (+) IgG (−) in March (p = 0.031) and April (p < 0.001) was still higher in female than in male. In health group, SARS‐CoV‐2 (−) IgM (+) IgG (−) prevalence was also higher in female than male (Table 5).

Table 4

Comparison of SARS‐CoV‐2 (−) IgM (+) IgG (−) in male and female among different age groups (n = 21 398)

	SARS‐CoV‐2 (−) IgM (+) IgG (−)				p value
	Male (11 230)		Female (10 168)
	N (total number)	% (95% CI)	N (total number)	% (95% CI)
Age groups, years (n)
≤14 (73)	0 (42)	0	0 (31)	0	NA
15–59 (18 848)	26 (9169)	0.27 (0.18–0.40)	68 (9679)	0.74 (0.58–0.94)	<0.001
≥60 (2477)	10 (1509)	0.66 (0.36–1.21)	6 (968)	0.62 (0.25–1.42)	0.897

Abbreviations: IgG, immunoglobulin G; IgG, immunoglobulin M; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2.

Table 5

Comparison of SARS‐CoV‐2 (−) IgM (+) IgG (−) prevalence in male and female in 15–59 age group among different time groups and case category (n = 18 848)

	SARS‐CoV‐2 (−) IgM (+) IgG (−)
	Male (9679)		Female (9169)
	N (total number)	% (95% CI)	N (total number)	% (95% CI)	p value
Time (n)
March (3835)	5 (1223)	0.41 (0.15–1.01)	29 (2612)	1.00 (0.67–1.48)	0.031
April (10 663)	17 (6084)	0.28 (0.17–0.46)	38 (4579)	0.83 (0.60–1.15)	<0.001
May (3941)	4 (2201)	0.18 (0.06–0.50)	1 (1740)	0.06 (0–0.38)	0.392
June (409)	0 (171)	0	0 (238)	0	NA
Case category (n)
Patient group (2236)	3 (1087)	0.28 (0.07–0.88)	5 (1149)	0.44 (0.16–1.08)	0.727
Health group (16 612)	23 (8592)	0.27 (0.18–0.41)	63 (8020)	0.79 (0.61–1.02)	<0.001

Abbreviations: CI, confidence interval; IgG, immunoglobulin G; IgG, immunoglobulin M; SARS‐CoV‐2, severe acute respiratory. syndrome coronavirus 2.

DISCUSSION

The positive rate of SARS‐CoV‐2 (−) IgM (+) IgG (+) is higher than that of SARS‐CoV‐2. It was reported that SARS‐CoV‐2 nucleic acid test could appear false negatives in throat swab, and the SARS‐CoV‐2 positive was more likely to be detected in the lower respiratory tract. , Serum antibodies in COVID‐19 were considered to have potential diagnostic value to COVID‐19. , Therefore, simultaneously conducting SARS‐CoV‐2 nucleic acid and serum antibody test can identify or screen SARS‐CoV‐2 infection in suspicious and close‐contact populations earlier and more quickly and effectively and can improve the accuracy of epidemiological monitoring, which is very important for patient management and epidemic prevention and control.

The positive rate of SARS‐CoV‐2 and IgM were very low among the public and gradually decreased over time in Wuhan, China. COVID‐19 was well controlled in Wuhan. The positive rate of SARS‐CoV‐2 (−) IgM (−) IgG (+) also decreased with time, which can be speculated that the previously produced IgG may disappear in a not too long time, but the durations of IgG were still unknown. It's reported that after 17–19 days postsymptom onset, IgG was positive in all patients with COVID‐19. Lack of longer monitoring to IgG may be responsible for no negative IgG in some patients reported in previous literatures.

The rate of SARS‐CoV‐2 (−) IgM (+) IgG (−) or SARS‐CoV‐2 (−) IgM (−) IgG (+) in female was significantly higher than that in male (p < 0.05). However, previous studies have shown that the number of women infected with SARS‐CoV‐2 is not more than that of men. , , It was reported that estrogens promoted the production of natural neutralizing antibodies. In a study of Wuhan Red Cross Hospital, from days 8 to 33 after infection symptoms appeared, 94.83% of the COVID‐19 patients had both IgM and IgG positive, and 1.72%, 3.45% had only IgM or only IgG positive. We speculate that high rate of SARS‐CoV‐2 (−) IgM (+) IgG (+) in female may be due to the effect of estrogen, which need to be further explored in the future.

Patient groups had a higher SARS‐CoV‐2 (−) IgM (+) IgG (+) rate than health group, especially tumor patients who had the highest SARS‐CoV‐2 (−) IgM (+) IgG (+) rate, and tumor patients had a higher rate of SARS‐CoV‐2 (−) IgM (−) IgG (+). These differences represented high SARS‐CoV‐2 infection rate in tumor patients. That tumor patients were susceptible to SARS‐CoV‐2 can be attributed to the increased chance of SARS‐CoV‐2 infection caused by the patient's multiple hospitalizations, and the inadequate immune function of the body. Tumor patients deserve attention during hospitalization, and hospitals should take preventive measures to avoid the risk of nosocomial infections.

The analysis discussion of the screening results shows that the inflect status of COVID‐19 are getting better. Conducting severe screening is a good way to find out the asymptomatic individuals. While universal screening can locate nucleic acid‐positive cases and enable countries to take proactive measures in advance to prevent a recurrence of the outbreak, this will undoubtedly increase the burden on the country's economy, especially in countries where free testing is available to the population. Therefore, it is necessary to conduct COVID‐19 screening in areas with severe epidemics rather than universal screening. Tumor patients should also be included to special populations for COVID‐19 screening. Besides, female aged 15–59 years are more likely to have single positive antibody while SARS‐CoV‐2 is negative.

CONFLICT OF INTERESTS

The authors declare that there are no conflict of interests.

AUTHOR CONTRIBUTIONS

Yufeng Shang and Yuxing Liang: analyzed data, drew pictures, wrote manuscript and revised manuscript. Tao Liu and Jingfeng Li: collected data. Fuling Zhou: designed project, provided professional guidance and revised manuscript.