Apparent and occult infections of medical staff in a COVID-19 designated hospital.

Since the outbreak of novel coronavirus (SARS-CoV-2)-infected pneumonia (COVID-19), numerous medical staff are fighting on the frontline. However, the possibility of occult infection in medical staff is ignored in many recent studies. Herein, we collected data in a COVID-19 designated hospital from January 22, 2020 to March 10, 2020. A total of 33 medical staff had at least one nucleic acid test of throat swab, immunoglobulin G (IgG) or IgM serum antibody test, and chest computed tomography (CT), were enrolled. Finally, we identified 25 cases (75.8%) were isolated for hospitalized treatment after positive virus detection. In addition, 4 cases who were all negative for nucleic acid test detection with no clinical symptoms, and none of their chest CT were abnormal. However, the results of serum IgG or IgM antibody test in these 4 cases were positive, suggesting the presence of occult infection. In conclusion, data from our single center indicated that SARS-CoV-2 had a high medical infection rate (29/33 = 87.9%) and might have a potential risk of occult infection.

Introduction

Since December 2020, novel coronavirus (SARS-CoV-2)-infected pneumonia (COVID-19) occurred in Wuhan, and rapidly spread throughout China [1,2]. Recently studies mainly focused on infections in patients, while little attention has been paid to the apparent and occult infections in medical staff.

Methods

Since the outbreak of COVID-19, Wuhan Red Cross Hospital was designated as the hospital for fever and COVID-19 on January 22, 2020. As of March 10, 2020, 33 staff had at least one nucleic acid test of throat swab for SARS-CoV-2, IgG-IgM combined serum antibody test for SARS-CoV-2, and chest computed tomography (CT) to screen potential infections.

The swab virus nucleic acid was detected by the RT-PCR assay method according to the manufacturer’s protocol (Shanghai BioGerm Medical Technology Co.,Ltd) [3]. The blood antibody was detected by the point-of-care lateral flow immunoassay method according to the manufacturer’s protocol (Shenzhen Yahuilong Biological Technology Co.,Ltd) [4]. The antibody test was reported with a reliable sensitivity of 88.66% and specificity of 90.63% [4].

This study was approved by the ethics committee of Wuhan Red Cross Hospital, and written informed consents were obtained.

Results

Table 1 showed the basic information of the included subjects. In brief, all medical staff worked in different departments, whereas they shared the same access to and from work. The 33 medical staff had an average age of 38.1 years (range: 25–56) and an average work duration of 13.9 days (range: 1–40) in the isolation ward (Fig. 1 ). Among these staff, 25 people (75.8%) were isolated for hospitalized treatment after positive virus detection.

Table 1

The basic information of 33 subjects.

Patients	Age	Gender	Department	Position
1	45	Male	Orthopedics (turned into fever ward)	Doctor
2	38	Female	Geriatrics (turned into fever ward)	Doctor
3	37	Female	Emergency	Nurse
4	42	Female	Color Doppler Ultrasound Room	Doctor
5	29	Female	Orthopedics (turned into fever ward)	Nurse
6	25	Female	Intensive care unit	Nurse
7	47	Female	Obstetrics and Gynecology (turned into fever ward)	Doctor
8	30	Female	Emergency	Nurse
9	30	Female	Gastroenterology (turned into fever ward)	Doctor
10	28	Female	General Surgery (turned into fever ward)	Nurse
11	26	Female	General Surgery (turned into fever ward)	Nurse
12	53	Male	Cardiology (turned into fever ward)	Doctor
13	45	Female	Intensive care unit	Nurse
14	46	Female	Logistics	Logistics
15	37	Female	Logistics	Logistics
16	33	Female	Pediatrics (turned into fever ward)	Doctor
17	36	Female	Logistics	Logistics
18	46	Male	Pharmacy	Pharmacist
19	42	Male	Logistics	Logistics
20	26	Female	Neurology (turned into fever ward)	Nurse
21	57	Male	Pharmacy	Pharmacist
22	38	Male	Pediatrics (turned into fever ward)	Doctor
23	28	Female	Breast surgery (turned into fever ward)	Nurse
24	30	Female	Orthopedics (turned into fever ward)	Nurse
25	43	Female	Oncology (turned into fever ward)	Doctor
26	46	Female	Endocrinology (turned into fever ward)	Nurse
27	48	Female	Registration	Registration
28	55	Female	Oncology (turned into fever ward)	Doctor
29	33	Female	Outpatient	Nurse
30	56	Male	Radiology (turned into fever ward)	Doctor
31	35	Female	Oncology (turned into fever ward)	Nurse
32	24	Female	Oncology (turned into fever ward)	Nurse
33	48	Female	Registration	Nurse

Fig. 1

The flowchart of analysis procedure.

Among the 8 staff with negative virus detection, 4 subjects were hospitalized for fever or respiratory symptoms. Other 4 subjects were asymptomatic, and chest CT scan showed no abnormalities.

The 4 medical staff are still working in the frontline because they do not meet the present diagnostic criteria [5]. As of March 10, they all had 48 days’ work experience in the isolation ward. Case 1 was a 34-year-old nurse who had a positive detection for IgG, whereas a negative detection for IgM. Case 2 was a 45-year-old doctor. Case 3 was a 39-year-old doctor. Case 4 was a 48-year-old support staff. These 3 cases had a positive detection for IgM, whereas a negative detection for IgG.

Discussion

Viral infection could be divided into apparent and occult infection according to the degree of infection symptoms. Occult infections usually had no or insignificant clinical symptoms and biochemical changes, which could only be detected by immunological testing.

In this study, although all cases undergo protection training before taking up their posts, our data indicate that COVID-19 is a highly contagious disease. There may be two reasons. First, due to a lack of understanding of the epidemiology of SARS-CoV-2 in January, several medical staff might be infected due to insufficient protection and in an incubation period before the hospital was converted into the COVID-19 designated hospital. Second, the hospital itself was a comprehensive hospital, and its transformation into a designated hospital might not completely meet the requirements of hospital for infectious disease. Therefore, even with strictly protective equipment, the apparent infection rate of medical staff reached 75.8%.

Moreover, we identified 4 cases who were all negative for nucleic acid test detection with no clinical symptoms, and none of their chest CT were abnormal. In addition, the serum antibody results showed that 3 cases had a positive detection for IgM, whereas a negative detection for IgG. The IgM positive indicated that patients tend to be in the acute phase of COVID-19 infection. Although a false negative result might be occurred in the nucleic acid test [6], positive results of nucleic acid tests were found in 3 times in case 2 and 2 times in case 3 and case 4. These findings suggested 3 cases with IgM-positive might be COVID-19 patients with occult infection. The remaining case 1 showed a negative result for IgM detection and a positive result for IgG detection, suggesting past exposure to SARS-CoV-2.

In previously SARS-CoV infection, occult infection was found in Heyuan, Guangdong, China [7]. Wang et al. indicated that 29 of the 1129 medical staff tested positive for coronavirus antibodies [8]. Therefore, we could reasonably speculate that occult infection also existed in COVID-19 patients. The proportion of occult infection was also higher in SARS-CoV-2 than SARS-CoV because of the higher infectiousness. However, the infectivity of these occult infections requires further study.

The study is limited to a small number of medical staff and cannot determine which types of work are more likely to develop occult infection. A larger cohort will help us understand the characteristics of occult infection of COVID-19. Additionally, nucleic acid test is not performed on several frequently touched sites in the working environment outside the isolation ward, such as computers, phones, or hand sanitizer buttons, to determine whether occult infection is a potential source of infection in clean office areas. Finally, more studies are needed to confirm that occult infection caused by SARS-CoV-2 are potential carriers of the virus.

Conclusion

In summary, data from our single center indicated that SARS-CoV-2 had a high medical infection rate (29/33 = 87.9%) and might have a potential risk of occult infection.

Funding

This work was supported by grants 2016YFC1306600 (to NX) and 2018YFC1314700 (to NX) from the National Key R & D Program of China, grants 81873782 (to NX) from the .

Competing interests

None declared.

Ethical approval

Not required.

Author contribution

GZL, CYH, JL and QH collected the data. GZL, NX and HZW prepared and revised the manuscript. GZL, NX and HZW were responsible for summarizing all data related to this study.