Positive Rate of Serology and RT-PCR for COVID-19 among healthcare workers during different periods in Wuhan, China.

Dear editor:

We have read with interest the recent paper of Tu H et al, which suggesting that healthcare workers have a high risk of infection when providing clinical care for patients with coronavirus disease 2019 (COVID-19). As of February 12, 2020, more than 3,000 healthcare workers in Hubei Province, China, have been infected, and most of them are from non-infectious disease departments. A total of 110 of 9684 healthcare workers were diagnosed with COVID-19 in Tongji Hospital, a large comprehensive tertiary hospital in Wuhan, with an infection rate of 1.1%. Here, we would like to share our study that reported the results of mass screenings among healthcare workers from a comprehensive tertiary hospital and assessed the infection status during different periods, which was a key step in tracking hospital infection and preventing the spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2).

This single-center study included 1059 cases of healthcare workers in Renmin Hospital of Wuhan University. All the subjects had been screened twice for SARS-CoV-2, the first from March 8 to April 19, 2020, and the second from May 13 to June 10, 2020. The blood samples and nasopharyngeal swabs from each participant were collected respectively for the SARS-CoV-2-specific serological test and RT-PCR test. According to the manufacturer's instructions, the anti-SARS-CoV-2 IgG and IgM were detected using the Diagnostic Kit for IgM/IgG Antibody to Coronavirus (Colloidal Gold Method) (Livzon Diagnostics Inc.). The presence of SARS-CoV-2 RNA in nasopharyngeal swab samples were detected using real-time RT-PCR assay with the Chinese Control and Prevention (China CDC) recommended Kit (DAAN Gene Co., Ltd. of Sun Yat-sen University). All analyses were performed using SPSS statistical software version 20.0 (IBM Corp).

Among the 1059 healthcare workers, 262 were male (24.7%) and 797 were female (75.3%). The median age was 32.69 (± 7.7) years. As shown in Table 1 , the positive rates of SARS-CoV-2 RNA among these healthcare workers were 1.8% from March 8 to April 19, and decreased to 0.3% from May 13 to June 10, with significantly statistical difference (χ2 = 11.759, P = 0.001). The positive rates of SARS-CoV-2-IgM antibodies were 3.5% from March 8 to April 19, and decreased to 1.4% from May 13 to June 10, with significantly statistical difference (χ2 = 9.542, P = 0.002). The positive rates of SARS-CoV-2-IgG antibodies were 11.7% from March 8 to April 19, and decreased to 9.3% from May 13 to June 10, with no statistical difference (χ2 = 3.133, P = 0.077). Among the 19 healthcare workers who were positive for SARS-CoV-2 RNA form March 8 to April 19, only one remained positive form May 13 to June 10, and the rest turned negative (94.7%). Among the 37 healthcare workers with IgM positive from March 8 to April 19, 15 (40.5%) healthcare workers remained positive from May 13 to June 10, and 22 (59.5%) healthcare workers turned negative. Among 124 healthcare workers with IgG positive from March 8 to April 19, 89 (71.8%) healthcare workers remained positive from May 13 to June 10, and 35 healthcare workers turned negative (28.2%). During the second screening from May 13 to June 10, there were 2 new cases positive for SARS-CoV-2 RNA, 10 new cases positive for IgG, and no new case positive for IgM.

Table 1

The positive rates of serology and RT–PCR tests among healthcare workers in different periods. (N = 1059)

	March 8 to April 19	May 13 to June 10	χ2	P value
RNA+ (%)	19 (1.8%)	3 (0.3%)	11.759	0.001
IgM+ (%)	37 (3.5%)	15 (1.4%)	9.542	0.002
IgG+ (%)	124 (11.7%)	99 (9.3%)	3.133	0.077

RT-PCR, reverse transcription-polymerase chain reaction

During the prevalence of COVID-19, healthcare workers are at high risk of infection due to exposure to droplets or aerosols from patients' respiratory tracts. This study showed that the positive rates of SARS-CoV-2 RNA and IgM in healthcare workers from March 8 to April 19 were higher than the periods from May 13 to June 10. This is because that people's understanding of the virus and the knowledge of infection control were relatively insufficient during the early outbreak. After the first screening, the routine infection control practices and contact precautions were released and implemented according to the WHO and CDC guidelines , . The importance of compliance with and proper training in infection control procedures were emphasized during these situations. Healthcare workers were urged to wear the correct personal protective equipment (PPE), such as surgical masks or N-95 respirators, disposable isolation gowns, disposable patient inspection gloves, work hat, goggles or marks and shoe covers, according to the risk level. The work schedules with appropriate numbers and lengths of shifts were provided for healthcare workers to ensure that they get adequate rest while coping with the increased workload. As is observed from the second screening, the infection rates were significantly decreased and the nosocomial infection were effectively controlled, which suggested that reasonable medical intervention measures and standardized personal protection protocols are very necessary for infection prevention and control. Hospital services should improve emergency capacity, timely formulate protection guidelines, and provide adequate supplies of protective equipments.

In this study, the infections among healthcare workers mainly peaked in the early stage of the Wuhan outbreak. Fewer new infections were detected in the second screening from May 13 to June 10. The presence of IgM antibodies was relatively short-lived and 59.5% cases became seronegative for IgM in the second screening. The presence of IgG antibodies lasted longer and 71.8% cases remained seropositive for IgG in the second screening. Shu H et al. had reported that the IgM fell to below the baseline level at about day 36, while IgG still maintained a relatively high level. Therefore, IgM was suitable for the detection of early infections, while IgG was a sensitive indicator for the detection of past infections. Mass screening of healthcare workers and rapid identification of potentially infected staff through serological tests contributed to protecting healthcare workers and reducing cross-infection.

In conclusion, early screening and standardized personal protection measures can effectively reduce the risk of cross-infection. The infection control guidelines designed for different levels of exposure risk have important implications for worker protection and nosocomial infection control.

Declaration of Competing Interest

None.