Regular screening of asymptomatic SARS-CoV-2 carriers may limit COVID-19 transmission

1. Health care workers who participated in COVID-19 treatment training were less likely to test positive for SARS-CoV-2 infection than those who did not participate in early training.

2. Among asymptomatic individuals, old age was significantly associated with abnormal findings on physical examination including IgM/IgG seropositivity and ground-glass appearance on computed tomography of the chest.

 Evidence Rating Level: 2 (Good)

Study Rundown: The transmission of SARS-CoV-2 can be rapid if preventative measures are not implemented promptly. One way to control its spread is by screening asymptomatic individuals that may serve as potential infectious sources. This single-center, cross-sectional study aimed to assess the infection status of asymptomatic staff at Zhongnan Hospital of Wuhan University in China to better inform effective infection control strategies. Individuals included in this study were hospital staff without clinical symptoms for COVID-19. Upon enrolment, participants were asked to undergo a series of tests which included: inspection of the chest via computed tomography (CT), IgM/IgG serology testing for SARS-CoV-2 antibodies, and reverse transcriptase-polymerase chain reaction (RT-PCR) for COVID-19 using throat swab samples. Hospital staff (health care workers, administrative staff, and labor staff) were re-examined each week for three weeks. In addition, health care workers were stratified into high-risk departments (HRDs; anesthesiology, pulmonology, critical care medicine, emergency medicine, intensive care unit, and infectious disease) and low-risk departments (LRDs) based on which unit they worked in. A small proportion of hospital staff had abnormal findings, and fewer tested positive for SARS-CoV-2 infection, indicated by a double positive result for IgM and RT-PCR. Although no statistical difference existed for the number of abnormal findings between male and female participants, old age was associated abnormal results. A limitation of this study is that it only included results from a single hospital in Wuhan, China. Hence, findings from this study cannot be generalized to other hospitals in the region. Similarly, this study did not explore the association between clinical findings (such as differences in biochemical, immune, and viral load) and asymptomatic infection, which could be used to anticipate the progression to active COVID-19.

Click to read the study in The Lancet EClinicalMedicine

Relevant Reading: Investigation of SARS-CoV-2 outbreaks in six care homes in London, April 2020 

In-depth [cross-sectional study]: This single-center, cross-sectional study included 2406 health care workers (HCWs; doctors or nurses), 505 administrative staff and 763 labor staff who did not present with clinical symptoms of COVID-19 at the time of enrolment. From March 16 to March 25, 2020, 3674 participants were enrolled in which the majority were female (67.7%; n=2486) and a large proportion (82.6%; n=3034) were between 18-50 years of age.

Among 3674 hospital staff, 126 had abnormal laboratory or radiological findings. This included individuals who tested IgM+ (0.71%; n=26), IgG+ (2.0%; n=73), IgM+/IgG+ (0.27%; n=10), and those with ground glass shadow on chest CT (1.09%; n=40). In total, 28 (0.76%) individuals were found to be asymptomatic carriers of COVID-19. On analysis, no statistically significant difference existed (p=0.386) in the number of positive infections between high-risk and low-risk departments at the Zhongnan Hospital. However, HCWs who partook in the COVID-19 treatment training were significantly less likely (p<0.01) to test positive for an asymptomatic infection than those who did not participate in training. In comparison to healthy individuals and those with COVID-19 in recovery, there was no statistical difference in IgM and IgG antibody titers of hospital staff with abnormal findings. While the overall proportion of asymptomatic infections was 0.76% (28 out of 3674), the rate of positive infection among labor staff (1.18%) was slightly higher compared to administrative staff (0.79%). It was found that, after isolation of asymptomatic patients for three weeks, the nucleic acid test became negative, but more than half of the individuals were still positive for IgM. Overall, the high proportion of asymptomatic carriers for SARS-CoV-2, in this study, is concerning. Regular screening of asymptomatic individuals may serve to be an effective strategy for prevention and control of COVID-19.

Image: PD

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