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Asymptomatic transmission of COVID-19

A small study discusses the risk of COVID-19 transmission from asymptomatic carriers. 

As scientists continue to work on slowing the spread of COVID-19, examining patterns of person to person disease transmission is crucial. However, the transmission of COVID-19 from asymptomatic carriers, with a normal chest computed tomography (CT), has not been investigated. Published in the Journal of the American Medical Association, one research team carried out a small study to highlight this issue. 

Carried out in January 2020, the study enrolled a familiar cluster of six patients in Anyang, China, including; five patients with fever and respiratory symptoms and one asymptomatic family member. The asymptomatic patient from Wuhan, travelled to Anyang to visit a relative in hospital along with five other relatives. Before the visit, there were no reports of COVID-19 at the hospital. After relatives of the asymptomatic patient developed symptoms, the asymptomatic patient was isolated and observed. All patients underwent testing for COVID-19, including chest CT imaging. 

On investigation, the asymptomatic patient had normal CT imaging, normal C-reactive and lymphocyte counts, and no fever, respiratory or gastrointestinal symptoms. Tests for COVID-19 (real-time reverse transcriptase-polymerase chain reaction tests) were negative on January 26, February 5, February 8, but positive on January 28. 

None of the other patients, who all developed COVID-19, had travelled to Wuhan or been in contact with anyone else from Wuhan. The patients who developed symptoms showed multifocal ground-glass opacities on chest CT imaging, as well as increased C-reactive and lymphocyte counts. 

All of the patients who developed COVID-19 had contact with the asymptomatic family member who had travelled from Wuhan. The timing of events suggests that the virus was transmitted by the asymptomatic family member. This patient tested positive for COVID-19 on one occasion, despite having no symptoms, and a false-positive is deemed unlikely. 

Researchers discuss a previous study reporting an asymptomatic patient with COVID-19, however, this patient showed changes on chest CT imagery. If COVID-19 transmission via asymptomatic patients is occurring, this makes prevention of the infection an even greater challenge. This study is only one small investigation. The concern that there is a risk of asymptomatic transmission of COVID-19 requires further research. 

Written by Helen Massy, BSc.

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Bai, Y., Yao, L., Wei, T., Tian, F., Jin, D., Chen, L. and Wang, M., 2020. Presumed Asymptomatic Carrier Transmission of COVID-19. JAMA.

Image by Gerd Altmann from Pixabay 



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