A team of Chinese researchers published a population-monitoring-based report, illustrating the profile of asymptomatic patients and asymptomatic phrases of COVID-19, from exposure to outcome. 

The report, for the first time, proposed that "asymptomatic" COVID-19 should be categorized into three different types: asymptomatic carrier, presymptomatic patients who develop symptoms after being detected, and patients with their symptom relieved during convalescent period. 

Differentiation of these three phrases would assist strategy making in disease monitoring and control, decision making for de-isolation in clinical practice as well as provide evidence for public disease control guidance. 

The report was based on investigation of the natural history and the dynamics of symptoms of confirmed cases of COVID-19 in east China’s Anhui Province. 

WENG Jianping, Vice President of the First Affiliated Hospital of the University of Science and Technology of China, conducted investigation into the epidemic of COVID-19 with his colleagues in three cities in Anhui, since January. 

With joint effort from the Anhui Provincial Centers for Disease Control and Prevention, the team kept track of data in the population based massive monitoring of all suspected individuals and the management of all confirmed COVID-19 cases in the designated hospitals. 

By April 6, statistics of 133,261 suspected individuals from the massive monitoring system was investigated, including 3,710 close contacts of confirmed cases. 307 were eventually detected with confirmed COVID-19 cases. Among them, 17 were asymptomatic when they first received SARS-CoV-2 test.  

Through close observation of these ‘asymptomatic’ patients from admission to discharge in designated hospitals, nine of the 17 cases developed COVID-19 relevant symptoms like fever and cough within a week after hospital-admission.  

Of the 307 confirmed cases, eight (2.6%) stayed asymptomatic throughout their disease course. In other words, the proportion of asymptomatic carriers, i.e. who had SARC-CoV-2 infection but presented with no symptoms, were low among all the COVID-19 patients. 

This work was supported by the Chinses Academy of Science and Epidemic Prevention and control Headquarters of Anhui Province.